A Quantitative Diagnostic Method Using 99mTc-pyrophosphate Lateral Planar Images to Distinguish Between Transthyretin Amyloid Cardiomyopathy and False-Positive Images Due to Blood Pools.

Background: This study investigated the feasibility of using a quantitative diagnostic method based on ^99mTc-pyrophosphate scintigraphy (PYP) lateral planar images to differentiate between PYP-positive (myocardial uptake) and false-positive (blood pool uptake) scans. Methods: The study included 93 consecutive patients with suspected transthyretin amyloid cardiomyopathy (ATTR-CM) who underwent PYP between April 2022 and December 2023. Patients were categorized using planar anterior PYP images according to the Perugini visual grading system; patients with grades ≥ 2 were analyzed. Whether the uptake of the ventricle was in the blood pool or the myocardium was confirmed by transaxial single-photon emission tomography (SPECT). The heart-to-mediastinum ratios (H/M ratio) of the left lateral planar images at 1- and 3-h were calculated by placing a circular region of interest in the heart and cephalodorsal side of the heart to determine optimal cut-off values. Results: Among the PYP images, the study analyzed 15 positives diagnosed as ATTR-CM and 10 false positives. Significant differences were observed in the H/M ratio at 1- and 3-h (both p<0.01), with 100% sensitivity and specificity using cut-off values of 1.22 and 1.21 at 1- and 3-h, respectively. The interclass correlation coefficients (2, 1) between the two readers were 0.919 and 0.958 for the 1- and 3-h H/M ratios, respectively. Conclusions: Lateral planar PYP imaging can exclude PYP false-positive cases caused by blood pools in a simple and quantitative manner using only a 1-h planar image, possibly obviating the need for SPECT imaging.