Head (a) and pelvic (b) phantoms used in the study. Contrast inserts starting from the lower, going clockwise: Head phantom: 1: cortical bone; 2: PMMA; 3: lipid; 4: adipose tissue; 5: muscle; and 6: breast tissue. Pelvic phantom: 1: prostate; 2: breast; 3: PMMA; 4: muscle; 5: adipose tissue 1; 6: adipose tissue 2; and 7: bone inserts.
CNR improvement ratio as function of phantom diameter for scans in full-fan (a) and half-fan (b) scanning modes for three different antiscatter-grid designs (ASG1, ASG2, and ASG3) with and without (w/o) the bow-tie filter (BTF). The transmission ratios (primary, scatter) for each grid design are ASG1 (0.7, 0.28), ASG2 (0.75, 0.31), and ASG3 (0.78, 0.4). (c) CNR vs. phantom diameter with and without subtractive scatter correction compared to CNR achieved in a hypothetical scatter-free imaging system in which only primary photons are detected, (d) Scatter-to-primary ratios for full- and half-fan scanning modes for cylindrical homogeneous water phantoms of varying diameters.
Transverse-axis scatter-to-primary ratios for the head and pelvic phantom. (a) Head phantom at 0° projection angle, (b) head phantom at 90°, (c) pelvic phantom at 0°, and (d) pelvic phantom at 90°. The VMS grid (ASG2) was assumed.
Transverse-central plane isodose maps illustrating the absolute dose distribution delivered by the standard Varian Medical System scanning protocols (all using the ASG2 grid) to the head and pelvic phantoms. (a) Head phantom scan without BTF, 475 mAs;( b) head phantom scan with BTF, 1320 mAs; (c) body phantom scan without BTF, 475 mAs; and (d) body phantom scan with BTF, 1320 mAs. Note that the Isodose levels and color codes vary from panel-to-panel. The illustrations were created by the Pinnacle treatment planning system.
Reconstructed images of the head phantom. The gray-scale window is ±20% of the value at the center of phantom. The BTF images assume unscaled doses (unparenthesized CNR and SNR values in Table I).
Reconstructed images of the pelvic phantom. The gray-scale window is ±20% of the value at the center of phantom. The BTF images assume unscaled doses (unparenthesized CNR and SNR values in Table II).
Scatterograms summarizing the impact of various scatter mitigation acquisition and correction techniques on relative image contrast (top row) and contrast-to-noise ratio (bottom row) for the head phantom (left column) and pelvic phantom (right row). The contrast values are normalized to the contrast observed when only primary radiation is detected and CNR is normalized to the value achieved when a bowtie filter but no antiscatter grid is used in conjunction with hypothetical scatter-free projections.
Image-quality indexes of head phantom reconstructed images.
Image-quality indexes of pelvic phantom reconstructed images.
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