A randomized trial on the optimization of 18F-FDG myocardial uptake suppression: implications for vulnerable coronary plaque imaging

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.

Non-Invasive Modalities in the Assessment of Vulnerable Coronary Atherosclerotic Plaques

Coronary atherosclerosis is a complex, multistep process that may lead to critical complications upon progression, revolving around plaque disruption through either rupture or erosion. Several high-risk features are associated with plaque vulnerability and may add incremental prognostic information. Although invasive imaging modalities such as optical coherence tomography or intravascular ultrasound are considered to be the gold standard in the assessment of vulnerable coronary atherosclerotic plaques (VCAPs), contemporary evidence suggests a potential role for non-invasive methods in this context. Biomarkers associated with deleterious pathophysiologic pathways, including inflammation and extracellular matrix degradation, have been correlated with VCAP characteristics and adverse prognosis. However, coronary computed tomography (CT) angiography has been the most extensively investigated technique, significantly correlating with invasive method-derived VCAP features. The estimation of perivascular fat attenuation as well as radiomic-based approaches represent additional concepts that may add incremental information. Cardiac magnetic resonance imaging (MRI) has also been evaluated in clinical studies, with promising results through the various image sequences that have been tested. As far as nuclear cardiology is concerned, the implementation of positron emission tomography in the VCAP assessment currently faces several limitations with the myocardial uptake of the radiotracer in cases of fluorodeoxyglucose use, as well as with motion correction. Moreover, the search for the ideal radiotracer and the most adequate combination (CT or MRI) is still ongoing. With a look to the future, the possible combination of imaging and circulating inflammatory and extracellular matrix degradation biomarkers in diagnostic and prognostic algorithms may represent the essential next step for the assessment of high-risk individuals.

Combined Cardiac Fluorodeoxyglucose-Positron Emission Tomography/Magnetic Resonance Imaging Assessment of Myocardial Injury in Patients Who Recently Recovered From COVID-19

IMPORTANCE

Although myocardial injury can occur with acute COVID-19, there is limited understanding of changes with myocardial metabolism in recovered patients.

OBJECTIVE

To examine myocardial metabolic changes early after recovery from COVID-19 using fluorodeoxyglucose-positron emission tomography (PET) and associate these changes to abnormalities in cardiac magnetic resonance imaging (MRI)-based function and tissue characterization measures and inflammatory blood markers.

DESIGN, SETTING, AND PARTICIPANTS

This prospective cohort study took place at a single-center tertiary referral hospital system. A volunteer sample of adult patients within 3 months of a diagnosis of COVID-19 who responded to a mail invitation were recruited for cardiac PET/MRI and blood biomarker evaluation between November 2020 and June 2021.

EXPOSURES

Myocardial inflammation as determined by focal fluorodeoxyglucose (FDG) uptake on PET.

MAIN OUTCOMES AND MEASURES

Demographic characteristics, cardiac and inflammatory blood markers, and fasting combined cardiac 18F-FDG PET/MRI imaging were obtained. All patients with focal FDG uptake at baseline returned for repeated PET/MRI and blood marker assessment 2 months later.

RESULTS

Of 47 included patients, 24 (51%) were female, and the mean (SD) age was 43 (13) years. The mean (SD) interval between COVID-19 diagnosis and PET/MRI was 67 (16) days. Most patients recovered at home during the acute infection (40 [85%]). Eight patients (17%) had focal FDG uptake on PET consistent with myocardial inflammation. Compared with those without FDG uptake, patients with focal FDG uptake had higher regional T2, T1, and extracellular volume (colocalizing with focal FDG uptake), higher prevalence of late gadolinium enhancement (6 of 8 [75%] vs 9 of 39 [23%], P = .009), lower left ventricular ejection fraction (mean [SD], 55% [4%] vs 62% [5%], P < .001), worse global longitudinal and circumferential strain (mean [SD], -16% [2%] vs -17% [2%], P = .02 and -18% [2%] vs -20% [2%], P = .047, respectively), and higher systemic inflammatory blood markers including interleukin 6, interleukin 8, and high-sensitivity C-reactive protein. Among patients with focal FDG uptake, PET/MRI, and inflammatory blood markers resolved or improved at follow-up performed a mean (SD) of 52 (17) days after baseline PET/MRI.

CONCLUSIONS AND RELEVANCE

In this study of patients recently recovered from COVID-19, myocardial inflammation was identified on PET in a small proportion of patients, was associated with cardiac MRI abnormalities and elevated inflammatory blood markers at baseline, and improved at follow-up.

An Intravenous 100-mL Lipid Emulsion Infusion Dramatically Improves Myocardial Glucose Metabolism Extinction in Cardiac FDG PET Clinical Practice

PURPOSE

Physiological myocardial accumulation of FDG impairs the diagnosis of inflammatory/infectious or tumoral myocardial detection by FDG PET/CT. We prospectively evaluated the addition, 3 hours before imaging, of an intravenous 100-mL lipid emulsion infusion (Intralipid) to a high-fat, low-carbohydrate diet (HFLCD) for at least 2 meals followed by a fast of at least 6 to 12 hours in patients referred for the diagnosis of myocardial inflammation, endocarditis, cardiac or paracardiac masses, intracardiac device, or prosthetic valve infections.

METHODS

Data of 58 patients consecutively included (28 Intralipid patients, 30 controls with HFLCD alone) were compared. FDG uptake in normal myocardium was scored from 0 (complete myocardial suppression) to 3 (high diffuse uptake). Myocardial maximal, peak, and mean SUV and the rate of interpretable images according to the clinical indication were measured.

RESULTS

Compared with controls, Intralipid infusion significantly improved the rate of score 0 (89% vs 63%, P = 0.021), of interpretable images according to the clinical indication (100% vs 72%, P = 0.0047) and decreased all myocardial SUV values (eg, SUVmax median, 1.9 [interquartile range, 1.7-2.5] vs 3.1 [interquartile range, 2.3-4.1]; P < 0.001).

CONCLUSIONS

A lipid emulsion infusion in addition to HFLCD better suppresses cardiac glucose metabolism than HFLCD alone.

Suppressing physiologic 18-fluorodeoxyglucose uptake in patients undergoing positron emission tomography for cardiac sarcoidosis: The effect of a structured patient preparation protocol

OBJECTIVE

Myocardial positron emission tomography (PET) to detect cardiac sarcoidosis requires adequate patient preparation; however, in many cases physiologic myocardial 18F-fluorodeoxyglucose (18F-FDG) uptake may not be adequately suppressed. We sought to evaluate the efficacy of a structured patient preparation protocol as recommended by the joint SNMMI/ASNC expert consensus document on the role of 18F-FDG PET/CT in cardiac sarcoid detection and therapy monitoring. The SNMMI/ASNC preparation protocol recommends at least two high-fat (> 35 g), low-carbohydrate (< 3 g) (HFLC) meals the day before testing followed by fasting for at least 4-12 hours.

METHODS

All unique PET scans performed for cardiac sarcoidosis before (group 1) and after (group 2) application of the new preparation protocol were included in the study. In group 1, patients were given a preparation protocol of HFLC meals with suggested meals examples, while patients in group 2 received detailed diet instructions, together with accepted and non-accepted meal examples along. In group 2, reinforcement of instructions by nursing staff and review of dietary log were performed prior to testing. All PET images were evaluated for suppression of physiologic myocardial 18F-FDG uptake.

RESULTS

Group 1 included 124 unique patients, and group 2 included 232 unique patients. There were no significant differences in baseline patient characteristics between the two groups. Suppression of physiologic myocardial 18F-FDG uptake was achieved in 91% of patients in group 2, compared to 78% of patients in group 1 (P < .001). A "diffuse" myocardial uptake pattern, indicating inadequate 18F-FDG suppression, was seen in 2% of studies in group 2 vs 12% in group 1 (P < .001).

CONCLUSION

In this single-center study, application of a structured preparation protocol was highly successful in achieving suppression of physiologic myocardial 18F-FDG uptake in patients undergoing myocardial PET for cardiac sarcoidosis.

Associations of physiologic myocardial 18F-FDG uptake with fasting duration, HbA1c, and regular exercise

OBJECTIVE

The variability of physiologic ¹⁸F-FDG uptake in the myocardium has hampered the accurate evaluation of cardiac glucose metabolism. We investigated the effects of multiple factors, including fasting duration and physical activity, on the physiologic uptake of ¹⁸F-FDG by the myocardium in healthy participants.

METHODS

A total of 446 participants (predominantly male, 91%) in a health screening program were included in this retrospective study. For the visual analysis of myocardial ¹⁸F-FDG uptake, the participants were categorized into three groups according to qualitative visual scales (QVS). For the quantitative analysis, the maximum SUV of the left ventricular myocardium was measured.

RESULTS

Significant differences were observed in fasting duration (p < 0.001), SUV_max (p < 0.001), aspartate aminotransferase (AST) (p < 0.001), alanine aminotransferase (ALT) (p < 0.001), gamma-glutamyl transpeptidase (γ-GTP) (p = 0.001), and uric acid (p = 0.015) among the QVS groups. Participants who regularly exercised with vigorous activity (p = 0.032) and HbA1c > 6% (p = 0.005) showed significant association with myocardial FDG uptake in the Chi-squared test. The median value of fasting duration decreased significantly as the QVS of the myocardium increased. Twenty-nine of the 31 participants (93.5%) who fasted for 21.5 h or more showed a suppressed FDG uptake (mean SUV_max = 2.1). In multivariate logistic regression analysis, fasting duration (OR = 0.74, 95% CI 0.69-0.80, p < 0.001), HbA1c > 6% (OR = 0.29, 95% CI: 0.12 - 0.66, p = 0.004), uric acid (OR = 0.82, 95% CI 0.68-1.00, p = 0.049) and regular exercise with vigorous activity (OR = 1.75, 95% CI 1.13-2.70, p = 0.012) were significant factors for physiologic myocardial FDG uptake.

CONCLUSIONS

Reduced physiologic ¹⁸F-FDG uptake of the myocardium was associated with longer fasting duration, higher level of HbA1c, and less frequency of regular exercise with vigorous activity. For the preparation of cardiac ¹⁸F-FDG PET, inclusion of longer fasting duration (more than 18 h) might be necessary for the adequate suppression of physiologic ¹⁸F-FDG myocardial uptake.

F-18 fluorodeoxyglucose positron emission tomography/computed tomography in the infection of heart

Infections involving the heart are becoming increasingly common, and a timely diagnosis of utmost importance, despite its challenges. F-18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) is a recently introduced diagnostic tool in cardiology. This review focuses on the current evidence for the use of FDG PET/CT in the diagnosis of infective endocarditis, cardiac implantable device infection, left ventricular assist device infection, and secondary complications. The author discusses considerations when using FDG PET/CT in routine clinical practice, patient preparation for reducing physiologic myocardial uptake, acquisition of images, and interpretation of PET/CT findings. This review also functions to highlight the need for a standardized acquisition protocol.

Combined PET/CT with thoracic contrast-enhanced CT in assessment of primary cardiac tumors in adult patients

Background

¹⁸F-FDG PET/CT is a key molecular imaging modality to noninvasively assess and differentiate benign and malignant cardiac tumors. However, few benign cardiac tumors can be characterized by increased ¹⁸F-FDG uptake, which makes differential diagnosis difficult. This study sought to retrospectively evaluate whether combined ¹⁸F-FDG PET/CT with thoracic contrast-enhanced CT (CECT) helps in assessing primary cardiac tumors in adult patients, compared with CECT or PET/CT alone.

Methods

Forty-six consecutive patients who were diagnosed as primary cardiac tumors were enrolled. All patients underwent ¹⁸F-FDG PET/CT followed by thoracic CECT before biopsy or surgery. Visual qualitative interpretation and quantitative analysis were performed, and diagnostic performance was evaluated.

Results

More than half (16/29) of benign tumors exhibited with mild ¹⁸F-FDG uptake. There were significant differences in ¹⁸F-FDG uptake and the degree of absolute enhancement between benign and malignant tumors (P < 0.001). The combination of two modalities improved the specificity from 79 to 93%, the positive predictive value from 73 to 89%, and the accuracy of diagnosis from 85 to 93%. There were significant differences between PET/CT alone or thoracic CECT alone and combined modalities (P = 0.034 and P = 0.026, respectively). The combination with the optimal SUVmax cutoff value generated 94% sensitivity, 100% specificity, 97% negative predictive values, 100% positive predictive values, and 98% accuracy rates.

Conclusions

Combining ¹⁸F-FDG PET/C with thoracic CECT significantly improved specificity and accuracy compared to CECT or PET/CT alone in detecting tumors. This combination of diagnostic imaging is effective in differentiating malignant from benign masses.

Characterization of a highly effective preparation for suppression of myocardial glucose utilization

BACKGROUND

With appropriate protocols, F-18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) can visualize myocardial inflammation. Optimal protocols and normative myocardial FDG uptake values are not well-established.

METHODS

We evaluated 111 patients referred for inflammation cardiac FDG PET/CT. Patients followed a low-carbohydrate, high-fat diet for 36 hours before imaging and received unfractionated heparin. Glucose and fatty acid metabolism biomarkers were obtained. Mean blood pool and maximum myocardial uptake (SUVmean, SUVmax) were measured, avoiding areas of abnormal FDG uptake or spillover.

RESULTS

Adequate suppression of myocardial FDG uptake occurred in 95% of patients (n = 106). Myocardial SUVmax was significantly below background blood pool SUVmean: septal myocardial to blood pool ratio 0.75 (95% CI 0.73-0.77; P < 0.001); lateral myocardial to blood pool ratio 0.70 (95% CI 0.68-0.72; P < 0.001). Glucose, insulin, and C-peptide correlated to blood pool SUVmean (Spearman rs = 0.39, P < 0.01; rs = 0.40, P < 0.01; rs = 0.35, P < 0.01) and myocardial SUVmax (Spearman rs = 0.31, P < 0.01; rs = 0.31, P < 0.01; rs = 0.26, P < 0.01). Fatty acid metabolism biomarkers did not correlate to myocardial SUVmax.

CONCLUSIONS

Patients following intensive metabolic preparation have myocardial FDG SUVmax below background SUVmean. Biomarkers of glucose metabolism modestly correlate to FDG uptake.

Atherosclerosis Immunoimaging by Positron Emission Tomography

The immune system's role in atherosclerosis has long been an important research topic and is increasingly investigated for therapeutic and diagnostic purposes. Therefore, noninvasive imaging of hematopoietic organs and immune cells will undoubtedly improve atherosclerosis phenotyping and serve as a monitoring method for immunotherapeutic treatments. Among the available imaging techniques, positron emission tomography's unique features make it an ideal tool to quantitatively image the immune response in the context of atherosclerosis and afford reliable readouts to guide medical interventions in cardiovascular disease. Here, we summarize the state of the art in the field of atherosclerosis positron emission tomography immunoimaging and provide an outlook on current and future applications.

18F-fluorodeoxyglucose use after cardiac transplant: A comparative study of suppression of physiological myocardial uptake

BACKGROUND

18F-fluorodeoxyglucose (FDG) has been useful in the evaluation of myocardial inflammatory processes. However, it is challenging to identify them due to physiological 18F-FDG uptake. There are no publications demonstrating the application of FDG in post-transplant rejection in humans yet. The aim of this study is to determine the feasibility of suppression of myocardial FDG uptake in post-transplant patients, comparing three different protocols of preparation.

METHODS

Ten patients after heart transplantation were imaged by FDG associated with three endomyocardial biopsies (EMB), scheduled in the first year after the procedure. Before each imaging, patients were randomized to one of three preparations: (1) hyperlipidic-hypoglycemic diet; (2) fasting longer than 12 hours; and (3) fasting associated with intravenous heparin. All patients would undergo the three methods. FDG images were analyzed using visual analysis scores and relative radiotracer cardiac uptake (RRCU).

RESULTS

The suppression rate of radiotracer activity ranged from 55% to 62%. Visual analysis showed that preparation 3 presented less efficacy in the suppression compared to the others. However, RRCU did not show difference between the preparations.

CONCLUSIONS

Suppression of physiological myocardial FDG uptake after cardiac transplantation is feasible. The usefulness of heparin in the suppression is unclear.

Myocardial Positron Emission Tomography for Evaluation of Cardiac Sarcoidosis: Specialized Protocols for Better Diagnosis

Sarcoidosis is a multisystemic granulomatous disease of unknown etiology with various clinical presentations depending on the organs involved. Since cardiac sarcoidosis (CS) portends a higher risk of morbidity and mortality, early diagnosis and aggressive medical treatment are essential to improve the prognosis. ¹⁸F-Fluorodeoxyglucose (FDG) positron emission tomography (PET) has emerged as an important tool with practical advantages in assessing disease activity and monitoring the treatment response in patients with CS. While it has high sensitivity, it also has great variability in specificity, probably due to normal physiologic myocardial FDG uptake, which interferes with the evaluation and follow-up of CS using FDG-PET. This review details the technical aspects of FDG-PET imaging for evaluating and diagnosing CS, assessing disease activity, and monitoring therapeutic response.

The role of positron emission tomography in the assessment of cardiac sarcoidosis

The myocardium and the cardiovascular system are often involved in patients with sarcoidosis. As therapy should be started as early as possible to avoid complications such as left ventricular dysfunction, a prompt and reliable diagnosis by means of non-invasive tests would be highly warranted. Among other techniques, 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) has emerged as a high sensitive tool to detect sites of inflammation before morphological changes are visible to conventional imaging techniques. We therefore aim at summarizing the most relevant findings in the literature on the use of 18F-fluorodeoxyglucose PET in the diagnostic workup of cardiac sarcoidosis and to underline future perspectives.

Myocardial Inflammation, Measured Using 18-Fluorodeoxyglucose Positron Emission Tomography With Computed Tomography, Is Associated With Disease Activity in Rheumatoid Arthritis

OBJECTIVE

To determine the prevalence and correlates of subclinical myocardial inflammation in patients with rheumatoid arthritis (RA).

METHODS

RA patients (n = 119) without known cardiovascular disease underwent cardiac 18-fluorodeoxyglucose (FDG) positron emission tomography with computed tomography (PET-CT). Myocardial FDG uptake was assessed visually and measured quantitatively as the standardized uptake value (SUV). Multivariable linear regression was used to assess the associations of patient characteristics with myocardial SUVs. A subset of RA patients who had to escalate their disease-modifying antirheumatic drug (DMARD) therapy (n = 8) underwent a second FDG PET-CT scan after 6 months, to assess treatment-associated changes in myocardial FDG uptake.

RESULTS

Visually assessed FDG uptake was observed in 46 (39%) of the 119 RA patients, and 21 patients (18%) had abnormal quantitatively assessed myocardial FDG uptake (i.e., mean of the mean SUV [SUV_mean ] ≥3.10 units; defined as 2 SD above the value in a reference group of 27 non-RA subjects). The SUV_mean was 31% higher in patients with a Clinical Disease Activity Index (CDAI) score of ≥10 (moderate-to-high disease activity) as compared with those with lower CDAI scores (low disease activity or remission) (P = 0.005), after adjustment for potential confounders. The adjusted SUV_mean was 26% lower among those treated with a non-tumor necrosis factor-targeted biologic agent compared with those treated with conventional (nonbiologic) DMARDs (P = 0.029). In the longitudinal substudy, the myocardial SUV_mean decreased from 4.50 units to 2.30 units over 6 months, which paralleled the decrease in the mean CDAI from a score of 23 to a score of 12.

CONCLUSION

Subclinical myocardial inflammation is frequent in patients with RA, is associated with RA disease activity, and may decrease with RA therapy. Future longitudinal studies will be required to assess whether reduction in myocardial inflammation will reduce heart failure risk in RA.

Imaging the event-prone coronary artery plaque

Acute coronary events, the dreaded manifestation of coronary atherosclerosis, remain one of the main contributors to mortality and disability in the developed world. The majority of those events are associated with atherosclerotic plaques-related thrombus formation following an acute disruption, that being rupture or erosion, of an event-prone lesion. These historically termed vulnerable plaques have been the target of numerous benchtop and clinical research endeavors, yet to date without solid results that would allow for early identification and potential treatment. Technological leaps in cardiovascular imaging have provided novel insights into the formation and role of the event-prone plaques. From intracoronary optical coherence tomography that has enhanced our understanding of the pathophysiological mechanisms of plaque disruption, over coronary computed tomography angiography that enables non-invasive serial plaque imaging, and positron emission tomography poised to be rapidly implemented into clinical practice to the budding field of plaque imaging with cardiac magnetic resonance, we summarize the invasive and non-invasive imaging modalities currently available in our armamentarium. Finally, the current status and potential future imaging directions are critically appraised.

A pilot study of cardiopulmonary exercise testing and cardiac stress positron emission tomography before major non-cardiac surgery

Cardiac events are a common cause of peri-operative morbidity. Cardiopulmonary exercise testing can objectively assess risk, but it does not quantify myocardial ischaemia. With appropriate dietary preparation to suppress basal myocardial glucose uptake, positron emission tomography with ¹⁸ F-fluorodeoxyglucose can identify post-ischaemic myocardium, providing an attractive complement to exercise testing. We aimed to investigate the feasibility of this diagnostic algorithm. Patients referred for cardiopulmonary exercise testing before major cancer surgery were prospectively recruited. Exercise testing and positron emission tomography imaging were performed after a high fat-low carbohydrate meal. Protocol feasibility (primary end-point) included compliance with pre-test diet instructions and the completion of tests. Stress myocardial perfusion imaging was performed if either exercise testing or positron emission tomography was equivocal or positive for ischaemia. We recorded cardiac complications for 30 postoperative days. We enrolled 26 participants, 20 of whom completed protocol. Twenty-one participants proceeded to surgery: myocardial injury or infarction was diagnosed in three participants, two of whom had positive or equivocal positron emission tomography but negative myocardial perfusion imaging. We have shown that pre-operative cardiac positron emission tomography after cardiopulmonary exercise testing is feasible; protocol deviations were minor and did not affect image quality. Our findings warrant further investigation to compare the diagnostic utility of cardiac positron emission tomography imaging with standard pre-operative stress tests.

The "3M" Approach to Cardiovascular Infections: Multimodality, Multitracers, and Multidisciplinary

Cardiovascular infections are associated with high morbidity and mortality. Early diagnosis is crucial for adequate patient management, as early treatment improves the prognosis. The diagnosis cannot be made on the basis of a single symptom, sign, or diagnostic test. Rather, the diagnosis requires a multidisciplinary discussion in addition to the integration of clinical signs, microbiology data, and imaging data. The application of multimodality imaging, including molecular imaging techniques, has improved the sensitivity to detect infections involving heart valves and vessels and implanted cardiovascular devices while also allowing for early detection of septic emboli and metastatic infections before these become clinically apparent. In this review, we describe data supporting the use of a Multimodality, Multitracer, and Multidisciplinary approach (the 3M approach) to cardiovascular infections. In particular, the role of white blood cell SPECT/CT and [¹⁸F]FDG PET/CT in most prevalent and clinically relevant cardiovascular infections will be discussed. In addition, the needs of advanced hybrid equipment, dedicated imaging acquisition protocols, specific expertise for image reading, and interpretation in this field are discussed, emphasizing the need for a specific reference framework within a Cardiovascular Multidisciplinary Team Approach to select the best test or combination of tests for each specific clinical situation.

Imaging Atherosclerotic Plaque Calcification: Translating Biology

Calcification of atherosclerotic lesions was long thought to be an age - related, passive process, but increasingly data has revealed that atherosclerotic calcification is a more active process, involving complex signaling pathways and bone-like genetic programs. Initially, imaging of atherosclerotic calcification was limited to gross assessment of calcium burden, which is associated with total atherosclerotic burden and risk of cardiovascular mortality and of all cause mortality. More recently, sophisticated molecular imaging studies of the various processes involved in calcification have begun to elucidate information about plaque calcium composition and consequent vulnerability to rupture, leading to hard cardiovascular events like myocardial infarction. As such, there has been renewed interest in imaging calcification to advance risk assessment accuracy in an evolving era of precision medicine. Here we summarize recent advances in our understanding of the biologic process of atherosclerotic calcification as well as some of the molecular imaging tools used to assess it.

Molecular imaging of postprandial metabolism

Disordered postprandial metabolism of energy substrates is one of the main defining features of prediabetes and contributes to the development of several chronic diseases associated with obesity, such as type 2 diabetes and cardiovascular diseases. Postprandial energy metabolism has been studied using classical isotopic tracer approaches that are limited by poor access to splanchnic metabolism and highly dynamic and complex exchanges of energy substrates involving multiple organs and systems. Advances in noninvasive molecular imaging modalities, such as PET and MRI/magnetic resonance spectroscopy (MRS), have recently allowed important advances in our understanding of postprandial energy metabolism in humans. The present review describes some of these recent advances, with particular focus on glucose and fatty acid metabolism in the postprandial state, and discusses current gaps in knowledge and new perspectives of application of PET and MRI/MRS for the investigation and treatment of human metabolic diseases.

Patient preparation for cardiac fluorine-18 fluorodeoxyglucose positron emission tomography imaging of inflammation

Although the number of clinical applications for fluorine-18 fluorodeoxyglucose (18F-FDG) cardiac positron emission tomography (PET) has continued to grow, there remains a lack of consensus regarding the ideal method of suppressing normal myocardial glucose utilization for image optimization. This review describes various patient preparation protocols that have been used as well as the success rates achieved in different studies. Collectively, the available literature supports using a high-fat, no-carbohydrate diet for at least two meals with a fast of 4-12 hours prior to 18F-FDG PET imaging and suggests that isolated fasting for less than 12 hours and supplementation with food or drink just prior to imaging should be avoided. Each institution should adopt a protocol and continuously monitor its effectiveness with a goal to achieve adequate myocardial suppression in greater than 80% of patients.

Clinical Utility and Future Applications of PET/CT and PET/CMR in Cardiology

Over the past several years, there have been major advances in cardiovascular positron emission tomography (PET) in combination with either computed tomography (CT) or, more recently, cardiovascular magnetic resonance (CMR). These multi-modality approaches have significant potential to leverage the strengths of each modality to improve the characterization of a variety of cardiovascular diseases and to predict clinical outcomes. This review will discuss current developments and potential future uses of PET/CT and PET/CMR for cardiovascular applications, which promise to add significant incremental benefits to the data provided by each modality alone.

Imaging inflammation and neovascularization in atherosclerosis: clinical and translational molecular and structural imaging targets

PURPOSE OF REVIEW

The purpose of this study is to showcase advances in molecular imaging of atheroma biology in living individuals.

RECENT FINDINGS

F-fluorodeoxyglucose (FDG) PET/computed tomography (CT) continues to be the predominant molecular imaging approach for clinical applications, particularly in the large arterial beds. Recently, there has been significant progress in imaging of neovascularization and inflammation to delineate high-risk atheroma and to evaluate drug efficacy. In addition, new hardware detection technology and imaging agents are enabling in-vivo imaging of new targets on diverse imaging platforms.

SUMMARY

In this review, we present recent exciting developments in molecular and structural imaging of atherosclerotic plaque inflammation and neovascularization. Building upon prior studies, these advances develop key technology that will play an important role in propelling new diagnostic and therapeutic strategies identifying high-risk plaque phenotypes and assessing new plaque stabilization therapies in clinical trials.

Future imaging of atherosclerosis: molecular imaging of coronary atherosclerosis with (18)F positron emission tomography

Atherosclerosis is characterized by the formation of complex atheroma lesions (plaques) in arteries that pose risk by their flow-limiting nature and propensity for rupture and thrombotic occlusion. It develops in the context of disturbances to lipid metabolism and immune response, with inflammation underpinning all stages of plaque formation, progression and rupture. As the primary disease process responsible for myocardial infarction, stroke and peripheral vascular disease, atherosclerosis is a leading cause of morbidity and mortality on a global scale. A precise understanding of its pathogenic mechanisms is therefore critically important. Integral to this is the role of vascular wall imaging. Over recent years, the rapidly evolving field of molecular imaging has begun to revolutionize our ability to image beyond just the anatomical substrate of vascular disease, and more dynamically assess its pathobiology. Nuclear imaging by positron emission tomography (PET) can target specific molecular and biological pathways involved in atherosclerosis, with the application of (18)Fluoride PET imaging being widely studied for its potential to identify plaques that are vulnerable or high risk. In this review, we discuss the emergence of (18)Fluoride PET as a promising modality for the assessment of coronary atherosclerosis, focusing on the strengths and limitations of the two main radionuclide tracers that have been investigated to date: 2-deoxy-2-((18)F)fluoro-D-glucose ((18)F-FDG) and sodium (18)F-fluoride ((18)F-NaF).

αVβ3 integrin-targeted microSPECT/CT imaging of inflamed atherosclerotic plaques in mice

Background

α_Vβ₃-integrin is expressed by activated endothelial cells and macrophages in atherosclerotic plaques and may represent a valuable marker of high-risk plaques. We evaluated ^99mTc-maraciclatide, an integrin-specific tracer, for imaging vascular inflammation in atherosclerotic lesions in mice.

Methods

Apolipoprotein E-negative (ApoE^−/−) mice on a Western diet (n = 10) and normally fed adult C57BL/6 control mice (n = 4) were injected with ^99mTc-maraciclatide (51.8 ± 3.7 MBq). A blocking peptide was infused in three ApoE^−/− mice; this condition served as another control. After 90 min, the animals were imaged via single-photon emission computed tomography (SPECT). While maintained in the same position, the mice were transferred to computed tomography (CT) to obtain contrast-enhanced images of the aortic arch. Images from both modalities were fused, and signal was quantified in the aortic arch and in the vena cava for subtraction of blood-pool activity. The aorta was carefully dissected after imaging for gamma counting, autoradiography, and histology.

Results

Tracer uptake was significantly higher in ApoE^−/− mice than in both groups of control mice (1.56 ± 0.33 vs. 0.82 ± 0.24 vs. 0.98 ± 0.11, respectively; P = 0.006). Furthermore, higher tracer activity was detected via gamma counting in the aorta of hypercholesterolemic mice than in both groups of control mice (1.52 ± 0.43 vs. 0.78 ± 0.19 vs. 0.47 ± 0.31 ^99mTc-maraciclatide %ID/g, respectively; P = 0.018). Autoradiography showed significantly higher tracer uptake in the atherosclerotic aorta than in the control aorta (P = 0.026). Finally, in the atherosclerotic aorta, immunostaining indicated that the integrin signal came predominantly from macrophages and was correlated with the macrophage CD68 immunomarker (r = 0.73).

Conclusions

^99mTc-maraciclatide allows in vivo detection of inflamed atherosclerotic plaques in mice and may represent a non-invasive approach for identifying high-risk plaques in patients.

Evaluation of Known or Suspected Cardiac Sarcoidosis

Sarcoidosis is a multisystem disorder of unknown cause, and cardiac sarcoidosis affects at least 25% of patients and accounts for substantial mortality and morbidity from this disease. Cardiac sarcoidosis may present with heart failure, left ventricular systolic dysfunction, AV block, atrial or ventricular arrhythmias, and sudden cardiac death. Cardiac involvement can be challenging to detect and diagnose because of the focal nature of the disease, as well as the fact that clinical criteria have limited diagnostic accuracy. Nevertheless, the diagnosis of cardiac sarcoidosis can be enhanced by integrating both clinical and imaging findings. This article reviews the various roles that different imaging modalities provide in the evaluation and management of patients with known or suspected cardiac sarcoidosis.