Novel method for quantitative evaluation of cardiac amyloidosis using (201)TlCl and (99m)Tc-PYP SPECT

The degree of myocardial technetium-(99m)-pyrophosphate ((99m)Tc-PYP) accumulation in cardiac amyloidosis is conventionally evaluated by the PYP score. This method involves qualitative visual evaluation on two-dimensional images. Here, we performed three-dimensional quantitative analysis using software developed in our laboratory.

We performed dual myocardial imaging using thallium-(201)-chloride ((201)Tl-Cl) and (99m)Tc-PYP in cases of suspected cardiac amyloidosis and calculated the PYP accumulation rates of all myocardial pixels showing (99m)Tc-PYP accumulation. We defined this procedure as quantitative evaluation of the degree of (99m)Tc-PYP accumulation in the myocardium. Patients were divided into two groups with and without a diagnosis of cardiac amyloidosis, and we examined the PYP accumulation rates in both groups. In addition, we examined the PYP scores of the two groups by conventional qualitative evaluation.

The PYP scores of the cardiac amyloidosis group were significantly higher than those of the other group. The PYP accumulation rates of the cardiac amyloidosis group were significantly higher than those of the other group. There were significant differences in the PYP accumulation rate and PYP score between the two groups. There was considered to be a threshold between the two groups in the case of the PYP accumulation rate.

When the threshold of the PYP score was defined as 3+ and that of the PYP accumulation rate as 41.5 %, the sensitivity of the PYP score and PYP accumulation rate was 84.6 %. However, the specificity of the PYP accumulation rate was higher than that of the PYP score. Quantitative evaluation by the PYP accumulation rate of the degree of (99m)Tc-PYP accumulation in the myocardium may be useful in the diagnosis of cardiac amyloidosis.