Quantification of myocardial 99mTc-labeled bisphosphonate uptake with cadmium zinc telluride camera in patients with transthyretin-related cardiac amyloidosis

Purpose We aimed to compare different methods for semi-quantitative analysis of cardiac retention of bone tracers in patients with cardiac transthyretin amyloidosis (ATTR). Methods Data from 67 patients with ATTR who underwent both conventional whole-body scan and a CZT myocardial SPECT (DSPECT, Spectrum Dynamics) 3 h after injection of Tc-99m-labeled bone tracer were analyzed. Visual scoring of cardiac retention was performed on whole-body scan according to Perugini 4-point grading system from 0 (no uptake) to 3 (strong cardiac uptake with mild/absent bone uptake). A planar heart-to-background (H:B) ratio was calculated using whole-body scan (wb-H:B). CZT SPECT was quantified using three methods: planar H:B ratio calculated from anterior reprojection (ant-H:B), left anterior oblique reprojection (LAO-H:B), and 3D-H:B ratio calculated from transaxial slices as mean counts in a VOI encompassing the heart divided by background VOI in the contralateral lung. Interventricular septal thickness was obtained using echocardiography. Results H:Bs obtained from planar and reprojected data were not statistically different (wb-H:B, 2.05 +/- 0.64, ant-H:B, 1.97 +/- 0.61, LAO-H:B, 2.06 +/- 0.64, all p = ns). However, 3D-H:B was increased compared to planar H:Bs (3D-H:B, 4.06 +/- 1.77, all p < 0.0001 vs. wb-H:B, ant-H:B, and LAO-H:B). Bland-Altman plots demonstrated that the difference between 3D and planar H:Bs increased with the mean value of myocardial uptake. 3D-H:B was best correlated to septal thickness (r = 0.45, p < 0.001). Finally, abnormal right ventricular uptake was associated with higher values of cardiac retention. Conclusion 3D semi-quantitative analysis of CZT SPECT optimized the assessment of Tc-99m-labeled bone tracer myocardial uptake in patients with cardiac amyloidosis.