Nuclear Medicine Flashcards
Name the components of a gamma camera
Collimator
Crystal
Photomultiplier tubes
Computer
Define sensitivity and resolution
Sensitivity - number of counts recorded for stated activity
Resolution - sharpness of the image FWHM
Name the different collimators and there purpose
Parallel hole:
LEHR - low energy high resolution
- longer narrower holes
LEAP - low energy all purpose
High energy - thicker septa to reduce penetration
Pinhole - magnifies image
How does increasing hole diameter effect the resolution and sensitivity?
Resolution reduces
Sensitivity increases
How does increasing hole length effect resolution and sensitivity?
Resolution increases
Sensitivity decreases
How does increasing septal thickness effect resolution and sensitivity?
Resolution unchanged
Sensitivity decreases
How does increasing patient to collimator distance effect resolution and sensitivity?
Resolution decreases
Sensitivity unchanged
How many photons are produced per keV in the crystal?
20-30
Give 2 advantages and 2 disadvantages of NaI
Short life time - allows for high count rate
Transparent - allows for large detectors
Fragile
Hygroscopic
Crystal thickness is a trade off between what factors?
Stopping efficiency - increases with thickness
Spatial resolution - decreases with thickness
Describe the components of a PMT
Glass window
Photocathode
Focusing grids
Dynodes
Anode
Connectors
How is the energy and position of an event reconstructed?
Energy - sum of all PMT signals
Position - relative signals from PMTs
Describe a bone scan
Static imaging
600-800MBq
HDP Tc99m
Wait 2-3 hours post injection
Tracer uptake - Osteoblastic activity
Bone mets, fracture, infection
Describe a kidney scan
DSMA
Renal cortex
Assess renal function, scarring
MAG3 renogram
80MBq
Image immediately
Assess obstruction, relative renal function
Dynamic
3 phases: Perfusion, filtration, excretion
Renogram curves - time activity curves
Diuretic (frusemide)
Describe a heart scan
Myocardial perfusion
ECG gating
SPECT
Tc99m Myoview
Stress and rest - demonstrate reversible ischemia
Image after 30-60 minutes
Assess cardiac ischaemia, left ventricle ejection fraction
MUGA
ECG gating
Inject PYP before
Label patients blood with Tc99m
800MBq
LEAP
45 degree angle to separate ventricles
Assess left ventricle ejection fraction
Describe a brain scan
DaTSCAN
I123 cocanie analogue
Binds to dopamine receptors
SPECT - reconstruct transverse slices
Acquire after 3-4 hours
Parkinson’s disease and Lewy body dementia
HMPAO
Brain perfusion
Tc99m
Crosses the blood brain barrier
Neurodegeneration, Alzheimer’s, dementia, epilepsy
What are dynamic acquisitions used for? What setting are used?
Fast physiological processes
Frame rate appropriate to speed of physiological process
LEAP collimator
Matrix size appropriate to spatial resolution of the collimator
Explain filtered back projection
Smears image with a 1/f filter
Image recovered by multiplying by a ramp filter
Amplifies noise
Modify ramp with smoothing filter
What are the advantages and disadvantages of filtered back projection?
Advantages:
Computationally quick
Ok for visual interpretation
Disadvantages:
Streaking/ noise
Difficult to apply image compensations
Describe iterative reconstruction
Initial image estimate
Estimate projections for guessed image
Compare to real projections
Update the image
Repeat
What are the advantages and disadvantages of iterative reconstruction?
Advantages:
Physics can be modelled - accurate image compensation possible
Can use subsets to speed up the process
Disadvantages:
Can be slow
Needs accurate models
Optimal number of iterations varies
Name 3 image corrections
Attenuation
Reduced counts
CT attenuation correction
Scatter
Poor energy resolution
Use CT info in iterative reconstruction
Collimator response
Poor spatial resolution
Point spread function
How long does it take for Tc99m to reach generator equilibrium?
24 hours
Draw the Tc99m/ Mo99 generator curve without elution and with elution once a day
