Assessment of Interobserver Agreement in the Interpretation of (99m)Tc-PYP SPECT Imaging of Cardiac Amyloidosis

Background: Technetium-99m pyrophosphate single photon emission computed tomography ((99m)Tc-PYP SPECT) imaging is widely used to diagnose cardiac amyloidosis, a disease characterized by amyloid protein deposits in the myocardium. The effects of viewing perspectives on interobserver agreement in the interpretation of (99m)Tc-PYP SPECT images for the diagnosis of cardiac amyloidosis remain unclear. Methods: A retrospective analysis of 32 consecutive patients who underwent (99m)Tc-PYP imaging for the diagnosis of cardiac amyloidosis at Nagasaki University Hospital between October 2017 and February 2020 was performed. Four evaluators independently reviewed coronal, sagittal, and transaxial images and then all images together and made a categorical diagnosis based on predefined criteria. Interobserver agreement was analyzed using Cohen's Kappa analysis. Results: Kappa coefficient values in the four-grade grading system (grades 0–3) ranged between 0.31 and 0.95, while those in the binary grading system (positive/negative) ranged between 0.88 and 1. The sagittal view showed the highest value in the four-grade grading system (0.95) and the lowest in the binary grading system (0.88). The transaxial view was more likely to show a consistently high kappa value in both the four-grade and binary grading systems. The use of the multiplanar view reduced the number of subjects classified as grade 1. Conclusion: Our study demonstrates that the transaxial view provides the most consistent interpretation of (99m)Tc-PYP SPECT images for the diagnosis of cardiac amyloidosis. The use of the multiplanar view may also reduce equivocal interpretations, which are graded as grade 1. Further studies with larger sample sizes and a quantitative analysis are needed to confirm the present results.