Gamma Cameras
Quantitative resolution
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This test is performed using capillary tubes filled with activity. The tubes are positioned in parallel at a known separation (normally 10cm). Ideally the image would just be a single row of pixels containing a high number of counts with all surrounding pixels at zero. In real imaging systems the image will be blurred out producing tails of counts either side of the line.
The image is analyzed by plotting the counts per pixel across the image. The width of the profile is used to define the resolution, usually as the Full Width at Half maximum (FWHM). This is the width of the profile where the counts are at 50% of this highest point in the profile.
Some times the Full Width Tenth Max (FWTM) is also quoted. Where the 50% and 10% levels fall between two data points interpolation should be used to estimate the actual width.
Two capillary tubes are used to allow the size of the pixels to be calibrated.
Typical values for FWHM at 10cm in air
Low energy high resolution collimators: FWHM = 7.4 mm
Low energy general purpose collimators FWHM = 8.8 mm
