Utility of high fat and low carbohydrate diet in suppressing myocardial FDG uptake

Diagnosis and Management of Cardiac Sarcoidosis: A Scientific Statement From the American Heart Association

Cardiac sarcoidosis is an infiltrative cardiomyopathy that results from granulomatous inflammation of the myocardium and may present with high-grade conduction disease, ventricular arrhythmias, and right or left ventricular dysfunction. Over the past several decades, the prevalence of cardiac sarcoidosis has increased. Definitive histological confirmation is often not possible, so clinicians frequently face uncertainty about the accuracy of diagnosis. Hence, the likelihood of cardiac sarcoidosis should be thought of as a continuum (definite, highly probable, probable, possible, low probability, unlikely) rather than in a binary fashion. Treatment should be initiated in individuals with clinical manifestations and active inflammation in a tiered approach, with corticosteroids as first-line treatment. The lack of randomized clinical trials in cardiac sarcoidosis has led to treatment decisions based on cohort studies and consensus opinions, with substantial variation observed across centers. This scientific statement is intended to guide clinical practice and to facilitate management conformity by providing a framework for the diagnosis and management of cardiac sarcoidosis.

Complete resolution of focal-on-diffuse myocardial activity pattern on FDG PET-CT by prolonging the dietary preparation protocol in cardiac sarcoidosis

Patient preparation is crucial for reliable interpretation of cardiac inflammation FDG PET. We share our experience of improved reporting confidence and propose a simple approach of prolonging preparation (from 24 to 48 hours) with the high-fat, no-carbohydrate, and protein-permitted diet followed by fasting in cardiac sarcoidosis in cases with diffuse or focal-on-diffuse myocardial FDG uptake.

Cardiac sarcoidosis: a comprehensive review of risk factors, pathogenesis, diagnosis, clinical manifestations, and treatment strategies

Cardiac Sarcoidosis (CS) is a deadly consequence of systemic sarcoidosis that inflames all three layers of the heart, especially the myocardium-clinical signs of CS range from asymptomatic disease to abrupt cardiac death. CS generally remains undiagnosed secondary to a lack of definitive diagnostic criteria, a high percentage of false negative results on endomyocardial biopsy, and ill-defining clinical manifestations of the disease. Consequently, there is a lack of evidence-based recommendations for CS, and the present diagnostic and therapeutic management depend on expert opinion. The aetiology, risk factors, clinical symptoms, diagnosis, and therapy of CS will be covered in this review. A particular emphasis will be placed on enhanced cardiovascular imaging and early identification of CS. We review the emerging evidence regarding the use of Electrocardiograms (ECGs), Magnetic Resonance Imaging (MRI), and Positron Emission Tomography (PET) imaging of the heart to identify and quantify the extent of myocardial inflammation, as well as to guide the use of immunotherapy and other treatment regimens, such as ablation therapy, device therapy, and heart transplantation, to improve patient outcomes.

Hot spot imaging in cardiovascular diseases: an information statement from SNMMI, ASNC, and EANM

This information statement from the Society of Nuclear Medicine and Molecular Imaging, American Society of Nuclear Cardiology, and European Association of Nuclear Medicine describes the performance, interpretation, and reporting of hot spot imaging in nuclear cardiology. The field of nuclear cardiology has historically focused on cold spot imaging for the interpretation of myocardial ischemia and infarction. Hot spot imaging has been an important part of nuclear medicine, particularly for oncology or infection indications, and the use of hot spot imaging in nuclear cardiology continues to expand. This document focuses on image acquisition and processing, methods of quantification, indications, protocols, and reporting of hot spot imaging. Indications discussed include myocardial viability, myocardial inflammation, device or valve infection, large vessel vasculitis, valve calcification and vulnerable plaques, and cardiac amyloidosis. This document contextualizes the foundations of image quantification and highlights reporting in each indication for the cardiac nuclear imager.

Myeloperoxidase PET Imaging Tracks Intracellular and Extracellular Treatment Changes in Experimental Myocardial Infarction

Myeloperoxidase (MPO) is a highly oxidative, pro-inflammatory enzyme involved in post-myocardial infarction (MI) injury and is a potential therapeutic target. While multiple MPO inhibitors have been developed, the lack of an imaging reporter to select appropriate patients and assess therapeutic efficacy has hampered clinical development. Thus, a translational imaging method to detect MPO activity non-invasively would help to better understand the role MPO plays in MI and facilitate novel therapy development and clinical validation. Interestingly, many MPO inhibitors affect both intracellular and extracellular MPO, but previous MPO imaging methods can only report extracellular MPO activity. In this study, we found that an MPO-specific PET imaging agent (18F-MAPP) can cross cell membranes to report intracellular MPO activity. We showed that 18F-MAPP can track the treatment effect of an MPO inhibitor (PF-2999) at different doses in experimental MI. The imaging results were corroborated by ex vivo autoradiography and gamma counting data. Furthermore, extracellular and intracellular MPO activity assays revealed that 18F-MAPP imaging can report the changes induced by PF-2999 on both intracellular and extracellular MPO activities. These findings support 18F-MAPP as a translational candidate to noninvasively report MPO activity and accelerate drug development against MPO and other related inflammatory targets.

The detection of infectious endocarditis may be enhanced by a repeat FDG-PET while maintaining patients on a ketogenic diet

BACKGROUND

This study aims to determine whether the suppression of myocardial FDG uptake and detection of infectious endocarditis (IE) may be enhanced when FDG-PET is repeated on the next day while maintaining patients on a ketogenic diet in the interim.

METHODS

Seventeen patients with definite IE underwent FDG-PET investigations both after a conventional metabolic preparation (> 12-hour fast after a low-carbohydrate evening meal) and a subsequent 12-hour extension of the low-carbohydrate diet followed by an additional > 12-hour fast.

RESULTS

Plasma biomarkers showed increased ketogenic metabolism between the two FDG-PET scans. A myocardial FDG uptake persisted on the 1st PET in 9 patients (53%) for whom myocardial FDG uptake decreased significantly on the 2nd PET (SUVmax: 6.05 ± 3.25 vs 4.32 ± 3.47, P = 0.021), resulting in an enhancement in the diagnostic confidence of IE in 6 cases. These enhancements were not documented in the 8 patients exhibiting a total suppression of myocardial FDG uptake on the 1st PET.

CONCLUSIONS

Better suppression of myocardial uptake and enhanced detection of IE may be achieved when an FDG-PET, showing an incomplete suppression of the myocardial FDG uptake, is repeated as soon as the next day, while maintaining patients on a ketogenic diet in the interim.

Various Aspects of Fasting on the Biodistribution of Radiopharmaceuticals

It is demonstrated that fasting can alter the biodistribution of radiopharmaceuticals in nuclear medicine. Various studies have highlighted that fasting is interpreted to be easy for physicians during PET study, fasting is one of the most important factors determining the usefulness of this protocol. It is well documented that fasting can suppress normal ¹⁸F-FDG PET uptake during nuclear cardiology. However, there is no consensus about the usefulness of fasting on radiopharmaceuticals, especially on ¹⁸F-FDG in PET imaging, but special attention should be paid to the setting of the fasting duration. Nevertheless, it does seem we still need extensive clinical studies in the future. The present study aims to review the various aspects of fasting, especially metabolic alteration on radiopharmaceutical biodistribution. In this study, we focused more on the effect of fasting on ¹⁸F-FDG biodistribution, which alters its imaging contrast in cardiology and cancer imaging. Therefore, shifting substrate metabolism from glucose to free fatty acids during fasting can be an alternative approach to suppress physiological myocardial uptake.

Nuclear Imaging in Pediatric Cardiology: Principles and Applications

Nuclear imaging plays a unique role within diagnostic imaging since it focuses on cellular and molecular processes. Using different radiotracers and detection techniques such as the single photon emission scintigraphy or the positron emission tomography, specific parameters can be assessed: myocardial perfusion and viability, pulmonary perfusion, ventricular function, flow and shunt quantification, and detection of inflammatory processes. In pediatric and congenital cardiology, nuclear imaging can add complementary information compared to other imaging modalities such as echocardiography or magnetic resonance imaging. In this state-of-the-art paper, we appraise the different techniques in pediatric nuclear imaging, evaluate their advantages and disadvantages, and discuss the current clinical applications.

OUP accepted manuscript

AIMS

The ketogenic diet (KD) is standard-of-care to achieve myocardial glucose suppression (MGS) for assessing inflammation using fluorine-18 fluorodeoxyglucose-positron emission tomography (FDG-PET). As KD protocols remain highly variable between centres (including estimation of nutrient intake by dietary logs for adequacy of dietary preparation), we aimed to assess the predictive utility of nutrient intake in achieving MGS.

METHODS AND RESULTS

Nineteen healthy participants underwent short-term KD, with FDG-PET performed after 1 and 3 days of KD (goal carbohydrate intake <20 g/day). Nutrient consumption was estimated from dietary logs using nutrition research software. The area under receiver operating characteristics (AUROC) of macronutrients (carbohydrate, fat, and protein intake) for predicting MGS was analysed. The association between 133 nutrients and 4 biomarkers [beta-hydroxybutyrate (BHB), non-esterified fatty acids, insulin, and glucagon] with myocardial glucose uptake was assessed using mixed effects regression with false discovery rate (FDR) correction. Median (25th-75th percentile) age was 29 (25-34) years, 47% were women, and 42% were non-white. Median (25th-75th percentile) carbohydrate intake (g) was 18.7 (13.1-30.7), 16.9 (10.4-28.7), and 21.1 (16.6-29.0) on Days 1-3. No macronutrient intake (carbohydrate, fat, or protein) predicted MGS (c-statistic 0.45, 0.53, 0.47, respectively). Of 133 nutrients and 4 biomarkers, only BHB was associated with myocardial glucose uptake after FDR correction (corrected P-value 0.003).

CONCLUSIONS

During highly supervised, short-term KD, approximately half of patients meet strict carbohydrate goals. Yet, in healthy volunteers, dietary review does not provide reassurance for adequacy of myocardial preparation since no clear thresholds for carbohydrate or fat intake reliably predict MGS.

PET Imaging in Cardiac Sarcoidosis: A Narrative Review with Focus on Novel PET Tracers

Sarcoidosis is a multi-system inflammatory disease characterized by the development of inflammation and noncaseating granulomas that can involve nearly every organ system, with a predilection for the pulmonary system. Cardiac involvement of sarcoidosis (CS) occurs in up to 70% of cases, and accounts for a significant share of sarcoid-related mortality. The clinical presentation of CS can range from absence of symptoms to conduction abnormalities, heart failure, arrhythmias, valvular disease, and sudden cardiac death. Given the significant morbidity and mortality associated with CS, timely diagnosis is important. Traditional imaging modalities and histologic evaluation by endomyocardial biopsy often provide a low diagnostic yield. Cardiac positron emission tomography (PET) has emerged as a leading advanced imaging modality for the diagnosis and management of CS. This review article will summarize several aspects of the current use of PET in CS, including indications for use, patient preparation, image acquisition and interpretation, diagnostic and prognostic performance, and evaluation of treatment response. Additionally, this review will discuss novel PET radiotracers currently under study or of potential interest in CS.

Best Practices for Imaging Cardiac Device-Related Infections and Endocarditis: A JACC: Cardiovascular Imaging Expert Panel Statement

The diagnosis of cardiac device infection and, more importantly, accurate localization of the infection site, such as defibrillator pocket, pacemaker lead, along the peripheral driveline or central portion of the left ventricular assist device, prosthetic valve ring abscesses, and perivalvular extensions, remain clinically challenging. Although transthoracic and transesophageal echocardiography are the first-line imaging tests in suspected endocarditis and for assessing hemodynamic complications, recent studies suggest that cardiac computed tomography (CT) or CT angiography and functional imaging with ¹⁸F-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) with CT (FDG PET/CT) may have an incremental role in technically limited or inconclusive cases on echocardiography. One of the key benefits of FDG PET/CT is in its detection of inflammatory cells early in the infection process, before morphological damages ensue. However, there are many unanswered questions in the literature. In this document, we provide consensus on best practices among the various imaging studies, which includes the detection of cardiac device infection, differentiation of infection from inflammation, image-guided patient management, and detailed recommendations on patient preparation, image acquisition, processing, interpretation, and standardized reporting.

18F-FDG-PET/CT in SARS-CoV-2 infection and its sequelae

In recent months, much of the scientific efforts have focused on research on SARSCoV-2 infection and its consequences in humans. Still, many aspects remain unknown. It is known that the damage caused by SARS-CoV-2 is multifactorial and that its extension goes beyond lung inflammation and the acute phase, with the appearance of numerous complications and sequelae. To date, knowledge about the usefulness of 18F-FDG-PET/CT in the acute phase has been limited to the incidental detection of SARS-CoV-2 unsuspected pneumonia. Recent studies have been appearing collecting the findings of 18F-FDG-PET/CT in long COVID-19 or persistent COVID-19 state as well as the alterations caused after mass vaccination of the population in the metabolic studies. This work aims to review the existing literature focusing on these three issues and to briefly present our own preliminary experience.

[18F-FDG-PET/CT in SARS-CoV-2 infection and its sequelae]

In recent months, much of the scientific efforts have focused on research on SARSCoV-2 infection and its consequences in humans. Still, many aspects remain unknown. It is known that the damage caused by SARS-CoV-2 is multifactorial and that its extension goes beyond lung inflammation and the acute phase, with the appearance of numerous complications and sequelae. To date, knowledge about the usefulness of 18F-FDG-PET/CT in the acute phase has been limited to the incidental detection of SARS-CoV-2 unsuspected pneumonia. Recent studies have been appearing collecting the findings of 18F-FDG- PET/CT in long COVID-19 or persistent COVID-19 state as well as the alterations caused after mass vaccination of the population in the metabolic studies. This work aims to review the existing literature focusing on these three issues and to briefly present our own preliminary experience.

Feasibility of somatostatin receptor-targeted imaging for detection of myocardial inflammation: A pilot study

BACKGROUND

Gallium-68 Dotatate binds preferentially to somatostatin receptor (sstr) subtype-2 (sstr-2) on inflammatory cells. We aimed at investigating the potential clinical use of sstr-targeted imaging for the detection of myocardial inflammation.

METHODS

Thirteen patients, with suspected cardiac sarcoidosis (CS) based on clinical history and myocardial uptake on recent fluorine-18 fluorodeoxyglucose (FDG) PET, were enrolled to undergo Dotatate PET after FDG-PET (median time 37 days [IQR 25-55]). Additionally, we investigated ex-vivo the immunohistochemistry expression of sstr-2 in 3 explanted sarcoid hearts.

RESULTS

All FDG scans showed cardiac uptake (focal/multifocal = 6, focal on diffuse/heterogeneous = 7), and 46% (n = 6) extra-cardiac uptake (mediastinal/hilar). In comparison, Dotatate scans showed definite abnormal cardiac uptake (focal/multifocal) in 4 patients, probably abnormal (heterogenous/patchy) in 3, and negative uptake in 6 cases. Similarly, 6 patients had increased mediastinal/hilar Dotatate uptake. Overall concordance of FDG and Dotatate uptake was 54% in the heart and 100% for thoracic nodal activity. Quantitatively, FDG maximum standardized uptake value was 5.0 times [3.8-7.1] higher in the heart, but only 2.25 times [1.7-3.0; P = .019] higher in thoracic nodes relative to Dotatate. Ex-vivo, sstr-2 immunostaining was weakly seen within well-formed granulomas in all 3 examined sarcoid heart specimens with no significant staining of background myocardium or normal myocardium.

CONCLUSION

Our preliminary data suggest that, compared to FDG imaging, somatostatin receptor-targeted imaging may be less sensitive for the detection of myocardial inflammation, but comparable for detecting extra-cardiac inflammation.

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.

Nuclear Imaging for the Assessment of Cardiotoxicity from Chemotherapeutic Agents in Oncologic Disease

PURPOSE OF REVIEW

In this review, we summarize the major known cardiac toxicities of common chemotherapeutic agents and the role of nuclear cardiac imaging for the surveillance and assessment of cancer therapeutics-related cardiac dysfunction in routine clinical practice.

RECENT FINDINGS

Cardiotoxicity from chemotherapy causes a significant mortality and limits potentially life-saving treatment in cancer patients. Close monitoring of cardiac function during chemotherapy is an accepted method for reducing these adverse effects especially in patients with cancer therapeutics-related cardiac dysfunction. Nuclear imaging is a sensitive, specific, and highly reproducible modality for assessment of cardiac function. Nuclear imaging techniques including equilibrium radio nucleotide angiography, myocardial perfusion imaging, and novel experimental molecular imaging are the various objective tools available in addition to conventional echocardiography and cardiac magnetic resonance imaging in the surveillance, assessment, and follow-up of cancer therapeutics-related cardiac dysfunction.

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.

Dynamic FDG PET Imaging to Probe for Cardiac Metabolic Remodeling in Adults Born Premature

Individuals born very premature have an increased cardiometabolic and heart failure risk. While the structural differences of the preterm heart are now well-described, metabolic insights into the physiologic mechanisms underpinning this risk are needed. Here, we used dynamic fluorodeoxyglucose (FDG) positron emission tomography/magnetic resonance imaging (PET-MRI) in young adults born term and preterm during normoxic (N = 28 preterm; 18 term) and hypoxic exposure (12% O2; N = 26 preterm; 17 term) to measure the myocardial metabolic rate of glucose (MMRglc) in young adults born term (N = 18) and preterm (N = 32), hypothesizing that young adults born preterm would have higher rates of MMRglc under normoxic conditions and a reduced ability to augment glucose metabolism under hypoxic conditions. MMRglc was calculated from the myocardial and blood pool time-activity curves by fitting the measured activities to the 3-compartment model of FDG kinetics. MMRglc was similar at rest between term and preterm subjects, and decreased during hypoxia exposure in both groups (p = 0.02 for MMRglc hypoxia effect). There were no differences observed between groups in the metabolic response to hypoxia, either globally (serum glucose and lactate measures) or within the myocardium. Thus, we did not find evidence of altered myocardial metabolism in the otherwise healthy preterm-born adult. However, whether subtle changes in myocardial metabolism may preceed or predict heart failure in this population remains to be determined.

Positron emission tomography in clinically suspected myocarditis - STREAM study design

AIM

Myocarditis is an inflammatory disease associated with increased glucose uptake. The hypothesis of this study assumes that 18F-2-fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography (FDG-PET/CT) may improve specificity and sensitivity in the diagnosis of myocarditis and referral for endomyocardial biopsy (EMB), adding additional information for post-discharge risk stratification. The aim of the study is to assess the diagnostic and prognostic feasibility of FDG-PET/CT in comparison to cardiac magnetic resonance (CMR) (alone or in combination) in patients with clinically suspected myocarditis undergoing EMB.

METHODS

Fifty hospitalized patients with clinically suspected myocarditis who meet the inclusion/exclusion criteria will be enrolled in a prospective, observational, multicentre, cohort study (NCT04085718). The primary endpoint is the sensitivity and specificity of FDG-PET/CT imaging in the diagnosis of myocarditis. The main secondary endpoints include correlation of FDG-PET/CT imaging with CMR, echocardiography, and EMB results. The patients will undergo the following evaluations: clinical examination, blood tests (including biomarkers of fibrosis and anti-heart autoantibodies (AHA)), ECG, 24 h Holter ECG, echocardiography, CMR, as well as resting single photon emission computed tomography (SPECT) to assess possible myocardial perfusion defects, cardiac FDG-PET/CT and right ventricular EMB. After 6-months a follow-up visit will be performed (including 24 h Holter ECG, echocardiography and CMR). Investigators evaluating individual studies (CMR, SPECT, FDG-PET/CT and EMB) are to be blinded to the other tests' results.

CONCLUSION

We believe that FDG-PET/CT alone or in combination with CMR may be a useful tool for improving diagnostic accuracy in patients with clinically suspected myocarditis.

Mediastinal Masses: 18F-FDG-PET/CT Features Based on the International Thymic Malignancy Interest Group Classification

Imaging plays a key role in the management of mediastinal masses. In an effort to standardize the analysis of the mediastinum, the International Thymic Malignancy Interest Group (ITMIG) has proposed a three compartments-based diagnostic classification, intended for clinicians and radiologists. Several articles have documented its usefulness to guide the diagnosis using cross-sectional imaging. Similarly, fluorine-18-radiolabeled fluorodeoxyglucose positron emission tomography combined to computed tomography (¹⁸F-FDG-PET/CT) can be useful in this setting, either as a first-line diagnostic technique, or in addition to cross-sectional imaging. In this article, which is thought as an aid for nuclear medicine physicians and radiologists, we aim to present, based on the ITMIG classification, the main mediastinal pathologies that can be observed with ¹⁸F-FDG-PET/CT, and the additional diagnostic value that can be expected from this technique. For this purpose, we segmented the mediastinum according to the ITMIG classification, and reviewed the available literature for each of the corresponding organs and/or disease. Given the importance of the clinical context for the interpretation of PET imaging, we presented each of the diseases according to: (1) their suggestive clinical context; (2) the suggestive features on nonenhanced CT (which is the standard in PET imaging); and (3) the typical ¹⁸F-FDG characteristics. The purpose of this article is to depict the main features of the most common mediastinal diseases that can be encountered with ¹⁸F-FDG-PET/CT, and to highlight its diagnostic value in this setting, alone or in combination with other imaging modalities.

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.

The value of 18F-FDG PET/CT for the diagnosis of device-related infections in patients with a left ventricular assist device: a systematic review and meta-analysis

Background

Left ventricular assist devices (LVADs) are increasingly used for the treatment of advanced heart failure. LVADs improve quality of life and decrease mortality, but the driveline carries substantial risk for major infections. These device-related LVAD and driveline infections are difficult to diagnose with conventional imaging. We reviewed and analysed the current literature on the additive value of ¹⁸F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDG-PET/CT) imaging for the diagnosis of LVAD-related infections.”

Materials/methods

We performed a systematic literature review using several databases from their inception until the 31st of December, 2019. Studies investigating the diagnostic performance of FDG-PET/CT in patients with suspected LVAD infection were retrieved. After a bias risk assessment using QUADAS-2, a study-aggregate meta-analysis was performed on a per examination-based analysis.

Results

A total of 10 studies were included in the systematic review, eight of which were also eligible for study-aggregate meta-analysis. For the meta-analysis, a total of 256 FDG-PET/CT scans, examining pump/pocket and/or driveline infection, were acquired in 230 patients. Pooled sensitivity of FDG-PET/CT was 0.95 (95% confidence interval (CI) 0.89–0.97) and pooled specificity was 0.91 (95% CI 0.54–0.99) for the diagnosis of device-related infection. For pump/pocket infection, sensitivity and specificity of FDG-PET/CT were 0.97 (95%CI 0.69–1.00) and 0.93 (95%CI 0.64–0.99), respectively. For driveline infection, sensitivity and specificity were 0.96 (95%CI 0.88–0.99) and 0.99 (95%CI 0.13–1.00) respectively. Significant heterogeneity existed across studies for specificity, mostly caused by differences in scan procedures. Predefined criteria for suspicion of LVAD and/or driveline infection were lacking in all included studies.

Conclusions

FDG-PET/CT is a valuable tool for assessment of device-related infection in LVAD patients, with high sensitivity and high, albeit variable, specificity. Standardization of FDG-PET/CT procedures and criteria for suspected device-related LVAD infections are needed for consistent reporting of FDG-PET/CT scans.

Electronic supplementary material

The online version of this article (10.1007/s00259-020-04930-8) contains supplementary material, which is available to authorized users.

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.

A 1-week extension of a ketogenic diet provides a further decrease in myocardial 18F-FDG uptake and a high detectability of myocarditis with FDG-PET

BACKGROUND

Short periods of fasting and/or low-carbohydrate diet have been proven beneficial for decreasing the myocardial uptake of 18F-fluorodeoxyglucose (18F-FDG) and enhancing the detection of inflammatory heart diseases by 18F-FDG positron emission tomography (PET). This study aimed at determining whether this benefit is increased when a low-carbohydrate ketogenic diet is prolonged up to 7 days.

METHODS

Wistar rats underwent serial 18F-FDG-PET imaging after an 18-hour fasting period and after 2, 4 and 7 days of a ketogenic diet (3% carbohydrate) and they were compared to rats submitted to the same protocol but with normal diet (44% carbohydrate). The 18F-FDG-PET/ketogenic protocol was also applied in rats with immune myocarditis (injection of porcine cardiac myosin).

RESULTS

The 7-day ketogenic diet was associated with (1) a sustained increase in circulating ketone bodies at an equivalent level to that reached after 18-hour fasting, (2) a gradual decrease in 18F-FDG uptake within normal myocardium reaching a lower level compared to fasting at the 7th day (myocardium-to-blood ratios: 1.68 ± 1.02 vs 3.25 ± 1.40, P < .05) and (3) a high 18F-FDG-PET detectability of myocarditis areas.

CONCLUSION

One-week extension of a ketogenic diet provides a further decrease in the 18F-FDG uptake of normal myocardium and a high detectability of inflammatory areas.

Infection and Inflammation Imaging: Beyond FDG

This review discusses nuclear imaging of inflammation using molecular probes beyond fluoro-d-glucose, is structured by cellular targets, and focuses on those tracers that have been successfully applied clinically.

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.

Molecular Imaging of Myocardial Inflammation With Positron Emission Tomography Post-Ischemia: A Determinant of Subsequent Remodeling or Recovery

Inflammation after myocardial ischemia influences ventricular remodeling and repair and has emerged as a therapeutic target. Conventional diagnostic measurements address systemic inflammation but cannot quantify local tissue changes. Molecular imaging facilitates noninvasive assessment of leukocyte infiltration into damaged myocardium. Preliminary experience with ¹⁸F-labeled fluorodeoxyglucose ([¹⁸F]FDG) demonstrates localized inflammatory cell signal within the infarct territory as an independent predictor of subsequent ventricular dysfunction. Novel targeted radiotracers may provide additional insight into the enrichment of specific leukocyte populations. Challenges to wider implementation of inflammation imaging after myocardial infarction include accurate and reproducible quantification, prognostic value, and capacity to monitor inflammation response to novel treatment. This review describes myocardial inflammation following ischemia as a molecular imaging target and evaluates established and emerging radiotracers for this application. Furthermore, the potential role of inflammation imaging to provide prognostic information, support novel drug and therapeutic research, and assess biological response to cardiac disease is discussed.

Effects of a Ketogenic Diet on [18F]FDG-PET Imaging in a Mouse Model of Lung Cancer

PURPOSE

Myocardial uptake can hamper visualization of lung tumors, atherosclerotic plaques, and inflammatory diseases in 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) studies because it leads to spillover in adjacent structures. Several preparatory pre-imaging protocols (including dietary restrictions and drugs) have been proposed to decrease physiological [¹⁸F]FDG uptake by the heart, although their effect on tumor glucose metabolism remains largely unknown. The objective of this study was to assess the effects of a ketogenic diet (as an alternative protocol to fasting) on tumor glucose metabolism assessed by [¹⁸F]FDG positron emission tomography (PET) in a mouse model of lung cancer.

PROCEDURES

PET scans were performed 60 min after injection of 18.5 MBq of [¹⁸F]FDG. PET data were collected for 45 min, and an x-ray computed tomograph (CT) image was acquired after the PET scan. A PET/CT study was obtained for each mouse after fasting and after the ketogenic diet. Quantitative data were obtained from regions of interest in the left ventricular myocardium and lung tumor.

RESULTS

Three days on a ketogenic diet decreased mean standard uptake value (SUVmean) in the myocardium (SUVmean 0.95 ± 0.36) more than one night of fasting (SUVmean 1.64 ± 0.93). Tumor uptake did not change under either dietary condition.

CONCLUSIONS

These results show that 3 days on high-fat diets prior to [¹⁸F]FDG-PET imaging does not change tumor glucose metabolism compared with one night of fasting, although high-fat diets suppress myocardial [¹⁸F]FDG uptake better than fasting.

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.

FDG PET-CT findings of extra-thoracic sarcoid are associated with cardiac sarcoid: A rationale for using FGD PET-CT for cardiac sarcoid evaluation

PURPOSE

This retrospective study investigates the relationship between cardiac and extra-thoracic sarcoid findings on FDG PET-CT using a 72-hour pretest high-fat, high-protein, and very low-carbohydrate (HFHPVLC) diet.

PATIENTS AND METHODS

A total of 196 consecutive FDG PET-CT scans with 72-hour HFHPVLC diet preparation were performed between December 2014 and December 2015 in known sarcoid patients. Of these scans, 5 were excluded for non-adherence to diet preparation or underlying cancer. Cardiac and extra-thoracic sarcoid lesions were categorized and measured for radiotracer uptake.

RESULTS

A total of 188 patients had 191 eligible FDG PET/CT scans (3 follow-up scans), of which there were 20 (10%) positive, 6 indeterminate (3%), and 165 (86%) negative for CS. Among the 20 scans positive for CS, 8 (40%) had findings of both cardiac and extra-thoracic sarcoid.

CONCLUSION

Our study shows that 40% of CS patients also have FDG PET-CT findings of extra-thoracic sarcoid. This makes an intriguing case for FDG PET-CT use with pretest diet prep over cardiac MRI (CMR) for cardiac sarcoid evaluation, given that CMR is likely to overlook these extra-thoracic sites of disease.

PET/CT Evaluation of Cardiac Sarcoidosis

The increasing implementation of advanced cardiovascular imaging in the form of cardiac PET/CT has had a significant impact on the management of cardiac sarcoidosis, which continues to evolve. This review summarizes the role of PET/CT imaging in sarcoidosis with a specific focus on (1) indications, (2) patient preparation, (3) test performance, (4) study interpretation, (5) clinical relevance of findings, (6) comparison to alternative imaging modalities, and finally (7) introduction of areas of anticipated development and research.

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.

Effect of prolonged fasting and low molecular weight heparin or warfarin therapies on 2-deoxy-2-[18F]-fluoro-D-glucose PET cardiac uptake

BACKGROUND

Whether anticoagulants other than unfractionated heparin are able to suppress cardiac PET uptake of 2-deoxy-2-[18F]-fluoro-D-glucose (18F-FDG) is unknown.

METHODS

One-hundred-seventy-four patients without history and clinical evidence of cardiac dysfunction and/or coronary heart disease underwent a 18F-FDG PET/CT study. All patients were studied with a >12-hours fasting and divided into 2 groups: group-1 without anticoagulant therapy (n:75); group-2 patients on low molecular weight heparin (n:60) or warfarin therapy (n:39). Cardiac 18F-FDG uptake was estimated qualitatively using a 4-point scale and semiquantitatively as total LV glycolysis (LVG) and metabolic volume (MV), drawing isocontour volume of interest (VOI) including the whole LV.

RESULTS

Qualitatively, LV 18-FDG uptake was scored 0 or 1, indicating a good suppression, in 10/75 (13%) patients of group-1 and 77/99 (78%) of group-2 (p < .001). Semiquantitatively, patients of group-1 showed higher values of 18-FDG uptake than patients of group-2, assessed as LVG (802,649 ± 468,442 vs 198,989 ± 261,439, p < .0001) or MV (219 ± 77 vs 57 ± 48 cm3, p < .0001). Subanalysis for anticoagulant drugs showed similar results.

CONCLUSIONS

Prolonged fasting combined to anticoagulants other than unfractionated heparin is able to minimize glucose cardiac metabolism. Our data confirm previous observation on the possibility to influence the metabolic pattern of the heart before the PET scan and broadens the spectrum of pharmacological options.

Cardiovascular magnetic resonance imaging and clinical performance of somatostatin receptor positron emission tomography in cardiac sarcoidosis

AIMS

Cardiac affection constitutes a major limiting condition in systemic sarcoidosis. The primary objective of this study was to investigate the persistence rate of cardiac sarcoid involvement by cardiovascular magnetic resonance (CMR) imaging in patients diagnosed with cardiac sarcoidosis (CS). Moreover, we examined the additional insights into myocardial damage's characteristics gained by somatostatin receptor scintigraphy.

METHODS AND RESULTS

In a pilot study, we had previously identified cardiac involvement-diagnosed by CMR imaging-to be present in 29 of 188 patients (15.4%) with histologically proven, extra-CS. Out of these initial 29 CS-positive patients, 27 patients (49.9 ± 11.8 years, 59.3% male) were presently re-examined and underwent a second CMR study and complementary standard clinical testing. Somatostatin receptor scintigraphy using the ligand 68 Ga-DOTATOC was additionally performed when clinically indicated (17 patients). Within a median follow-up period of 2.6 years, none of the initial 29 patients deceased or experienced aborted sudden cardiac death. However, two patients developed third-degree atrioventricular block that required device therapy. Among the 27 re-examined CS patients, pathological CMR findings persisted in 14 of 27 patients (51.9%). CS remission was primarily due to a resolution of acute inflammatory processes. 68 Ga-DOTATOC positron emission tomography/computed tomography (PET/CT) identified one patient with regions of raised tracer uptake that concorded with acute inflammatory changes, as assessed by CMR; this patient received no immunosuppressive medication at the time of PET/CT execution.

CONCLUSIONS

Within follow-up, CS persisted in barely half the patients, and the patients were not afflicted with cardiac death. Additional 68 Ga-DOTATOC PET/CT allowed for visualization of acute myocardial inflammation.

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.

Cardiac 18F-FDG PET/CT procedure for the diagnosis of prosthetic endocarditis and intracardiac devices

Infective endocarditis (IE) is a serious condition with a poor prognosis, its mortality unchanged significantly despite diagnostic and therapeutic advances in the last 30years. The diagnostic ability of the modified Duke criteria in prosthetic endocarditis and/or devices does not exceed 50%, so new tools are necessary for the diagnosis of this entity in this context. The ¹⁸F-FDG PET/CTA combines a highly sensitive technique to detect inflammatory-infectious activity with a technique with high anatomical resolution to assess the structural lesions associated with endocarditis. With a diagnostic sensitivity between 91-97%, this hybrid technique has become a useful diagnostic tool for patients with prosthetic valves or devices and suspicion of IE, becoming a major criterion in the diagnostic algorithm of current guidelines. This excellent diagnostic ability depends directly on the quality of the obtained exploration and the knowledge at the time of interpreting the images. The aim of this review is to describe and standardize the methodology of cardiac ¹⁸F-FDG PET/CTA in the diagnosis of endocarditis in prosthetic valves and intracardiac devices, with special emphasis on the particularities of the patient's preparation, the PET and CT acquisition procedures, and the subsequent imaging postprocessing and interpretation.