Assessment of myocardial perfusion and function with PET and PET/CT

Comprehensive diagnostic workup in patients with suspected heart failure and preserved ejection fraction

Diagnosis of heart failure with preserved ejection fraction (HFpEF) can be challenging and it could require different tests, some of which are affected by limited availability. Nowadays, considering that new therapies are available for HFpEF and related conditions, a prompt and correct diagnosis is relevant. However, the diagnostic role of biomarker level, imaging tools, score-based algorithms and invasive evaluation, should be based on the strengths and weaknesses of each test. The aim of this review is to help the clinician in diagnosing HFpEF, overcoming the diagnostic uncertainty and disentangling among the different underlying causes, in order to properly treat this kind of patient.

Prognostic value of global myocardial flow reserve in patients with history of coronary artery bypass grafting

AIMS

It is not well understood whether positron emission tomography (PET)-derived myocardial flow reserve (MFR) is prognostic among patients with prior coronary artery bypass grafting (CABG).

METHODS AND RESULTS

Consecutive patients with a clinical indication for PET were enrolled in the Houston Methodist DeBakey Heart and Vascular Center PET registry and followed prospectively for incident outcomes. The primary outcome was a composite of all-cause death, myocardial infarction (MI)/unplanned revascularization, and heart failure admissions. Cox proportional hazards models were used to study the association between MFR (<2 vs. ≥2) and incident events adjusting for clinical and myocardial perfusion imaging variables. The study population consisted of 836 patients with prior CABG; mean (SD) age 68 (10) years, 53% females, 79% Caucasian, 36% non-Hispanic, and 66% with MFR <2. Over a median (interquartile range [IQR]) follow-up time of 12 (4-24) months, there were 122 incident events (46 HF admissions, 28 all-cause deaths, 23 MI, 22 PCI/3 repeat CABG 90 days after imaging). In adjusted analyses, patients with impaired MFR had a higher risk of the primary outcome [hazard ratio (HR) 2.06; 95% CI 1.23-3.44]. Results were significant for admission for heart failure admissions (HR 2.92; 95% CI 1.11-7.67) but not for all-cause death (HR 2.01, 95% CI 0.85-4.79), or MI/UR (HR 1.93, 95% CI 0.92-4.05).

CONCLUSION

Among patients with a history of CABG, PET-derived global MFR <2 may identify those with a high risk of subsequent cardiovascular events, especially heart failure, independent of cardiovascular risk factors and perfusion data.

Prognostic value of positron emission tomography derived myocardial flow reserve: A systematic review and meta-analysis

BACKGROUND AND AIMS

Positron Emission Tomography (PET)-derived myocardial flow reserve (MFR) has been shown to have a role in the diagnosis and prognosis of patients with coronary artery disease (CAD). We performed a systematic review and meta-analysis to summarize the body of literature and synthesize the evidence on the prognostic role of PET-derived MFR in patients with known or suspected CAD.

METHODS

A comprehensive literature search of the Medline database from its inception to August 2023, in humans, in any language, was conducted for clinical studies examining the prognostic value of PET imaging in patients of any age, sex, and CAD status. Systematic screening and data extraction of the identified studies were followed by quantitative meta-analysis of PET-MFR's role in predicting adverse clinical events using random effect model. Studies were appraised using the modified Newcastle-Ottawa tool.

RESULTS

A total of 21 studies assessing the prognostic role of PET derived MFR in 46,815 patients with known and/or suspected CAD were included (mean (SD) age 66 (4) years, 48% women). The mean follow-up duration was 36 months (range 10-96). Cardiovascular risk factors were prevalent (73% hypertension, 35% diabetes and 67% dyslipidemia). The definition of the composite outcome varied between studies, with various combinations of mortality, non-fatal myocardial infarction, hospitalization, and coronary revascularization. Pooled impaired MFR was significantly associated with an increased risk of adverse outcomes (RR = 2.94, 95% CI 2.42-3.56, p < 0.001). Results were similar in a subgroup of patients with suspected CAD.

CONCLUSIONS

The available body of evidence shows that impaired PET-derived MFR measured using different tracers and PET systems is strongly associated with an increased risk of adverse cardiovascular events. Limitations of this review include observational nature of studies, marked heterogeneity in patient populations, inconsistency in thresholds to define abnormal MFR, and differing components for the composite outcome.

Quantitative Assessment of Myocardial Ischemia With Positron Emission Tomography

Recent advances in positron emission tomography (PET) technology and reconstruction techniques have now made quantitative assessment using cardiac PET readily available in most cardiac PET imaging centers. Multiple PET myocardial perfusion imaging (MPI) radiopharmaceuticals are available for quantitative examination of myocardial ischemia, with each having distinct convenience and accuracy profile. Important properties of these radiopharmaceuticals ( 15 O-water, 13 N-ammonia, 82 Rb, 11 C-acetate, and 18 F-flurpiridaz) including radionuclide half-life, mean positron range in tissue, and the relationship between kinetic parameters and myocardial blood flow (MBF) are presented. Absolute quantification of MBF requires PET MPI to be performed with protocols that allow the generation of dynamic multiframes of reconstructed data. Using a tissue compartment model, the rate constant that governs the rate of PET MPI radiopharmaceutical extraction from the blood plasma to myocardial tissue is calculated. Then, this rate constant ( K1 ) is converted to MBF using an established extraction formula for each radiopharmaceutical. As most of the modern PET scanners acquire the data only in list mode, techniques of processing the list-mode data into dynamic multiframes are also reviewed. Finally, the impact of modern PET technologies such as PET/CT, PET/MR, total-body PET, machine learning/deep learning on comprehensive and quantitative assessment of myocardial ischemia is briefly described in this review.

Value of PET ECG gating in a cross-validation study of cardiac function assessment by PET/MR imaging

BACKGROUND

This work investigated the impact of different cardiac gating methods on the assessment of cardiac function by FDG-PET in a cross-validation PET/MR study.

METHODS AND RESULTS

MR- and PET-based left ventricular end-diastolic, end-systolic volumes, and ejection fraction (EDV, ESV, and EF) were delineated in 30 patients with a PET/MR examination. Cardiac PET imaging was performed using three ECG gating methods: fixed number of gates per beat (STD), STD with a beat acceptance window (STD-BR), and fixed gate duration (FW). High MR-PET correlations were found in all the values. ESVs correlated better than EDVs and EFs: Pearson's r coefficient [0.92, 0.92, 0.92] in ESV vs [0.75, 0.81, 0.80] in EDV and [0.79, 0.91, 0.87] in EF, for each method [STD, STD-BR, FW]. Biases with respect to MRI for all the evaluated PET methods were less than 13% in EDV, 5% in ESV, and 14% in EF, but with wide limits of agreements, in the range (59-68)% in EDV, (65-70)% in ESV, and (49-71)% in EF. STD showed the strongest disagreement, while there were no marked differences between STD-BR and FW.

CONCLUSION

Based on these findings, PET- and MR-based cardiac function parameters were highly correlated but in substantial disagreement with variabilities introduced by the selected PET ECG gating method. The most significant differences were associated with the ECG gating method susceptible to highly irregular beats, while similar performance was observed in the methods using uniform adjustment of gates width per beat with the beat acceptance window, and fixed gate width along all the beats. Thus, strict quality controls of R peak detection are needed to minimize its impact on the function assessment.

Advances in Digital PET Technology and Its Potential Impact on Myocardial Perfusion and Blood Flow Quantification

PURPOSE OF REVIEW

In this review, we explore the development of digital PET scanners and describe the mechanism by which they work. We dive into some technical details on what differentiates a digital PET from a conventional PET scanner and how such differences lead to better imaging characteristics. Additionally, we summarize the available evidence on the improvements in the images acquired by digital PET as well as the remaining pitfalls. Finally, we report the comparative studies available on how digital PET compares to conventional PET, particularly in the quantification of coronary blood flow.

RECENT FINDINGS

The advent of digital PET offers high sensitivity and time-of-flight (TOF), which allow lower activity and scan times, with much less risk of detector saturation. This allows faster patient throughput, scanning more patients per generator, and acquiring more consistent image quality across patients. The higher sensitivity captures more of the potential artifacts, particularly motion-related ones, which presents a current challenge that still needs to be tackled. The digital silicon photomultiplier (SiPM) positron emission tomography (PET) machine has been an important development in the technological advancements of non-invasive nuclear cardiovascular imaging. It has enhanced the utility for PET myocardial perfusion imaging (MPI) and myocardial blood flow (MBF) quantification.

Incremental prognostic value of digital positron emission tomography derived myocardial flow reserve: A prospective cohort study

BACKGROUND

Positron Emission Tomography (PET) Myocardial Perfusion Imaging (MPI) is a robust diagnostic and prognostic test in patients with suspected or known coronary artery disease (CAD). We aimed to assess the incremental prognostic value of myocardial flow reserve (MFR) using the latest generation of digital PET scanners.

METHODS

Consecutive patients with clinically indicated PET MPI for suspected or known CAD were included. Myocardial blood flow (MBF) in ml/min/g was obtained from dynamic images at rest and peak hyperemia, and the myocardial flow reserve (MFR) was calculated as the ratio of stress to rest MBF. Patients were followed from the date of PET imaging for the occurrence of the primary outcome (composite of all-cause death, myocardial infarction, and Percutaneous Coronary Intervention or Coronary Artery Bypass Graft occurring >90 days after imaging). Nested multivariable Cox regression models were used to assess the incremental prognostic role of MFR over traditional risk factors and PET relative perfusion parameters.

RESULTS

The final cohort consisted of 3534 patients (mean age 67 ± 12 years, 48% female, 67% Caucasian, 53% obese, 55% hypertension, 32% diabetes, 42% dyslipidemia). During a median follow-up of 8.5 (3.0-15.4) months, 229 patients (6.5%, 6.4 per 1000 person-years) experienced the primary outcome. In nested multivariable Cox models, impaired MFR (MFR < 2) was significantly associated with the primary outcome (HR 2.9, 95% CI 2.0-4.1, p < 0.001) and significantly improved discrimination (Harrell's C 0.77, p = 0.002).

CONCLUSION

MFR derived from digital PET scanners has an independent and incremental prognostic role in patients with suspected or known CAD.

Current Concepts and Future Applications of Non-Invasive Functional and Anatomical Evaluation of Coronary Artery Disease

Over the last decades, significant advances have been achieved in the treatment of coronary artery disease (CAD). Proper non-invasive diagnosis and appropriate management based on functional information and the extension of ischemia or viability remain the cornerstone in the fight against adverse CAD events. Stress echocardiography and single photon emission computed tomography are often used for the evaluation of ischemia. Advancements in non-invasive imaging modalities such as computed tomography (CT) coronary angiography and cardiac magnetic resonance imaging (MRI) have not only allowed non-invasive imaging of coronary artery lumen but also provide additional functional information. Other characteristics regarding the plaque morphology can be further evaluated with the latest modalities achieving a morpho-functional evaluation of CAD. Advances in the utilization of positron emission tomography (PET), as well as software advancements especially regarding cardiac CT, may provide additional prognostic information to a more evidence-based treatment decision. Since the armamentarium on non-invasive imaging modalities has evolved, the knowledge of the capabilities and limitations of each imaging modality should be evaluated in a case-by-case basis to achieve the best diagnosis and treatment decision. In this review article, we present the most recent advances in the noninvasive anatomical and functional evaluation of CAD.

Fractal Analysis of Dynamic Stress CT-Perfusion Imaging for Detection of Hemodynamically Relevant Coronary Artery Disease

BACKGROUND

Combined computed tomography-derived myocardial blood flow (CTP-MBF) and computed tomography angiography (CTA) has shown good diagnostic performance for detection of coronary artery disease (CAD). However, fractal analysis might provide additional insight into ischemia pathophysiology by characterizing multiscale perfusion patterns and, therefore, may be useful in diagnosing hemodynamically significant CAD.

OBJECTIVES

The purpose of this study was to investigate, in a multicenter setting, whether fractal analysis of perfusion improves detection of hemodynamically relevant CAD over myocardial blood flow quantification (CTP-MBF) using dynamic, 4-dimensional, dynamic stress myocardial computed tomography perfusion (CTP) imaging.

METHODS

In total, 7 centers participating in the prospective AMPLIFiED (Assessment of Myocardial Perfusion Linked to Infarction and Fibrosis Explored with Dual-source CT) study acquired CTP and CTA data in patients with suspected or known CAD. Hemodynamically relevant CAD was defined as ≥90% stenosis on invasive coronary angiography or fractional flow reserve <0.80. Both fractal analysis and CTP-MBF quantification were performed on CTP images and were combined with CTA results.

RESULTS

This study population included 127 participants, among them 61 patients, or 79 vessels, with CAD as per invasive reference standard. Compared with the combination of CTP-MBF and CTA, combined fractal analysis and CTA improved sensitivity on the per-patient level from 84% (95% CI: 72%-92%) to 95% (95% CI: 86%-99%; P = 0.01) and specificity from 70% (95% CI: 57%-82%) to 89% (95% CI: 78%-96%; P = 0.02). The area under the receiver-operating characteristic curve improved from 0.83 (95% CI: 0.75-0.90) to 0.92 (95% CI: 0.86-0.98; P = 0.01).

CONCLUSIONS

Fractal analysis constitutes a quantitative and pathophysiologically meaningful approach to myocardial perfusion analysis using dynamic stress CTP, which improved diagnostic performance over CTP-MBF when combined with anatomical information from CTA.

Advances in Multimodality Cardiovascular Imaging in the Diagnosis of Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is a syndrome defined by the presence of heart failure symptoms and increased levels of circulating natriuretic peptide (NP) in patients with preserved left ventricular ejection fraction and various degrees of diastolic dysfunction (DD). HFpEF is a complex condition that encompasses a wide range of different etiologies. Cardiovascular imaging plays a pivotal role in diagnosing HFpEF, in identifying specific underlying etiologies, in prognostic stratification, and in therapeutic individualization. Echocardiography is the first line imaging modality with its wide availability; it has high spatial and temporal resolution and can reliably assess systolic and diastolic function. Cardiovascular magnetic resonance (CMR) is the gold standard for cardiac morphology and function assessment, and has superior contrast resolution to look in depth into tissue changes and help to identify specific HFpEF etiologies. Differently, the most important role of nuclear imaging [i.e., planar scintigraphy and/or single photon emission CT (SPECT)] consists in the screening and diagnosis of cardiac transthyretin amyloidosis (ATTR) in patients with HFpEF. Cardiac CT can accurately evaluate coronary artery disease both from an anatomical and functional point of view, but tissue characterization methods have also been developed. The aim of this review is to critically summarize the current uses and future perspectives of echocardiography, nuclear imaging, CT, and CMR in patients with HFpEF.

Cardiac perfusion by positron emission tomography

Myocardial perfusion imaging (MPI) with positron emission tomography (PET) is an established tool for evaluation of obstructive coronary artery disease (CAD). The contemporary 3-dimensional scanner technology and the state-of-the-art MPI radionuclide tracers and pharmacological stress agents, as well as the cutting-edge image reconstruction techniques and data analysis software, have all enabled accurate, reliable and reproducible quantification of absolute myocardial blood flow (MBF), and henceforth calculation of myocardial flow reserve (MFR) in several clinical scenarios. In patients with suspected coronary artery disease, both absolute stress MBF and MFR can identify myocardial territories subtended by epicardial coronary arteries with haemodynamically significant stenosis, as defined by invasive coronary fractional flow reserve measurement. In particular, absolute stress MBF and MFR offered incremental prognostic information for predicting adverse cardiac outcome, and hence for better patient risk stratification, over those provided by traditional clinical risk predictors. This article reviews the available evidence to support the translation of the current techniques and technologies into a useful decision-making tool in real-world clinical practice.

PET/CT Myocardial Perfusion Imaging Acquisition and Processing: Ten Tips and Tricks to Help You Succeed

PURPOSE OF REVIEW

Positron emission tomography (PET) is a leading non-invasive modality for the diagnosis of coronary artery disease due to its diagnostic accuracy and high image quality. With the latest advances in PET systems, clinicians are able to assess for myocardial ischemia and myocardial blood flow while exposing patients to extremely low radiation doses. This review will focus on the basics of acquisition and processing of hybrid PET/CT systems from appropriate patient selection to common artifacts and pitfalls.

RECENT FINDINGS

The continued development of hybrid PET/CT technology is producing scanners with exquisite sensitivity capable of generating high-quality images while exposing patients to low radiation doses. List mode acquisition is an essential component in all modern PET/CT scanners allowing simultaneous dynamic and ECG-gated imaging without lengthening scan duration. Various PET radiotracers are currently being developed but rubidium-82 and 13N-ammonia remain the most commonly used perfusion radiotracers. The development of mini 13N-ammonia cyclotrons is a promising tool that should increase access to this radiotracer. Misregistration, attenuation from extra-cardiac activity, and patient motion are the most common causes of artifacts during perfusion imaging. Techniques to automatically realign images and correct respiratory or patient motion artifacts continue to evolve. Despite the continuous evolution of PET imaging techniques, basic knowledge of scan parameters, acquisition techniques, and post processing tools remains essential to ensure high-quality images are produced and artifacts are recognized and corrected. Future research should focus on optimizing scanners to allow for shorter scan protocols and lower radiation exposure as well as continue developing techniques to minimize and correct for motion and misregistration artifacts.

Fluorodeoxyglucose Applications in Cardiac PET: Viability, Inflammation, Infection, and Beyond

With its high temporal and spatial resolution and relatively low radiation exposure, positron emission tomography (PET) is increasingly being used in the management of cardiac patients, particularly those with inflammatory cardiomyopathies such as sarcoidosis. This review discusses the role of PET imaging in assessing myocardial viability, inflammatory cardiomyopathies, and endocarditis; describes the different protocols needed to acquire images for specific imaging tests; and examines imaging interpretation for each image dataset-including identification of the mismatch defect in viability imaging, which is associated with significant improvement in LV function after revascularization. We also review the role of fluorodeoxyglucose PET in cardiac sarcoidosis diagnosis, the complementary role of magnetic resonance imaging in inflammatory cardiomyopathy, and the emerging use of cardiac PET in prosthetic valve endocarditis.

The Vulnerable Plaque: Recent Advances in Computed Tomography Imaging to Identify the Vulnerable Patient

PURPOSE OF REVIEW

This review aims to summarize the role of coronary computed tomography plaque analysis in identifying high-risk patients and plaques.

RECENT FINDINGS

In this review, we will describe the histopathological features of a vulnerable plaque as well as the coronary computed tomography characteristics including spotty calcification, low-attenuation fatty core, positive remodeling, and thin fibrous cap. We will also review several studies that assessed features of a vulnerable plaque on non-invasive imaging and evaluated them as risk predictors of future acute coronary events. Multiple recent studies suggested that coronary computed tomography angiography can accurately identify high-risk features of plaque that will predict future events.

Myocardial Perfusion Imaging Using Positron Emission Tomography

Coronary artery disease (CAD), also known as ischemic heart disease, is a major cause of morbidity and mortality worldwide, and timely noninvasive diagnosis of clinical and subclinical CAD is imperative to mitigate its burden on individual patients and populations. Positron emission tomography (PET) is a versatile tool that can perform relative myocardial perfusion imaging (MPI) with high accuracy; furthermore, it provides valuable information about the coronary microvasculature using rest and stress myocardial blood flow (MBF) and coronary flow reserve (CFR) measurements. Several radiotracers are approved by the US Food and Drug Administration to help with MPI, MBF, and CFR evaluation. A large body of evidence indicates that evaluation of the coronary microcirculation using MBF and CFR provides strong diagnostic and prognostic data in a multitude of patient populations. This review describes the technical aspects of PET compared to other modalities and discusses its clinical uses for diagnosis and prognosis of coronary arterial epicardial and microcirculatory disease.

The role of cardiac imaging in the management of non-ischemic cardiovascular diseases in human immunodeficiency virus infection

Infection with human immunodeficiency virus (HIV) has become the pandemic of the new century. About 36.9 million people are living with HIV worldwide. The introduction of antiretroviral therapy in 1996 has dramatically changed the global landscape of HIV care, resulting in significantly improved survival and changing HIV to a chronic disease. With near-normal life expectancy, contemporary cardiac care faces multiple challenges of cardiovascular diseases, disorders specific to HIV/AIDS, and those related to aging and higher prevalence of traditional risk factors. Non-ischemic cardiovascular diseases are major components of cardiovascular morbidity and mortality in HIV/AIDS. Non-invasive cardiac imaging plays a pivotal role in the management of these diseases. This review summarizes the non-ischemic presentation of the HIV cardiovascular spectrum focusing on the role of cardiac imaging in the management of these disorders.

Stress Myocardial Perfusion PET Provides Incremental Risk Prediction in Patients with and Patients without Diabetes

PURPOSE

To evaluate the prognostic value of myocardial perfusion PET in patients with and patients without diabetes mellitus.

MATERIALS AND METHODS

The authors performed a retrospective analysis of prospectively acquired data from a multicenter registry cohort of 7061 patients, including 1966 with diabetes mellitus, who underwent clinically indicated rest-stress rubidium 82 (⁸²Rb) myocardial perfusion PET. The mean patient age (±standard deviation) was 63.3 years ± 13. Of the 7061 patients, 3348 were women (47.4%), 2296 (32.5%) had known coronary artery disease, and 1895 (26.8%) had previously undergone revascularization. The primary end point was cardiac death (n = 169) assessed at a mean of 2.5 years ± 1.5. The authors used Cox proportional hazards models and risk reclassification measures stratified according to diabetes status.

RESULTS

In multivariable models adjusting for established clinical predictors, increasing magnitude of stress myocardial perfusion abnormality was associated with greater risk of cardiac death in patients with diabetes (hazard ratio [HR]: 7.2; 95% confidence interval [CI]: 3.1, 16.8) for severely abnormal myocardium compared with normal myocardium. The addition of stress myocardial perfusion imaging results significantly improved the fit of a clinical model for predicting cardiac death in patients with and patients without diabetes. Myocardial perfusion PET improved risk reclassification for cardiac death in patients with diabetes (category-based net reclassification index: 0.39; 95% CI: 0.15, 0.60, P < .001). Among diabetic patients, an abnormal myocardial perfusion PET scan was associated with increased risk of cardiac death (HR: 4.4; 95% CI: 2.0, 9.7) in all important clinical subgroups based on age, sex, obesity, or prior revascularization.

CONCLUSION

In a large cohort of patients referred for clinical ⁸²Rb stress PET, myocardial perfusion imaging results provided incremental risk prediction of cardiac death in patients with and patients without diabetes mellitus.© RSNA, 2019Supplemental material is available for this article.

Assessment of myocardial blood flow and coronary flow reserve with positron emission tomography in ischemic heart disease: current state and future directions

Positron emission tomography (PET) is a versatile imaging technology that allows assessment of myocardial perfusion, both at a spatially relative scale and also in absolute terms, thereby enabling noninvasive evaluation of myocardial blood flow (MBF) and coronary flow reserve (CFR). Assessment of MBF using FDA-approved PET isotopes, such as ⁸²Rb and ¹³N-ammonia, has been well validated, and several software packages are currently available, thereby allowing for MBF evaluation to be incorporated into routine workflow in contemporary nuclear laboratories. Incremental diagnostic and prognostic information provided with the knowledge of MBF has the potential for widespread applications. Improving the ability to identify the true burden of obstructive epicardial coronary stenoses and allowing for noninvasive assessment of coronary micro circulatory function can be achieved with MBF assessment. On the other hand, attenuated CFR has been shown to predict adverse cardiovascular prognosis in a variety of clinical settings and patient subgroups. With expanding applications of MBF, this tool promises to provide unique insight into the integrity of the entire coronary vascular bed beyond what is currently available with relative perfusion assessment. This review intends to provide an in-depth discussion of technical and clinical aspects of MBF assessment with PET as it relates to patients with ischemic heart disease.

Cardiorespiratory Fitness and Cardiovascular Disease Prevention: an Update

PURPOSE OF REVIEW

Cardiovascular diseases account for nearly one third of all deaths globally. Improving exercise capacity and cardiorespiratory fitness (CRF) has been an important target to reduce cardiovascular events. In addition, the American Heart Association defined decreased physical activity as the fourth risk factor for coronary artery disease. Multiple large cohort studies have evaluated the impact of CRF on outcomes. In this review, we will discuss the role of CRF in reducing cardiovascular morbidity and mortality.

RECENT FINDINGS

Recent data suggest that CRF has an important role in reducing not only cardiovascular and all-cause mortality, but also incident myocardial infarction, hypertension, diabetes, atrial fibrillation, heart failure, and stroke. Most recently, its role in cancer prevention started to emerge. CRF protective effects have also been seen in patients with prior comorbidities like prior coronary artery disease, heart failure, depression, end-stage renal disease, and stroke. The prognostic value of CRF has been demonstrated in various patient populations and cardiovascular conditions. Higher CRF is associated with improved survival and decreased incidence of cardiovascular diseases (CVD) and other comorbidities including hypertension, diabetes, heart failure, and atrial fibrillation.

Mitochondrial-Targeted Molecular Imaging in Cardiac Disease

The present study aimed to discuss the role of mitochondrion in cardiac function and disease. The mitochondrion plays a fundamental role in cellular processes ranging from metabolism to apoptosis. The mitochondrial-targeted molecular imaging could potentially illustrate changes in global and regional cardiac dysfunction. The collective changes that occur in mitochondrial-targeted molecular imaging probes have been widely explored and developed. As probes currently used in the preclinical setting still have a lot of shortcomings, the development of myocardial metabolic activity, viability, perfusion, and blood flow molecular imaging probes holds great potential for accurately evaluating the myocardial viability and functional reserve. The advantages of molecular imaging provide a perspective on investigating the mitochondrial function of the myocardium in vivo noninvasively and quantitatively. The molecular imaging tracers of single-photon emission computed tomography and positron emission tomography could give more detailed information on myocardial metabolism and restoration. In this study, series mitochondrial-targeted ^99mTc-, ¹²³I-, and ¹⁸F-labeled tracers displayed broad applications because they could provide a direct link between mitochondrial dysfunction and cardiac disease.

Comparative evaluation of the algorithms for parametric mapping of the novel myocardial PET imaging agent 18F-FPTP

Objective

(¹⁸F-fluoropentyl)triphenylphosphonium salt (¹⁸F-FPTP) is a new promising myocardial PET imaging tracer. It shows high accumulation in cardiomyocytes and rapid clearance from liver. We performed compartmental analysis of ¹⁸F-FPTP PET images in rat and evaluated two linear analyses: linear least-squares (LLS) and a basis function method (BFM) for generating parametric images. The minimum dynamic scan duration for kinetic analysis was also investigated and computer simulation undertaken.

Methods

¹⁸F-FPTP dynamic PET (18 min) and CT images were acquired from rats with myocardial infarction (MI) (n = 12). Regions of interest (ROIs) were on the left ventricle, normal myocardium, and MI region. Two-compartment (K₁ and k₂; 2C2P) and three-compartment (K₁–k₃; 3C3P) models with irreversible uptake were compared for goodness-of-fit. Partial volume and spillover correction terms (V_a and α = 1 − V_a) were also incorporated. LLS and BFM were applied to ROI- and voxel-based kinetic parameter estimations. Results were compared with the standard ROI-based nonlinear least-squares (NLS) results of the corresponding compartment model. A simulation explored statistical properties of the estimation methods.

Results

The 2C2P model was most suitable for describing ¹⁸F-FPTP kinetics. Average K₁, k₂, and V_a values were, respectively, 6.8 (ml/min/g), 1.1 (min⁻¹), and 0.44 in normal myocardium and 1.4 (ml/min/g), 1.1 (min⁻¹), and 0.32, in MI tissue. Ten minutes of data was sufficient for the estimation. LLS and BFM estimations correlated well with NLS values for the ROI level (K₁: y = 1.06x + 0.13, r² = 0.96 and y = 1.13x + 0.08, r² = 0.97) and voxel level (K₁: y = 1.22x − 0.30, r² = 0.90 and y = 1.26x + 0.00, r² = 0.92). Regional distribution of kinetic parametric images (αK₁, K₁, k₂, V_a) was physiologically relevant. LLS and BFM showed more robust characteristics than NLS in the simulation.

Conclusions

Fast kinetics and highly specific uptake of ¹⁸F-FPTP by myocardium enabled quantitative analysis with the 2C2P model using only the initial 10 min of data. LLS and BFM were feasible for estimating voxel-wise parameters. These two methods will be useful for quantitative evaluation of ¹⁸F-FPTP distribution in myocardium and in further studies with different conditions, disease models, and species.

Electronic supplementary material

The online version of this article (doi:10.1007/s12149-017-1171-6) contains supplementary material, which is available to authorized users.

The diagnostic accuracy of myocardial perfusion scintigraphy in athletes with abnormal exercise test results

Background Previous studies revealed a relatively high prevalence of electrocardiographic findings indicative for myocardial ischemia in asymptomatic athletes undergoing pre-participation screening. Myocardial perfusion scintigraphy is generally considered a valuable diagnostic and prognostic modality and often used for further diagnostic evaluation in these subjects. However, data on the diagnostic accuracy of myocardial perfusion scintigraphy in athletes are scarce. Objectives The main purpose of this study was to investigate the positive predictive value of myocardial perfusion scintigraphy for detection of coronary artery disease in asymptomatic athletes with abnormal exercise testing results during pre-participation screening. The secondary aim was to evaluate the prognostic value of myocardial perfusion scintigraphy. Methods Electronic charts of asymptomatic athletes who underwent myocardial perfusion scintigraphy following an abnormal exercise testing were retrospectively reviewed. Myocardial perfusion scintigraphy and exercise testing studies were revised. Athlete characteristics and cardiovascular risk factors were evaluated. Results One hundred and forty-three athletes were included. 29 athletes (20%) showed concordant abnormal exercise testing and myocardial perfusion scintigraphy results. Coronary imaging was performed in 20 of these 29 athletes. Four athletes showed significant coronary artery disease (positive predictive value = 20%). The positive predictive value increased to 33% when athletes were selected who should have undergone exercise testing according to the guideline recommendations. During a mean follow-up interval of 4.7 ± 2.2 years, eight cardiac events occurred. Athletes with an abnormal myocardial perfusion scintigraphy result had a fourfold increased risk at a future cardiac event (2.9%/year versus 0.75%/year, p = 0.031). Conclusions The positive predictive value of myocardial perfusion scintigraphy for the detection of significant coronary artery disease in asymptomatic athletes with a positive exercise testing result is low, even in a selection of athletes with a relatively high cardiovascular risk. Although an abnormal myocardial perfusion scintigraphy result was associated with a fourfold higher annual event rate, the absolute annual event rate in this group was still low. Efforts should be made to develop better diagnostic strategies to evaluate asymptomatic athletes with abnormal exercise testing results during pre-participation screening.

Assessment of myocardial perfusion and viability by positron emission tomography

An important evolution has taken place recently in the field of cardiovascular Positron Emission Tomography (PET) imaging. Being originally a highly versatile research tool that has contributed significantly to advance our understanding of cardiovascular physiology and pathophysiology, PET has gradually been incorporated into the clinical cardiac imaging portfolio contributing to diagnosis and management of patients investigated for coronary artery disease (CAD). PET myocardial perfusion imaging (MPI) has an average sensitivity and specificity around 90% for the detection of angiographically significant CAD and it is also a very accurate technique for prognostication of patients with suspected or known CAD. In clinical practice, Rubidium-82 ((82)Rb) is the most widely used radiopharmaceutical for MPI that affords also accurate and reproducible quantification in absolute terms (ml/min/g) comparable to that obtained by cyclotron produced tracers such as Nitrogen-13 ammonia ((13)N-ammonia) and Oxygen-15 labeled water ((15)O-water). Quantification increases sensitivity for detection of multivessel CAD and it may also be helpful for detection of early stages of atherosclerosis or microvascular dysfunction. PET imaging combining perfusion with myocardial metabolism using (18)F-Fluorodeoxyglucose ((18)F FDG), a glucose analog, is an accurate standard for assessment of myocardial hibernation and risk stratification of patients with left ventricular dysfunction of ischemic etiology. It is helpful for guiding management decisions regarding revascularization or medical treatment and predicting improvement of symptoms, exercise capacity and quality of life post-revascularization. The strengths of PET can be increased further with the introduction of hybrid scanners, which combine PET with computed tomography (PET/CT) or with magnetic resonance imaging (PET/MRI) offering integrated morphological, biological and physiological information and hence, comprehensive evaluation of the consequences of atherosclerosis in the coronary arteries and the myocardium.

Myocardial perfusion scintigraphy using rubidium-82 positron emission tomography

INTRODUCTION

Myocardial perfusion scintigraphy (MPS) is an established non-invasive technique for the diagnosis and management of patients with suspected or known coronary artery disease. Because of the wealth of prognostic data, MPS single photon emission computed tomography (SPECT) is the most commonly used functional test to detect inducible ischaemia. However, the increasing availability of positron emission tomography (PET) scanners for oncology along with the introduction of the generator-produced PET tracer rubidium-82 (⁸²Rb) has helped the growth of MPS PET.

SOURCES OF DATA

Relevant review articles, primary literature and clinical guidelines identified through medical literature search engines.

AREAS OF AGREEMENT

PET offers advantages over SPECT, including increased patient throughput because of rapid scanning protocols, reduced radiation exposure to patients and the ability to quantify tracer distribution accurately and hence measure myocardial perfusion in millilitre per gram per minute and hence myocardial perfusion reserve (MPR).

AREAS OF CONTROVERSY

Although PET has advantages over SPECT, there are no large-scale prognostic or cost-effectiveness data to support it use as the primary MPS technique.

GROWING POINTS

A wider use of absolute measurements of perfusion has the potential to improve diagnostic accuracy and to add prognostic value over relative assessment of myocardial perfusion.

AREAS TIMELY FOR DEVELOPING RESEARCH

Assessment of absolute myocardial perfusion may provide insight into the effects of traditional risk factors on perfusion reserve and the impact of risk factor modifications on progression of coronary artery disease.

Multimodality imaging in the assessment of myocardial viability

The prevalence of heart failure due to coronary artery disease continues to increase, and it portends a worse prognosis than non-ischemic cardiomyopathy. Revascularization improves prognosis in these high-risk patients who have evidence of viability; therefore, optimal assessment of myocardial viability remains essential. Multiple imaging modalities exist for differentiating viable myocardium from scar in territories with contractile dysfunction. Given the multiple modalities available, choosing the best modality for a specific patient can be a daunting task. In this review, the physiology of myocardial hibernation and stunning will be reviewed. All the current methods available for assessing viability including echocardiography, cardiac magnetic resonance imaging, nuclear imaging with single photon emission tomography and positron emission tomography imaging and cardiac computed tomography will be reviewed. The effectiveness of the various techniques will be compared, and the limitations of the current literature will be discussed.

Image registration and analysis for quantitative myocardial perfusion: application to dynamic circular cardiac CT

Large area detector computed tomography systems with fast rotating gantries enable volumetric dynamic cardiac perfusion studies. Prospectively, ECG-triggered acquisitions limit the data acquisition to a predefined cardiac phase and thereby reduce x-ray dose and limit motion artefacts. Even in the case of highly accurate prospective triggering and stable heart rate, spatial misalignment of the cardiac volumes acquired and reconstructed per cardiac cycle may occur due to small motion pattern variations from cycle to cycle. These misalignments reduce the accuracy of the quantitative analysis of myocardial perfusion parameters on a per voxel basis. An image-based solution to this problem is elastic 3D image registration of dynamic volume sequences with variable contrast, as it is introduced in this contribution. After circular cone-beam CT reconstruction of cardiac volumes covering large areas of the myocardial tissue, the complete series is aligned with respect to a chosen reference volume. The results of the registration process and the perfusion analysis with and without registration are evaluated quantitatively in this paper. The spatial alignment leads to improved quantification of myocardial perfusion for three different pig data sets.

Rational chemical design of the next generation of molecular imaging probes based on physics and biology: mixing modalities, colors and signals

In recent years, numerous in vivo molecular imaging probes have been developed. As a consequence, much has been published on the design and synthesis of molecular imaging probes focusing on each modality, each type of material, or each target disease. More recently, second generation molecular imaging probes with unique, multi-functional, or multiplexed characteristics have been designed. This critical review focuses on (i) molecular imaging using combinations of modalities and signals that employ the full range of the electromagnetic spectra, (ii) optimized chemical design of molecular imaging probes for in vivo kinetics based on biology and physiology across a range of physical sizes, (iii) practical examples of second generation molecular imaging probes designed to extract complementary data from targets using multiple modalities, color, and comprehensive signals (277 references).