Reproducibility of Semi-automated Quantitative Analyses of Tc-99m Pyrophosphate Uptake from Myocardial Perfusion Planar and SPECT Images

The aim of this study was to investigate intra- and inter-observer reproducibility of quantitative assessments of Technetium-99 m (Tc-99m) pyrophosphate (PYP) uptake from cardiac planar and SPECT images using a new method.

Our study cohort comprised 95 consecutive subjects referred for Tc-99m PYP imaging based on clinical suspicion of transthyretin cardiac amyloidosis. Myocardial uptake of Tc-99m PYP was quantified as Heart (H)/Contralateral (CL) ratio using a semi-automatic region growing (RG) scheme and a conventional (CONV) manual processing approach. Additionally, a separate cohort of 23 Grade 1 patients was selected for Tc-99m PYP planar imaging followed by SPECT/CT imaging with attenuation correction. Planar images were quantified using the RG method to calculate H/CL ratio, and SPECT images were quantified via a new approach to assessing heart (H)/ mediastinal (M) ratio and mean standard uptake value (SUV) of Tc-99m PYP uptake in the myocardium.

Intra-observer reproducibility of H/CL quantification was excellent for RG (R² = 0.89) and CONV (R² = 0.887) approaches. Inter-observer reproducibility for both approaches was similar (R² = 0.7914 vs. 0.7859). The assessments of agreement were excellent. H/CL ratios calculated using RG approach were significantly greater than those from CONV approach (1.31 ± 0.24 vs. 1.29 ± 0.23; p < 0.0001). For Grade 1 patients, planar H/CL, SPECT H/M and SPECT SUV quantified by the same operator (Intra) were 1.17 ± 0.17, 2.25 ± 1.97, and 5.11 + 1.62, respectively; and those quantified by two different operators (Inter) were 1.19 ± 0.16, 2.18 ± 1.73 and 5.15 ± 1.45, respectively. Intra- and inter-reproducibilities were high and COVs were minimal for H/CL and SUV quantification, while were relatively poor and broad for H/M.

This study demonstrates excellent intra- and inter- observer reproducibilities of Tc-99m PYP quantitative assessments of H/CL ratio via RG and CONV approaches. The mean SUV assessment of myocardial PYP uptake via Tc-99m SPECT imaging using the new method is highly reproducible.