Gamma Camera Uniformity Test

Uniformity of Detector Response

• A conventional gamma camera is expected to provide a uniform response to a uniform field, which is checked using a flood field or sheet phantom.
• A flood field consists of a flat, sealed plate larger than the field of view (FOV), typically filled with cobalt-57 (57Co).
• Cobalt-57 has a similar gamma emission to technetium-99m (99mTc) but has a longer half-life.
• The flood field test should produce a uniform image with the collimator in place, allowing identification of defective photomultipliers as areas of reduced counts.
• Crystal defects, such as cracks, appear as linear defects in the image.
• Non-uniformity due to minor differences in photomultiplier performance is analyzed by counting pixels, and image data can be automatically compensated based on this analysis.
• Regular checks are necessary to monitor photomultiplier deterioration over time.

Background Radiation Checks

• Background radiation checks help identify contamination on the gamma camera or collimator, or the presence of a local unshielded source.
• High readings, regardless of camera orientation, indicate contamination on the crystal or camera head.
• Subsequent high readings, obtained with the collimator in place, suggest collimator contamination.