18 Questions
What is the conversion rate of 1 millicurie to megabecquerel?
37
What is the purpose of a flood field or sheet phantom?
To check uniformity of detector response
What type of radiation is used in a flood field or sheet phantom?
Cobalt-57 (57Co)
What would a defective photomultiplier show as in the image?
An area of reduced counts
What would a cracked crystal show as in the image?
A linear defect
Why are regular checks needed for photomultipliers?
To monitor for deterioration
What is the purpose of background radiation checks?
To identify contamination
What does a high reading obtained with the collimator in place indicate?
Contamination on the collimator
What type of radiation is similar to 99mTc in gamma emission?
Cobalt-57 (57Co)
What is the primary function of a flood field or sheet phantom?
To check the uniform response of the detector
What is the result of a non-uniform detector response?
An area of reduced counts in the image
What is the purpose of analyzing counts in each pixel?
To compensate for non-uniform detector response
What is indicated by a high reading obtained with the camera orientation changed?
Contamination on the crystal or camera head
Why is cobalt-57 used in a flood field or sheet phantom?
Because it has a similar gamma emission to 99mTc
What is the purpose of a gamma camera?
To produce a uniform image of a uniform field
What is the result of a defective photomultiplier?
An area of reduced counts in the image
What is the purpose of regular checks on photomultipliers?
To monitor any deterioration in the photomultipliers
What is the result of a cracked crystal?
A linear defect in the image
Study Notes
Converting Units
- 1 millicurie (mCi) is equal to 37 megabecquerel (MBq)
Characteristics and Quality Assurance of Gamma Images
- A conventional gamma camera should give a uniform response to a uniform field
- A flood field or sheet phantom is used to check uniformity of detector response
- Flood field consists of a flat sealed plate, larger than the FOV, and usually filled with cobalt-57 (57Co)
- 57Co has a similar gamma emission to 99mTc but is longer-lived
- Uniform image with collimator in place indicates proper functioning
- Defective photomultiplier appears as an area of reduced counts in the image
- Cracked crystal appears as a linear defect
Uniformity of Detector Response
- Non-uniformity caused by individual photomultiplier differences can be analyzed and compensated automatically
- Regular checks are necessary to monitor photomultiplier deterioration
- Background radiation checks identify contamination of the gamma camera, collimator, or local unshielded source
- High reading obtained regardless of camera orientation indicates contamination on the crystal or camera head
- High reading obtained with collimator in place indicates collimator contamination
Test your knowledge of gamma cameras, radiation units, and quality assurance in nuclear medicine. Learn about the conversion of mCi to MBq, characteristics of gamma images, and uniformity of detector response.
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