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Background <p>The heart-to-contralateral lung (H/CL) ratio, derived from planar imaging, is a standard quantitative metric in <sup>99m</sup>Tc-pyrophosphate (<sup>99m</sup>Tc-PYP) studies. However, cardiac-dedicated cadmium-zinc-telluride cameras, which primarily generate single-photon emission computed tomography (SPECT) images, cannot produce planar images. We propose the myocardium-to-cavity (M/C) ratio, derived from simultaneous dual-isotope <sup>99m</sup>Tc-PYP/<sup>201</sup>Tl SPECT imaging, as an alternative quantitative measure. This study evaluates the clinical utility of the M/C ratio by comparing it to the H/CL ratio.</p> Methods/results <p>We retrospectively analyzed 121 consecutive patients with suspected cardiac amyloidosis who underwent dual-isotope <sup>99m</sup>Tc-PYP/<sup>201</sup>Tl imaging. Anterior planar images were acquired using an Anger camera at 1&#xa0;h after <sup>99m</sup>Tc-PYP injection. Dual-isotope D-SPECT <sup>99m</sup>Tc-PYP/<sup>201</sup>Tl images were acquired from 10&#xa0;min after <sup>201</sup>Tl injection at 1 and/or 3&#xa0;h after <sup>99m</sup>Tc-PYP injection. For M/C ratio calculation, circular regions of interest of equal diameter were set on the myocardium and left ventricular cavity using <sup>201</sup>Tl images, then superimposed on <sup>99m</sup>Tc-PYP images. The optimal cut-off values were 1.5 for H/CL and 1.0 for M/C ratios to distinguish <sup>99m</sup>Tc-PYP positive and negative uptake. Of 121 patients, 19 (16%) were classified as <sup>99m</sup>Tc-PYP positive with planar and SPECT imaging, following the stepwise diagnostic flow recommended by the Japanese Society of Nuclear Cardiology (adapted for D-SPECT). Both H/CL and M/C ratios were significantly higher in patients with <sup>99m</sup>Tc-PYP-positive than in negative cases. Notably, five false-positive cases with H/CL ratios &gt; 1.5 had M/C ratio &lt; 1.0, correctly distinguishing them from <sup>99m</sup>Tc-PYP-positive patients. The M/C ratio demonstrated 100% sensitivity, specificity, and predictive values, irrespective of imaging time. In contrast, the H/CL ratios showed 100% sensitivity, 95% specificity, 79% positive predictive value, and 100% negative predictive value. The inter- and intra-observer reproducibility of the M/C ratio was excellent with correlation coefficients exceeding 0.99. Additionally, 13 of the 19 (68%) <sup>99m</sup>Tc-PYP positive patients exhibited a mismatch pattern with decreased <sup>201</sup>Tl uptake corresponding to high <sup>99m</sup>Tc-PYP uptake.</p> Conclusions <p>The M/C ratio demonstrated superior diagnostic accuracy compared to the H/CL ratio, particularly in eliminating false positive cases. Its simplicity and reproducibility make it a promising alternative for routine clinical practice, potentially replacing the H/CL ratio in dual-isotope imaging.</p>

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Myocardium-to-cavity ratio derived from simultaneous 99mTc-PYP/201Tl dual-isotope SPECT imaging to differentially diagnose transthyretin cardiac amyloidosis

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  • 发表日期：

    2025年7月1日

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  • Shozo Yamashita,
  • Kenichi Nakajima,
  • Teppei Kitano,
  • Hiromu Kato,
  • Tatsuya Yoneyama,
  • Haruki Yamamoto,
  • Kunihiko Yokoyama

摘要

Background

The heart-to-contralateral lung (H/CL) ratio, derived from planar imaging, is a standard quantitative metric in 99mTc-pyrophosphate (99mTc-PYP) studies. However, cardiac-dedicated cadmium-zinc-telluride cameras, which primarily generate single-photon emission computed tomography (SPECT) images, cannot produce planar images. We propose the myocardium-to-cavity (M/C) ratio, derived from simultaneous dual-isotope 99mTc-PYP/201Tl SPECT imaging, as an alternative quantitative measure. This study evaluates the clinical utility of the M/C ratio by comparing it to the H/CL ratio.

Methods/results

We retrospectively analyzed 121 consecutive patients with suspected cardiac amyloidosis who underwent dual-isotope 99mTc-PYP/201Tl imaging. Anterior planar images were acquired using an Anger camera at 1 h after 99mTc-PYP injection. Dual-isotope D-SPECT 99mTc-PYP/201Tl images were acquired from 10 min after 201Tl injection at 1 and/or 3 h after 99mTc-PYP injection. For M/C ratio calculation, circular regions of interest of equal diameter were set on the myocardium and left ventricular cavity using 201Tl images, then superimposed on 99mTc-PYP images. The optimal cut-off values were 1.5 for H/CL and 1.0 for M/C ratios to distinguish 99mTc-PYP positive and negative uptake. Of 121 patients, 19 (16%) were classified as 99mTc-PYP positive with planar and SPECT imaging, following the stepwise diagnostic flow recommended by the Japanese Society of Nuclear Cardiology (adapted for D-SPECT). Both H/CL and M/C ratios were significantly higher in patients with 99mTc-PYP-positive than in negative cases. Notably, five false-positive cases with H/CL ratios > 1.5 had M/C ratio < 1.0, correctly distinguishing them from 99mTc-PYP-positive patients. The M/C ratio demonstrated 100% sensitivity, specificity, and predictive values, irrespective of imaging time. In contrast, the H/CL ratios showed 100% sensitivity, 95% specificity, 79% positive predictive value, and 100% negative predictive value. The inter- and intra-observer reproducibility of the M/C ratio was excellent with correlation coefficients exceeding 0.99. Additionally, 13 of the 19 (68%) 99mTc-PYP positive patients exhibited a mismatch pattern with decreased 201Tl uptake corresponding to high 99mTc-PYP uptake.

Conclusions

The M/C ratio demonstrated superior diagnostic accuracy compared to the H/CL ratio, particularly in eliminating false positive cases. Its simplicity and reproducibility make it a promising alternative for routine clinical practice, potentially replacing the H/CL ratio in dual-isotope imaging.