The comparison of resolutions and quantitative indices by reconstruction methods in Tl-201 myocardial perfusion SPECT

Objectives The Xpress3.cardiacTM, which is a type of wide beam reconstruction (WBR) method developed by UltraSPECT(Haifa, Israel), enables the acquisition of data at quarter time while maintaining the image quality. The aim of this study was to examine the usefulness of the WBR method for decreasing the scan times and comparing it with a filtered back projection (FBP), which is the method used routinely

Methods Phantom and clinical studies were conducted. The anthropomorphic torso phantom was made on an equality with counts from the patient’s body. The Tl-201 concentrations in the compartments were 74 kBq(2 µCi)/cc in the myocardium, 11.1 kBq(0.3 µCi)/cc in the soft tissue, and 2.59 kBq(0.07 µCi)/cc in the lung. The non-gated Tl-201 myocardial perfusion SPECT data were acquired with the phantom. The former study was scanned for 50 seconds per frame using the FBP method. The latter study was acquired for 13 seconds per frame using the WBR method. The full width at half maximum (FWHM) and the average image contrast were compared using Xeleris ver. 2.0551. In clinical studies, 30 patients, who were examined by Tl-201 gated myocardial perfusion SPECT in the department of nuclear medicine at Asan Medical Center from January to April 2015, were analyzed. The patients were imaged at full time (50 second per frame) using the FBP algorithm and again at quarter-time (13 second per frame) with the WBR algorithm. Using the 4DM (4DMSPECT), QPS (Quantitative Perfusion SPECT), and QGS (Quantitative Gated SPECT) software, the summed stress score (SSS), summed rest score (SRS), summed difference score (SDS), end-diastolic volume (EDV), end-systolic volume (ESV), and ejection fraction (EF) were analyzed for their correlations and statistical comparison using a paired t-test.

Results As a result of the phantom study, the WBR method improved the FWHM by more than 30% compared to the FBP method (WBR data 5.47 mm, FBP data 7.07 mm). The average image contrast of the WBR method was also higher than that of the FBP method. The results of the quantitative indices, SSS, SDS, SRS, EDV, ESV, and EF, revealed significant differences between the WBR and FBP (p<0.01). Regarding the correlation of SSS, SDS, and SRS, there were significant differences between the WBR and FBP (0.18, 0.34, 0.08). On the other hand, the EDV, ESV, and EF showed a good correlation with the WBR and FBP (0.88, 0.89, and 0.71). The phantom study results confirmed that the WBR method reduces the acquisition time and improves the image quality compared to the FBP method.

Conclusions Nevertheless, the significant differences in the quantitative indices should be considered. An evaluation test will be needed to apply a clinical study to find the cause of the differences between the phantom and clinical results.