Evaluation of ATTR-cardiac amyloidosis employing Tc-99m pyrophosphate scintigraphy using planar, SPECT and gated SPECT imaging on dedicated cardiac CZT camera

Background/Introduction Recent recognition that ATTR cardiac amyloidosis (ATTR-CA) is not uncommon and the emergence of novel therapeutic opportunities resulted in the publication of “Expert Consensus Recommendations for Multimodality Imaging in Cardiac Amyloidosis”. However, almost all data were derived from general purpose NaI cameras, while new cardiac dedicated CZT cameras are becoming more widespread. Purpose To evaluate Tc-99m pyrophosphate (PYP) scintigraphy on D-SPECT cardio dedicated CZT camera (Spectrum Dynamics) in suspected ATTR-CA patients. Methods Seventy three consecutive patients suspected for ATTR-CA underwent planar (5 min), SPECT and gated SPECT (10 min, 8 bins) scintigraphy 89±26 min after injection of Tc99m-PYP 740 MBq, followed by late scintigraphy after 92±36 min in 65 consecutive patients. Perguini visual score, planar H/CL and SPECT derived H/CL ratio were evaluated by two blinded independent experienced readers. Diagnosis was based on visual interpretation after blood pool and monoclonal gammopathy were excluded. Results Very good to excellent planar and SPECT image quality was observed in almost all patients. PYP scintigraphy was positive in 6/73 patients, with left ventricular wall uptake clearly evident in the planar images of most patients. There was perfect agreement between readers regarding positive/negative interpretation. There was also substantial inter-observer agreement regarding the Perguini scoring (Cohen's k with linear weighting 0.819, 95% CI 0.701–0.937). Inter-observer agreement for H/CL ratio was also good (Pearson's correlation coefficient r(71)=0.873). SPECT and gated SPECT images were helpful only in one positive patient, and did not have an added value in any of the negative studies. Slightly better images were observed during late scintigraphy, but there was no change in interpretation, and H/CL ratio was not significantly changed (median difference −0.01, IQR 0.09). Alas, Inter-observer agreement of H/CL ratio was lower (Pearson's correlation coefficient r(64)=0.633). We also evaluated H/CL ratio derived from SPECT based application of the camera manufacturer. Agreement between early planar and early SPECT based H/CL ratio was good for both readers (r(69)=0.778 and r(66)=0.747), but inter-observer agreement was lower (r(66)=0.697). Conclusions ATTR PYP scintigraphy using cardiac dedicated CZT camera yielded excellent images in almost all patients, and uptake in the left ventricular wall could be easily identified in positive patients. Inter-observer agreement was excellent for both visual scoring and planar H/CL ratio. Early planar images were high quality, and limited additional diagnostic value was observed for both SPECT and gated SPECT scintigraphy and from later acquisition. Funding Acknowledgement Type of funding source: None