Technetium Pyrophosphate Scintigraphy with Cadmium Zinc Telluride Cameras is a Highly Sensitive and Specific Imaging Modality to Diagnose Transthyretin Cardiac Amyloidosis

Background: Transthyretin cardiac amyloidosis (ATTR) is a rare, but underdiagnosed, cardiomyopathy. Traditionally diagnosed invasively, ATTR can be diagnosed with non-invasive Technetium pyrophosphate (Tc-PYP) planar scintigraphy. Non-planar imaging has not been validated for ATTR diagnosis. Here, we develop and validate a Cadmium Zinc Telluride (CZT) protocol for diagnosing ATTR.

Methods: Forty-three subjects (24 ATTR, 19 non-ATTR) were imaged with Philips Dual-Head Anger (planar) and General Electric CZT cameras. Myocardial uptake was quantified by heart-to-contralateral (H/CL) ratios. CZT scans were quantified by two readers blinded to planar H/CL, with one repeating blinded quantification. Using the previously validated diagnostic threshold (H/CL ≥ 1.5), sensitivity and specificity of CZT scintigraphy was measured. McNemar's test and Pearson's correlation coefficient were calculated.

Results: Among subjects (76.7% male, age 77 ± 9), there was no significant difference in proportion of ATTR-positive identification between modalities. There was high correlation between CZT and planar H/CL ratios (r = 0.92, P < 0.0001), with low intra- [ICC = 0.89 (0.80-0.94)] and inter-observer [ICC = 0.80 (0.65-0.89)] variability. CZT scintigraphy had 100% sensitivity and specificity for diagnosing ATTR.

Conclusion: Tc-PYP CZT imaging is as highly sensitive and specific diagnosing ATTR as planar imaging. These findings are clinically salient given the emergence of disease-modifying ATTR therapies, as it could expand diagnostic capability.