A Routine PET/CT Protocol with Streamlined Calculations for Assessing Cardiac Amyloidosis Using (18)F-Florbetapir

Radionuclide Imaging of Cardiac Amyloidosis: An Update and Future Aspects

Cardiac amyloidosis (CA) is caused by the misfolding, accumulation and aggregation of proteins into large fibrils in the extracellular compartment of the myocardium, leading to restrictive cardiomyopathy, heart failure and death. The major forms are transthyretin (ATTR) CA and light-chain (AL) CA, based on the respective precursor protein. Each of them requires early diagnosis for a timely treatment initiation that will improve patient outcomes. For this, radionuclide imaging is essentially used as single-photon emission computed tomography (SPECT) with bone-avid radiotracers or as positron emission tomography (PET) with amyloid-binding radiotracers. Both offer unprecedented specificity for the diagnostic of CA. SPECT has even revolutionized the diagnosis of ATTR-CA by making it non-invasive. Indeed, SPECT has now entered the standard diagnostic pathway to CA and has led to earlier diagnosis of the disease. SPECT also modified the epidemiology of ATTR-CA, highlighting that the disease is much more frequent than previously believed, and showing that ATTR-CA plays a substantial role in HFpEF and aortic stenosis, particularly among elderly patients. In parallel, amyloid-binding radiotracers for PET have accumulated a substantial amount of evidence, but are not approved for clinical use in CA yet. Further studies are needed to refine acquisition protocols and validate results in broader populations. Unlike bone-avid SPECT radiotracers, PET radiotracers have been specifically created to bind to amyloid fibrils. Thus, PET is the only imaging method that is truly specific for amyloid deposits and very sensitive to any amyloid type. Indeed, PET can not only detect ATTR-CA, but also AL-CA and rare hereditary forms. For both SPECT and PET, advances in quantitation of myocardial uptake have generated more granular and reproducible findings, paving the way for progress in earlier diagnosis, risk stratification and therapeutic response monitoring. Encouraging findings have shown that SPECT and PET are sensitive to early CA when other diagnostic methods are negative. Both radionuclide imaging techniques can predict adverse outcomes, but more evidence is needed to determine how to use them in conjunction with usual prognostic staging scores. Studies on follow-up imaging after therapy suggested that SPECT and PET can capture myocardial changes in CA, but again, more data are needed to meaningfully interpret such changes. Based on all these promising results, radionuclide imaging has the potential to further impact the landscape of CA in diagnosis, prognosis and follow-up, but also to substantially contribute to the assessment of novel therapies that will improve the lives of patients with CA.

Kinetic analysis of cardiac dynamic 18F-Florbetapir PET in healthy volunteers and amyloidosis patients: A pilot study

Objectives

This study aimed to explore the potential of full dynamic PET kinetic analysis in assessing amyloid binding and perfusion in the cardiac region using 18F-Florbetapir PET, establishing a quantitative approach in the clinical assessment of cardiac amyloidosis disease.

Materials & methods

The distribution volume ratios (DVRs) and the relative transport rate constant (R1), were estimated by a pseudo-simplified reference tissue model (pSRTM2) and pseudo-Logan plot (pLogan plot) with kidney reference for the region of interest-based and voxel-wise-based analyses. The parametric images generated using the pSRTM2 and linear regression with spatially constrained (LRSC) algorithm were then evaluated. Semi-quantitative analyses include standardized uptake value ratios at the early phase (SUVREP, 0.5-5 min) and late phase (SUVRLP, 50-60 min) were also calculated.

Results

Ten participants [7 healthy controls (HC) and 3 cardiac amyloidosis (CA) subjects] underwent a 60-min dynamic 18F-Florbetapir PET scan. The DVRs estimated from pSRTM2 and Logan plot were significantly increased (HC vs CA; DVRpSRTM2: 0.95 ± 0.11 vs 2.77 ± 0.42, t'(2.13) = 7.39, P = 0.015; DVRLogan: 0.80 ± 0.12 vs 2.90 ± 0.55, t'(2.08) = 6.56, P = 0.020), and R1 were remarkably decreased in CA groups, as compared to HCs (HC vs CA; 1.08 ± 0.37 vs 0.56 ± 0.10, t'(7.63) = 3.38, P = 0.010). The SUVREP and SUVRLP were highly correlated to R1 (r = 0.97, P < 0.001) and DVR(r = 0.99, P < 0.001), respectively. The DVRs in the total myocardium region increased slightly as the size of FWHM increased and became stable at a Gaussian filter ≥6 mm. The secular equilibrium of SUVR was reached at around 50-min p.i. time.

Conclusion

The DVR and R1 estimated from cardiac dynamic 18F-Florbetapir PET using pSRTM with kidney pseudo-reference tissue are suggested to quantify cardiac amyloid deposition and relative perfusion, respectively, in amyloidosis patients and healthy controls. We recommend a dual-phase scan: 0.5-5 min and 50-60 min p.i. as the appropriate time window for clinically assessing cardiac amyloidosis and perfusion measurements using 18F-Florbetapir PET.

Positron emission tomography in the diagnosis and follow-up of transthyretin amyloid cardiomyopathy patients: A systematic review

PURPOSE

Transthyretin (ATTR) amyloidosis is a progressive protein misfolding disease with frequent cardiac involvement. This review aims to determine the value of PET in diagnosis, assessment of disease progression or treatment response and its relation to clinical outcome in follow-up of ATTR amyloid cardiomyopathy (ATTR-CM) patients.

METHODS

Medline, Cochrane Library, Embase and Web of Science databases were searched, from the earliest date available until December 2022, for studies investigating the use of PET in ATTR-CM patients. Studies containing original data were included, except for case reports. Risk of bias was assessed by QUADAS-2.

RESULTS

Twenty-one studies were included in this systematic review, investigating five different tracers: carbon-11 Pittsburgh compound B ([11C]PIB), fluorine-18 Florbetaben ([18F]FBB), fluorine-18 Florbetapir ([18F]FBP), fluorine-18 Flutemetamol ([18F]FMM) and fluorine-18 Sodium Fluoride (Na[18F]F). In total 211 ATTR amyloidosis patients were included. A majority of studies concluded that [11C]PIB, [18F]FBP and Na[18F]F can distinguish ATTR amyloidosis patients from controls, and that [11C]PIB and Na[18F]F, but not [18F]FBP, can distinguish ATTR-CM patients from patients with cardiac light chain amyloidosis. Evidence on the performance of [18F]FBB and [18F]FMM was contradictory. No studies on the use of PET in follow-up were found.

CONCLUSION

[11C]PIB, Na[18F]F and [18F]FBP can be used to diagnose cardiac amyloidosis, although [18F]FBP may not be suitable for the distinction of different types of amyloid cardiomyopathy. No studies on PET in the follow-up of ATTR amyloidosis patients were found. Future research should focus on the use of these PET tracers in the follow-up of ATTR amyloidosis patients.

The flutemetamol analogue cyano-flutemetamol detects myocardial AL and ATTR amyloid deposits: a post-mortem histofluorescence analysis

BACKGROUND

[18F]flutemetamol is a PET radioligand used to image brain amyloid, but its detection of myocardial amyloid is not well-characterized. This histological study characterized binding of fluorescently labeled flutemetamol (cyano-flutemetamol) to amyloid deposits in myocardium.

METHODS

Myocardial tissue was obtained post-mortem from 29 subjects with cardiac amyloidosis including transthyretin wild-type (ATTRwt), hereditary/variant transthyretin (ATTRv) and immunoglobulin light-chain (AL) types, and from 10 cardiac amyloid-free controls. Most subjects had antemortem electrocardiography, echocardiography, SPECT and cardiac MRI. Cyano-flutemetamol labeling patterns and integrated density values were evaluated relative to fluorescent derivatives of Congo red (X-34) and Pittsburgh compound-B (cyano-PiB).

RESULTS

Cyano-flutemetamol labeling was not detectable in control subjects. In subjects with cardiac amyloidosis, cyano-flutemetamol labeling matched X-34- and cyano-PiB-labeled, and transthyretin- or lambda light chain-immunoreactive, amyloid deposits and was prevented by formic acid pre-treatment of myocardial sections. Cyano-flutemetamol mean fluorescence intensity, when adjusted for X-34 signal, was higher in the ATTRwt than the AL group. Cyano-flutemetamol integrated density correlated strongly with echocardiography measures of ventricular septal thickness and posterior wall thickness, and with heart mass.

CONCLUSION

The high selectivity of cyano-flutemetamol binding to myocardial amyloid supports the diagnostic utility of [18F]flutemetamol PET imaging in patients with ATTR and AL types of cardiac amyloidosis.

Novel Tracers for the Imaging of Cardiac Amyloidosis

Radionuclide scintigraphy with technetium-labeled bisphosphonates has brought a paradigm shift in diagnosing cardiac amyloidosis (CA), with transthyretin CA now being effectively diagnosed without the need for tissue biopsy. Yet, deficits remain, such as methods for the noninvasive diagnosis of light-chain CA, means to detect CA early, prognostication, monitoring, and therapy response assessment. To address these issues, there has been growing interest in the development and implementation of amyloid-specific radiotracers for PET. The aim of this review is to educate the reader on these novel imaging tracers. Though still investigational, these novel tracers-given their many advantages-are clearly the future of nuclear imaging in CA.

[Current role of imaging techniques in cardiac amyloidosis]

Cardiac amyloidosis (CA) is an underdiagnosed disease and, if left untreated, rapidly fatal. Emerging therapies for CA increase the urgency of developing non-invasive diagnostic methods for its early detection and for monitoring therapeutic response. Classic imaging features on echocardiography and cardiac magnetic resonance, although typical for cardiac amyloidosis, are not specific enough to distinguish light chain amyloidosis from transthyretin. Myocardial bone-avid radiotracer uptake is highly specific for transthyretin cardiac amyloidosis when plasma cell dyscrasia has been excluded; it is now replacing the need for biopsy in many patients. Detection of early cardiac amyloidosis, quantitation of its burden, and assessment of response to therapy are important next steps for imaging to advance the evaluation and management of cardiac amyloidosis.

Cardiac amyloidosis characterization by kinetic model fitting on [18F]florbetaben PET images

OBJECTIVE

To evaluate the feasibility of kinetic modeling-based approaches from [18F]-Flobetaben dynamic PET images as a non-invasive diagnostic method for cardiac amyloidosis (CA) and to identify the two AL- and ATTR-subtypes.

METHODS AND RESULTS

Twenty-one patients with diagnoses of CA (11 patients with AL-subtype and 10 patients with ATTR-subtype of CA) and 15 Control patients with no-CA conditions underwent PET/CT imaging after [18F]Florbetaben bolus injection. A two-tissue-compartment (2TC) kinetic model was fitted to time-activity curves (TAC) obtained from left ventricle wall and left atrium cavity ROIs to estimate kinetic micro- and macro-parameters. Combinations of kinetic parameters were evaluated with the purpose of distinguishing Control subjects and CA patients, and to correctly label the last ones as AL- or ATTR-subtype. Resulting sensitivity, specificity, and accuracy for Control subjects were: 0.87, 0.9, 0.89; as far as CA patients, the sensitivity, specificity, and accuracy were respectively 0.9, 1, and 0.97 for AL-CA patients and 0.9, 0.92, 0.97 for ATTR-CA patients.

CONCLUSION

Pharmacokinetic analysis based on a 2TC model allows cardiac amyloidosis characterization from dynamic [18F]Florbetaben PET images. Estimated model parameters allows to not only distinguish between Control subjects and patients, but also between AL- and ATTR-amyloid patients.

18F-flutemetamol positron emission tomography in cardiac amyloidosis

PURPOSE

Bone-tracer scintigraphy has an established role in diagnosis of cardiac amyloidosis (CA) as it detects transthyretin amyloidosis (ATTR). Positron emission tomography (PET) with amyloid tracers has shown high sensitivity for detection of both ATTR and light-chain (AL) CA. We aimed to investigate the accuracy of 18F-flutemetamol in CA.

METHODS

We enrolled patients with CA or non-amyloid heart failure (NA-HF), who underwent cardiac 18F-flutemetamol PET/MRI or PET/CT. Myocardial and blood pool standardized tracer uptake values (SUV) were estimated. Late gadolinium enhancement (LGE) and T1 mapping/ extracellular volume (ECV) estimation were performed.

RESULTS

We included 17 patients (12 with CA, 5 with NA-HF). PET/MRI was conducted in 13 patients, while PET/CT was conducted in 4. LGE was detected in 8 of 9 CA patients. Global relaxation time and ECV were higher in CA (1448 vs. 1326, P = 0.02 and 58.9 vs. 33.7%, P = 0.006, respectively). Positive PET studies were demonstrated in 2 of 12 patients with CA (AL and ATTR). Maximal and mean SUV did not differ between groups (2.21 vs. 1.69, P = 0.18 and 1.73 vs. 1.30, P = 0.13).

CONCLUSION

Although protein-independent binding is supported by our results, the diagnostic yield of PET was low. We demonstrate here for the first time the low sensitivity of PET for CA.

Multimodality Imaging in Cardiomyopathies with Hypertrophic Phenotypes

Multimodality imaging is a comprehensive strategy to investigate left ventricular hypertrophy (LVH), providing morphologic, functional, and often clinical information to clinicians. Hypertrophic cardiomyopathy (HCM) is defined by an increased LV wall thickness not only explainable by abnormal loading conditions. In the context of HCM, multimodality imaging, by different imaging techniques, such as echocardiography, cardiac magnetic resonance, cardiac computer tomography, and cardiac nuclear imaging, provides essential information for diagnosis, sudden cardiac death stratification, and management. Furthermore, it is essential to uncover the specific cause of HCM, such as Fabry disease and cardiac amyloidosis, which can benefit of specific treatments. This review aims to elucidate the current role of multimodality imaging in adult patients with HCM.

The Role of New Imaging Technologies in the Diagnosis of Cardiac Amyloidosis

Cardiac amyloidosis is an infiltrative disorder caused by transthyretin or immunoglobulin free light-chain deposition, which determines clinical disease with similar phenotype but different time course, prognosis and therapy. Multimodality imaging is the cornerstone for disease diagnosis and management. Multimodality imaging has revolutionized the approach to the disease favoring its awareness and simplifying its diagnosis, especially in ATTR cardiac amyloidosis. This describes the different imaging tools, from the traditional to the more novel ones, and highlights the different approach in each different setting (prognosis, subtyping, prognosis, monitoring disease progression, and response to therapy).

The utility of positron emission tomography in cardiac amyloidosis

Cardiac amyloidosis, characterized by progressive restrictive cardiomyopathy, presents unusual diagnostic challenges. Conventional cardiac scintigraphy has shown limited utility in the quantification of disease burden and serial follow-up of cardiac amyloidosis. The advent of specialized positron emission tomography with specific amyloid-binding radiotracers has the potential to change currently employed diagnostic algorithms for the imaging of cardiac amyloidosis. This review aims to discuss the diagnostic utility of amyloid-binding radiotracers, including Pittsburg compound B, florbetapir, florbetapan, and sodium fluoride. These tracers have promising potential for the early detection of the particular type of cardiac amyloidosis, pursuing relevant medical intervention, assessing amyloid burden, monitoring treatment response, and overall prognostication.

Pilot Study of F18-Florbetapir in the Early Evaluation of Cardiac Amyloidosis

Background: Cardiac amyloidosis is an increasingly recognized etiology of heart failure, in part due to the rise of non-invasive nuclear bone scintigraphy. Molecular imaging using positron emission tomography (PET) has promised the direct visualization of cardiac amyloid fibrils. We sought to assess the performance of F18-florbetapir PET in patients with a potential for cardiac amyloidosis in order to identify early disease.

Methods: We performed a pilot study of 12 patients: one with asymptomatic transthyretin cardiac amyloidosis, seven with a potential for developing cardiac amyloidosis (two smoldering myeloma and five with extracardiac biopsy demonstrating transthyretin amyloid deposits and negative technetium pyrophosphate scans), and four controls. Patients were imaged with PET/CT in listmode 10–20 min after receiving F18-florbetapir. Static images were created from this acquisition, and mean standardized uptake values (SUVs) of the left ventricular myocardium, blood pool, paraspinal muscles, and liver were calculated.

Results: All 12 patients demonstrated radiotracer uptake in the myocardium with mean SUV of 2.3 ± 0.4 and blood pool SUV of 0.8 ± 0.1. The patient with cardiac amyloidosis had SUV of 3.3, while mean SUV for patients at risk was 2.3 ± 0.4 and for controls was 2.2 ± 0.3. After 3 years of follow-up, one patient with SUV below the mean was subsequently diagnosed with ATTR cardiac amyloidosis.

Conclusion: In this cohort, PET with F18-florbetapir demonstrated non-specific radiotracer uptake in the myocardium in all patients using a static image protocol; though, the highest values were noted in a patient with ATTR cardiac amyloidosis. There was no difference in the intensity of F18-florbetapir uptake in at-risk patients and controls. Future studies should continue to investigate metabolic PET tracers and protocols in cardiac amyloidosis, including in early disease.

The Importance of Multimodality Imaging in the Diagnosis and Management of Patients with Infiltrative Cardiomyopathies: An Update

Infiltrative cardiomyopathies (ICMs) comprise a broad spectrum of inherited and acquired conditions (mainly amyloidosis, sarcoidosis, and hemochromatosis), where the progressive buildup of abnormal substances within the myocardium results in left ventricular hypertrophy and manifests as restrictive physiology. Noninvasive multimodality imaging has gradually eliminated endomyocardial biopsy from the diagnostic workup of infiltrative cardiac deposition diseases. However, even with modern imaging techniques’ widespread availability, these pathologies persist in being largely under- or misdiagnosed. Considering the advent of novel, revolutionary pharmacotherapies for cardiac amyloidosis, the archetypal example of ICM, a standardized diagnostic approach is warranted. Therefore, this review aims to emphasize the importance of contemporary cardiac imaging in identifying specific ICM and improving outcomes via the prompt initiation of a targeted treatment.

Practical recommendations for the diagnosis and management of transthyretin cardiac amyloidosis

Cardiac amyloidosis (CA) is an infiltrative restrictive cardiomyopathy caused by accumulation in the heart interstitium of amyloid fibrils formed by misfolded proteins. Most common CA types are light chain amyloidosis (AL) caused by monoclonal immunoglobulin light chains and transthyretin amyloidosis (ATTR) caused by either mutated or wild-type transthyretin aggregates. Previously considered a rare disease, CA is increasingly recognized among patients who may be misdiagnosed as undifferentiated heart failure with preserved ejection fraction (HFPEF), paradoxical low-flow/low-gradient aortic stenosis, or otherwise unexplained left ventricular hypertrophy. Progress in diagnosis has been due to the refinement of cardiac echocardiographic techniques (speckle tracking imaging) and magnetic resonance (T1 mapping) and mostly due to the advent of bone scintigraphy that has enabled noninvasive diagnosis of ATTR, limiting the need for endomyocardial biopsy. Importantly, proper management of CA starts from early recognition of suspected cases among high prevalence populations, followed by advanced diagnostic evaluation to confirm diagnosis and typing, preferentially in experienced amyloidosis centers. Differentiating ATTR from other types of amyloidosis, especially AL, is critical. Emerging targeted ATTR therapies offer the potential to improve outcomes of these patients previously treated only palliatively.

In Vivo Quantification of Myocardial Amyloid Deposits in Patients with Suspected Transthyretin-Related Amyloidosis (ATTR)

Background: Current diagnosis of Transthyretin-related Amyloidosis (ATTR) using bone scintigraphy is primarily based on visual scoring and semi-quantitative indices. With the introduction of new potential life-prolonging drugs for ATTR, a more precise quantification of myocardial amyloid burden is desirable for improved response prediction and therapy monitoring. Methods: At first, quantification experiments using an anthropomorphic thorax phantom were performed. Second, 32 patients underwent both planar whole body [^99mTc]- 3,3-Diphosphono-1,2-Propanodicarboxylic Acid (DPD)-scintigraphy and quantitative Single-Photon Emission Computed Tomography/Computed Tomography (SPECT/CT) of the thorax. SPECT/CT standardized myocardial uptake values SUVpeak and SUVpeak normalized to bone uptake (nSUVpeak) were determined. Results: Phantom measurements showed a strong linear relationship between the activity in the myocardial insert and the measured activity (r = 0.9998, p = 0.01), but the measured activity was systematically underestimated by approximately 30%. Receiver operating characteristics (ROC) analysis revealed a 100% sensitivity and specificity at a cut-off of 3.1 for SUVpeak for the differentiation of both patient groups. Conclusion: SUV quantification of ATTR amyloid burden is feasible using novel SPECT/CT technology. With a SUVpeak cut-off of 3.1, patients with Perugini grade 2 and 3 could be clearly separated from those with Perugini grade 0 and 1. Besides ATTR diagnostics, quantification of amyloid deposits could potentially be used for therapy monitoring and prognostication in patients with cardiac ATTR.

Role of Nuclear Imaging in Cardiac Amyloidosis Management: Clinical Evidence and Review of Literature

Cardiac amyloidosis (CA) is an infiltrative disease characterized by the extracellular deposition of fibrils, amyloid, in the heart. The vast majority of patients with CA has one of two types between transthyretin amyloid (ATTR) and immunoglobulin light chain associated amyloid (AL), that have different prognosis and therapeutic options. CA is often underdiagnosed. The histological analysis of endomyocardial tissue is the gold standard for the diagnosis, although it has its limitations due to its invasive nature. Nuclear medicine now plays a key role in the early and accurate diagnosis of this disease, and in the ability to distinguish between the two forms. Recent several studies support the potential advantage of bone-seeking radionuclides as a screening technique for the most common types of amyloidosis, in particular ATTR form. This review presents noninvasive modalities to diagnose CA and focuses on the radionuclide imaging techniques (bone-seeking agents scintigraphy, cardiac sympathetic innervation and positron emission tomography studies) available to visualize myocardial amyloid involvement. Furthermore, we report the case of an 83-year old male with a history of prostate cancer, carcinoma of the cecum and kidney cancer, submitted to bone scan to detect bone metastasis, that revealed a myocardial uptake of 99mTC-HMPD suggestive of ATTR CA. An accurate and early diagnosis of CA able to distinguish beyween AL and ATTR CA combined to the improving therapies could improve the survival of patients with this disease.

[18F]-Florbetaben PET/CT for Differential Diagnosis Among Cardiac Immunoglobulin Light Chain, Transthyretin Amyloidosis, and Mimicking Conditions

OBJECTIVES

This study aimed to test the diagnostic value of [18F]-florbetaben positron emission tomography (PET) in patients with suspicion of CA.

BACKGROUND

Diagnosis of cardiac involvement in immunoglobulin light-chain-derived amyloidosis (AL) and transthyretin-related amyloidosis (ATTR), which holds major importance in risk stratification and decision making, is frequently delayed. Furthermore, although diphosphonate radiotracers allow a noninvasive diagnosis of ATTR, demonstration of cardiac amyloidosis (CA) in AL may require endomyocardial biopsy.

METHODS

Forty patients with biopsy-proven diagnoses of CA (20 ALs, 20 ATTRs) and 20 patients referred with the initial clinical suspicion and later diagnosed with non-CA pathology underwent a cardiac PET/computed tomography scan with a 60-min dynamic [18F]-florbetaben PET acquisition, and 4 10-min static scans at 5, 30, 50, and 110 min after radiotracer injection.

RESULTS

Visual qualitative assessment showed intense early cardiac uptake in all subsets. Patients with AL displayed a high, persistent cardiac uptake in all the static scans, whereas patients with ATTR and those with non-CA showed an uptake decrease soon after the early scan. Semiquantitative assessment demonstrated higher mean standardized uptake value (SUV_mean) in patients with AL, sustained over the whole acquisition period (early SUV_mean: 5.55; interquartile range [IQR]: 4.00 to 7.43; vs. delayed SUV_mean: 3.50; IQR: 2.32 to 6.10; p = NS) compared with in patients with ATTR (early SUV_mean: 2.55; IQR: 1.80 to 2.97; vs. delayed SUV_mean: 1.25; IQR: 0.90 to 1.60; p < 0.001) and in patients with non-CA (early SUV_mean: 3.50; IQR: 1.60 to 3.37; vs. delayed SUV_mean: 1.40; IQR: 1.20 to 1.60; p < 0.001). Similar results were found comparing heart-to-background ratio and molecular volume.

CONCLUSIONS

Delayed [18F]-florbetaben cardiac uptake may discriminate CA due to AL from either ATTR or other mimicking conditions. [18F]-florbetaben PET/computed tomography may represent a promising noninvasive tool for the diagnosis of AL amyloidosis, which is still often challenging and delayed. (A Prospective Triple-Arm, Monocentric, Phase-II Explorative Study on Evaluation of Diagnostic Efficacy of the PET Tracer [18F]-Florbetaben [Neuraceq] in Patients With Cardiac Amyloidosis [FLORAMICAR2]; EudraCT number: 2017-001660-38).

Multimodality Imaging in the Evaluation and Management of Cardiac Amyloidosis

Systemic amyloidosis is a heterogeneous group of disorders where misfolded proteins deposit in the various organs as nonbranching fibrils with a β-pleated-sheet structure called amyloid. Extensive extracellular deposition of these amyloid fibrils eventually leads to organ dysfunction. Involvement of the heart, termed as cardiac amyloidosis, leads to heart failure if left untreated and carries high morbidity and mortality. Current interest in cardiac amyloidosis is growing rapidly thanks to the recent development of effective targeted treatment options, driving the need for better and earlier detection of the condition, which is largely underdiagnosed and far commoner than recognized. Timely diagnosis of cardiac amyloidosis is challenging, but is poised to improve with emergence of newer noninvasive imaging techniques, potentially obviating the need for endomyocardial biopsy in some patients and providing prognostic information. With recent advances in the therapeutic options for cardiac amyloidosis, an area of immense interest is the adoption of imaging as biomarkers for longitudinal assessment of disease progression and treatment response. In this article, we provide an overview of cardiac amyloidosis, discuss the role of imaging modalities in cardiac amyloidosis, and explore future directions for imaging in cardiac amyloidosis.

Improved Quantification of Cardiac Amyloid Burden in Systemic Light Chain Amyloidosis: Redefining Early Disease?

OBJECTIVES

The purpose of this study was to determine phenotypes characterizing cardiac involvement in AL amyloidosis by using direct (fluorine-18-labeled florbetapir {[18F]florbetapir} positron emission tomography [PET]/computed tomography) and indirect (echocardiography and cardiac magnetic resonance [CMR]) imaging biomarkers of AL amyloidosis.

BACKGROUND

Cardiac involvement in systemic light chain amyloidosis (AL) is the main determinant of prognosis and, therefore, guides management. The hypothesis of this study was that myocardial AL deposits and expansion of extracellular volume (ECV) could be identified before increases in N-terminal pro-B-type natriuretic peptide or wall thickness.

METHODS

A total of 45 subjects were prospectively enrolled in 3 groups: 25 with active AL amyloidosis with cardiac involvement (active-CA), 10 with active AL amyloidosis without cardiac involvement by conventional criteria (active-non-CA), and 10 with AL amyloidosis with cardiac involvement in remission for at least 1 year (remission-CA). All subjects underwent echocardiography, CMR, and [18F]florbetapir PET/CT to evaluate cardiac amyloid burden.

RESULTS

The active-CA group demonstrated the largest myocardial AL amyloid burden, quantified by [18F]florbetapir retention index (RI) 0.110 (interquartile range [IQR]: 0.078 to 0.139) min-1, and the lowest cardiac function by global longitudinal strain (GLS), median GLS -11% (IQR: -8% to -13%). The remission-CA group had expanded extracellular volume (ECV) and [18F]florbetapir RI of 0.097 (IQR: 0.070 to 0.124 min-1), and abnormal GLS despite hematologic remission for >1 year. The active-non-CA cohort had evidence of cardiac amyloid deposition by advanced imaging metrics in 50% of the subjects; cardiac involvement was identified by late gadolinium enhancement in 20%, elevated ECV in 20%, and elevated [18F]florbetapir RI in 50%.

CONCLUSIONS

Evidence of cardiac amyloid infiltration was found based on direct and indirect imaging biomarkers in subjects without CA by conventional criteria. The findings from [18F]florbetapir PET imaging provided insight into the preclinical disease process and on the basis of interpretation of expanded ECV on CMR and have important implications for future research and clinical management of AL amyloidosis. (Molecular Imaging of Primary Amyloid Cardiomyopathy [MICA]; NCT02641145).

Diagnosing cardiac amyloidosis in every-day practice: A practical guide for the cardiologist

Cardiac amyloidosis (CA) has emerged as a previously underestimated cause of heart failure and mortality. Underdiagnosis resulted mainly from unawareness of the true disease prevalence and the non-specific symptoms of the disease. CA results from extracellular deposition of misfolded protein fibrils, commonly derived from transthyretin (ATTR) or immunoglobulin light chains (AL). A significant proportion of older patients with heart failure and other extracardiac manifestations suffer from ATTR-CA, whereas AL-CA is still considered a rare disease. This article provides an overview of CA with a special focus on current and emerging diagnostic modalities. Furthermore, we provide a diagnostic algorithm for the evaluation of patients with suspected CA in every-day practice.

Cardiac amyloidosis imaging with amyloid positron emission tomography: A systematic review and meta-analysis

BACKGROUND

Recent progress in amyloid positron emission tomography (PET) has enabled the targeted imaging of cardiac amyloidosis with accuracy. We performed a systematic review and meta-analysis on the diagnostic performance of cardiac amyloidosis using amyloid PET.

METHODS

A systematic search was performed using key words: cardiac amyloidosis, amyloid, and PET. We estimated the pooled sensitivity, specificity, positive and negative likelihood ratio (LR), and diagnostic odds ratio (DOR). Furthermore, the semiquantitative parameters of PET were evaluated to diagnose cardiac amyloidosis and discern its type [systemic light chain amyloidosis (AL) vs transthyretin amyloidosis (ATTR)] using the pooled standardized mean difference (SMD).

RESULTS

In total, six eligible studies with a total of 98 subjects were included in this meta-analysis. The pooled sensitivity was 0.95, the specificity was 0.98, positive LR was 10.130, negative LR was 0.1, and DOR was 148.83. The semiquantitative parameters of amyloid PET showed significantly higher values for cardiac amyloidosis patients than those for controls (pooled SMD = 1.42; P < .001), and in AL than ATTR (pooled SMD = 0.96; P < .001).

CONCLUSION

Amyloid PET imaging can be a useful method for diagnosing cardiac amyloidosis. The semiquantitative parameters of amyloid PET can help diagnose cardiac amyloidosis and discern its type.

How to Image Cardiac Amyloidosis: A Practical Approach

Cardiac amyloidosis (CA) is one of the most rapidly progressive forms of heart disease, with a median survival from diagnosis, if untreated, ranging from <6 months for light chain amyloidosis to 3 to 5 years for transthyretin amyloidosis. Early diagnosis and accurate typing of CA are necessary for optimal management of these patients. Emerging novel disease modifying therapies increase the urgency to diagnose CA at an early stage and identify patients who may benefit from these life-saving therapies. The goal of this review is to provide a practical approach to echocardiography, cardiac magnetic resonance, and radionuclide imaging in patients with known or suspected CA.

Expert Consensus Recommendations for the Suspicion and Diagnosis of Transthyretin Cardiac Amyloidosis

Cardiomyopathy is a manifestation of transthyretin amyloidosis (ATTR), which is an underrecognized systemic disease whereby the transthyretin protein misfolds to form fibrils that deposit in various tissues and organs. ATTR amyloidosis is debilitating and associated with poor life expectancy, especially in those with cardiac dysfunction, but a variety of treatment options have recently become available. Considered a rare disease, ATTR amyloidosis may be more prevalent than thought, particularly in older persons. Diagnosis is often delayed because of a lack of disease awareness and the heterogeneity of symptoms at presentation. Given the recent availability of effective treatments, early recognition and diagnosis are especially critical because treatment is likely more effective earlier in the disease course. The Amyloidosis Research Consortium recently convened a group of experts in ATTR amyloidosis who, through an iterative process, agreed on best practices for suspicion, diagnosis, and characterization of disease. This review describes these consensus recommendations for ATTR associated with cardiomyopathy as a resource to aid cardiologists and others in the recognition and diagnosis of ATTR associated with cardiomyopathy. Included in this review is an overview of red flag signs and symptoms and a recommended diagnostic approach, including testing for monoclonal protein, scintigraphy, or biopsy and, if ATTR associated with cardiomyopathy is identified, TTR genotyping.

Cardiac Amyloidosis: Updates in Imaging

PURPOSE OF REVIEW

We summarize key features pertaining to the two most commonly encountered types of cardiac amyloidosis (CA), monoclonal immunoglobulin light chain (AL) and transthyretin type (ATTR), expanding upon the clinical application and utility of various imaging techniques in diagnosing CA.

RECENT FINDINGS

Advances in imaging have led to earlier identification, improved diagnosis of CA and higher discriminatory power to differentiate CA from other hypertrophic phenocopies. The application of cardiac magnetic resonance imaging (CMR) has led to a deeper understanding of underlying pathophysiological processes in CA, owing largely to its intrinsic tissue characterization properties. The widespread adoption of bone scintigraphy algorithms has reduced the need for cardiac biopsy and improved diagnostic confidence in ATTR CA. As new treatments for CA are rapidly developing, there will be even greater reliance on imaging, as the requirement to diagnose disease earlier, monitor response and amend treatment strategies accordingly intensifies.

State-of-the-art radionuclide imaging in cardiac transthyretin amyloidosis

Cardiac amyloidosis, once considered untreatable, is now gaining well-deserved attention due to advances in imaging and the recent approval of targeted breakthrough therapies. In this paper, we discuss the role of radionuclide imaging in the evaluation and management of patients with the most common form of amyloidosis-cardiac transthyretin amyloidosis (ATTR). We provide a comprehensive summary of the literature interspersed with our institutional experience as appropriate, to deliver our perspective.

A pilot study demonstrating cardiac uptake with 18F-florbetapir PET in AL amyloidosis patients with cardiac involvement

¹⁸F-florbetapir is a promising tracer in amyloidosis. This study evaluates its use in patients with systemic AL amyloidosis (AL) before and after treatment as well as its serial utility in monitoring. Fifteen AL patients with cardiac involvement underwent ¹⁸F-florbetapir PET imaging and three patients underwent repeat imaging after chemotherapy. All patients had demonstrable cardiac uptake with ¹⁸F-florbetapir. Cardiac uptake appeared greater in chemotherapy-naïve vs. chemotherapy-established AL patients median (left ventricular retention index 0.21 vs. 0.14 min^-1, respectively) and greater in patients that had not achieved at least a partial haematological response (left ventricular retention index 0.2 vs. 0.14 min^-1, respectively). There was no interval difference in cardiac uptake and no correlation in cardiac uptake with cardiac biomarkers or serum free light chains. This is the largest study of ¹⁸F-florbetapir in patients with AL amyloidosis. It is the first study to include patients prior to starting chemotherapy and uniquely includes patients who underwent repeat imaging after chemotherapy. All patients had cardiac uptake with ¹⁸F-florbetapir, regardless of haematological or NT-proBNP response to chemotherapy. There was a suggestion that treatment-naïve patients may have higher cardiac uptake. Larger studies are required to establish the role of this tracer in screening patients with amyloidosis for cardiac involvement, discriminating between ATTR and AL amyloidosis, and in disease monitoring.

18Fluorine sodium fluoride positron emission tomography, a potential biomarker of transthyretin cardiac amyloidosis

BACKGROUND

Non-invasive imaging to diagnose and quantify amyloid load, progression, and response to treatment are central for the care of patients with cardiac amyloidosis. 18Fluorine-labeled sodium fluoride (18F-NaF) is a widely available radioisotope and PET imaging allows for absolute quantification of tracer uptake.

METHODS

Patients with biopsy-proven transthyretin (ATTR-CA) and light-chain cardiac amyloidosis (AL) (3 ATTRwt, 2 ATTRV122I, 2 AL) and controls (n = 5), underwent 18F-NaF PET imaging. Scans were assessed visually for radiotracer uptake and analyzed using standard uptake values in the entire myocardium (SUVm) and in a 17-segment cardiac model. Wilcoxon rank-sum tests were used for statistical analyses.

RESULTS

Qualitative 18F-NaF uptake was absent in controls and AL patients. There was qualitative 18F-NaF uptake in ATTR-CA patients, with slightly increased uptake in wild-type patients. SUVm for controls and AL patients overlapped at 0.8(0.4-0.9) and 0.95(0.9-1.0), respectively (P = 0.434). At 1.5(1.4-1.7), SUVm for ATTR-CA patients was ≈1.5*SUVm of controls (P = 0.012) and AL patients (P = 0.078). While there was diffuse 18F-NaF myocardial in ATTR-CA patients, the degree of uptake varied according to cardiac segment.

CONCLUSION

18F-NaF PET effectively imaged and differentiated ATTR-CA patients. Semi-automatic software enabled quantification of radiotracer uptake and regional distribution. 18F-NaF PET may be useful for disease monitoring and localizing amyloid deposition in ATTR-CA patients.

Clinical PET/MRI: 2018 Update

OBJECTIVE

The purpose of this article is to provide an update on clinical PET/MRI, including current and developing clinical indications and technical developments.

CONCLUSION

PET/MRI is evolving rapidly, transitioning from a predominant research focus to exciting clinical practice. Key technical obstacles have been overcome, and further technical advances promise to herald significant advancements in image quality. Further optimization of protocols to address challenges posed by this hybrid modality will ensure the long-term success of PET/MRI.

Utility of the 18F-Florbetapir positron emission tomography in systemic amyloidosis

Amyloidosis comprises a group of heterogeneous conditions. To ascertain the burden of disease is important because it can determine the treatment as well as the evolution of the disease. Recent reports have shown good results in diagnosing cardiac amyloidosis using ¹⁸F-florbetapir. We hypothesize that combining whole body PET/CT with ¹⁸F-Florbetapir can be useful to characterize the burden of the disease. We included 25 patients, 13 of them with different types of amyloidosis, and 12 with Alzheimer's disease as controls. Target-to-background ratio was computed for multiple organ using maximum standardized uptake values. Organ involvement was described (standardized techniques versus PET) according to different kinds of amyloidosis showing promising results in AA and AL types. Heart involvement showed poorer results when compared to tongue, lung or thyroid gland. Multiple organ involvement in patients previously labelled as having negative organ affectation could be identified. This is the first study to evaluate the utility of ¹⁸F-florbetapir in the assessment of the global extension of disease. Our results show that this technique is useful for its diagnosis.

Extracardiac 18F-florbetapir imaging in patients with systemic amyloidosis: more than hearts and minds

Purpose

¹⁸F-Florbetapir has been reported to show cardiac uptake in patients with systemic light-chain amyloidosis (AL). This study systematically assessed uptake of ¹⁸F-florbetapir in patients with proven systemic amyloidosis at sites outside the heart.

Methods

Seventeen patients with proven cardiac amyloidosis underwent ¹⁸F-florbetapir PET/CT imaging, 15 with AL and 2 with transthyretin amyloidosis (ATTR). Three patients had repeat scans. All patients had protocolized assessment at the UK National Amyloidosis Centre including imaging with ¹²³I-serum amyloid P component (SAP). ¹⁸F-Florbetapir images were assessed for areas of increased tracer accumulation and time–uptake curves in terms of standardized uptake values (SUV_mean) were produced.

Results

All 17 patients showed ¹⁸F-florbetapir uptake at one or more extracardiac sites. Uptake was seen in the spleen in 6 patients (35%; 6 of 9, 67%, with splenic involvement on ¹²³I-SAP scintigraphy), in the fat in 11 (65%), in the tongue in 8 (47%), in the parotids in 8 (47%), in the masticatory muscles in 7 (41%), in the lungs in 3 (18%), and in the kidney in 2 (12%) on the late half-body images. The ¹⁸F-florbetapir spleen retention index (SRI) was calculated. SRI >0.045 had 100% sensitivity/sensitivity (in relation to ¹²³I-SAP splenic uptake, the current standard) in detecting splenic amyloid on dynamic imaging and a sensitivity of 66.7% and a specificity of 100% on the late half-body images. Intense lung uptake was seen in three patients, one of whom had lung interstitial infiltration suggestive of amyloid deposition on previous high-resolution CT. Repeat imaging showed a stable appearance in all three patients suggesting no early impact of treatment response.

Conclusion

¹⁸F-Florbetapir PET/CT is a promising tool for the detection of extracardiac sites of amyloid deposition. The combination of uptake in the heart and uptake in the spleen on ¹⁸F-florbetapir PET/CT, a hallmark of AL, suggests that this tracer holds promise as a screening tool for AL.

Electronic supplementary material

The online version of this article (10.1007/s00259-018-3995-2) contains supplementary material, which is available to authorized users.

Standardization of 99mTechnetium pyrophosphate imaging methodology to diagnose TTR cardiac amyloidosis

BACKGROUND

Technetium pyrophosphate (99mTc-PYP) imaging to diagnose transthyretin cardiac amyloidosis (ATTR-CA) has been increasingly utilized. The objective of this study is to provide a standardized 99mTc-PYP imaging protocol to diagnose ATTR-CA.

METHODS

104 scans from 45 subjects with biopsy-proven ATTR-CA or light-chain cardiac amyloidosis (AL) were assessed. Multiple scans were obtained using different counts (750 vs 2000 K), times to acquisition (1 vs 2 to 4 hours), processing matrix (256 vs 128), and 99mTc-PYP dose. Image quality and extracardiac activity was assessed. Quantitative methods using heart-to-contralateral ratios (H/CL) and a visual semiquantitative scale were used to diagnose ATTR-CA.19 The correlation between H/CL ratios and reproducibility of semiquantitative visual scores, acquired using various imaging parameters, were evaluated.

RESULTS

All imaging parameters had good to excellent image quality. 750 vs 2000 K counts, 1 hour acquisition and 256 matrix, had lower extracardiac activity (P = .00018). 10 mCi of 99mTc-PYP v. higher doses showed excellent image quality and less extracardiac activity (P = .0015). Correlation of H/CL ratios was strong (r ≥ 0.92) and reproducibility of semiquantitative visual scores was high (Kappa = 95%).

CONCLUSION

An imaging protocol using 750 K counts, 10 mCi of 99mTc-PYP, and a 256 matrix was chosen as the standardized imaging protocol since it provided the shortest overall study time (1 vs 2 to 4 hours) and lowest radiation exposure (3 vs 8 to 10 mSv).

Targeted Nuclear Imaging Probes for Cardiac Amyloidosis

PURPOSE OF REVIEW

The aim of the present manuscript is to review the latest advancements of radionuclide molecular imaging in the diagnosis and prognosis of individuals with cardiac amyloidosis.

RECENT FINDINGS

^99mTechnetium labeled bone tracer scintigraphy had been known to image cardiac amyloidosis, since the 1980s; over the past decade, bone scintigraphy has been revived specifically to diagnose transthyretin cardiac amyloidosis. ¹⁸F labeled and ¹¹C labeled amyloid binding radiotracers developed for imaging Alzheimer's disease, have been repurposed since 2013, to image light chain and transthyretin cardiac amyloidosis. ^99mTechnetium bone scintigraphy for transthyretin cardiac amyloidosis, and amyloid binding targeted PET imaging for light chain and transthyretin cardiac amyloidosis, are emerging as highly accurate methods. Targeted radionuclide imaging may soon replace endomyocardial biopsy in the evaluation of patients with suspected cardiac amyloidosis. Further research is warranted on the role of targeted imaging to quantify cardiac amyloidosis and to guide therapy.

Tc-99m Radiolabeled Peptide p5 + 14 is an Effective Probe for SPECT Imaging of Systemic Amyloidosis

PURPOSE

Systemic peripheral amyloidosis is a rare disease in which misfolded proteins deposit in various organs. We have previously developed I-124 labeled peptide p5 + 14 as a tracer for positron emission tomography imaging of amyloid in patients. In this report, we now document the labeling efficiency, bioactivity, and stability of Tc-99m labeled p5 + 14 for single-photon emission computed tomography (SPECT) imaging of amyloidosis, validated in a mouse model of systemic amyloidosis.

PROCEDURES

Radiochemical yield, purity, and biological activity of [(99m)Tc]p5 + 14 were documented by instant thin-layer chromatography (ITLC), SDS-PAGE and a quantitative amyloid fibril pulldown assay. The efficacy and stability were documented in serum amyloid protein A (AA) amyloid-bearing or wild-type (WT) control mice imaged with SPECT/X-ray computed tomography (CT) at two time points. The uptake and retention of [(99m)Tc]p5 + 14 in hepatosplenic amyloid was evaluated using region of interest (ROI) and tissue counting measurements.

RESULTS

Tc-99m p5 + 14 was produced with a radiochemical yield of 75 % with greater than 90 % purity and biological activity comparable to that of radioiodinated peptide. AA amyloid was visualized by SPECT/CT imaging with specific uptake seen in amyloid-laden organs at levels ∼5 folds higher than in healthy mice. ROI analyses of decay-corrected SPECT/CT images showed <20 % loss of radiolabel from the 1 to 4 h imaging time points. Biodistribution data confirmed the specificity of the probe accumulation by amyloid-laden organs as compared to non-diseased tissues.

CONCLUSION

[(99m)Tc]p5 + 14 is a specific and stable radiotracer for systemic amyloid in mice and may provide a convenient and inexpensive alternative to imaging of peripheral amyloidosis in patients.

Transthyretin Cardiac Amyloidosis in Older Adults: Optimizing Cardiac Imaging to the Corresponding Diagnostic and Management Goal

PURPOSE OF REVIEW

Transthyretin cardiac amyloidosis is increasingly recognized as an important cause of heart failure in older adults. Many cardiac imaging modalities have evolved to evaluate transthyretin cardiac amyloidosis and include 2D echocardiography with tissue Doppler and speckle-strain imaging, nuclear scintigraphy, cardiac magnetic resonance imaging, and positron emission tomography. The purpose of this review is to highlight the optimal selection of advanced cardiac imaging techniques with corresponding diagnostic goals including raising suspicion, making an early diagnosis, and subtyping transthyretin cardiac amyloid, as well as management goals including assessment of ventricular impairment, prognosticating, and monitoring disease progression. Potential benefits of optimizing cardiac imaging in the elderly patient with transthyretin cardiac amyloidosis may include enhanced and earlier diagnosis and refined long-term management.

RECENT FINDINGS

Advances in cardiac imaging techniques are changing diagnostic and management algorithms for transthyretin cardiac amyloidosis.

SUMMARY

With a new era of novel therapeutics, enhanced recognition, and earlier diagnosis approaching, selecting the appropriate non-invasive cardiac imaging modality will be essential for optimal care in the elderly patient with transthyretin cardiac amyloidosis.

Novel Noninvasive Nuclear Medicine Imaging Techniques for Cardiac Inflammation

PURPOSE OF REVIEW

Inflammation is a key player in a wide range of cardiovascular and myocardial diseases. Given the numerous implications of inflammatory processes in disease initiation and progression, functional imaging modalities including positron emission tomography (PET) represent valuable diagnostic, prognostic, and monitoring tools in patient management. Since increased glucose metabolism is a hallmark of inflammation, PET using the radiolabeled glucose analog [18F]-2-deoxy-2-fluoro-d-glucose (FDG) is the mainstay diagnostic test for nuclear imaging of (cardiac) inflammation. Recently, new approaches using more specific tracers to overcome the limited specificity of FDG have emerged.

RECENT FINDINGS

PET imaging has proven its value in a number of inflammatory conditions of the heart including myocarditis, endocarditis, sarcoidosis, or reactive changes after myocardial infarction. In infection-related endocarditis, FDG-PET and white blood cell scintigraphy have been implemented in current guidelines. FDG-PET is considered as nuclear medical gold standard in myocarditis, pericarditis, or sarcoidosis. Novel strategies, including targeting of somatostatin receptors or C-X-C motif chemokine receptor CXCR4, have shown promising results in first studies.

SUMMARY

Nuclear medicine techniques offer valuable information in the assessment of myocardial inflammation. Given the possibility to directly visualize inflammatory activity, they represent useful tools for diagnosis, risk stratification, and therapy monitoring.

Comparative evaluation of p5+14 with SAP and peptide p5 by dual-energy SPECT imaging of mice with AA amyloidosis

Amyloidosis is a protein-misfolding disorder characterized by the extracellular deposition of amyloid, a complex matrix composed of protein fibrils, hyper-sulphated glycosaminoglycans and serum amyloid P component (SAP). Accumulation of amyloid in visceral organs results in the destruction of tissue architecture leading to organ dysfunction and failure. Early differential diagnosis and disease monitoring are critical for improving patient outcomes; thus, whole body amyloid imaging would be beneficial in this regard. Non-invasive molecular imaging of systemic amyloid is performed in Europe by using iodine-123-labelled SAP; however, this tracer is not available in the US. Therefore, we evaluated synthetic, poly-basic peptides, designated p5 and p5+14, as alternative radiotracers for detecting systemic amyloidosis. Herein, we perform a comparative effectiveness evaluation of radiolabelled peptide p5+14 with p5 and SAP, in amyloid-laden mice, using dual-energy SPECT imaging and tissue biodistribution measurements. All three radiotracers selectively bound amyloid in vivo; however, p5+14 was significantly more effective as compared to p5 in certain organs. Moreover, SAP bound principally to hepatosplenic amyloid, whereas p5+14 was broadly distributed in numerous amyloid-laden anatomic sites, including the spleen, liver, pancreas, intestines and heart. These data support clinical validation of p5+14 as an amyloid radiotracer for patients in the US.