Scintillation Camera Quality Control Flashcards
The _____ of the PHA is evaluated by
using a source that radiates the whole crystal.
photopeak window
Irradiation of the whole crystal may be
achieved using a ____, or a ____ at a distance.
sheet source, point source
The photopeak window is checked ____
daily
____is the ability of the scintillation
camera to reproduce a uniform distribution of activity.
Field uniformity
_____ and ___ in the crystal contribute to nonuniformity.
Differences in the PMT response, transmission of light
Nonuniformities of greater than ___ from the mean are unacceptable for clinical imaging.
5%
Modern cameras have a uniformity of better than ___ between adjacent areas
2%
Field uniformity is commonly checked daily by placing a large-area disc made of ___ in front of the camera
57Co
57Co emits ___ photons and has a half-life of ___
122 keV, 270 days
____ are obtained with the collimator in place and will assess the system performance including the collimator.
Extrinsic flood images
___ are performed without the
collimator and assess the performance of Nal crystal and associated light detectors.
Intrinsic floods
the ability to separate two points
Resolution
Resolution (i.e., the ability to separate two points) is checked using a ____
quadrant bar phantom
Quadrant bar phantoms have four sets of parallel bars, with each rotated through ___ degrees, with
dimensions of _____.
90, 3.5, 3.0, 2.5, and 2.0 mm
____ also check for linearity (i.e., ability to image straight lines).
Bar pattern phantoms
• A _____ is an ionization chamber used to measure the activity of a radioisotope dose
dose calibrator
Dose calibrators make measurements in ____
MBq or mCi
____ is checked daily by measuring the same standard source that has a long half-life.
Constancy
____ has a half-life of 30 years and is therefore ideal for measuring calibrator constancy.
137Cs
____is checked at installation and annually using ____
Accuracy, calibrated sources
Accuracy is checked at installation and ___ using calibrated sources
annually
____ is checked quarterly by measuring the decay of 99mTc over 72 hours or more.
Linearity
Linearity is checked ___ by measuring the decay of ____ over ____ hours or more.
quarterly, 99mTc, 72
___can also be checked by using a
source placed into a calibrated cylinder of lead that attenuates the source by a known amount.
Linearity
____is the difference in intensity (counts) in any abnormality compared to the intensity in the surrounding normal anatomy (background).
Contrast
____ is the difference in activities in the
abnormality and surrounding normal anatomy.
Subject contrast
_____is the corresponding difference in image counts in the abnormality and normal anatomy
Image contrast
Excellent localization in an organ of interest is known as “_____” imaging.
hot spot
The ratio of organ-specific uptake to unwanted uptake in other tissues is called the _____
target to background ratio
___ is affected by septal penetration and scatter
Contrast
Nuclear medicine ____ is the ability to distinguish two adjacent radioactive sources.
resolution
An image of a line is known as the ____
line spread function
Measurement of the ___ of the line spread function is the most common measure of resolution in nuclear medicine
full width half maximum (FWHM)
____ refers to the performance of
the camera without the collimator.
Intrinsic resolution
____ assesses the performance of the Nal crystal, light detectors (PMT), and associated electronics.
Intrinsic resolution
Intrinsic resolution of a scintillation camera is typically between ____
3 and 5 mm
System resolution (R) depends on the ____ and ____.
intrinsic resolution of the scintillation camera (Ri), resolution of the collimator (Rc)
FWHM in NM is generally ~ ___ with the low- energy high-resolution (LEHR) collimator most commonly used in clinical imaging.
8 mm
A FWHM of 8 mm corresponds to a limiting spatial resolution of 1/(2 × 8 Ip/mm, or ___
0.06 Ip/mm
Spatial resolution of commercial PET systems can approach __ FWHM when imaging a line source
of activity
5 mm
____is any unwanted counts in a nuclear medicine image that can interfere with the detection of abnormalities.
Noise
Noise may be classified as ___
random or structured
____ results from statistical variation in pixel counts and is called quantum mottle.
Random noise
____ is a major factor in SPECT due to the low number of photons used to reconstruct each voxel.
Quantum mottle
PET images have ___ counts and ___ levels of image mottle.
high, lower
___ includes nonuniformities in the
scintillation camera.
Structured noise
Uptake in the gastrointestinal tract when imaging the kidneys is an example of _____
structured noise
____ produce defects in the image, whose characteristics reflect the shape of the crack.
Cracked crystals
____ may also produce a cold defect and shows up well on a flood image.
PMT failure
____ refers to the increased brightness at the edge of the crystal.
Edge packing
