The use of a novel method for SPECT/CT quantification of 99m-Tc-PYP uptake in the evaluation of ATTR cardiac amyloidosis

Abstract

\n \n \n Type of funding sources: None.\n Background/Introduction:\xa0 Bone scintigraphy with 99m-Technecium-Pyrophosphate (99m-Tc-PYP) with planar and SPECT imaging is now commonplace for the non-invasive diagnosis of ATTR cardiac amyloidosis. However, the quantification of 99m-Tc-PYP uptake is based on a semi-quantitative visual score and a heart to contralateral lung ratio which suffer from poor reproducibility. A more robust method of quantifying uptake and reporting results would be beneficial and may be possible using volumetric assessment with fused SPECT/CT acquisition.\n \n \n \n \xa0 The aim of this study was to evaluate the performance of a novel semi-automated quantitative software to diagnose ATTR cardiac amyloidosis in patients with a clinical suspicion of cardiac amyloidosis who underwent 99m-Tc-PYP SPECT/CT imaging.\n \n \n \n This was a retrospective, single-center study of consecutive patients who underwent 99m-Tc-PYP SPECT/CT imaging from September to December 2020. Quantification software was used to obtain standardized uptake values (SUVs) of 99m-Tc-PYP activity in the whole heart using SPECT/CT data. The total SUVs, mean SUVs, and percentage of injected tracer dose in the heart, as well as two other sets of these measurements adjusted for residual blood pool activity were obtained. Activity in the lung and bone was used to calculate heart to bone and heart to right lung ratios. The results from the software quantification were compared to the results from planar imaging as well as to the final clinical diagnosis of amyloidosis.\n \n \n \n \xa0 A total of 59 patients were imaged during this time with an average age of 74.1 ± 11.8, and 32 (54.2%) were male. After excluding 8 patients for technical issues, 12 patients were found to be positive for amyloid, 39 were negative, and the average imaging delay time was 75.0 ± 15.2 minutes. 13 methods of assessment were evaluated with the metric of the percentage of injected tracer dose found in the heart that was adjusted for the mean residual blood pool activity having the best discrimination between abnormal and normal studies. The mean percentage of injected dose in positive patients was 2.87% vs 0.98% in the patients without amyloidosis (p < 0.0001). Using a cutoff of 2% to ensure that no patients with amyloid would be missed by screening, there was 100% sensitivity, 94.9% specificity, and 96.1% accuracy. There was a significant difference in the percentage injected dose based on gradations of planar heart to contralateral lung ratio and planar visual score.\n \n \n \n Volumetric software quantification may be a superior method of evaluating 99m-Tc-PYP cardiac amyloidosis studies. This methodology may allow for a quantitative definition of a normal or abnormal 99m-Tc-PYP cardiac amyloid study and provide for the potential of following response to therapy.\n