Volumetric evaluation of (99m)Tc-pyrophosphate SPECT/CT for transthyretin cardiac amyloidosis: Methodology and correlation with cardiac functional parameters

BACKGROUND: Volumetric evaluation of (99m)Technetium-pyrophosphate ((99m)Tc-PYP) SPECT/CT is a useful method for assessing transthyretin cardiac amyloidosis (ATTR-CA). We investigated the methodology and assessed its relationship with conventional parameters. METHODS AND RESULTS: We retrospectively evaluated (99m)Tc-PYP SPECT/CT scans of 25 patients who underwent endomyocardial biopsy and/or gene testing. Fourteen (56%) patients were diagnosed with ATTR-CA. SPECT/CT images were acquired at 3 hours after injection. Total volumes of the myocardial regions where uptakes were > 1.2 and 1.4 × aortic blood pool SUVmax were evaluated and defined as cardiac pyrophosphate volume (CPV1.2 and CPV1.4). The heart-to-contralateral lung (H/CL) ratio and myocardial SUVmax were also calculated. CPV1.2 achieved the highest sensitivity and specificity in diagnosing ATTR-CA. In patients diagnosed with ATTR-CA (n = 14), CPV1.2 negatively correlated with left ventricular ejection fraction and positively correlated with left ventricular posterior wall thickness and QRS duration. The correlation was stronger in CPV1.2 than in the H/CL ratio and SUVmax. CONCLUSION: Volumetric evaluation of (99m)Tc-PYP SPECT/CT may be superior to the H/CL ratio and SUVmax in assessing the disease burden of ATTR-CA. Larger studies are warranted to clarify whether volumetric measurement can assess prognosis and disease progression. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12350-021-02857-7.