Nuclear medicine Flashcards
in vivo
measured as it leaves the body. eg bone scans from gamma camera
in vitro
no images, given to patient then biopsies taken
what are examples of non nuclear imaging?
Contrast enhanced ultrasound
optical imaging
MRI spec
CEUS with ligands is used or preclinical
it is preclinical
looking for things like VEGF, ICAM1 (inflammatory markers)
what are the two types of optical luminescence?
bioluminsecne
fluorescence
Bioluminescence
luciferase enzyme in cells.
Lucinferin is injected, chemical reaction with photon produced.
what type of cells contain luciferase?
Tumour cells
Fluorescence
an injected molecule is activiated with a an external light source/wavelength,
good as can be repeatably excited
what are the three ways of producing radioisoptopes
Cyclotron
Generator
Nuclear reactor
Cyclotron creates them how>
Bombardes.
Dee (D shaped electrodes either sid eof a vacuum)
- spin them in a circle with an AC current.
What isotopes are produced by bombardement in Cycltron?
Tehcnetium 99m (Molybdenum is blasted).
Fluorine 18 (oxygen rich water is bombarded)
Gallium 67
Thallium 201
gallium 67 used in what?
inflammation nad tumours
Thallium 201 used in what?
heart scans
How are RI produced in a nuclear reactor?
Uranium 235 - fission -
Uranium 236. Makes lots of neutrons.
Create neutron rich RI
Neutron rich RI will decay how?
Via B negative emission.
Proton rich –> proton and negative thing
What are nuclear reactor created RI?
Molybdenum98 (then used in cycltrons!)
Iodine 131
Xenon 133
Why is Xenon 133 better than crypton for ventilation tudies?
Xenon has a half life of 5 days so easier to traonsport.
As apposed to 13 seconds.
Radionuclide generator creates RI how?
Slow decaying element absorbed on to a surface like alumina.
encased in lead.
the decayed daughter RI is then used by elluting with sodium chloride.
Generator produced RI?
Tehcnetium 99m
What is the pathway for making Tech99
Nuclear reactor makes Moly98
Cyclotron takes Moly98 and makes Moly 99
Moly 99 goes to Tech99`
which way is krypton make?
Generator
Ideal property of radioisotope
- half life
long enough to achieve image
short enough to limit radiation dose
ideal 1.5 x length of imaging
Ideal property of radioisotope
- gamma ray energy
high enough to reach the gamma camera.
if low energy they are absorbed by the body increasing the dose.
Mono energetic gamma emitter between 100 and 250kEv.
Ideal property of radioisotope
- deays to what
a stable isotope
Ideal property of radioisotope
- binding
easy to bind
Ideal pharmaceutical
high target: non-target uptake ratio
Easy and cheap
non toxic
does not alter physiology that you are measuring
Cardiac imaging uses
Thalium 201
- to see perfusion of muscle immediately and later
Technetium 99m tetrofosmin
myocardial perfusion
MUGA is used in what
Ventriculography. labelled blood ells.
Wall motion and chamber size
Iodine 131 is used in?
Neuroendocrine.
Renal imaging RI?
Tech99 DMSA - cortical function
Tech99 MAG3 - eGFR
CNS imaging examples
Brian SPECT tech99
Iodine 123. for parkinsons
Iodine 123 is used in which scan
DaTscan
what are the positiron emittors?
PET FLOC GAL
Gallium67
Fl18
Oxygen
Carbon 11
How are the positron emittors made?
Cycltron
What are the componenets of a gamma camera?
Collimator
radiation detector (Scint and PMT)
Electronic
Collimators are usualy made of what?
Lead
what is the purpose of the collimator?
for spatial mapping
NOT to do with scatter
diverging causes what to the image
minification
diverges at the object
converging causes what
mag
converges at the object
the collimators need to be able to absrob what energy gamma rays
150 - 400
Low collimators are used for which RI
99mTC
High energy collimators used for which RI
Iodine 131
Gamma camera - what is the scintallator used
Sodium Iodide with a hint of thallium in an aluminium can
How thick is the scintallator
6-13mm
in a gamma camera what is a light pipe?
Perspex slab.
between the crystal and PMT.
How does a PMT work
light photon hits a photocathode - gives an electron.
Accelerated between dynodes and multiplies.
Detected as an electrical charge.
how many PMTs are there?
30 - 100
how does the gamma photon interact with the scintillation?
By PE or compton.
What is FWHM
full width at half maximum
Energy resolution =
FWHM kEV / photopeak x 100
How is scatter removed?
NOt by the collimator
By energy discrimination. A 20% window either side of the peak kV .
More than one peak can be used
down side of removing scatter by energy discrimination this?
removes low energy scatter but also low energy unscattered.
planar imaging gets images in what way?
2D
Static planar imaging is good for what
size, shape, uptake DMSA
Dynamic planar imaging is good for…
when the uptake changes over time (rapidly) MAG3
Gated - planar imaging
regular motion organs like the heart.
Are collimators used in planar imaging?
yes. can change them based on scan
How can SNR be increased in planar imaging
increase the count density by
- increasing imaging time
- increase adminisitred radiation
- ensure acceptable gamma camera sensitivity
Matrix relationship with SNR
large matrix more pixels
- more resolution
Less SNR
Typical matrix in planar imaging?
64 x 64 for gated
256 x 256 for dynamic
How can orietnation assist in planar imaging?
Continuous movement
Step and shoot
If the detector is closer to the patient what does this improve?
the resolution
in planar imaging how can we achieve contrast enhanement
windowing
ROI
Area of interest to assit with count number
planar imaging - what are time activity curves
ROI count rate can be plotted as a graph.
- time to reach peak
- area under the curve
- washout rate
In SPECT - what should the distribution be of the radiopharmaceutical be?
The distribution should not shange over the 20 - 40 mins of the scan
how many heads on a gamma camera?
at least 2 - rotate.
How does CT come into SPECT
can put the XR beam between the cameras.
Helps to do attenuation corrections for the nuclear medicine through DIRECT measurement.
in SPECT - non - parallel collimator can only be used with what?
Circular orbits.
NOT body contouring
normal matrix size for dual headed system?
128 x 128
how does the spect gantry roate
step and shoot
cardiac spect is what matrix
64 x 64
PET -
distance of where the positron is emitted and where it annihilates is….
variable
Ideal PET scintillation
high LAC for 511keV photons
PE more than Compton interaction
lots of light phtons produced per gamma photon absorbed
short scsinilattion light decay time
What scintillation crystal is use din pET
Bismuth germinate
downside of BGO (why we use LGO and GSO)
light output and decay time are inferior to NaI
How many PMT to each scintilattor block in PET
4
in PET what are the detector elements?
each crystal is subdivided into detector elements with reflective elements to prevenet cross talk
PET - what is a coincidence?
co - incidene t
detection at the same time by the gamma detectors
line between points of coincidence is called the
linear response line.
how can collimation be used for 2D vs 3D
2D - single plane
tungsten collimator ensures only photons from a single plane are received.
how does 3D imaging and collimation worl?
no collimation
higher counts
how to avoid scatter in PET
energy discrimination for photopeak window..
But not great as has to be wide due to poor energy resolution of the scintillators.
What causes increased random coincidence
more radionuclide
3D acquisition
increased coincidience window (normally 1ns)
PET - how to correct for attenuation through the body of the photons
Gallium rod without the patient measured
Then with the patient present.
how to account for dead time
most problemtaic in 3D
have mathematial equations
how to account for radioactive decay
counts are corrected for time
what is the contrast equatin for NM
c = Lesion - Surrounding tissue activity amount ) / surrounding tissue activity amount
subject contrast depends on….
activity difference of the tissues
image contrast depends on….
counts per unit area difference
Is RN noisy
yes
types of noise
structured
random noise
types of structured noise
(non random types)
- nearby tissue uptake
- imaging system artefact like non uniormity of gamma camera
not very significant compared to random noise
types of random noise
same as quantum mottle and statistical noise
- random variation in count density due to random decay
noise contrast equation
= 1 / square root of counts
what is the intrinsic resolution
max resolution achievable by the detecotr and electronics
collimator spatial resolution equation?
R = hole diameter (1+distance from radiation source to collimator / hole length)
types of spatial resoltuon for NM
Intrinsic
Collimator
System spactial resolution
system takes into account what?
Intrinsic and collimator
System resolution equation
square root of(int square added to collimator squared)
