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A Method to Remove Artifacts in Attenuation-Corrected Myocardial Perfusion SPECT Introduced by Misalignment Between Emission Scan and CT-Derived Attenuation Maps

Institute of Molecular Biophysics, Radiopharmacy and Nuclear Medicine, Heart and Diabetes Center North Rhine-Westphalia, Bad Oeynhausen, Germany

View larger version (16K): [in a new window]   FIGURE 1. Histograms of pixel values of sagittal CT (A) and SPECT (B) slices. Thresholds determined from the histograms are marked as white columns.

View larger version (24K): [in a new window]   FIGURE 2. Detection of body surface in sagittal CT (A) and SPECT (B) slices. Outer contours corresponding to thresholds and estimated positions are marked as green dots (A) or white dots (B). The study shown is correctly aligned.

View larger version (89K): [in a new window]   FIGURE 3. (A) Coregistration: displays from fusion tool supplied by General Electric Medical Systems. Left, CT slices; center, SPECT slices; right, fused images. Top row, misalignment in craniocaudal direction (y-direction). Bottom row, corrected study. (B) Vertical long-axis slices of reconstructed SPECT study without AC (IRNC), after AC (IRAC), and after correction for misalignment (IRAC-MC). Arrows mark defects in apical anterior wall, which are not visible in non–attenuation-corrected slices and are improved in slices corrected for misalignment.

View larger version (87K): [in a new window]   FIGURE 4. Phantom study: polar maps from 4D-MSPECT. Top left, homogeneously filled heart phantom with AC. Other pictures from the same study show increasing craniocaudal misalignment (simulated) between CT and SPECT (pixel size = 7 mm).

View larger version (32K): [in a new window]   FIGURE 5. Phantom study, as in Figure 4. Ordinate, relative uptake per segment; abscissa, artificial misalignment in y-direction (1 pixel = 7 mm). In apical, anterior, and septal walls, uptake decreases with degree of misalignment; in inferior wall, declining uptake is apparent only in apical segment (x).

View larger version (34K): [in a new window]   FIGURE 6. Artifacts (arrows) caused by limited transaxial field of view of Hawkeye device. In this obese female patient, breasts are outside field of view.

View larger version (19K): [in a new window]   FIGURE 7. Patient studies: semiquantitative analysis of polar maps from 4D-MSPECT. (A) Mean differences between studies without (IRNC) and with AC (IRAC). (B) Mean differences between studies without (IRNC) and with AC after correction for misalignment (IRAC-MC). (C) Mean differences between attenuation-corrected studies before (IRAC) and after correction for misalignment (IRAC-MC). NS = not significant.