Nuclear Medicine Final Exam Questions
and answers with 100% Complete
solutions | verified &updated 2024
What limits intrinsic spatial resolution? - ✔✔Multiple scattering of gamma
ray photons within the detector.
Statistical fluctuation of distribution of light photons among the PMT's from one
scintillation event to the next.
Intrinsic spatial resolution worsens with higher or lower energy gamma rays? -
✔✔Lower; lower energy gamma rays produce fewer light photons per
scintillation event, and smaller numbers of light photons result in larger statistical
fluctuations in their distribution. Greater blurring with lower energies.
How does intrinsic spatial resolution depend on crystal thickness? - ✔✔Thicker
crystals result in greater spreading of scintillation light before it reaches the PMT.
,Also a greater likelihood of detecting multiple compton scattering
events, particularly with higher energy radionuclides.
Detection Efficiency - ✔✔Improves with thicker crystals, at the expense
of intrinsic spatial resolution. Decreases with higher energy gamma rays.
Energy Resolution - ✔✔Determines the efficiency with which detector
can perform pulse height analysis.
Depends largely on the statistical fluctuations in the number of light photons
collected from a scintillation event; good light collection efficiency is
needed.
Advantages of improved energy resolution: - ✔✔Narrower photopeak; more
efficient detection of unscattered photons within the chosen energy window.
Gamma rays scattered through large angles are rejected more efficiently, thus
improving image contrast.
,Both result in improved image quality.
Performance at high counting rates: - ✔✔Most gamma cameras have
paralyzable systems. Dead time losses can occur with high counting rates.
Effects of pulse pile up on gamma camera performance: - ✔✔Counting losses
and image distortion.
Image Nonlinearity - ✔✔Pincushion and barrel distortion. Occurs when XY
position signals do not change linearly with displacement distance of a
radiation source across the face of the detector.
Image Nonuniformity - ✔✔Can be evaluated using flood. Causes
include nonuniform detection efficiency and nonlinearities.
, Nonuniformity Correction Techniques - ✔✔Spatially varying energy corrections
using intrinsic flood. Tune PMT to ensure consistent performance over time.
Limiting factor in gamma camera performance: - ✔✔Collimator
Collimator Resolution - ✔✔Defined as the FWHM of the radiation profile from
a point or line source of radiation projected by the collimator onto the detector
(PSF or LSF).
Collimator resolution improves with: - ✔✔The ratio of septal hole diameter to
effective length is made smaller. Long, narrow holes provide better resolution.
Collimator resolution degrades with: - ✔✔Increasing source to collimator
distance. As this distance increases, the max height of the PSF decreases,
but width increases so total area under the curve does not change although
resolution is degraded.
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