Quantitative technetium pyrophosphate and cardiovascular magnetic resonance in patients with suspected cardiac amyloidosis

The Accuracy of Technetium-99 m Pyrophosphate Imaging in Diagnosing Transthyretin Cardiac Amyloidosis and Its Impact on Patient Management

PURPOSE OF REVIEW

This review evaluates recent advancements in Technetium-99 m pyrophosphate (99mTc-PYP) imaging for transthyretin amyloid cardiomyopathy (ATTR-CM). We summarize the advantages of single-photon emission computed tomography (SPECT) over planar imaging, the potential impact of quantitative methods, and emerging data for quantifying response to therapy.

RECENT FINDINGS

The current literature demonstrates the superior diagnostic accuracy of SPECT compared with planar imaging in 99mTc-PYP studies. Emerging quantitative methods, using hybrid SPECT/CT and artificial intelligence, show promise for enhancing diagnostic precision and risk assessment. Recent studies have also highlighted the potential of 99mTc-PYP quantification for monitoring treatment response. 99mTc-PYP SPECT imaging has exceptional diagnostic accuracy for ATTR-CM. Quantitative techniques, which can be facilitated by artificial intelligence, improve risk stratification and may aid in treatment monitoring. Future research should focus on clarifying the clinical role and optimal approach for quantification.

Single-photon emission computed tomography/computed tomography quantification of Tc-99m pyrophosphate uptake to assess tafamidis treatment response in transthyretin cardiac amyloidosis

BACKGROUND

Cardiac imaging with bone-avid tracers for the diagnosis of transthyretin amyloid (ATTR) cardiac amyloidosis uses only limited quantification, but single-photon emission computed tomography/computed tomography (SPECT/CT) acquisition can provide volumetric assessment with quantification of tracer uptake. Tafamidis is routinely used in the treatment of cardiac amyloidosis, but there are scant data on changes in imaging results during therapy. The purpose of this study was to perform a longitudinal assessment of Tc-99m-pyrophosphate (PYP) imaging to determine if tafamidis therapy results in any change in quantitative measures of tracer uptake.

METHODS

The study incorporated a prospective, single-center study of ATTR patients being treated with tafamidis using Tc-99m-PYP SPECT/CT to quantify cardiac tracer uptake in the whole heart and left ventricle. Standardized uptake values (SUVs) were adjusted for blood pool activity. Comparison of baseline activity was made to values obtained approximately every 6 months during treatment.

RESULTS

Twenty-two patients (77.0±7.5 years old, 86.4% male) were on tafamidis for 15.3±4.0 months, with an average time between baseline and final follow-up study of 16.8±4.7 months. Thirteen patients (59.1%) had multiple follow-up amyloid studies. Statistically significant reductions in total SUVs, SUV volume, and percentage of injected dose were seen. Adjusted for the maximal aortic SUV, the total SUV in the left ventricle decreased by 36.9%, the SUV volume by 38.7%, and the percentage of injected dose decreased by 34.9% (all P values≤0.0001). Over the study duration, there was a decrease of 7.7%/month in the measured metrics.

CONCLUSION

The quantitative SUV measurements from Tc-99m-PYP SPECT/CT revealed an overall decrease in scintographic amyloid burden during the course of tafamidis therapy, but additional work is needed to determine the optimal metrics and improve the reproducibility of the quantification.

Deep Learning-Enabled Quantification of 99mTc-Pyrophosphate SPECT/CT for Cardiac Amyloidosis

Transthyretin cardiac amyloidosis (ATTR CA) is increasingly recognized as a cause of heart failure in older patients, with 99mTc-pyrophosphate imaging frequently used to establish the diagnosis. Visual interpretation of SPECT images is the gold standard for interpretation but is inherently subjective. Manual quantitation of SPECT myocardial 99mTc-pyrophosphate activity is time-consuming and not performed clinically. We evaluated a deep learning approach for fully automated volumetric quantitation of 99mTc-pyrophosphate using segmentation of coregistered anatomic structures from CT attenuation maps. Methods: Patients who underwent SPECT/CT 99mTc-pyrophosphate imaging for suspected ATTR CA were included. Diagnosis of ATTR CA was determined using standard criteria. Cardiac chambers and myocardium were segmented from CT attenuation maps using a foundational deep learning model and then applied to attenuation-corrected SPECT images to quantify radiotracer activity. We evaluated the diagnostic accuracy of target-to-background ratio (TBR), cardiac pyrophosphate activity (CPA), and volume of involvement (VOI) using the area under the receiver operating characteristic curve (AUC). We then evaluated associations with the composite outcome of cardiovascular death or heart failure hospitalization. Results: In total, 299 patients were included (median age, 76 y), with ATTR CA diagnosed in 83 (27.8%) patients. CPA (AUC, 0.989; 95% CI, 0.974-1.00) and VOI (AUC, 0.988; 95% CI, 0.973-1.00) had the highest prediction performance for ATTR CA. The next highest AUC was for TBR (AUC, 0.979; 95% CI, 0.964-0.995). The AUC for CPA was significantly higher than that for heart-to-contralateral ratio (AUC, 0.975; 95% CI, 0.952-0.998; P = 0.046). Twenty-three patients with ATTR CA experienced cardiovascular death or heart failure hospitalization. All methods for establishing TBR, CPA, and VOI were associated with an increased risk of events after adjustment for age, with hazard ratios ranging from 1.41 to 1.84 per SD increase. Conclusion: Deep learning segmentation of coregistered CT attenuation maps is not affected by the pattern of radiotracer uptake and allows for fully automatic quantification of hot-spot SPECT imaging such as 99mTc-pyrophosphate. This approach can be used to accurately identify patients with ATTR CA and may play a role in risk prediction.

Correlation of 99mTc-DPD bone scintigraphy with histological amyloid load in patients with ATTR cardiac amyloidosis

BACKGROUND

The significance of measuring 99mTc-labelled-3,3-diphosphono-1,2-propanodicarboxylic acid (99mTc-DPD) in transthyretin (ATTR) cardiac amyloidosis has not been adequately studied. This single-centre observational study evaluated the correlation between 99mTc-DPD scintigraphy and histological amyloid load in endomyocardial biopsy (EMB).

METHODS

Twenty-eight patients with biopsy-proven ATTR amyloidosis and concomitantly available 99mTc-DPD scintigraphy were included. Visual Perugini scoring, and (semi-)quantitative analysis of cardiac 99mTc-DPD uptake by planar whole-body imaging and single photon emission computed tomography (SPECT/CT) using regions of interest (ROI) were performed. From this, heart-to-whole-body ratio (H/WB) and heart-to-contralateral-chest ratio (H/CL) were calculated. The histological amyloid load was quantified using two different staining methods.

RESULTS

Increased cardiac tracer uptake was documented in all patients (planar: ROImean 129 ± 37 cps; SPECT/CT: ROImean 369 ± 142 cps). Histological amyloid load (19 ± 13%) significantly correlated with Perugini score (r = 0.69, p < .001) as well as with cardiac 99mTc-DPD uptake (planar: r = 0.64, p < .001; H/WB: r = 0.50, p = .014; SPECT/CT: r = 0.53, p = .008; H/CL: r = 0.43, p = .037) (results are shown for correlations with Congo Red-staining).

CONCLUSION

In ATTR, cardiac 99mTc-DPD uptake significantly correlated with histological amyloid load in EMB. Further studies are needed to implement thresholds in cardiac 99mTc-DPD uptake measurements for risk stratification and guidance of therapy.

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.

Cardiac Amyloidosis Imaging, Part 2: Quantification and Technical Considerations

^99mTc-pyrophosphate imaging has been around for a long time. In the 1970s, it was used to image recent myocardial infarction. However, it has recently been recognized for its value in detecting cardiac amyloidosis, leading to widespread use across the United States. Increased use led to considerable procedure variability. As the evidence base to support formal guidelines was being developed, experts from several professional medical societies issued imaging and interpretation recommendations titled "ASNC/AHA/ASE/EANM/HFSA/ISA/SCMR/SNMMI Expert Consensus Recommendations for Multimodality Imaging in Cardiac Amyloidosis: part 1 of 2-Evidence Base and Standardized Methods of Imaging." To reach a consensus on a protocol that would benefit the bulk of laboratories, the experts considered several parameters and radiotracer kinetics. The most critical parameters concerned injection-to-imaging delay and planar imaging versus SPECT. Accordingly, the standardized protocol recommends the injection of 370-740 MBq (10-20 mCi) of ^99mTc-pyrophosphate with imaging 3 h later. Planar images of the chest are acquired in the anterior and lateral views accompanied by SPECT images. Both the planar and the SPECT images are used to semiquantitatively grade the degree of myocardial uptake compared with the amount of uptake in the ribs using a 0-3 scale. A grade of 2 or 3 on the SPECT images is considered positive for cardiac amyloidosis. The planar images are used to calculate a heart-to-contralateral-lung ratio. A ratio greater than 1.3 at 3 h helps to confirm the diagnosis of cardiac amyloid if the SPECT images have positive findings. This article is part of a 3-part series in this issue of the Journal of Nuclear Medicine Technology Part 1 details the etiology of cardiac amyloidosis and ^99mTc-pyrophosphate imaging acquisition parameters. Part 2, this article, describes the procedure evolution over 50 y, image processing, and quantification. It further discusses radiotracer kinetics and 2 important technical considerations: injection-to-imaging delay and planar imaging versus SPECT. Part 3 covers study interpretation along with cardiac amyloidosis diagnosis and treatment.

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.

Does [99mTc]-3,3-diphosphono-1,2-propanodicarboxylic acid (DPD) soft tissue uptake allow the identification of patients with the diagnosis of cardiac transthyretin-related (ATTR) amyloidosis with higher risk for polyneuropathy?

BACKGROUND

With the introduction of several drugs for the therapy of transthyretin-related amyloidosis (ATTR) which slow down the disease, early detection of polyneuropathy (PNP) is becoming increasingly of interest. [99mTc]-3,3-Diphosphono-1,2-Propanodicarboxylic Acid (DPD) bone scintigraphy, which is used for the diagnosis of cardiac (c)ATTR, can possibly make an important contribution in the identification of patients at risk for PNP.

METHODS

Fifty patients with cATTR, who underwent both planar whole-body DPD scintigraphy and nerve conduction studies (NCS) were retrospectively evaluated. A subgroup of 22 patients also underwent quantitative SPECT/CT of the thorax from which Standardized Uptake Values (SUVpeak) in the subcutaneous fat tissue of the left axillar region were evaluated.

RESULTS

The Perugini score was significantly increased in patients with cATTR and additional diagnosis of PNP compared to patients without (2.51 ± 0.51 vs 2.13 ± 0.52; P = 0.03). Quantitative SPECT/CT revealed that DPD uptake in the subcutaneous fat of the left axillar region was significantly increased in cATTR patients with compared to patients without (1.36 ± 0.60 vs 0.74 ± 0.52; P = 0.04).

CONCLUSION

This study suggests that DPD bone scintigraphy is a useful tool for identification of patients with cATTR and a risk for PNP due to increased DPD soft tissue uptake.