Radionuclide Imaging Flashcards
What are the radionuclide imaging principles?
- Radiochemistry - Label small amounts of molecules with a radionuclide
- Administer the radiotracer to the biological system
- Detect the signal of radionuclide decay
- Convert the signal into a meaningful biomedical image
What are the features of a tracer?
It is used to measure concentration
The tracer is unstable
It allows you to determine function
It does not change the biology of the material
Why is it important that only small amounts of molecules are labelled with a radionuclide?
If it is not a small amount, it will damage DNA. This can change cell biology. Also, do not want competitive behaviour.
What are the components of radiochemistry involved in radionuclide imaging?
- Label molecules with radionuclides*
- Radiotracer amounts are very small (pico/nano molar)
- The radionuclide is PURE
- Consider radiotracer half-life range
- The radiotracer is PURE
What does it mean to say a radionuclide is pure?
There are no alternative ways of decay
Will decay in the way that you want them to
Will be alpha OR beta OR gamma
Otherwise there will be a lot of background radiation
What are the features of the radiotracer half life that should be considered?
It should be as low as is reasonable.
Needs to be in the range of the biological and experimental requirements
Normal half life is between 1 and 2 hours
What are the components of pharmokinetics involved in radionuclide imaging?
- Administer the radiotracer to the biological system*
- All tracer molecules need to travel quickly to the abnormal area (through the blood stream)
- Then they need to stay there to allow for imaging to occur
- Needs to have very few radiometabolites created, otherwise you can stop following the tracer and start following the radio-metabolite (and get a signal from it)
- These metabolites DO NOT compete with the tracer or it can suppress biological processes
What are the components of nuclear engineering involved in radionuclide imaging?
- Detect the signal of radionuclide decay*
- Emitted particle should pass through the body (some won’t due to interaction with body matter)
- It should arrive at the detector in a predictable manner in order to detect where the gamma ray came from (usually straight if no interaction with matter
- The detector should be able to discriminate each decay event
What are the components of biomathematics involved in radionuclide imaging?
Convert the signal into a meaningful biomedical image
2D = planar imaging, gamma camera 3D = Tomography/PET and SPECT 4D = image changes with time due to pharmokinetics 5D = image changes with time due to pharmokinetics and subject motion
What does SPECT stand for?
Single Photon Emission Computed Tomography
What are the common radionuclides used in SPECT?
99m-Tc
123-I
111-In
67-Ga
What is the main feature of radiotracers used in SPECT?
They are photo-emitting
What is the half life of 99m-Tc?
6 hours
What is the half life of 123-I?
13 hours
What is the half life of 111-In?
67 hours
What is the half life of 67-Ga?
78 hours
What is an example of a SPECT tracer that uses 99m-Tc as the nuclide?
HMPAO
Hexa Methyl Propylene Amine Oxime
What is an example of a SPECT tracer that uses 123-I as the nuclide?
Iodine
What is HMPAO used for clinically?
Cerebral perfusion
What is an example of a SPECT tracer that uses 67-Ga as the nuclide?
Gallium nitrate
What is 67-Gallium nitrate used for in SPECT clinically?
Osteomyelitis
What are the features of SPECT tracers?
- Photo emitting
- Relatively low energy gamma photons
What are the features of SPECT tracers?
- Photo emitting
- Relatively low energy gamma photons
- Heavy nuclides
- Label large molecules (peptides)
- Not commonly organic molecules
- Majority use 99m-Tc
- Can see single molecules within the body
What is the average gamma photon energy from a SPECT tracer?
100-400keV
What is the main feature of a PET tracer?
They are positron emitting
What does PET stand for?
Positron emitting tomography
What are nuclides used most commonly in PET?
15-O
11-C
13-N
18-F
What is the half life of 15-O?
2 minutes
What is the half life of 11-C?
20 minutes
What is the half life of 13-N?
10 minutes
What is the half life of 13-N?
10 minutes
What is the half life of 18-F?
110 minutes
What does FDG stand for?
Fluoro-Deoxy-Glucose
What are the features of PET tracers?
- Short half life
- Cyclotron required for production
- Relatively low energy gamma photons
- Biological elements
- Has a wide range of clinical applications
- Mainly used in oncology
- More natural elements
- Most research and investigations are carbon based
What are the consequences of the short half life of PET tracers?
Less time to do imaging
Expensive
Cyclotron needs to be close to the scanner
What are the 3 elementary particles?
alpha
beta
gamma
Describe an alpha particle and its properties
4He
2
Travel straight but has a coulomb interaction with tissue the stops them within a few micrometres of travel
Not possible to image
Describe an alpha particle and its properties
4He
2
Travel straight but has a coulomb interaction with tissue the stops them within a few micrometres of travel
Not possible to image
Describe a beta particle and its properties
0 e OR 0 beta+
-1 +1
Interact with coulomb force but because they are small, they do not travel straight
Average tissue range is 1-5mm
In vivo imaging possible
Positrons annihilate and create 2 gamma particles (511kev)
Describe a gamma particle and its properties
Interact with matter through the photoelectric effect and compton scattering High energy (100-500KeV) helps them escape human tissue
What are the layers within a gamma camera?
Collimator Scintillation crystal Light Guide PMTs Processing electronics Lead casing
What are the layers within a gamma camera?
Collimator Scintillation crystal Light Guide PMTs Processing electronics Lead casing
What are the features of an image generated by a gamma camera?
Creates a 2D image
It is a projection image
No depth information
Can determine direction not location
What are the basics behind a gamma camera?
Emits gamma ray Collimators stop any non parallel rays Scintillator absorbs gamma photons Emits optical photons Converted to electrical current
What are the 4 steps in that occur in the scintillator crystal?
Absorption: gamma ray ejects electrons (via Compton or photoelectric effect)
Excitation: the electron is excited to the conduction band (can move through the crystal)
Relaxation: the electron relaxes back to valence band
Emission: subsequent emission if visible light (characteristic) radiation
What are the scintillation crystals in gamma cameras commonly made of?
Sodium iodide
NaI
Doped in thallium
What are the scintillation crystals in gamma cameras doped in? Why?
Doped in thallium to achieve efficient scintillation at room temperature.
Without this, it only scintillates at liquid nitrogen temperatures
What are the basics behind a gamma camera?
Emits gamma ray Collimators stop any non parallel rays Scintillator absorbs gamma photons Emits optical photons Converted to electrical current
What are the 4 steps in that occur in the scintillator crystal?
Absorption: gamma ray ejects electrons (via Compton or photoelectric effect)
Excitation: the electron is excited to the conduction band (can move through the crystal)
Relaxation: the electron relaxes back to valence band
Emission: subsequent emission if visible light (characteristic) radiation
What are the scintillation crystals in gamma cameras commonly made of?
Sodium iodide
NaI
Doped in thallium
What are the scintillation crystals in gamma cameras doped in? Why?
Doped in thallium to achieve efficient scintillation at room temperature.
Without this, it only scintillates at liquid nitrogen temperatures
What are the basics behind the workings of a gamma camera?
Gamma ray emitted Collimators block out non-parallel rays Scintillator absorbs gamma rays Converts to optical photons Optical photons are converted to electrical current
What are the 4 steps that occur in a scintillation crystal?
Absorption: gamma ray ejects electrons (via Compton or photoelectric effect)
Excitation: the electron is excited to the conduction band (can move through the crystal)
Relaxation: the electron relaxes back to the valence band
Emission: with subsequent emission of characteristic frequency radiation (visible light)
What are gamma camera scintillation crystals commonly made of?
NaI
Sodium iodide
Doped with thalium
What are the ideal properties of a scintillation crystal?
- High scintillation efficiency (high gamma to light conversion)
- Linear conversion (light yield is proportional to deposited energy)
- Low optical absorption (optically transparent crystal)
- Short decay time of induced luminescence
- Able to be manufactured in large sizes to image patients
- Index of refraction = glass for efficient coupling to PMTs
- Low cost
What are the advantages of using NaI for gamma camera scintillators?
Very cheap to produce
Puts it into the visible light range
Allows it to occur at room temperature
What happens if you increase the thickness of the scintillation crystal in a gamma camera?
Stops more gamma rays
What happens if you do not use grease for optical coupling?
The air/solid interface between the scintillation crystal and the PMT photocathode would cause total internal refractions
How does a photomultiplier tube work
In an vacuum
Incident light photons enter the PMT through the photocathode
Light strikes the photocathode
A photoelectron is emitted
The electron strikes anodes of ascending voltages
It gains energy and it ejects further electrons from the next dynode
It produces an amplified signal
What is optical coupling?
It ensures that there is little leakage of light from the crystal before it reaches the PMT
How is efficient optical coupling achieved?
Silicon grease or oil of a similar optical index to the crystal and photocathode should be used as a light guide between the surfaces.
Regular re-greasing at services
What happens if you do not use grease for optical coupling?
The air/solid interface between the scintillation crystal and the PMT photocathode would cause total internal refractions
How does a photomultiplier tube work
Incident light photons enter the PMT through the photocathode
Light strikes the photocathode
A photoelectron is emitted
The electron strikes anodes of ascending voltages
How is the location of a gamma photon emission calculated in a gamma camera?
For each event, a signal is generated in each PMT
The information is used to work back the initial location
There will be more signal at some PMTs due to the position - light will hit multiple PMTs are light does not travel in a straight line
What are the methods used in gamma cameras to remove scatter?
Pulse height analyser
Collimation
What is a pulse height analyser?
Excludes scatter
Scattered photons will generally have lower energy than non-scattered
It measures the energy and only accepts those that fall within a certain range +/- X%
What needs to be determined in a pulse height analyser?
Bandwidth - the range of energies that will be accepted
Why do you need a range of values in a pulse height analyser?
It is experimental
There are small inaccuracies
If the range is too small, may exclude some primary rays
What is the purpose of a collimator in gamma cameras?
Excludes all radiation not parallel to the detector
Reduces scatter
In SPECT what radioisotope is used most commonly and what is its energy?
99m-Tc
140keV (low energy)
What collimator properties need to be considered?
Needs to be made of lead Size Septal thickness Hole depth Hole size Distance from detector
Different radioisotopes need different collimators
What happens if you increase the amount of collimation?
Get a decrease in resoltion
Why does PET provide a higher resolution than SPECT?
Many photons are absorbed by the collimators and this results in a loss of information and a reduction in resolution
In SPECT what radioisotope is used most commonly and what is its energy?
99m-Tc
140keV (low energy)
What happens if you increase the septal thickness of a collimator?
Increased thickness =
Increased imaging energy
Decreased sensitivity
Septa must be thick enough to stop radiation with the energy of the imaged isotope
What are the properties of a shallow holed collimator?
High sensitivity - allows most rays through
Low resolution
Decrease radiation for the same count
Why is the resolution increased by using smaller holes in a collimator?
Each collimator hole sees a smaller region.
What are the consequences of increasing the hole depth of a collimator?
Increased hole depth = Increase resolution Decrease specificity Increase radiation dose required No change in the imaging energy
What are the consequences of decreasing collimator hole size?
Decrease hole size =
Decrease sensitivity
Increased resolution
No change in imaging energy
Why is the sensitivity of a collimator decreased when using smaller holes?
Smaller holes means more holes
This means more area is taken up from lead septa which decreases sensitivity
Why is the resolution increased by using smaller holes in a collimator?
Each collimator hole sees a smaller region.
What is the effect of increasing the distance between the collimator and the detector?
Increasing the distance
Increased noise in the image
Decreased image quality
Describe the basic mechanism of PET imaging
Positron emitted
Finds nearby electron and annhiliates with it
This creates 2 gamma photons (511kEV) that spreads in opposite directions
What is the energy of the gamma photons in PET imaging?
2 x 511keV
What determines spatial resolution in PET? What is the usual resolution?
The size of the crystal
3mm
In PET what is a coincidence?
The gamma rays hit 2 detectors at the same time
Describe the detector blocks used in PET imaging
4x4 array of crystal elements each of dimensions 4mmx4mmx30mm
They are segmented
The cuts in the crystal serve to distribute scintillation light between the 4 square PMTs
PMTs from all crystals
How is the location of the gamma event determined in PET?
The interaction crystal is identified by comparing light collected by each PMT as in gamma camera
Can determine which crystal event it occurred in
What determines spatial resolution in PET? What is the usual resolution?
The size of the crystal
3mm
In PET what is a coincidence?
The gamma rays hit 2 detectors at the same time
In PET how are coincidences determined?
There is uncertainty in coincidences due to the resolving time (approx 1ns)
A coincidence window ‘gate’ is set
Take events that occur within a window
In PET how many events are there per s?
Roughly 1000s per s
What is the probability of a random coincidence occurring?
R = 2 x S1 x S2
This occurs when 2 gates overlap by chance and these need to be accounted for
What is the result of not using attenuation correction?
Artefacts
Describe the attenuation in PET
Most gamma photons will not leave the body
Most interactions with matter are through Compton scattering
Both gamma rays need to escape to register a coincidence
There is increased attenuation in larger objects and it appears there is an activity reduction
Thinner parts of the body would emit more radiation
What are the advantages of fusing PET with MR?
Allows for imaging with less radiation
Combines functional and anatomical information
How are attenuation problems fixed in PET?
Attenuation correction using CT
CT measures the attenuation factor
The true count rate measured by the emission scan is divided by the attenuation factor
What is the result of not using attenuation correction?
Artefacts
What are the advantages of fusing PET with CT?
CT provides anatomical information
PET provides functional information
Can do attenuation correction
What are the advantages of fusing PET with MR?
Allows for imaging with less radiation
Combines functional and anatomical information
What are the disadvantages of PET and SPECT?
- Biological hazard, uses ionising radiation
- Complicated chemistry
- Need CT and/or MRI (increase in expense and training)
- Complex physics and inverse mathematical problems
- Complex logisitcs: radiation decay and protection
What is the concept behind a 2m body PET scanner?
Measures all photons at once Get 40x more photons Less radiation Uses short life isotopes No gaps Decrease in time
What is the basic method used for image reconstruction?
Back projection
Can be filtered or unfiltered
It projects backwards the data and uses an analytical approach
What are the advantages used in filtered back projection?
Fast = approximately 1 minute
Linear
Well-known
What are the disadvantages used in filtered back projection?
Low resolution
Streak artefacts
Describe the nuclides used for beta minus decay?
Neutron excess nuclides
Why does decay occur?
Decay occurs due to an imbalance between protons and neutrons
Unstable nuclides do no not necessarily exist in nature as their decay is rapid
What are the disadvantages of iterative reconstruction?
Relatively slow = 10 mins
Stopping criteria can be hard to determine
Get salt and pepper noise
Describe the nuclides used for beta plus decay?
Neutron deficient nuclides
Describe the nuclides used for beta minus decay?
Neutron excess nuclides
Why does decay occur?
Decay occurs due to an imbalance between protons and neutrons
Unstable nuclides do no not necessarily exist in nature as their decay is rapid
How are unstable nuclides produced?
Nuclear reactions
Cyclotrons
How is an unstable nuclide created in a nuclear reaction?
Add a proton to a stable atom
Proton goes inside the nucleus
Give an example of a nuclear reaction to produce an unstable atom
14 N + 1 H –> 11 C + 4 He
7 1 6 2
15 N + 1 H –> 15 O + 1 n
7 1 8 0
How does a cyclotron work?
It gives energy to protons by accelerating them
This creates a proton beam which bombards the target to produce PET radionuclides
Particle is confined to a circular path by a magnetic field
Energy increases with each rotation
High energies possible with compact design
Within a vacuum chamber
What is the energy of the proton beam in a cyclotron?
15MeV
What are the pros and cons of a shielded room vs. self shielded cyclotron?
Shielded room - expensive, easy to access for maintenance and target development
Self-shielded - compact, can work nearby, cheap, but more difficult to access
What is the disadvantage of cyclotrons?
Very expensive to run and build
Cost 1-1.5 million
How is the circular motion created in a cyclotron?
A charged particle in a magnetic field has a circular motion
The oscillator changes the direction
What is the advantage of the circular design of a cyclotron?
Can be more compact than linear
Increase in rotations causes an increase in energy
What are the pros and cons of a shielded room vs. self shielded cyclotron?
Shielded room - expensive, easy to access for maintenance and target development
Self-shielded - compact, can work nearby, cheap, but more difficult to access
Give examples of cyclotron produced nuclides
Mainly beta + decay: 18F 11C 13N 15O
Mixed decay:
124I
64Cu
What is the branching ratio and half life of: 18F?
97% beta +
109.6 minutes
What is the branching ratio and half life of: 11C?
99% beta +
20.3 minutes
What is the branching ratio and half life of: 13N?
100% beta +
9.96 minutes
What is the benefit of a long half life?
You have to isolate the patient :(
Can see longer biological pathways and process
Also allows for repeat scanning from the same radiation does to see a process in stages
Why can multiple types of decay be useful?
Can combine radionuclide therapy with imaging
For example if mixed alpha and beta +
What does Emax mean in relation to cyclotron produced nuclides?
Maximum energy a positron can have
Different nuclei have different energies
What is the effect of increasing the energy a positron has?
Decreases resolution
What is the benefit of a long half life?
You have to isolate the patient :(
Can see longer biological pathways and process
Also allows for repeat scanning from the same radiation does to see a process in stages
What occurs in a nuclear reactor?
- Uranium decays and creates neutrons
- Reaction increases exponentially
- Target of heavy elements in reactor core
- Nuclei absorb THERMAL NEUTRONS and undergo FISSION
- Fission products are neutron rich and decay via beta minus decay
What radionuclides are produced in a nuclear reactor (fission)?
131 I
99 Mo
137 Cs
133 Xe
What is the problem with fission?
It is unpredictable - it is uncertain how it will split
There are many branches and potential fission biproducts
What is a nuclear generator and how does it work?
- Generators serve as a source of a short lived radionuclides
- Constructed on a decay-growth relationship
- Product a daughter nuclide from a parent nuclide (both of which must be distinctly different)
- Makes SPECT cheaper
Give an example of radionuclides (beta plus decay) that can be created in a generator
82Sr -> 82Rb
68Ge -> 68Ga
62Zn -> 62Cu
Describe the decay of 99Mo
99Mo –> decays via beta negative decay with a half life of 67 hours to –> 99mTc
99mTc –> decays via gamma decay with a half life of 6 hours to 99Tc
What are the regulations in place for the generation of radionuclides?
- Radiochemistry quality control
- Good manufacturing practice
- Manufacturing licence
Meeting all regulations is expensive and hard to set up
How common are generators for beta plus radionuclides?
Several PET nuclides can be generator produced but they are not commonly used
Likely to change
Give an example of radionuclides (beta plus decay) that can be created in a generator
82Sr -> 82Rb
68Ge -> 68Ga
62Zn -> 62Cu
Describe the formation of a radioactive molecule to be injected into the patient
Radionuclide needs to be attached to another molecule
This needs to be done quickly with minimal human interaction
Generate more than you need to allow for the decay
Needs to be made as automatic as possible and needs to be a quick process
What are the regulations in place for the generation of radionuclides?
- Radiochemistry quality control
- Good manufacturing practice
- Manufacturing licence
Meeting all regulations is expensive and hard to set up
What does radiopharmaceutical quality control state?
Need good reproducibility of these factors:
- Radiochemical purity
- Chemical purity
- pH
- Sterility
- Apyrogenicity
- Very low toxicity
Define radiochemical purity
The fraction of a specific radionuclide present in the desired chemical form and in the specified molecular position
What causes radiochemical impurities?
Incomplete reactions
Side reactions
Incomplete removal of protecting groups
What are the design considerations for creating a radio-molecular?
- FUNCTION: a platform that meets the radiochemists requirements
- SAFETY: radiation, remote processing, health and safety regulations
- QUALITY: reliability, reproducibility, validation
- FINANCE: funding, manufacturing costs, running costs, resources
- DELIVERABLES: synthesis yield, synthesis speed, size, simplicity
What are the features of tracer synthesis that needs to be considered?
- Large amounts of radioactivity are needed (need shielding and robotics)
- Radioactive half life
- Very small molar quantities
- High specific activity is usually required
- Very high radiochemical yield and reliability
Why is it important to ensure chemical purity?
Mandatory for tracers to avoid adverse reactions and pharmacological or toxic effects.
Impurities result in poor quality images due to the high background in surrounding tissues
What is outlined by Good Manufacturing Practice with regards to radionuclide creation?
Ensures the products are consistently produced and controlled to the quality standards appropriate to their intended use:
- Personel
- Premises and equipment
- Documentation
- Production
What are the design considerations for creating a radio-molecular?
- FUNCTION: a platform that meets the radiochemists requirements
- SAFETY: radiation, remote processing, health and safety regulations
- QUALITY: reliability, reproducibility, validation
- FINANCE: funding, manufacturing costs, running costs, resources
- DELIVERABLES: synthesis yield, synthesis speed, size, simplicity
What are the features of tracer synthesis that needs to be considered?
- Large amounts of radioactivity are needed (need shielding and robotics)
- Radioactive half life
- Very small molar quantities
- High specific activity is usually required
- Very high radiochemical yield and reliability
What are microfluidic devices (MFD)?
Reactions take place in very small places Fully automated syntheses can be conducted Very advanced technology Used for fast FGD production 40% 18-FDG yield in 10-12 minutes - 6 mins drying - 2 minutes radiolabelling - 2 minutes purification
What are the steps involved in tracer distribution?
- Fixed site with cyclotron and scanner
- Tracer sent to sites with a fixed scanner and no cyclotron
- Tracer sent to mobile scanner
- Stand alone production facility to support mobile scanners OR fixed sites
What are the benefits and negatives of mobile PET scanners?
Very complicated procedure to control
Planes can be used to transport FDG
Allows for PET scanning in remote areas
Describe the kinetic rates of FDG
Measure the change of radioactivity over time to calculate kinetic parameters
Transport and phosphorylation of de-oxy glucose differs only a term from glucose *.
This is termed the lump constant (0.89)
What is FDG?
Fluoro-deoxy glucose
Deoxyglucose is an analogue of glucose with H replaced by OH
Deoxyglucose is then labelled with 18F.
It cannot be isomerised to fructose-6-phosphate and metabolised further and is trapped in mitochondria
What is the decay time of 18FDG?
2 hours
What happens to FDG in tissue?
It is trapped within the cells.
This is at a rate proportional to glucolysis.
Tracer amount accumulates and get a higher intensity signal.
Describe the kinetic rates of FDG
Measure the change of radioactivity over time to calculate kinetic parameters
Transport and phosphorylation of de-oxy glucose differs only a term from glucose *.
This is termed the lump constant (0.89)
What are the 3 possible scanning protocols in PET?
Static: Inject, wait, scan an area
Whole body: Inject, wait, scan in sections by moving the bed
Dynamic: Inject then scan in sections
What is the normal scanning protocols for using FDG?
Inject and leave for 1 hour
Scan for 20 minutes
This allows FDG time to accumulate
Why are shallow breathing protocols used in CT?
1-3cm variation with breathing
Large discrepancy in liver and lungs
Can create a strong artefact in PET (due to attenuation correction)
How is a whole body SPECT or PET generated?
7-8 bed movements with approximately 3 minutes at each
What are the new advances in PET/CT?
Multiple passes per bed position
Possible continuous bed motion
Respiratory motion correction (track motion mathematically or externally)
How is a CT scan acquired in a PET-CT?
- First have a scout scan to determine body position
- CT at lower dose than diagnostic CT and is used for localisation. Can do full dose if you require the CT
- Used for CT attenuation correction
- Normally without contrast agents
- Normally with shallow breathing protocols
Why are shallow breathing protocols used in CT?
1-3cm variation with breathing
Large discrepancy in liver and lungs
Can create a strong artefact in PET (due to attenuation correction)
What methods are used to standardise SUV?
Lean body mass
Geometric body surface area
Ideal body weight
18FDG body surface area
What are the new advances in PET/CT?
Multiple passes per bed position
Possible continuous bed motion
Respiratory motion correction (track motion mathematically or externally)
How do you calculate a SUV?
Standardised Uptake Value
SUV = tissue concentration (MBq/ml) /
Injected dose (MBq) / Body weight in kg
What is SUV?
Standardised uptake value
- Standardised way of comparing different patients
- Changes day to day, scan to scan, hard to tell accuracy
It doesnt include an error estimate
What methods are used to standardise SUV?
Lean body mass
Geometric body surface area
Ideal body weight
18FDG body surface area
What is SUV max?
Maximum SUV value in a region
What is SUV mean?
Average SUV in a region
What are the difficulties with defining the region of a tumour?
- Manual deliniation (variations between individuals)
- Automatic thresholding (e.g. include all voxels 40% SUVmax)
- 3D imaging can be time consuming to delineate
SUV max is commonly used
What are the disadvantages of using SUV?
Rough description of tracer kinetics
Limits on testing drug efficacy
Doesnt fully exploit characteristics of different tracers
Semi-quantitative
Only works for tracers of flux (e.g. FDG) where uptake is not too influenced by perfusion
What is the advantages of dynamic PET imaging?
Offers a more complete framework of analysiss
Tracks tracer over time and use this for SUV
Can do kinetic modelling to determine the chemistry of the biological process
Can do volumetric chemistry over time
Parametric imaging
Has units - not an arbritary number
What is required for dynamic pet imaging?
Need to measure radioactivity in plasma
Need multiple snap shots
Need to know how fast the process is (number of counts per s)
What radionuclides are used in bone imaging?
99m-Tc- diphosphonates
Organic phosphate compounds
MDP = methylene diphosphonates HDP = hydroxyl-methylene diphosphonates
Can choose which
In terms of bone imaging what does tracer uptake depend on?
Blood flow - lesion must have blood flow
Activity of osteoblasts - bone turnover
Local Ca2+/PO4 2-
What the indications for bone imaging?
Suspected metastases Radiographic lesion Persistent pain with normal radiograph Acute symptoms Assessment of joint disease
What legislations must be met for NM imaging?
IRMER
ARSAC
Local rules
Quality control
What radionuclides are used in bone imaging?
99m-Tc- diphosphonates
Organic phosphate compounds
MDP = methylene diphosphonates HDP = hydroxyl-methylene diphosphonates
Can choose which
In terms of bone imaging what does tracer uptake depend on?
Blood flow - lesion must have blood flow
Activity of osteoblasts - bone turnover
Local Ca2+/PO4 2-
What the indications for bone imaging?
Suspected metastases Radiographic lesion Persistent pain with normal radiograph Acute symptoms Assessment of joint disease
What is the protocol used for bone imaging?
20-25 minutes in the scanner
Wait 2-4 hours after injection
Need to wait as a low percentage of cardiac output to the bone
Allows time for tracer to collect in bones
Children have active growth rates and therefore there are increased tracer at plates
What are the radionuclides used in lung imaging?
99mTc- MAA (macroaggregated albumin) for perfusion
99mTc- technegas for ventilation
How is 99mTc-MAA administered?
Used for lung perfusion
It is injected
Particles 10-30um in size, blocks 0.1-0.3% of pre-capillary arteries
How is 99mTc-technegas administered?
Used for lung ventilation
It is inhaled
Particles 0.1-0.5um in size and are deposited on bronchoalveolar cell lining
What are the indications for lung imaging?
Suspected PE
Relative lung function
Suspected right to left shunts
What are the reasons for VQ imaging over CT?
When CT can’t be done:
Allergic to contrast
Renal failure (from contrast)
Pregnancy
What is the process for determining renal function using imaging?
Draw ROI over organ See how radioactivity decays in the area Plot time activity curve Done with diuretic Can determine: shape, morphology, function and split function (%R&%L)
What is 99mTc-MAG3 used for?
Renal imaging
Used for dynamic renal function and drainage
It is cleared by tubular secretion
Can see drainage and whether there is an obstruction
What is 99mTc-DMSA used for?
Used for static renal function
Localises to the cortex (proximal tubular cells)
What are the indications of renal imaging?
MAG3: dilated collecting system or obstruction
DMSA: relative renal function and scarring
What is the process for determining renal function using imaging?
Draw ROI over organ See how radioactivity decays in the area Plot time activity curve Done with diuretic Can determine: shape, morphology, function and split function (RvL)
What are the radionuclides used in cardiac imaging?
99mTc-pertechnetate
99mTc-tetrofosmin (sestamibi)
What is 99m-Tc pertechnetate used for?
Cardiac image
Tracer stays in blood
Can be used to look for LV ejection fraction
Reserved only for patients on chemotherapy that is cardiotoxic.
Very producible and not user dependent
How does 99mTc- sestamibi work (tetrofosmin)?
Tracer is taken up where there is a high concentration of mitochondria
Lipophilic cation which diffuses across the cell membrane and localises in mitochondria
What is the use of 99Tc- sestamibi and what are its indications for use?
Measures myocardial perfusion at rest and at stress
Indications: IHD, function significance of known CAD, risk stratification
What radionuclide is used for heptaobiliary imaging?
99mTc- HIDA
What is 99mTc HIDA used for?
Hepatobiliary imaging
It shows the formation, excretion and drainage of bile,
It is a bile salt analogue and it allows you to calculate a GB ejection fraction under stress (meal)
What the indications for hepatobiliary imaging using 99mTc-HIDA?
Biliary dyskinesia
Sphincter of Oddi dysfunction
Biliary atresia or biliary leaks
What radionuclide is used for gastric imaging?
99m-Tc labelled solid component meal
Give the patient a standard meal - need to be aware of the effect of other drugs on stomach emptying
What is the purpose of gastric imaging?
Allows the study of the rate of gastric emptying
What radionuclides are used in thyroid imaging?
Benign = 99mTc-pertechnetate Cancer = 123I and 131I
How does 99mTc-pertechnetate work in thyroid imaging and what are the indications/
It is trapped by the thyroid in follicular cells. It measures uptake.
Indications: demonstration of functioning thyroid tissue and investigation of thyrotoxicosis
What radionuclides are used when imaging thyroid cancer and how do they work?
123I and 131I
It relies on trapping and organification
123I is used for imaging
131I is used for imaging and therapy
What are the indications for thyroid imaging using I?
Treatment - complete ablation with high dose radiation (GBq) of 131I
Imaging residual disease and metastases (MBq) doses with either 123 or 131
Need to remove all thyroid cells to allow for more effective recurrance detection
What radionuclide is used in lymphatic imaging?
99mTc labelled nanocolloid
How is lymphatic imaging done?
99mTcc labelled nanocolloid is injected either intradermally or subcutaneously.
Intradermal is quicker as there is a greater lymphatic network.
Nuclide then cleared by lymphatic channels.
What are the indications for lymphatic imaging
Sentinel node imaging in cancer
lymphoedema
What radionuclide is used in brain imaging?
99mTc-HMPAO - cerebral perfusion
123I - ioflupane = dopaminergic pathways
What is 99mTc-HMPAO used for?
Brain imaging
Used to measure cerebral perfusion
Need to by hydrophilic to cross the BBB
What are the indications for brain imaging using 99mTc-HMPAO?
Cognitive impairment
Dementia image - diagnosis
Epilepst
Stroke imaging
Moving towards PET
What radionuclide would you use to image dopaminergic pathways in the brain? What are the indications
123I -ioflupane (DaTSCAN)
The uptake depends on selective binding to pre-synaptic dopamine receptors
Indications: investigation of suspected Parkinsons (90% accurate)
What radionuclide is used for oncological imaging?
18F-FDG
Glucose analogue labelled with positron emitting isotope
What are the main applications of SPECT imaging?
Brain
Heart
Musuloskeletal
Endocrine
What are the physical limitations of SPECT?
Scatter
Attenuation
Partial volume effects
Describe an original SPECT/CT system?
15 years ago
Rudimetary CT using xray tube
Low quality CT - used for localisation not characterisation
Describe a new generation SPECT/CT scanner
Latest multidetector CT technology - diagnostic CT, 64 detector rows
Allows for more accurate localisation and characterisation
Advanced gamma camera and CT = facilitates low dose imaging and faster data acquisition
Iterative reconstruction (lower dose or speed up)
Mulit-modality work station and additional PACS software required
How can SPECT/CT improve clinical utility of nuclear medicine examinations?
- Providing more accurate localisation
- Detecting additional lesions
- Excluding physiological tracer uptake
- Charactering equivocal anatomical lesions
- Providing reliable CT based attenuation correction
- Facilitating one stop shop imaging
- Reducing the need for multi-layered testing
What are the consequences of specificity and sensitivity with using SPECT/CT>?
Increase specificity = increased localisation
Increased sensitivity = increased lesions detected
The increase in specificity is greater than sensitivity
What are the clinical applications of SPECT/CT?
Bone imaging Neuroendocrine tumour imaging Parathyroid imaging Thyroid imaging Hepatobiliary imaging RBC imaging Infection/inflammation imaging
In SPECT/CT how long does each component take?
SPECT = approx 10 mins CT = seconds
What is a blood pool image?
Initial phase = tracer is in the blood and it is mainly used for looking at soft tissue uptake e.g. hyperaemia
What is a dual phase scan?
Scans at an initial and delayed phase - common in bone scans.
What is the protocol for suspected scaphoid fracture?
No clear guidance.
After X ray, MR recommended but there are problems with availability
If a bone scan is negative - 99% confident no fracture
It can miss if done in elderly or within 24 hours
When in bone imaging is SPECT/CT suggested?
When it affects the axial skeleton or proximal long bones as plain X-ray is poor here
It is also good for pathology of the ankle
When there is metal work (new CT have minimal artefacts)
What are neuroendocrine tumours?
Diverse group of rare neoplasms accounting for 2% of all cancers.
What are the 3 subtypes of neuroendocrine tumours?
- Neural crest origin - phaechromocytoma, paraganglionoma, neuroblastoma
- Meduallry thyroid cancer (MTC) - rare and complex to image
- Gastroenteropancreatic (GEP) tumours - carcinoid and endocrine pancreatic tumours (EPTs) they are hormonally active and hard to diagnose
How are neuroendocrine tumours imaged?
They express somatostatin receptors (SSR) subtypes 2 and 5
Imaged with SSR analogues e.g. 111-Indium labelled pentreotide (octreoscan)
Must use SPECT/CT
Neural crest tumours are imaged with guanethidine analogues e.g. 123Iodine-mIBG
What is the protocol for thyroid cancer imaging?
Done after resection and ablation
Allows more effective monitoring of thyroiglobulin
131-I kills all thyroid cells
Image 3 days after administration due to very high radiation levels
Can pick up any metastases
What radionuclide is used in parathyroid imaging?
99mTc- sestamibi
What is the purpose of parathyroid imaging?
Used for primary parathyroid cancers
Allows for more specific localisation of adenoma to have minimally invasive surgery
Parathyroid holds onto radiation longer than thyroid which washes out
What are the reasons for doing sentinel node imaging?
It is the first draining node of an area
- well esablished in breast cancer and adenoma
- prevents resecting multiple lymph nodes
- prevents long term morbidity
How is WBC imaging done?
Label the patients own WBCs and inject back into the patient
Useful in infection and inflammation
Why is RBC imaging used?
Used for GI blood loss
Can find source of bleeding
Can find smaller bleeding rates than CT angiography
(High uptake in spleen due to sequestering)
In PET/CT what are the variables that can be changed in CT?
- Can acquire diagnostic level CT
- If not required can have low dose CT
- Non-contrast
- Shallow breathing protocol
In PET/CT what are the variables that can be changed in PET?
- Number of bed positions (7-8)
- Time per bed position (2-5 mins)
- Movement artefact (increases with scan time)
- Dual time point
- Decrease dose and increase scan time or VV
What are the common PET radioisotopes?
18F
11C
13N
15O
Describe PET tracers
Different tracers for different purposes
Location of cyclotron limits what procedures you can do
Most produced in cyclotron
Short half life
Measures physiological processes e.g. glucose metabolism, blood flow, hypoxia, proliferation etc
What is the most common PET tracer?
FDG - most cancers demonstrate an increased glucose uptake
Cancers upregulate GLUT1 receptors
What is the Warberg effect?
Most cancers demonstrate an increased glucose uptake
Cancers upregulate GLUT1 receptors
What is the basics behind PET imaging?
Administer tracer (positron emitting)
Positron annihilates with electron
This produces 2x511keV gamma photons
Use coindence to detect locations
What are the features of FDG?
It competes with glucose for transport and into cancer cells
It becomes phosphorylated and trapped within the mitochondria
What are the benefits of PET/CT?
- Combines functional and anatomical info
- More accurate localisation
- Better detection
- Increased sensitivity and specificity
- has significant impact on patient management
- Able to see disease not on normal CT
- Fused data sets increase correct imaging reading
Where is PET/CT commonly used?
Lung Colorectal Lymphoma Head and Neck Oesophageal
What is the networking strategy?
Aim to have 1 PET/CT scanner per 1.5 million population
Funded by the department of health
National program
Spread throughout country
What is the cost of an average PET/CT scan compared to just CT?
PET/CT = = £1000 CT = £150
What are the most common PET/CT uses?
47% lung 16% lymphoma 10% oesophagus 8% colorectal 6% head and neck
What are the established uses of 18F-FDG PET/CT in oncology?
Lung Lymphoma Head and Neck Oesophagus Colorectal Melanoma Breast Thyroid Cervical Heptaobiliary Unknown primary malignancy
What are the emerging uses of 18F-FDG PET/CT in oncology
Neuroendocrine tumours
Brain tumours
Bone and soft tissue sarcomas
What are the 7 steps in the role of FDG PET/CT in oncology?
- Characterisation
- Staging
- Re-staging
- Response assessment
- Recurrence detection
- Radiotherapy planning
- One stop shop imaging
What is characterisation in relation to pet/ct?
It is determining the nature of lesions detected on imaging
hard to tell if a mass is malignant or benign without pet/ct
What is staging and how is it done with pet/ct
It is determinig the extent of disease
PET/CT increases the sensitivity and specificity
Can guide appropriate treatment
Can change the risk profile of nodules/findings
Can detect multiple sites which a CT can miss
What is restaging and how is it done with pet/ct
Determining the extent of disease (again) after treatment to determine efficacy
Can pick up sites miseed on ct
lymphoma not normally seen on ct
What is response assessment using pet/ct
Checks if a treatment has worked and this is a rapidly growing area
Guides treatment decisions - tailored therapy
- Can change therapy, stop chemo, track effectiveness, change midway if prognosis poor
PET/CT FDG shows changes before anatomical changes
Can predict overall response and disease free survival
Can determine end of treatment response: Can’t tell residual disease vs fibrosis with just ct
What is recurrence detection and how is done using pet/Ct
Differentiating fibrosis from recurring disease
Can tell with multiple CT scans over time but not with just one CT.
Adds metabolic activity
Can pick up occult disease missed on anatomical imaging
What does radiotherapy planning using pet/ct involve?
It allows for a more targeted therapy - to get higher doses to smaller areas
Outline the:: GTV - gross tumour volume CTV - clinical target volume PTV - planning target volume TV - treated volume IV - irradiated volume
Increases accuracy. It decreases toxicity by decreasing the area
What are the newer applications for 18F-FDG PET/CT
Infections
Inflammation
Cardiology
Neurology
What are the new applications in PET/CT not using FDG?
Oncology (choline)
Cardiology (rubidium)
Neurology (amyloid plaques)
What is 18F used for?
Waste product of FDG
Marker of osteoblastic activty
Good for imaging bone mets
PET has better resolution than SPECT
What is 18F-Choline used for?
Marker of membrane synthesis
Useful in prostate cancer
Prostate is not very metabolically active so has limited glucose uptake - can be picked up with choline
Can also be used for occult node involvement and bone mets
Can image the process you are targeting
What non fdg radionuclides are used in PET oncology?
68Ga-DOTA-ocreotate
Used in neuroendocrine tumour receptor imaging
Can use 111 Indium octeotide
How is infection and inflammation imaged using PET?
FDG uptake is non-specific and is increased in infection and inflammation - can’t distinguish from cancer
Needs confirming with tissue samples
- Can measure baseline and treatment response
- Can be used to image large vessel vasculitis as this can’t be seen on CT
- Can be used to find pyrexia of unknown origin e.g. aortic graft rejection
- Can be used for sarcoidosis (uncommon as benign)
What radionuclides are used in cardiology PET?
Oxygen - research
nitrogen - research
rubidium
FDG
What are the uses of cardiology PET?
Myocardial perfusion and myocardial viability
PET perfusion = rubidium
SPECT perfusion = 99mTc
PET viability = FDG
What are the uses of neurology PET?
FDG
- Epilepsy - hypometabolism
- Dementia
- Neuro-oncology
Non FDG
- amyloid plaque imaging in Alzheimers
How is dementia imaging done in PET?
Image if the causes is unknown
Assessed metabolic activity in the brain - hypometabolism
Aims to detect patients early e.g. pre-symptomatic and use therapies to delay onset
Can pick amyloid deposition
Can pick up whether they are 11C - PIB positive or negative. 82% of those who are positive go on to get Alzheimers
Amyvid can assess amyloid plaques but it very expensive
What are the technical difficulties of PET/MR?
MRI doesnt give density map MR needs attenuation correction Scan times are longer Decreased quality of MR to shorten time Can have artefacts in mR very expensive
What are the clinical applications of PET/MR?
Paediatrics Oncology Gynae imaging Multiparametric assessment Neurology Cardiology
What is the definition of molecular imaging?
Measuring/locating a molecular process or gene expression
It does not image anatomy or structure
it does not image function processes like perfusion
What imaging techniques are best for molecular imaging?
PET
Optical
What is optical imaing?
Used in preclinical research and detects light rather than gamma rays
Useful for molecular imaging
What are the different types of ionising radiation??
beta + beta - alpha gamma X-ray
What ionising radiation does PET imaging use?
Beta + (positron)
2 gamma rays
What ionising radiation does SPECT imaging use?
Gamma
What ionising radiaition foes radionuclide therapy use?
beta minus and alpha
What are the key attributes to radionuclide imaging (PET and SPECT)?
- Tracer quantities are pico or nano molar (much lower than CT and MR)
- Should not ellicit physiological response
- Low risk of toxicity
- Radiation risks should be calcuable (radiation purely from tracer)
- Rapidly translated to clinical studyy
- Quantitative
- Non- invasive
- Whole body
- Molecular rather than anatomical
What are the advantages of pet over spect?
Pet has better resolution (5-10mm)
Pet has better sensitivity
Pet has better quantification of images
Uses lower levels of radiation as it does not need to over Collimators
What are the advantages of spect over pet?
Spect is cheaper
It is more widely available
Multitracer imaging is possible
Improving performance imaging
What is the principle behind radionuclide therapy?
It turns toxicity to your advantage.
It is the selective delivery of radiation to the tumour using the same principles as imaging
Uses beta or alpha emission
Low penetration and therefore create a high local dose and kills the cells
Give examples of radionuclide therapy
Thyroid cancer 131- I
Bone metastasis 188-Re or 153-Sm or 233-radium (alpha)
Lymphoma
Neuroblastoma
What are the 7 steps involved in creating a new radionuclide?
- Find a molecular target
- Consider chemistry - attach radionuclide to particle
- Consider molecular biology/cell biology
- Small animal models
- Imaging
- Computer modelling
- Clinical imaging
Repeat 1-6 until suitable for clinical
Give examples of molecular targets
Sodium iodide symporter (iodine or pertechnetate)
Tumour specific antigen
Neuropeptide receptor (somatostatin or calcitonin)
Glucose transporter (FDG)
Amino acid transporter (f18 tyrosine)
Angiogenesis (rgd peptides)
Transferrin receptor (Ga 67)
What are the uses for molecular imaging?
Clinical diagnosis and decision making Location and detection of disease Molecular characterisation of disease Bio markers to predict or measure therapy outcome Drug development tool Basic biomedical research Therapy
What are the advantages of using radioactivity for imaging?
Tissue penetration is greater than light
Increased sensitivity
Risk generally very small - risk of not scanning greater
What are the disadvantages of using radioactivity for imaging?
Increased radiation dose Cost of radioisotopes and technology Development is expensive Avoid in children and pregnant women Needs to be avoided if unnecessary
How is the thyroid imaged using molecular imaging?
Human sodium iodine symporter hNIS is imaged
It is essential for thyroid function (production of thyroid hormone) and is over active or under active in some cancers
Useful for staging and shows loss of thyroid and any metastatic spread
Where is hNIS present?
Thyroid
Stomach
Mammary glands
What are the substrates used to image hNIS?
123 I iodide. Spect 131 I iodide. Therapy 124 I iodide. Pet Perchlorate (competitive inhibitor) 99m Tc pertechnetate. Spect F18 tetrafluoroborate. Pet
What do all hNIS substrates have in common?
They all have a single negative charge
Very similar size
Body can’t differentiate molecules
I-, At-, TcO4-, BF4-
What can FDG and glucose metabolism be used to detect?
High metabolism and replication
Low oxygen
Anaerobic metabolism
Increased glucose consumption
What happens in tissues that have increased glucose uptake?
Increased glycolysis requires increased glucose
Glut1 expression is increased
Glut1 is translocated to cell membrane
Hexokinase is increased
What happens to FDG in the cells?
It is an analogue of glucose and is a substrate for glut1 and hexokinase
It enters the cell and is phosphorylated by hexokinase to FDG-6P
It cannot be broken down further and is trapped with in the cell
Why are somatostatin receptors imaged?
It is a hormone that regulates the endocrine system and is involved in neuro transmission and cell proliferation
It is switched on in neuroendocrine tumours and is not strongly expressed in adults
Target for therapy and imaging
How are somatostatin receptors imaged?
Using 68Ga octreotide - it has the same binding area as somatostatin.
Somatostatin is very unstable and breaks down rapidly.
Octreotide has a DOTA chelate which makes it more stable.
It is broken down slower
What is the principle behind hypoxia imaging?
It is an oxygen deficiency that causes changes in cell biology.
These changes can be detected using molecular imaging.
Hypoxia cells have increased free electrons and this breaks down the molecule.
This causes an accumulation of copper/radionuclide in the cell and causes the copper to dissociate from the molecule
Why is hypoxia imaging useful?
Hypoxia can cause resistance to radiotherapy and chemotherapy.
It is also an indicator that a tumour is more aggressive.
It can also be used in IHD and stroke
What is the pet imaging agent used in hypoxia?
Cu-ATAM
18F-FMISO
What is the spect imaging agent used for hypoxia imaging?
99m Tc HL91
What is angiogenesis and what is it associated with?
It is the formation of new blood vessels and is associated with: Tumour growth Wound healing Tissue remodelling Inflammation
What is metastasis?
It is when cancer cells are transported by the circulatory system to distant sites. It requires angiogenesis.
Cancerous tumour cells release molecules that send signals to surrounding tissue and this activates certain genes that encourage blood vessel growth.
When does angiogenesis occur in normal development?
Vasculogenesis - creates the primary network of vascular endothelial cells that will become the major blood vessels
Angiogenesis - remodels the network into the new small vessels that complete the system
When is angiogenesis normal in adults?
Menstrual cycle
Necessary for repair and regeneration of tissue during would healing
What contributes to rare cell division?
Inhibitors are high
Activators are low
What contributes to frequent cell division?
Inhibitors low
Activators high
What are the molecular targets for imaging angiogenesis?
Integrins alphav beta3 - they are present on the surface of endothelial cells. They bind matrix macromolecules and proteinase a
VEGF- affects permeability
Ang 1 and ang 2 - stabilises the vessels
Plasminogen activators
What radionuclide is used to image angiogenesis, what does high uptake indicate?
18F-galacto-RGD
Binds to avb3 integrins
Very high in angiogenic tumours - sign of an aggressive tumour
How does multidrug resistance occur in chemotherapy?
Cells have machinery to export potentially toxic substances
Example: MDR1 gene product, this is found in bbb, liver and tumour cells.
This is a problem for chemotherapy
Increased expression of MDR1 can lead to increasing amount of drugs being exported out of the cell
Describe the function of MDR1/ PgP
It recognises a wide range of molecules, especially lipophilic cations.
It is located in the cell membrane and the presence can be induced by hypoxia and chemotherapy.
It captures the drug inside the cell and transports it out
Imaging this can be used to measure quantity and make decisions about chemotherapy
How do you image PgP?
Label with 99mTc or 64Cu
Measure uptake - it is trapped in mitochondria
Then measure clearance - clearance is faster with PgP, this requires dynamic sampling
Can repeat the scan after injection of a PgP inhibitor to check (verapamil)
What is transferrin?
It transports iron in the blood to deliver it to cells
How are transferrin receptors imaged?
Ga3+ binds to transferrin and it mimics iron due to its similar size and charge.
Inject 67 or 68 Ga and it binds to transferrin and receptors
Why is imaging transferrin receptors useful?
Transferrin receptors are over expressed in lymphoma and prostate cancer.
The Ga is internalised and it shows cells with increased iron requirement
Increased fe in melanoma
What is the normal distribution of gallium in the body when administered?
It is where lactoferrin is present: milk, saliva, tears and nasal secretions.
Also high in liver as this is where radio metals are metabolised
What are the usual nonmetallic PET tracers?
15O
13N
11C
18F
What are the usual metallic PET tracers?
64Cu
86Y
89Zr
94mTc
What is the half life of 64Cu?
12.7 hours
What is the half life of 86Y?
14.7 hours
What is the half life of 89Zr?
78hours
What are the features of metallic tracers used in pET?
Long half life (days-hours) Produced via cyclotron or generator Have redox chemistry Bio metal mimics Label large molecules, not small
What are the features of nonmetallic pet tracers?
Short half life (mins to hours) Produced in cyclotron No redox chemistry Label small molecules Can label large molecules but they have very short half life
What does it mean when a tracer has redox chemistry?
Metallic elements have a very rich redox chemistry
This is the addition or removal of electrons
They have several states available
What are the advantages or disadvantages of tracers having redox chemistry?
Advantage: used in hypoxia imaging using copper
Disadvantages: problems with stability
What are the disadvantages of metallic tracers?
- Higher energy particle bombardment, but several are still in the cyclotron range
- labelling is simpler but the processing is more complex
- inorganic - it is not easily used with small organic molecules and the uses reflect this
- needs a chelator to increase stability
What are the uses of metallic tracers?
Peptides Antibodies Nano particles Processes that needs a long half life Biological and radiological half life need to be matched
What is a bio metal mimic?
It can be used to look at where the metal goes normally
What is the chelate effect?
When 1 ligand is bound it increases the probability of the 2nd and 3rd binding etc.
this increases the stability constant
It requires specific geometry and needs to be designed
Describe metal ligand bonding
It is not a one way reaction
It is in equilibrium
Increasing the stability constant decreases the likelihood of being broken down
What are the problems with chelators?
It causes a significant modification of molecule
Increases the size
If it was a small molecule the change will be significant and it will no longer behave as the original
If the molecule is large e.g. Antibodies, the change is insignificant
What are the requirements for a radio metal PET imaging agent?
- Half life needs to be matched to biological half life
- Chelator is required to increase stability (need to be specifically designed)
- Emission properties - beta plus range, beta plus emission dose
- Effect of labelling and or chelating - on bio distribution or pharmokinetics
- Specific activity - increased specific activity is increased radioactivity per gram
What are the applications of using radio metals in pet imaging?
Mimicking bio metals 82Rb mimics K+ (myocardial imaging) 52Fe to see iron metabolism 64Cu to see Copper metabolism 83Sr to see bone metabolism (calcium analogue)
What are the important features and uses of 82Rb?
Rubidium 82 is injected as an atom
It is produced from a Sr generator (half life of 25 days)
It is used in myocardial perfusion and it identifies regions of poor blood flow
Half life -76s
It is a potassium analogue and can be used to image Na/K pump
What are the important features and uses of 64Cu?
It uses oxidation and reduction states of copper
Half life - 13hours
Small cation +1 or 2
What is the chemistry of 68Ga?
Used for SSR imaging Hard small cation \+3 charge Similar to iron No redox Binding to Ligands is weak
Why can chelators be a problem?
Change the shape and stop working
Hard to design
Expensive to develop
Can involve heating which can damage the molecule e.g. Antibodies
What is the chemistry of 89Zr?
Long half life 78hours Suitable for imaging antibodies Zr 4+ Binds readily to oxygen It is very selective Binds to prostate cancers
How can radionuclides be used as a therapy?
Beta emitters with a long half life can be delivered to the area
Drug loaded nano particles can deliver chemo drugs to a specific area via receptors
If beta and gamma can image and treat at the same time
What are the advantages of using radio metals in pet imaging?
Generator availability
Longer half life for transportation
Longer half life to image longer biological processes
Specific metabolic and chemical properties
Linked with therapeutic analogues
What are the advantages of molecular imaging?
Non invasive
Real time
In living tissues and cells
Allows you to study in the natural environment
Why are animals used in preclinical imaging?
It is transferable to humans
Saves a lot of lives
What are the steps involved to producing a new imaging technique?
- Select biochemical process
- Find a molecular target
- Choose imaging modality
- Chemistry
- Labelling
- Molecular/cell biology
- Small Animal models
- Large animal models
- Imaging
- Computer modelling
- Clinical imaging
What are the features to consider when choosing the modality for preclinical imaging?
Spatial resolution Sensitivity Whether it is dynamic Whole body or region Temporal resolution required Penetration depth Quantitative Can repeat studies be done Is it clinically relevant
What are the features of CT?
Excellent spatial resolution Poor sensitivity Not dynamic Whole body or region Ok temporal resolution Limitless depth of penetration Quantitative Can repeat but dose High clinical relevance
What are the features of MR?
Excellent spatial resolution Very poor sensitivity Not dynamic Whole body or region Poor temporal resolution Limitless depth of penetration Semi quantitative Can repeat High clinical relevance
What are the features of a PET scan? Preclinical
Lowest spatial resolution Highest sensitivity Dynamic Whole body or region Very good temporal resolution Limitless depth of penetration Fully quantitative Repeats but dose High clinical relevance
What are the features of a spect scan? Preclinical
Low spatial resolution Good sensitivity Dynamic Whole body and region Very good temporal resolution Limitless depth of penetration Quantitative Repeat but dose High clinical relevance
What staff are involved in the development of preclinical imaging techniques?
MDT
Radiochemist, chemist, molecular biologist, geneticist, cell biologist, immunologist, animal model expert, medical physicist, clinician
What is the normal development time for a preclinical imaging technique?
Between 12 weeks and 3 years
What are the steps involved in producing new preclinical imaging technique?
Target or ligand discovery DNA cloning Expression system Protein production Imaging agent development In vitriol studies Preclinical imaging
What are the pros and cons of cone beam ct?
Faster
More expensive so not used preclinically
Image quality limited due to noise
HU less accurate
What corrections need to be done in preclinical ct?
Offset Gain Bad pixel Geometrical calibration HU Beam hardening
In spect how many photons make it through the Collimators?
1 in 1000
What is different about preclinical spect?
Uses pin hole Collimator
Increase resolution
What is a pin hole collimator?
It either magnifies or shrinks the image It flips the image upside down Has much smaller field of view 6x the resolution Better sensitivity
What determines spect resolution?
Intrinsic - noise in pmt signal, spread of energy deposition in detector due to scattering
Acceptance angle In which incident photons are accepted
Septal penetration
Septal scatter
What determines the resolution in Pet?
Crystal pitch Positron range Ring diameter Location of source Optical encoding error
What is the resultant change in pet resolution as you increase pixel pitch?
Increase pitch = decrease resolution
What happens to pet resolution as positron range increases?
Decreases
What happens to pet resolution as ring diameter increases?
Decreases
What can be done to increase pet resolution?
Decrease pixel pitch
Use computer correction for positron range
What are urge consequences of decreasing pixel pitch in pet?
Increase resolution
Increase inter crystal error
Increase cost
What is the partial volume effect?
It is when organs of different sizes appear different with the same activity concentration.
Smaller objects look colder
What can be done to increase sensitivity of pet?
Increase length of crystals
Increased the solid angle
Increase detector surface
Describe preclinical pet mr
Very expensive
Very recent due to production of mr compatible detectors
Currently sequential, mr then pet or vv
What are the key differences between preclinical pet and spect
Pet has decreased resolution than spect
Pet has increased sensitivity than spect
What are the uses of preclinical imaging in oncology
Angiogenesis Hypoxia Proliferation Tumour metabolism Apoptosis Metastasis
What are the uses of preclinical imaging in neurology
FDG uptake in seizures
Dopamine system
What are the challenges in preclinical imaging?
Need new imaging agents Biomarker discovery Production is not very efficient Technology Communication between different fields Clinical translation Sensitivity Practical aspects
Why use pinhole for preclinical spect?
Increased magnification
Increase sensitivity
Increased resolution
What new technologies could appear in the future?
Pet mr
Spect mr
What modality would you use to view mouse lymph nodes?
Pet mr due to soft tissue and sensitivity
Can do pet ct with contrast
Spect
Describe radio labelling for theragonostics
Combine gamma with beta
Beta is highly energetic and is absorbed by tissue and damages DNA
Can track therapy with gamma and measure response
Use Lut177 16% gamma 84% beta
Can predict outcome to treatment and indicate level of response
What are the features of functional imaging?
Images physiological function e.g. Glucose metabolism
Spatial resolution 4-15mm
Physiology nor always correlated with anatomy
More specific but not useful without anatomy
What are the features do anatomical imaging?
Images anatomical properties e.g. Attenuation or t1/t2 times
Spatial resolution is around 1mm
Can take a long time to detect anatomical changes
What are the features doe selecting an ideal spect isotope?
Type of emission - is it a pure photon emission
Energy of emitted photons - 100-200keV
Half life - allows Imaging and chemistry to take place. Needs to be long enough to view the process but as short as possible to reduce dose
Production - cyclotron or generator
What are the features of 99mTc?
99mTc --> gamma + 99Tc 6hour half life Produced from 99Mo Gamma are 140keV It is reactor produced Can be kept in the hospital and alluded when needed Only gamma, no therapeutic doses
What are the features of 201 Tl, thallium
201Tl –> gamma + 210Hg
Cyclotron produced
K analogue so can see sodium potassium pump
Gamma emission is 167keV and 135 keV
Most are X-ray rang 69-80kev from 210Hg
Images are noisier as you have to use less dose
What is the consequence of a high dose per unit activity?
Have to use less dose so less units of activity Decreased quality image Needs increasing smoothing Increased blurring Decreased contrast
How much restriction do the Collimators apply?
Restrict the direction of photons
1%
Can be less depends on Collimators
How is the position of the event determined in spect?
The position is calculated by the weighted position of each pmt based on the amount of light detected
Anger logic - uses the coordinates of the centre of each pmt x amount of light at each / total light
Describe the pmt array in spect?
Closely packed to increase effectiveness at collecting light
Some use hexagonal pmts to increase coverage of the NaI(Tl) crystal
What is pulse height analysis?
Reads z pulses to determine the energy of each gamma ray
If photons are scattered they lose energy
Don’t want to include as they provide false information
Use a narrow energy window, usually 20% centred at the peak
99mTc 126-154keV
What is uniformity correction?
It is done by applying an inverse image to all subsequent images
What is the spect spatial resolution?
6-7mm better in preclinical
Depends on the type of collimator
Describe a parallel hole collimator
Image is the same size as object
Fov is independent of the distance from the face of the collimator
Count rate is independent of the distance from the face of collimator
What type of collimator is used for 99mTc imaging?
Low energy
Describe a high energy collimator
Thick septa to stop high energy photons
Increased hole diameter
Used for iodine
What happens to resolution with collimation as you increase the distance from the source?
Increases dispersion and decreases resolution
Describe the spect crystal
NaI(TI) crystal
Detects individual rays by gamma scintillation
Converts to light
Thickness is 9.5mm or 12.7mm
When is vq imaging done using nuclear medicine?
99mTc is done for perfusion
Inhaled gas is used for ventilation
Normally done with ct not possible e.g. Pregnancy or allergic to contrast agent
How does whole body scanning work in nm?
A window or ramp opens up along the camera face and scans down the body slowly.
It ramps down as the camera reaches the end of the body
Sensors ensure it stays close to the patient
How does dynamic imaging work in nuclear medicine?
Inject radio pharmaceutical Want to know how fast it arrives and is cleared Plot time activity curve in ROI Can quantify degree of abnormality Scan at repeated periods
How is ventricular function determined?
Using ventricular ejection fraction
Ef = edv-esv / edv
Can measure regional wall motion to check for abnormalities
Can label RBCs or track the wall edge
What is the spatial resolution , temporal resolution and sensitivity of spect?
Spatial is 8-16mm
Temporal 2-10mins
Sensitivity 0.15%
What is the spatial resolution , temporal resolution and sensitivity of pet?
Spatial resolution 3-8mm
Temporal sec-min
Sensitivity 0.5-5%
How is spect different from gamma camera?
Rotates the gamma camera around to get multiple projections
Sums all data into a matrix -SINOGRAM
Why do you use a sinogram in spect
Easier for calculation and slice reconstruction
Can use FBP or iterative reconstruction
Can reorient set to get a standard view
How are multimodality images combined?
Image registration - minimise the distance between landmarks on the 2 images
If the patient moves it alters alignment
Can use cross correlation, mutual information, landmarks and similarity criteria
In pet,ct or spect,ct the centroid displacement between the 2 is calculated and applied to all subsequent images
Why is attenuation important?
Different depths have different levels of attenuation
If there is no correction then the internal or thicker areas has lower uptake due to increased absorption. Values are underestimated at the centre.
Ct allows you to correct this
What are the 3 methods for applying attenuation correction in pet?
Image segmentation
Bilinear scaling
Hybrid scaling
How is ct attenuation correction done using image segmentation?
The HU image is segmented into regions and pixel values are replaced with the expected values for 511keV mu for the region
How is ct attenuation correction done using Bilinear scaling?
A scaling factor is applied to all hu values to convert to u values at 511
There are 2 separate scaling factors
-1000 to 0
Hu greater than 0
How is ct attenuation correction done using hybrid scaling?
Apply a scaling factor to HU to get u 511.
2 separate scales, one for soft tissue and one for bone
What must be done to apply ctac to pet?
Spatial resolution in ct must be adjusted to that of pet
Must use iterative reconstruction
What are the problems with iterative reconstruction?
It can take a long time
Need to optimise the number of iterations to the application
Increasing iterations increases noise - however it also creates a uniform resolution
Safest to over iterate and smooth
What is the current idea to replace collimators in spect?
Solid state detectors
Get the energy of the incident photon
You know the angle of incidence
Can potentially reconstruct using advanced mathematics
What is DSPECT?
New design in cardiology
Small multiple gamma camera can rotate and align with the ROI
Increases scan time over ROI and increases sensitivity
Also decreases resolution due to the wide collimation
You know the percentage decrease in resolution so can correct
What happens when you increase the distance of the subject from the gamma camera?
Decrease resolution
Increase sensitivity
What is resolution recovery
It is the mathematical calculation that aims to correct for a decrease in resolution due to using wide collimators
It takes into account specific performance characteristics like knowledge of system and user control
What are the common agents used in radionuclide therapy.
131 I (NaI) for thyroid 131 I mIBG for neuroblastoma 177Lu-DOTA for neuroendocrine tumours 90Y-DOTA for neuroendocrine tumours 90Sr for bone mets
Who is involved in delivering radionuclide therapy?
Nurses Clinicians Radio pharmacy Physicists Technicians
What is peptide receptor radionuclide therapy?
pRRT
Somatostatin receptors are targeted by peptides e.g. 111 In DTPA octreotide to deliver harmful radioactivity to the area
What shielding should be used for beta producing radionuclides?
Perspex as you want to minimise the production of secondary X-rays
What shielding should be used for gamma producing radionuclide?
Lead
What are the features of X-ray and gamma in terms of radiation protection?
Range in air is many metres
Can transverse the body
Relative harmfulness 1
What are the features of Beta radiation in terms of radiation protection?
Range in air is 10s of cm
Range in tissue is mm
Relative harmfulness is 1
What are the features of neutrons in terms of radiation protection?
Range in air is many m
Can transverse the body
Relative harmfulness is 5-10
What are the features of alpha particles in terms of radiation protection?
Range in air is cm
Range in tissue is less than 1mm
Relative harmfulness 20
Define absorbed dose
Energy absorbed per unit mass
Gy
Define effective dose
Absorbed dose X factors for radiation type and tissue sensitivity
Sv
Define dose rate
Measure do how quickly you are receiving radiation dose
mSvh-1
What are the effect of radiation?
Can have no effect, kill cell or damage the cell and it can be incorrectly repaired
Stochastic is long term
Deterministic is short term
What are the effects of a radiation dose greater than 1000mSv?
Skin damage
Radiation sickness
Decreased fertility
Death
What is the consequence of 1mSv of radiation?
Fatal cancer risk of 1 in 20,000
What are the 2 main principles of radiation protection?
Justification - exposure to ionising radiation should only occur to produce a net benefit
Optimisation - dose, the number of people and the likelihood of exposure should be kept ALARP
Define ALARP
As low as reasonably practicable
What are the standard dose limits?
Should be reduced to acceptable levels
Employee is 20mSv per year
Trainees 6, general public 1
1mSv to the foetus during the declared term of pregnancy
What is the normal exposure for a chest x ray and a nuclear medicine bone scan
Chest X-ray 0.02mSv
Nuclear bone scan 3mSv
Describe the care of sealed sources
Must be kept secure
Any losses to be reported to police, health and safety executive and the environment agency
Damage should be checked using leak tests
What are external radiation hazards?
X-ray sets
Linear accelerates
Sealed and unsealed sources
What are internal radiation hazards?
Unsealed sources
What are the 3 main steps to reduce radiation dose
Time
Distance (inverse square law)
Shielding
What is the photon energy from 99mTc?
140keV
Compare radionuclide for pet and spect in terms of radiation protection
SPECT has lower energy
SPECT has lower TVL and HVL
Spect has a lower dose rate
What are the protection steps involved in dispensing radionuclides?
Controlled area
Enclosed prep cabinet
Shielding for generator and eluted cavity
Washing, changing and monitoring facilities
What are the protection steps involved in dispensing and injecting?
Shielded container to carry the syringe Syringe shield Spill tray with absorbent material Control of waste materials Room may be a controlled area
How do you protect against internal hazards?
Containment
Prevent ingestion
Decontamination
Procedures and monitoring
How should spills of radioactivity be dealt with.
According to local rules
Use decontamination kit
Isolate, decontaminate, report
What legislation is in place for radiation protection?
Ionising radiation regulations 1999
Ionising radiation (medical exposures) regulations 2000
Medicines (administration of radioactive substances) regulations 1978
What is outlined in IRR 1999?
Ionising radiation regulations 1999 Protection of workers and public Enforced by health and safety executive Controlled and supervised areas Radiation protection advisor Radiation protection supervisor Local rules Personal dosimeter Instructions and training
What is outlines in the ionising radiation (medical exposures) regulation 2000?
Protection of patients
Justifying medical exposures
Optimising medical exposures
Adequately trained staff
What is quality assurance?
System to maintain and verify expected performance
It compares performance with other scans using standardised tests
It characterises any deterioration in performance
What is quality control?
Specific aspects of quality assurance e.g. Equipment tests
What are the quality control parameters checked at acceptance and 6 monthly in SPECT?
Spatial resolution Spatial linearity Uniformity Count rate capability System sensitivity Energy resolution Whole body scanning performance Multiple window spatial registration
Shield leakage - only at acceptance
Define spatial linearity
Parameter which characterises the amount of positional distortion caused by the camera with respect to incident gamma events entering the detector
A line source will appear wavy without correction due to positioning of PMTs
How is intrinsic uniformity tested?
Measure the repsonse of the camera to a homogeneous flux of radiation WITHOUT collimator
Point source 5 x FOV away
How is system uniformity tested?
Sheet source (57Co) 122keV throug a collimator
Measure the ability of the overall system to respond correctly to a homogenous flux of radiation
How do you calculate integral non-uniformity?
Max pixel - min pixel / (max pixel + min pixel)
x100
For whole image
How do you calculate differential non-uniformity?
For all groups of 5 adjacent pixels
Max pixel - min pixel/ max pixel + min pixel x100
What do you need to do to test gamma camera uniformity?
Acquire enough counts per pixel to allow the system non-uniformities to be seen as distinct from Poisson noise - around 10000 counts per pixel
How do you test spatial linearity
Phantom with lines is place on top of sheet source - if straight then correction is working
qualitiative
also gives you an idea of spatial resoltion
What is intrinsic uniformity testing?
The optical coupling between the crystal and the PMT
If poor - regrease
USE A POINT SOURCE
What are collimators made out of?
Most are made of lead
Can be tungsten - better performance but more expensive
What is the difference between integral and differential non-uniformity?
Integral is max and min pixel from anywhere in the image
Differential, they must be within 5 pixel of each other
Why is uniformity so important in SPECT?
In spect any errors are magnified in the reconstruction process
What is the main phantom used to test SPECT?
Jaszczak phantom
Industry standard for SPECT testing
It assessed uniformity and spatial resolution
Tank of Tc with cold object within e.g. spheres, parallel rods of varying sizes and pitch
What is the centre of rotation?
The computer assumes that the gamma camera will rotate in a smooth manner around the postition
Computer must know where the cameras are in order to reconstruct
How do you test centre of rotation?
Place a point source in the centre and it should execute a sinusoidal pattern
What is the typical PET/CT QC schedule?
Acceptance and annually - NEMA tests *count rate performance, image quality, spatial resolution and sensitivty)
Daily - CT warm up, air calibration, SUV check (PET)
Weekly - PET/CT alignment
Quarterly SUV calibration and check
What are the daily PET detector checks?
Expose PET crystal to positron emitting point source
Check uniformity and energy peaking/resolution and coincident timing
SUV check
How do you check SUV daily?
test using a uniform cylinder containing known activity and mass
Calculate SUV daily to monitor
Check fit for use
What are the features of the flat source that should be considered
Appropriate emission to the modality
Known decay method and activity and mass
Long half life so don’t have to replace often
How do you calculate SUV?
SUV = activity concentration from the image / (injection activity/patient body mass)
How do you check PET/CT alignment
Weekly CT moves so could get misregistered Use phantom with some attenuation characteristic of tissue with 5 radioactive sealed sources on them. metallic encapsulation so show up on CT Check they overlap
How do you check SUV quarterly
Check calibration is right
need to check dose calibrator corresponds correctly to the dose seen by the camera
Update and check correction factors
What is the annual NEMA tests required? in PET
Sensitivty Spatial resolution Image quality Count rate performance Accuracy of cont loss corrections
What is the NEMA definition of sensitivty? PET
Mean cps/kBq from an un-attenuated line source at the centre of FOV and offset 10cm.
Low activity count so count losses are insignificant
Sensitivty decreases linearly as you move out of the centre
How do you test for spatial resolution annually in PET?
Small sources infiedl of view and determine how big they look
NEMA: 1 source 1cm off axis and 2x10cm off axis
Line sources - look at line spread function - measure FWHM
If it is wide will decrease quality of the image
How is overall image quality checked inPET
6 coplanar spheres - hot background. they are fillable.
- Some hotter than background
- Some colder (no activity)
Check attenuation correction by filling one with sample representing lung tissue - challenge attenuation correction
Put object with activity around it to represent the body to challenge the scatter correction
Can measure contrast, variability and whether they appear to have same concentration
why does attenuation correction matter more in pet?
It has double the distance to go
Therefore increases attenuation
How do you test count rate in PET?
Fill line source with high activity (GBq)
Line source scanned in centre
All profiles should be summed to get integrated counts for sinogram
Any events outside width of line = scatter
True count rate (remove scatter and random) = assume linear interpolation from outside the line.
How do you analyse count rate?
From testing:
Get scatter and random counts
Get total counts
Get system measures of random counts
Calculate scatter fraction and noise equivalent count rate
How do you Calculate scatter fraction?
A measure of the liely effect of scatter on images
Counts from random+scatter - random counts / (total counts - random counts)
How do you calculate noise equivalent count rate (NECR)
A global measure of the likely image SNR
NECR = (total counts - counts from scatter and random)^2 / total counts
How do you test for correction accuracy in count losses and randoms in PET?
Net error is computed which expresses the error in count rate after the corrections are applied
What material is a pet scintillator crystal made of.
Bismuth germanate
List clinical applications of spect/ct
Hyperparathyroidism (sestamibi) Infection/inflammation (white cells) Bleeding studies (red blood cell) Hepatobiliary (hida) Neuroendocrine tumours (octreotide) Thyroid cancer (iodine)
Describe the manufacturing of 99mTc
It is produced from 99mo which is primarily obtained from nuclear reactors
What is anticipated to be the major issue with respect to 99mTc scanning in the global market?
as the number of nuclear generators reduces globally there will be limited access and high price of 99mTc, therefore cost of scanning is expected to increase significantly
Define a kinetic constant
Defined as the rate of molecular exchange from one compartment to another
What are the advantages of using SUV in pet?
Simple and versatile
Suitable for clinical use
Useful for diagnosis, staging and therapy
What are the disadvantages of using SUV in pet?
Only works for tracers of flux
Limited efficacy of drug testing
Semi quantitative
Rough description of tracer kinetics
Doesn’t exploit the characteristics of different tracers
SUV use has to be alway a priori validated
Outline the main physical processes that take place between the emission of positron and the formation of an electric signal in a pet
Positron emission
Positron travelling /scattering with range mm
Collide with electron
Annihilation producing 2x511keV gamma rays in opposite directions
Travels through body, some will be attenuated via Compton scatter, some will leave the body.
Those that leave the body will hit the scintillator crystal
This produces an optical photon from the gamma
This passes into pmt where signal is amplified and produces an electrical signal
Then calculate position based on light and coincidences
What are the reasons for expanding the use of PET
Can be combined with Ct to combine anatomical and functional data
FDG is oncology to stage cancer
Novel indications (treatment assessment )
Better access to tracers (now cyclotron and generator)
Cost reduction
What are the difficulties with expanding pet imaging
Cost is expensive Development of new tools are expensive New tracers are slow and expensive to develop Lag in patient referrals Complexity of reporting Logistics Current economic climate
What is the main difference of the FDG molecule compared to glucose with respect to their biochemical pathways inside the human body?
FDG is phosphorylated and the product is trapped in the cell at a rate proportional to glycolysis. The glucose is not trapped and moves through the cycle
What are the advantages of hybrid imaging systems.
Combines functional and anatomical
Can correct for attenuation problems in nuclear imaging
Provides more accurate localisation of lesions
Detects additional lesion
Assists in the exclusion of physiological tracer uptake thereby improving accuracy of image interpretation
Better identification of inflammatory lesions
Reduce time imaging by combining
What are the disadvantages of using hybrid imaging systems?
Longer scanning time
Increased radiation dose
Increased cost of development and production
Increase cost per scan
Artefacts which affects images if there is misalignment or incorrect attenuation provided
Increased staff training
Increased quality control requirements
What is the most common clinical indication for FDG pet/ct?
Oncology cancer
Which part of the body of a normal person scanned with FDG would show most physiological uptake?
Brain
What kind of cell function is measured with 18F fluorothymidine and 18f choline?
Cell membrane proliferation
FLT - imaging Biomarker do cell proliferation
FCH- choline. Imaging Biomarker of malignancy induced over expression of choline kinase
Give an example of a particular disease that imaging with FLT or f-choline may be more useful than FDG?
Prostate cancer
Has low glucose metabolism/requirement but high cell proliferation (f-choline)
FLT: brain tumour. FDG has a high uptake in the brain and cancer can’t be easily distinguished from normal. FLT does not have high uptake in the brain as standard
What the properties of an ideal generator.
Parent free Sterile Easy to use High yield of daughter nuclide Compact Daughter decays to stable nuclide Parent free
How does a technicium generator work?
Saline (NaCl) is washed through to obtain 99mTc
This runs through an exchange column
The molybdenum decays and it attached to alumina.
99TcO4- binds with sodium to give 99m Tc o4na (pertechnetate) which can then be eluted
