Background: Technetium pyrophosphate (99mTc-PYP) imaging to diagnose transthyretin cardiac amyloidosis (ATTR-CA) has been increasingly utilized. The objective of this study is to provide a standardized 99mTc-PYP imaging protocol to diagnose ATTR-CA.
Methods: 104 scans from 45 subjects with biopsy-proven ATTR-CA or light-chain cardiac amyloidosis (AL) were assessed. Multiple scans were obtained using different counts (750 vs 2000 K), times to acquisition (1 vs 2 to 4 hours), processing matrix (256 vs 128), and 99mTc-PYP dose. Image quality and extracardiac activity was assessed. Quantitative methods using heart-to-contralateral ratios (H/CL) and a visual semiquantitative scale were used to diagnose ATTR-CA.19 The correlation between H/CL ratios and reproducibility of semiquantitative visual scores, acquired using various imaging parameters, were evaluated.
Results: All imaging parameters had good to excellent image quality. 750 vs 2000 K counts, 1 hour acquisition and 256 matrix, had lower extracardiac activity (P = .00018). 10 mCi of 99mTc-PYP v. higher doses showed excellent image quality and less extracardiac activity (P = .0015). Correlation of H/CL ratios was strong (r ≥ 0.92) and reproducibility of semiquantitative visual scores was high (Kappa = 95%).
Conclusion: An imaging protocol using 750 K counts, 10 mCi of 99mTc-PYP, and a 256 matrix was chosen as the standardized imaging protocol since it provided the shortest overall study time (1 vs 2 to 4 hours) and lowest radiation exposure (3 vs 8 to 10 mSv).
Keywords: 99mTc-PYP; ATTR-CA; amyloid; amyloidosis; non-invasive; standardized imaging protocol.