Discrepant Tc-99m PYP Planar Grade and H/CL Ratio: Which Correlates Better with Diffuse Tracer Uptake on SPECT?

1633 Introduction: Planar Tc-99m pyrophosphate (PYP) scans can be interpreted using the Perugini grade (≥ 2 considered positive) and the heart to contralateral lung ratio (H/CL, ≥ 1.5 considered positive). The frequency of a discrepancy between the Perugini grade and H/CL, and its implications are unknown. Method and Result: We analyzed the 1-hour images of 373 PYP scans of which 38 (10%) had a discrepancy between the Perugini grade and H/CL. Diffuse tracer uptake on SPECT was considered the final arbitrator of PYP positive or negative status. In 29 (76%) of the discrepant cases, the planar grade corresponded with the SPECT finding (p=0.001, table1, figure 1). All 9 cases where the grade was discordant with SPECT occurred in grades 1 and 2. Conclusions: In PYP scans with discrepant Perugini grade and H/CL, the grade corresponded more often with SPECT. Discordance between Perugini grade and SPECT occurred only when the grade was marginally negative or positive (1 or 2) and may reflect subjectivity of interpretation.