Volumetric evaluation of 99mTc-pyrophosphate SPECT/CT for transthyretin cardiac amyloidosis: Methodology and correlation with cardiac functional parameters

Transthyretin amyloid cardiomyopathy disease burden quantified using 99mTc-pyrophosphate SPECT/CT: volumetric parameters versus SUVmax ratio at 1 and 3 hours

BACKGROUND

Various parameters derived from technetium-99m pyrophosphate (99mTc-PYP) single-photon emission computed tomography (SPECT) correlate with the severity of transthyretin amyloid cardiomyopathy (ATTR-CM). However, the optimal metrics and image acquisition timing required to quantify the disease burden remain uncertain.

METHODS AND RESULTS

We retrospectively evaluated 99mTc-PYP SPECT/CT images of 23 patients diagnosed with ATTR-CM using endomyocardial biopsies and/or gene tests. All patients were assessed by SPECT/CT 1 hour after 99mTc-PYP injection, and 13 of them were also assessed at 3 hours. We quantified 99mTc-PYP uptake using the volumetric parameters, cardiac PYP volume (CPV) and cardiac PYP activity (CPA). We also calculated the SUVmax ratios of myocardial SUVmax/blood pool SUVmax, myocardial SUVmax/bone SUVmax, and the SUVmax retention index. We assessed the correlations between uptake parameters and the four functional parameters associated with prognosis, namely left ventricular ejection fraction, global longitudinal strain, myocardial extracellular volume, and troponin T. CPV and CPA correlated more closely than the SUVmax ratios with the four prognostic factors. Significant correlations between volumetric parameters and prognostic factors were equivalent between 1 and 3 hours.

CONCLUSIONS

The disease burden of ATTR-CM was quantified more accurately by volumetric evaluation of 99mTc-PYP SPECT/CT than SUVmax ratios and the performance was equivalent between 1 and 3 hours.

Diagnostic accuracy of bone scintigraphy imaging for transthyretin cardiac amyloidosis: systematic review and meta-analysis

BACKGROUND

Bone scintigraphy imaging is frequently used to investigate patients with suspected transthyretin cardiac amyloidosis (ATTR-CM). However, the reported accuracy for interpretation approaches has changed over time. We performed a systematic review and meta-analysis to determine the diagnostic accuracy of visual planar grading, heart-to-contralateral (HCL) ratio, and quantitative analysis of SPECT imaging and evaluate reasons for shifts in reported accuracy.

METHODS

We performed a systematic review to identify studies of the diagnostic accuracy of bone scintigraphy for ATTR-CM from 1990 until February 2023 using PUBMED and EMBASE. Studies were reviewed separately by two authors for inclusion and for risk of bias assessment. Summary receiver operating characteristic curves and operating points were determined with hierarchical modeling.

RESULTS

Out of a total of 428 identified studies, 119 were reviewed in detail and 23 were included in the final analysis. The studies included a total of 3954 patients, with ATTR-CM diagnosed in 1337 (39.6%) patients and prevalence ranging from 21 to 73%. Visual planar grading and quantitative analysis had higher diagnostic accuracy (.99) than HCL ratio (.96). Quantitative analysis of SPECT imaging had the highest specificity (97%) followed by planar visual grade (96%) and HCL ratio (93%). ATTR-CM prevalence accounted for some of the observed between study heterogeneity.

CONCLUSIONS

Bone scintigraphy imaging is highly accurate for identifying patients with ATTR-CM, with between study heterogeneity in part explained by differences in disease prevalence. We identified small differences in specificity, which may have important clinical implications when applied to low-risk screening populations.

Diagnostic value of heart-to-mediastinum ratio in 99mTc-pyrophospate SPECT/CT for transthyretin cardiac amyloidosis

BACKGROUND

In transthyretin cardiac amyloidosis (ATTR-CA), 99mTc-pyrophosphate myocardial scintigraphy (99mTc-PYP) is a diagnostic tool that utilizes visual and quantitative evaluation. However, false positive cases can occur because of tracer accumulation in the blood. We investigated the effectiveness of the heart-to-mediastinum (H/M) ratio of 99mTc-PYP in ATTR-CA diagnosis.

METHODS

We retrospectively included 164 patients who underwent 99mTc-PYP single-photon emission computed tomography/computed tomography between March 2019 and January 2022. The diagnostic accuracy of ATTR-CA was examined by the heart-to-contralateral lung (H/CL) and H/M ratio calculated at 3 hours post-tracer administration.

RESULTS

After the exclusion of patients who did not undergo endomyocardial biopsy, 30 patients (15 each with ATTR-CA and without ATTR-CA) were included. The receiver operating characteristic curve used to distinguish ATTR-CA from non-ATTR-CA patients revealed an area under the curve of 0.986 and 0.943, respectively. A H/M ratio of > 1.41 identified ATTR-CA patients with a sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 100, 93.3, 93.3, and 100%, respectively. Conversely, an H/CL ratio of > 1.3 identified ATTR-CA patients with 100% sensitivity, 40.0% specificity, 62.5% PPV, and 100% NPV.

CONCLUSION

The H/M ratio obtained at 3 hours post-injection has the potential to be a novel indicator for ATTR-CA.

Review of cardiovascular imaging in the Journal of Nuclear Cardiology 2022: single photon emission computed tomography

In this review, we will summarize a selection of articles on single-photon emission computed tomography published in the Journal of Nuclear Cardiology in 2022. The aim of this review is to concisely recap major advancements in the field to provide the reader a glimpse of the research published in the journal over the last year. This review will place emphasis on myocardial perfusion imaging using single-photon emission computed tomography summarizing advances in the field including in prognosis, non-perfusion variables, attenuation compensation, machine learning and camera design. It will also review nuclear imaging advances in amyloidosis, left ventricular mechanical dyssynchrony, cardiac innervation, and lung perfusion. We encourage interested readers to go back to the original articles, and editorials, for a comprehensive read as necessary but hope that this yearly review will be helpful in reminding readers of articles they have seen and attracting their attentions to ones they have missed.

[Utility of the Method for Calculating the Heart to Contralateral Ratio for Cardiac Amyloidosis by Using Ray-summation Images in 99mTc-pyrophosphate Scintigraphy]

PURPOSE

The purpose of this study was to avoid the influence of background activity in the calculation of heart to contralateral ratio (H/CL) in ^99mTc-pyrophosphate (PYP) scintigraphy for diagnosis of cardiac amyloidosis. Therefore, we investigated the utility of the H/CL calculation method using ray-summation (ray-sum) images created by multi-planar reconstruction and summing slices of the heart range from single-photon emission computed tomography (SPECT) images.

METHODS

The subjects were 33 patients who underwent ^99mTc-PYP planar and SPECT/CT at 3 hours after injection. Ray-summation axial (ray-sum axial) and ray-summation coronal (ray-sum coronal) images were created and H/CL was calculated. We compared the differences in sensitivity, specificity, accuracy, and area under the curve (AUC) between the conventional method and our method, and calculated the cutoff values.

RESULTS

Comparison of the conventional method and our method showed no significant difference in sensitivity and AUC, while specificity was significantly improved to 97% (p=0.003) of ray-sum axial image and 90% (p=0.01) of ray-sum coronal image, and accuracy was significantly improved to 94% (p=0.02) of ray-sum axial image.

CONCLUSION

The H/CL calculation method using ray-sum images had higher diagnostic performance than the conventional method, with optimal cutoff of ray-sum axial images 3.07 and ray-sum coronal images 2.77.