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Techniques of Molecular Medicine > Imaging techniques > Flashcards

Imaging techniques Flashcards

1
Q

What is a preclinical modality?

A

Related to modalities investigating animal models

Pre-therapeutic

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2
Q

Which pre-clinical modalities can imaging techniques be applied to?

A

Neurology

Oncology

Cardiology

Cell tracking

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3
Q

What can clinical imaging be used for?

A

Diagnosis

Prognosis

Determine the location of the disease

Monitor the response to therapy

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4
Q

What can preclinical imaging be used for?

A

Validating clinical imaging methods - confirm using histology

Interpreting mechanisms of human disease and therapy - look at uptake of therapeutic cells, combine with other imaging technique to look at therapeutic response

Developing new clinical imaging technology

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5
Q

What is light?

A

A form of electrical radiation

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6
Q

What are the two states light can be found?

A

At some wavelengths it takes form in visible light

At some wavelengths it takes a form of radiation we cannot see

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7
Q

What type of light are X-rays?

A

Short wavelengths

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8
Q

Why can X-rays be used to observe the body?

A

Some X-rays are absorbed by the body

Some X-rays are attenuated by the body

Bones contain calcium, making them denser than other tissues = shadows

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9
Q

What are X-rays usually used for?

A

Revealing fractures

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10
Q

What are CT scans?

A

Multiple cross-sectional images of the body using X-rays

Computer processing techniques bring them together

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11
Q

How are CT scans better than X-rays?

A

More detailed

Can reveal bones, tissues and organs

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12
Q

How do CT scans produce more detailed images than X-rays?

A

X-rays use a fixed tube that sends X-rays in one direction

CT scanner uses a motorised X-ray source that shoots beams of X-rays as it revolves around the patient

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13
Q

How is image reconstruction of a CT carried out?

A

Digital X-ray detectors detect the signal

These are found opposite to the X-ray source

As the X-ray passes through the patient, they are picked up by detectors and transmitted to a computer

2D image slices are stacked together into 3D images

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14
Q

What are the advantages of CT scans?

A

Great bone-soft tissue contrast

High spatial resolution

Whole body coverage

Non-invasive

Cheap compared to MRI

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15
Q

What are the limitations of CT scans?

A

Ionising

Limited soft tissue contrast

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16
Q

Why are CT scans often used in neurology?

A

Cheaper than MRI

Broad diagnosis of neurological disorders

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17
Q

What are ways to improve CTs?

A

Contrast agents

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18
Q

Definition of radioactivity

A

Process in which unstable atomic nuclei spontaneously emit ionizing radiation

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19
Q

What type of scan is a PET scan?

A

Nuclear scan

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20
Q

What techniques do PET scans use to obtain an image?

A

Radioactive techniques

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21
Q

What does PET stand for?

A

Positron Emission Tomography

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22
Q

What are alpha particles?

A

He nuclei

Large

Don’t travel far in space

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23
Q

What are gamma rays?

A

Highly energetic photons

Similar properties to X-rays

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24
Q

What are beta particles?

A

Electrons

Don’t travel far

Absorbed by the body

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25
What are positrons?
Antimatter of electrons = positive electron Similar properties to electrons Don't cause damage until they collide and cause annihilation
26
What is annihilation?
When a positron and an electron collide Causes the release of two gamma rays at 180 degrees from one another Allows to pinpoint the place in the body where annihilation occurs
27
How do PET scans produce images?
Uses positrons and electron interactions Tracers are made up of carrier molecules covalently bonded to radioactive isotopes The gamma rays 180 degrees apart formed through annihilation are detected by coincidence Detectors measure these photons and use the information to create a 3D image
28
How are tracers administered to the body?
Intravenously
29
Advantages of PET scans
Sensitive (nM-pM) Half-life of tracers is long (20 minutes - few hours) Large range of tracers
30
Disadvantages of PET scans
Single signal Resolution is relatively low Ionising radiation High cost due to the use of tracers
31
What do radiotracers target?
Biomarkers
32
What are biomarkers?
Anything biological that is of interest in disease states
33
What criteria must a target fulfill in order to be considered a biomarker?
The target should be biologically informative The target must be differentially expressed over the background The unbound radiotracer should be cleared quickly by the body The radiotracer must be delivered to and specifically interact with the target Background activity should clear within the lifetime of the radioactivity : contrast
34
Examples of multimodal imaging in PET
PET-CT PET-MRI
35
Uses of PET-CT and PET-MRI
CT dosen't show biochemistry of disorder PET retained in tumour cells show the regions of cancer ``` CT = anatomy PET = glow of cancer cells ```
36
How can PET be used to image cancer?
Through cancer metabolism Tumour cells have enhanced metabolic activity, as both glycolysis and oxidative phosphorylation are turned on
37
Example of PET scan tracer used in cancer
FDG
38
What is FDG?
Modified form of glucose with unstable fluorine 18 used as a radioactive tracer Since FDG can no longer undergo metabolic degeneration, it is trapped inside the tissues
39
What is the distribution of FDG?
Brain - takes up 60% of glucose in normal functioning Salivary Myocardium Renal excretion
40
Applications of FDG in oncology
Diagnosis Staging Response monitoring
41
What are the problems with FDG?
Cannot detect tumour types in organs with glucose as primary source of energy (prostate, brain cancer) FDG is taken up by inflammatory cells
42
What is the goal of future biomarkers?
Aim at complex biochemical pathways involved in cancer metabolism Try to find associated radiotracers
43
What do MRI use?
Protons which are abundant in the human body Manipulate the magnetisation of the hydrogen protons to create an image
44
What is the major source of protons in the body?
Water
45
What are the three components of an MRI machine?
A big magnet (3T in hospitals, 9.4T preclinically) Radio frequency pulse transmitter and receiver Magnetic field
46
Explain how MRIs work
1. All protons spin, creating a small magnetic charge 2. When a strong magnetic field is introduced, the protons align with the field 3. The MRI generates a stable magnetic field parallel to how the patient lies 4. The MRI technician then introduces a radiofrequency pulse using a radiofrequency pulse transmitter in the opposite direction to the magnetic field 5. This disrupts the proton and forces it either into a 90 degree or 180 degree realignment 6. Since the radiofrequency pulse push the proton against its nature, once the force is turned off, the protons realign with their magnetic field in a process called precessing 7. As the nuclei are precessing, there is release of electromagnetic energy
47
How does MRI distinguish between tissues?
Detection of the electromagnetic energy as they precess Differentiation of the tissues based on how quickly they release energy after the pulse is turned off
48
What does the Larmor equation explain?
The magnetic field strength emitted from the CT machine increases with distance
49
What is the importance of the Larmor equation?
Allows to differentiate between the front and back of the brain The lower magnetic frequencies come fro the front of the brain
50
What is another name for precession?
Relaxation
51
Why do different tissue types have different relaxation?
Relaxation is determined by the environment of the water molecules
52
What does T1 measure?
The time required for the spins to go back to their original axis (applied magnet) Water spins quickly = more time needed to go back to axis = darker T1 Lipids spin slowly = more time needed to go back to axis = lighter T1
53
What does T2 measure?
The coordination of the H+ spins Water spins quickly = quicker for the spins to be random = lighter T2 Lipids spin slower = more time needed for spins to be random = darker T2
54
What are the advantages of MRI?
Great soft tissue contrast High spatial resolution Non-invasive Non-ionising Can image structure and function
55
What are the disadvantages of MRI?
Expensive Can lack specificity Lack of temporal resolution
56
What is functional MRI?
Indirectly measures neuronal firing
57
What is measured in fMRI?
NOT measure neuronal firing But rather the blood flow changes that happens in response through the neurovascular coupling in the brain More active brain regions = more blood flow
58
What signal is measured in fMRI?
BOLD Blood Oxygen Dependent Signal BOLD increases with neronal firing
59
How is fMRI useful?
Differences in the T2 signal between oxygenated and deoxygenated blood T2 of oxygenated is longer than T2 in deoxygenated blood
60
What is requires to capture the BOLD signal?
Fast imaging Gradient-Echo Planar Imaging
61
What type of system underlies the ultrasound?
Acoustic based system Works between 1-100 mHz
62
What is needed to carry an fMRI out?
Task - neuronal stimuli Increased neuronal firing Vessel dilation Increased cerebral blood flow from the baseline Increased BOLD signal
63
Describe how an ultrasound works
Transducer uses an array of pizoelectrical crystals These vibrate when an electric signal is applied Produce a high frequency sound or compressional waves called ultrasounds Crystals also work in reverse, producing electric signals when sensing high frequency of compressional sounds
64
What ate sound waves?
Propagating fluctuations in pressure, density, temperature and particle motion
65
How does an ultrasound use sound waves to create an image?
Some tissues with high densities echo sound waves Some tissues with lower densities allow sound waves to pass through the body The echoed sound waves are captured by the pizoelectric crystal, transducing the signal into an electric one
66
What does ultrasund measure?
The boundaries between materials which have different acoustic impedance
67
What changes the electric signals into points of brightness on the image?
Computer
68
What is the image formed by an ultrasound called?
A sonogram
69
What allows a sonogram to form a real time motion?
Crystals are repeatedly activated many times so a complete image frame is completed 20 times per second
70
What are sonograms used for?
Looking at babies during pregnancies Heart during cardiac investigations
71
What are the advantages of ultrasound?
Cheap Portable Non-invasive Non-ionising
72
What are the disadvantages of ultrasound?
Spatial resolution and contrast Depth Cannot image the adult brain because of the skull

Techniques of Molecular Medicine (12 decks)

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