Click on image to view larger version.
FIGURE 5. (A) COR misalignment and resulting image-blurring artifacts in rotating-
-camera SPECT. Degree of blurring is related to magnitude of spatial misalignment of mechanical and electronic CORs. Misalignment as small as 3.2 mm (or 0.5 pixel for 64 x 64 image matrix) can produce perceptible blurring in SPECT images, with blurring substantially worse for misalignment of 6.4 mm (1 pixel). (Adapted from reference (29) with permission.) Note that for cross-sectional image of line source, COR misalignment blurs expected point into full or partial circle depending on position of source in FOV: if it is at or near center of FOV, line source appears as full circle in cross-section; if it is near periphery of FOV, it appears as partial circle. (B) COR misalignment can be measured and corrected on basis of acquiring 360° circular SPECT study of 99mTc point source and constructing graphs of x- and y-positions (perpendicular and parallel to axis of rotation, respectively) of position of maximum-count pixel in each projection image vs. angular position. x- and y-position vs. angle graphs should be sinusoidal curve and straight line, respectively. Angle-by-angle deviation between x-position on best-fit sine curve and x-position of actual maximum-count pixel thus yields correction table, indicating offset by which each projection image must be shifted at each angular position to align CORs. Alternatively, average of offsets may used at each angular position. (Adapted from reference (15) with permission.)
