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Medical Physics > Nuclear Medicine > Flashcards

Nuclear Medicine Flashcards

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1
Q

Name the components of a gamma camera

A

Collimator
Crystal
Photomultiplier tubes
Computer

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2
Q

Define sensitivity and resolution

A

Sensitivity - number of counts recorded for stated activity
Resolution - sharpness of the image FWHM

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3
Q

Name the different collimators and there purpose

A

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

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4
Q

How does increasing hole diameter effect the resolution and sensitivity?

A

Resolution reduces
Sensitivity increases

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5
Q

How does increasing hole length effect resolution and sensitivity?

A

Resolution increases
Sensitivity decreases

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6
Q

How does increasing septal thickness effect resolution and sensitivity?

A

Resolution unchanged
Sensitivity decreases

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7
Q

How does increasing patient to collimator distance effect resolution and sensitivity?

A

Resolution decreases
Sensitivity unchanged

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8
Q

How many photons are produced per keV in the crystal?

A

20-30

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9
Q

Give 2 advantages and 2 disadvantages of NaI

A

Short life time - allows for high count rate
Transparent - allows for large detectors

Fragile
Hygroscopic

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10
Q

Crystal thickness is a trade off between what factors?

A

Stopping efficiency - increases with thickness
Spatial resolution - decreases with thickness

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11
Q

Describe the components of a PMT

A

Glass window
Photocathode
Focusing grids
Dynodes
Anode
Connectors

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12
Q

How is the energy and position of an event reconstructed?

A

Energy - sum of all PMT signals
Position - relative signals from PMTs

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13
Q

Describe a bone scan

A

Static imaging
600-800MBq
HDP Tc99m
Wait 2-3 hours post injection
Tracer uptake - Osteoblastic activity
Bone mets, fracture, infection

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14
Q

Describe a kidney scan

A

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)

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15
Q

Describe a heart scan

A

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

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16
Q

Describe a brain scan

A

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

17
Q

What are dynamic acquisitions used for? What setting are used?

A

Fast physiological processes

Frame rate appropriate to speed of physiological process
LEAP collimator
Matrix size appropriate to spatial resolution of the collimator

18
Q

Explain filtered back projection

A

Smears image with a 1/f filter
Image recovered by multiplying by a ramp filter
Amplifies noise
Modify ramp with smoothing filter

19
Q

What are the advantages and disadvantages of filtered back projection?

A

Advantages:
Computationally quick
Ok for visual interpretation

Disadvantages:
Streaking/ noise
Difficult to apply image compensations

20
Q

Describe iterative reconstruction

A

Initial image estimate
Estimate projections for guessed image
Compare to real projections
Update the image
Repeat

21
Q

What are the advantages and disadvantages of iterative reconstruction?

A

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

22
Q

Name 3 image corrections

A

Attenuation
Reduced counts
CT attenuation correction

Scatter
Poor energy resolution
Use CT info in iterative reconstruction

Collimator response
Poor spatial resolution
Point spread function

23
Q

How long does it take for Tc99m to reach generator equilibrium?

A

24 hours

24
Q

Draw the Tc99m/ Mo99 generator curve without elution and with elution once a day

A
25
Q

Describe a radionuclide generator

A

Mo99 is absorbed into aluminium oxide column
Decays to pertechnetate which is less bound to the column
Pull saline through to wash off the pertechnetate

26
Q

Describe the components of a generator

A

Tubing - allows column to be washed
Filters - to contain aluminium within column and remove small particles
Lead shielding - operator safety

27
Q

Describe a radionuclide calibrator

A

Ionisation chamber
Pressurised gas, plates at high voltage
Radiation causes ionisation
Measure current
Proportional to activity

28
Q

What factors is a radionuclide calibrator dependent on?

A

Energy
Source geometry - self absorption
Measurement position
Composition and pressure of gas
Applied voltage
Activity

29
Q

Draw the voltage response curve and label the regions

A
30
Q

Why is the ion saturation region used for dose calibrators?

A

Not as dependent on voltage fluctuations

31
Q

Describe the energy response curve

A

Very low energy - radiation absorbed before reaching gas
Rapid increase - more penetrating
50keV - photoelectric absorption probability decreases so response decreases
200keV - Compton scatter dominates
Higher energy - more ionisation so more current

32
Q

Describe calibrator QC

A

Daily - relative response
Check long lived source against baseline

Annually - accuracy
NPL reference source

Linearity - check response over full activity range
Leave source to decay in calibrator taking regular measurements

33
Q

How are beta emitters measured?

A

Using a copper filter and calibration factor

34
Q

List the radio pharmacy quality control tests

A

Radionuclide purity
Ratio of radioactivity of radionuclide to total radioactivity
Molybdenum breakthrough test

Radiochemical purity
Fraction of activity in declared chemical form
Chromatography test

Chemical purity
Fraction of mass in declared chemical form
Indicator paper

35
Q

Describe a PET camera

A

Scintillator - cuts in crystal act as light guide
PMTs
Multiple rings of detectors
Signal processing

No collimator

36
Q

List ideal scintillator criteria

A

High efficiency
High probability of photoelectric absorption
High conversion efficiency to light photons
Transparent
Wavelength matching to PMTs
Short scintillation time
Mechanically robust

37
Q

How are PET images reconstructed?

A

Iterative - OSEM

38
Q

Give examples of matrix size and scans

A

64x64 renogram - sensitivity
128x128 bone - balance
256x256 datscat - spatial res

39
Q

Give examples of matrix size and scans

A

64x64 renogram - sensitivity
128x128 bone - balance
256x256 datscat - spatial res

Medical Physics (4 decks)

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