Brief ReportComparison of cardio-focal and chest reconstruction of technetium-99m pyrophosphate scintigraphy for diagnosis of transthyretin cardiac amyloidosis: a quality assurance study
Introduction
Technetium-99m pyrophosphate (PYP) scintigraphy is an established technique for confirming the diagnosis of transthyretin (ATTR) CA.1 PYP scintigraphy has undergone rapid evolution, fueled by its widespread acceptance for accurate diagnosis of ATTR-CA and an exponential growth in its clinical application.2 Initial data supported the high diagnostic accuracy of planar PYP imaging among patients with biopsy-proven ATTR-CA;3 however, recent evidence has highlighted the importance on performance of tomographic imaging to limit false interpretations.4,5 Multisocietal consensus document now recommends the routine performance of SPECT for accurate identification of ATTR-CA.6 While the consensus statement recognizes imaging of a cardiac field of view (FOV) as a requirement, a chest FOV has been given an optional recommendation. Although ability to acquire a larger FOV is a property of traditional Anger systems, more laboratories have now been utilizing cardio-focal PYP scintigraphy using high-resolution cadmium-zinc-telluride (CZT) crystal cameras. Additionally, Anger SPECT systems are now equipped with computed tomography (CT), and hybrid SPECT/CT is likely to improve diagnostic accuracy, due to its ability to co-localize myocardial uptake and provide better differentiation from blood pool activity. However, there are no data comparing the diagnostic accuracy of cardio-focal reconstruction of PYP scintigraphy with chest reconstruction. In this quality assurance study, we aimed to compare the findings on PYP SPECT/CT, when scintigraphy data are reconstructed only in a cardio-focal manner, similar to myocardial perfusion SPECT (without CT co-registration) to when it is reconstructed for the entire chest (with CT co-registration).
Section snippets
Methods
This is a retrospective analysis of clinical and imaging data of consecutive patients referred for PYP scintigraphy, at Western University, London, ON, Canada, between November 2017 and February 2021. This analysis was a part of a quality assurance initiative within the nuclear medicine department and therefore institutional review board approval was waived. Referrals for PYP scintigraphy were based on high clinical suspicion for ATTR-CA. These were generally guided by a combination of the
Results
Data from 102 patients were evaluated in the study. The mean age of the patients was 76 ± 11 years, with 68 (67%) being men. The mean left ventricular ejection fraction was 55% ± 14%. Coronary artery disease, chronic kidney disease, and atrial fibrillation were present in 56%, 14%, and 62% of the patients, respectively. A total of 41 PYP scans were considered to be positive based on chest SPECT evaluation. Patient characteristics, stratified by results of chest SPECT, are provided in the Table 1
Discussion
The application of PYP scintigraphy for diagnosis of ATTR-CA has grown at a fast pace.2 As a result, there has been rapid increase in clinical experience with performance of PYP scintigraphy, which has been coupled with several improvements in image acquisition and interpretation. Initial criteria for diagnosis of ATTR-CA from PYP scintigraphy was based on findings on planar imaging alone.3 This lead to the use of Perugini score ≥ 2 and/or H/CL ratio ≥ 1.5 to be considered diagnostic for
Limitations
Interpretation of PYP scintigraphy was performed by experienced readers, both with > 5 years of experience with PYP scintigraphy and a collective interpretation of over 400 studies. Thus, the similar performance of cardio-focal and chest PYP SPECT reconstructions cannot be generalized to less-experienced laboratories and readers. Given that there is a possibility of misclassifying studies with focal PYP uptake as negative, full chest reconstruction should be strongly considered over only
Conclusion
When reviewed by experienced readers, there is excellent concordance for interpretation of PYP scintigraphy data when performed with chest reconstruction to that performed in a cardio-focal manner. In a significant proportion of patients suspected with ATTR-CA, myocardial PYP uptake may not be diffuse in nature. Thus, given the possibility of misclassification of non-diffuse PYP uptake on cardio-focal reconstruction, routine large FOV acquisition and chest reconstruction of PYP SPECT should be
New knowledge gained
Myocardial PYP uptake may not always be diffuse, and care should be taken to not misclassify non-diffuse PYP uptake as being falsely negative. While cardio-focal and chest reconstruction of PYP tomographic data have similar diagnostic value for ATTR-CA, chest reconstruction may identify focal myocardial uptake more reliably.
Disclosure
Cigdem Akincioglu received research support from Pfizer; Mukunthan Murthy had none; Jonathan Romsa had none to disclose; James Warrington had— none to disclose; Saurabh Malhotra received research support from ASNC/Pfizer Inc., is one of the members in Speakers Bureau for Pfizer Inc. and Alnylam, and is an advisory board member for Pfizer, Alnylam, and BridgeBio.
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Cited by (2)
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2024, Journal of Medical Imaging and Radiation SciencesSingle photon emission computed tomography pyrophosphate imaging for transthyretin cardiac amyloid
2023, Journal of Nuclear Cardiology
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