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FIGURE 5. SPECT short-axis slices and corresponding circumferential count profiles for normal phantom in 15-cm off-center position and straight orientation using 180° and 360° acquisition orbits. Visually, images acquired with 180° orbit are inhomogeneous (top). Mild defects are present (arrows). These segments of phantom wall were closest to rotating detectors. Images acquired with 360° orbit are visually homogeneous (bottom). Quantitative analysis by circumferential count profiles of apical, midventricular, and basal slices shows marked inhomogeneity of images obtained with 180° orbit. Arrows indicate troughs in profiles that correspond to visual defects in images. Circumferential count profiles of images acquired with 360° acquisition display only mild inhomogeneity similar to that in Figure 4.
