Objective To explore the clinical application value of ⁹⁹Tc^m-pyrophosphate (PYP) dual-phase planar imaging and tomographic imaging in the diagnosis of transthyretin-related cardiac amyloidosis (ATTR-CA).

Methods This retrospective study was conducted on 157 patients with suspected cardiac amyloidosis (CA) at Fuwai Hospital, Chinese Academy of Medical Sciences, from March 2020 to January 2023, including 108 males and 49 females, aged (58.9±14.8) years, ranging from 10 to 88 years old. The patients were intravenously injected with 740 MBq ⁹⁹Tc^m-PYP, and planar imaging and tomographic imaging were performed at 1 h (hereinafter referred to as early imaging) and 3 h (hereinafter referred to as delayed imaging) after injection. The Perugini method and semi-quantitative analysis method were used for the positive diagnosis of ATTR-CA in planar imaging, while the semi-quantitative scoring method was used for the positive diagnosis of ATTR-CA in tomographic imaging. Using clinical classification as the grouping criteria, all patients were divided into light chain cardiac amyloidosis (AL-CA) group, ATTR-CA group, and non-CA group. Diagnostic results of the Perugini method in planar imaging (positive for ≥2 points), semi-quantitative analysis method in planar imaging (positive for the uptake ratio of heart to contralateral lung ≥1.5), and semi-quantitative scoring method in tomographic imaging (positive for 2 points) were compared among the groups, and the ⁹⁹Tc^m-PYP imaging characteristics and diagnostic efficacy of different acquisition phases and different acquisition methods were analyzed. One-way analysis of variance and Bonferroni test were used to analyze the intergroup differences in measurement data. The χ² test or Fisher′s exact probability method was used to analyze intergroup differences in counting data. In addition, the Kappa test was used to analyze the intergroup consistency of counting data, and the paired χ² test (McNemar test) was used to compare the differences in diagnostic efficiencies among various diagnostic methods.

Results According to clinical diagnosis, of the 157 suspected patients with CA, 83 were confirmed to have CA (including 23 cases of ATTR-CA and 60 cases of AL-CA), and 74 cases were identified as non-CA. The sensitivity, specificity, and accuracy of the semi-quantitative scoring method for delayed tomographic imaging in the diagnosis of ATTR-CA were 91.3%, 98.5%, and 97.5%, respectively, compared with other diagnostic methods with different acquisition phases and different acquisition methods, and the accuracy was the highest. On the contrary, the sensitivity, specificity, and accuracy of the Perugini method for early planar imaging were 100%, 40.3%, and 49.0%, respectively, compared with various diagnostic methods, and the accuracy was the lowest. After pairwise comparison of the diagnostic results for various different acquisition phases and methods, early tomographic imaging and delayed tomographic imaging showed good consistency in the semi-quantitative scoring method for the diagnosis of ATTR-CA (Kappa=0.835), but the difference in diagnostic efficacy was not statistically significant (χ²=110.883, P=0.219). The Perugini method of delayed planar imaging and the semi-quantitative scoring method of delayed tomographic imaging also had good consistency in the diagnosis of ATTR-CA (Kappa=0.784), and the difference in diagnostic efficacy was statistically significant (χ²=101.258, P=0.004), with the latter having a higher diagnostic accuracy. Moreover, the diagnostic consistency among other diagnostic methods with different acquisition phases and methods was average or poor (Kappa is 0.135–0.679).

Conclusions Misdiagnosis was found in the diagnosis of ATTR-CA using early planar imaging. Early tomographic imaging and delayed tomographic imaging, as well as delayed planar imaging, had high diagnostic accuracy for ATTR-CA.