BODY CONTOUR DETERMINATION AND VALIDATION FOR BREMSSTRAHLUNG SPECT IMAGING

The purpose of this study was to validate a previously reported body c ontour measurement using Compton backscatter sources with bremsstrahlu ng SPECT imaging. Methods: Bremsstrahlung SPECT imaging was performed with P-32 using a dual-headed camera system fitted with medium-energy, parallel-hole collimators. Two sources of Tc-99m were placed directly on each collimator, Energy windows of 100 keV +/- 25% were used to im age the P-32 and also to record the Compton scatter from the Tc-99m so urces, Eleven patients enrolled in clinical Phase I therapeutic protoc ols were injected with P-32-chromic phosphate and SPECT images were ac quired and reconstructed in the transaxial plane, The P-32 distributio n and the patient body contour were both visualized in these slices, T he anteroposterior and lateral patient dimensions were measured by gen erating count profiles parallel to the anteroposterior and lateral bod y contour, respectively, at the midline in a transaxial slice. The dis tance in centimeters between the two centroids of each profile is repr esentative of the anteroposterior and lateral dimensions and was deter mined for each patient, These anteroposterior and lateral dimensions w ere compared to the same distance measurements made in these patients by CT in an anatomically comparable transaxial slice, A cylindrical SP ECT phantom was also studied to further validate the contour measureme nts, Results: The mean percent difference in the patient dimension mea surements between SPECT and CT was -0.8% with a range of -8.5% to 9.9% . The percent difference between the known and SPECT measured dimensio ns in the cylindrical phantom was 0.5%. Conclusion: The two external C ompton scatter source method is accurate for determining the body cont our.