The Potential of FDG PET/CT for Early Diagnosis of Cardiac Device and Prosthetic Valve Infection Before Morphologic Damages Ensue

Hybrid Imaging: Calcium Score and Myocardial Perfusion Imaging

Coronary heart disease (CHD) remains the top cause of death due to cardiovascular conditions worldwide, with someone suffering a myocardial infarction every 40 seconds. This highlights the importance of non-invasive imaging technologies like myocardial perfusion imaging (MPI), which are crucial for detecting coronary artery disease (CAD) early, even before symptoms appear. However, the reliance solely on MPI has shifted due to its limitations in definitively ruling out atherosclerosis, leading to the adoption of hybrid imaging techniques. Hybrid imaging combines computed tomography (CT) with MPI techniques such as positron emission tomography (PET) and single photon emission computed tomography (SPECT). This integration, often within a single gantry system, enhances the diagnostic accuracy by allowing for attenuation correction (AC), acquisition of the coronary artery calcium score (CACS), and more precise tracing of radiotracer uptake. The built-in CT in modern MPI systems assists in these functions, which is essential for better diagnosis and risk assessment in patients. The addition of CACS to MPI, a method involving the assessment of calcified plaque in coronary arteries, notably enhances diagnostic and prognostic capabilities. CACS helps in identifying atherosclerosis and predicting potential cardiac events, facilitating personalized risk management and the initiation of tailored interventions like statins and aspirin. Such comprehensive imaging strategies not only improve the accuracy of detecting CAD but also help in stratifying patient risk more effectively. In this paper, we discuss how the incorporation of CAC into MPI protocols enhances the diagnostic sensitivity for detecting obstructive CAD, as evidenced by several studies where the addition of CAC to MPI has led to improved outcomes in diagnosing CAD. Moreover, CAC has been shown to unmask silent coronary atherosclerosis in patients with normal MPI results, highlighting its incremental diagnostic value. We will discuss the evolving role of hybrid imaging in guiding therapeutic decisions, particularly the use of statins for cardiovascular prevention. The integration of CAC assessment with MPI not only aids in the early detection and management of CAD but also optimizes therapeutic strategies, enhancing patient care through a more accurate and personalized approach. Such advancements underscore the need for further research to fully establish the benefits of combining CAC with MPI in the clinical assessment of cardiovascular risk.

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.

Molecular Imaging of Valvular Diseases and Cardiac Device Infection

The use of positron emission tomography imaging with 18F-fluorodeoxyglucose in the diagnostic workup of patients with suspected prosthetic valve endocarditis and cardiac device infection (implantable electronic device and left ventricular assist device) is gaining momentum in clinical practice. However, in the absence of prospective randomized trials, guideline recommendations about 18F-fluorodeoxyglucose positron emission tomography in this setting are currently largely based on expert opinion. Measurement of aortic valve microcalcification occurring as a healing response to valvular inflammation using 18F-sodium fluoride positron emission tomography represents another promising clinical approach, which is associated with both the risk of native valve stenosis progression and bioprosthetic valve degeneration in research trials. In this review, we consider the role of molecular imaging in cardiac valvular diseases, including aortic stenosis and valvular endocarditis, as well as cardiac device infections.

Nuclear Methods for Immune Cell Imaging: Bridging Molecular Imaging and Individualized Medicine

Inflammation is a key mechanistic contributor to the progression of cardiovascular disease, from atherosclerosis through ischemic injury and overt heart failure. Recent evidence has identified specific roles of immune cell subpopulations in cardiac pathogenesis that diverges between individual patients. Nuclear imaging approaches facilitate noninvasive and serial quantification of inflammation severity, offering the opportunity to predict eventual outcome, stratify patient risk, and guide novel targeted molecular therapies against specific leukocyte subpopulations. Here, we will discuss the established and emerging nuclear imaging methods to label and track exogenous and endogenous immune cells, with a particular focus on clinical situations in which targeted molecular inflammation imaging would be advantageous. The expanding options for imaging inflammation provide the foundation to bridge between molecular imaging and individual therapy.

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.

Infection of cardiac prosthetic valves and implantable electronic devices: early diagnosis and treatment

There has been a recent rise in the use of implantable cardiac devices, mostly valves but also electronic ones, such as pacemakers, and implantable defibrillators. The increasing use of these devices had as a consequence the raised incidence of endocarditis, an infrequent but morbid complication of these procedures. Thus, early diagnosis of the implantable cardiac devices related infection and endocarditis became pivotal for appropriate management. For diagnostic purposes, the modified Duke criteria are widely used, which are based on clinical and imaging findings, in addition to serological analyses and blood cultures. 18F-fluoro-2-deoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) is a recently employed method in order to improve the early diagnosis of endocarditis as well as infection of the implantable device. It is likely, that combining the modified Duke criteria with the FDG PET/CT, will increase the sensitivity and specificity of diagnosis and will guide the treating physician to an early and appropriate management.

Utility of positron emission tomography imaging in the diagnosis of chronic Q fever: A Systematic Review

Chronic Q fever is a diagnostic challenge. Diagnosis relies on serology and/or the detection of DNA from blood or tissue samples. PET-CT identifies tissues with increased glucose metabolism, thus identifying foci of inflammation. Our aim was to review the existing literature on the use of PET-CT to help diagnose chronic Q fever. A literature search was conducted in PubMed and Google Scholar to ascertain publications that included the terms 'Positron Emission Tomography' and 'PET CT' in combination with subheadings 'chronic Q fever' and 'Coxiella burnetii' within the search. To broaden our search retrieval, we used the terms 'chronic Q fever' and 'PET-CT'. Published literature up to 16^th April 2020 was included. 274 articles were initially identified. Post-exclusion criteria, 46 articles were included. Amongst case reports and series, the most frequent focus of infection was vascular, followed by musculoskeletal then cardiac. 79.5% of patients had a focus detected with 55.3% of these having proven infected prosthetic devices. Amongst the retrospective and prospective studies, a total of 394 positive sites of foci were identified with 186 negative cases. Some had follow-up scans (53), with 75.5% showing improvement or resolution. Average timeframe for documented radiological resolution post-initiating treatment was 8.86 months. PET-CT is a useful tool in the management of chronic Q fever. Knowledge of a precise focus enables for directed surgical management helping reduce microbial burden, preventing future complications. Radiological resolution of infection can give clinicians reassurance on whether antimicrobial therapy can be ceased earlier, potentially limiting side effects.

[18F-fluorodeoxyglucose PET/CT in the diagnosis of vascular graft infection]

OBJECTIVE

To investigate diagnostic role of 18F-fluorodeoxyglucose PET/CT in patients with suspected vascular graft (VG) infection.

MATERIAL AND METHODS

A prospective analysis included data of 30 PET/CT examinations for suspected infection of aortic VG (n=27) and bypass grafts (n=3) after surgical treatment (median 48 months). In 77% (23/30) of cases, the diagnosis was initially «possible» (n=11) or «rejected» (n=12) in accordance with common diagnostic criteria. All PET/CT results were verified by clinical, laboratory and intraoperative («=20) data. VG infection was confirmed in 18 patients and ruled out in 12 cases.

RESULTS

PET/CT confirmed VG infection in 94% (17/18) and excluded in 50% (6/12) of cases. False PET/CT results were obtained in 23% (7/30) cases: false positive in 6 cases and false negative in 1 case. Thus, sensitivity, specificity and diagnostic accuracy of PET/CT were 94%, 50% and 77%, respectively; positive and negative predictive value - 74% and 86%. PET/CT results allowed correct reclassifying 33% (10/30) of cases. VG infection was confirmed in 73% (8/11) of patients with initially «possible» diagnosis and excluded in 17% (2/12) of patients with initially «rejected» infection. Moreover, whole body PET/CT revealed unknown inflammation foci outside VG in 73% (22/30) of cases. These data were applied to correct treatment approach in 80% (24/30) of cases.

CONCLUSION

Our results showed high efficacy of 18F-fluorodeoxyglucose PET/CT in the diagnosis of VG infection. Despite low specificity, this technique has high sensitivity and accuracy that allowed reclassifying 33% of cases.

Infective endocarditis in patients with aortic grafts

BACKGROUND

Infective endocarditis (IE) in patients with a valve-tube ascending aortic graft (AAG) is a rare entity with a challenging diagnosis and treatment. This study describes the clinical features, diagnosis and outcome of these patients.

METHODS

Between 1996 and 2019, 1654 episodes of IE were recruited in 3 centres, of which 37 patients (2.2%) had prosthetic aortic valve and AAG-IE (21 composite valve graft, 16 supracoronary graft) and conformed our study group.

RESULTS

Patients with aortic grafts were predominantly male (91.9%) and the mean age was 67.7 years. Staphylococci were the most frequently isolated microorganisms (32%). Viridans group streptococci were only isolated in patients with composite valve graft. TEE was positive in 89.2%. PET/CT was positive in all 15 patients in whom it was performed. Surgical treatment was performed in 62.2% of patients. In-hospital mortality was 16.2%. Heart failure and the type of infected graft (supracoronary aortic graft) were associated with mortality. Mortality among operated patients was 21.7%. Interestingly, 14 patients received antibiotic therapy alone, and only one died. Mortality was lower among patients with a composite valve graft compared to those with a supracoronary graft (4.8% vs 31.3%; p = 0.03).

CONCLUSIONS

In patients with AAG and prosthetic aortic valve IE, mortality is not higher than in other patients with prosthetic IE. Multimodality imaging plays an important role in the diagnosis and management of these patients. Heart failure and the type of surgery were risk factors associated with in-hospital mortality. Although surgical treatment is usually recommended, a conservative management might be a valid alternative treatment in selected patients.

State of the art of 18F-FDG PET/CT application in inflammation and infection: a guide for image acquisition and interpretation

AIM

The diagnosis, severity and extent of a sterile inflammation or a septic infection could be challenging since there is not one single test able to achieve an accurate diagnosis. The clinical use of 18F-fluorodeoxyglucose ([¹⁸F]FDG) positron emission tomography/computed tomography (PET/CT) imaging in the assessment of inflammation and infection is increasing worldwide. The purpose of this paper is to achieve an Italian consensus document on [¹⁸F]FDG PET/CT or PET/MRI in inflammatory and infectious diseases, such as osteomyelitis (OM), prosthetic joint infections (PJI), infective endocarditis (IE), prosthetic valve endocarditis (PVE), cardiac implantable electronic device infections (CIEDI), systemic and cardiac sarcoidosis (SS/CS), diabetic foot (DF), fungal infections (FI), tuberculosis (TBC), fever and inflammation of unknown origin (FUO/IUO), pediatric infections (PI), inflammatory bowel diseases (IBD), spine infections (SI), vascular graft infections (VGI), large vessel vasculitis (LVV), retroperitoneal fibrosis (RF) and COVID-19 infections.

METHODS

In September 2020, the inflammatory and infectious diseases focus group (IIFG) of the Italian Association of Nuclear Medicine (AIMN) proposed to realize a procedural paper about the clinical applications of [¹⁸F]FDG PET/CT or PET/MRI in inflammatory and infectious diseases. The project was carried out thanks to the collaboration of 13 Italian nuclear medicine centers, with a consolidate experience in this field. With the endorsement of AIMN, IIFG contacted each center, and the pediatric diseases focus group (PDFC). IIFG provided for each team involved, a draft with essential information regarding the execution of [¹⁸F]FDG PET/CT or PET/MRI scan (i.e., indications, patient preparation, standard or specific acquisition modalities, interpretation criteria, reporting methods, pitfalls and artifacts), by limiting the literature research to the last 20 years. Moreover, some clinical cases were required from each center, to underline the teaching points. Time for the collection of each report was from October to December 2020.

RESULTS

Overall, we summarized 291 scientific papers and guidelines published between 1998 and 2021. Papers were divided in several sub-topics and summarized in the following paragraphs: clinical indications, image interpretation criteria, future perspectivess and new trends (for each single disease), while patient preparation, image acquisition, possible pitfalls and reporting modalities were described afterwards. Moreover, a specific section was dedicated to pediatric and PET/MRI indications. A collection of images was described for each indication.

CONCLUSIONS

Currently, [¹⁸F]FDG PET/CT in oncology is globally accepted and standardized in main diagnostic algorithms for neoplasms. In recent years, the ever-closer collaboration among different European associations has tried to overcome the absence of a standardization also in the field of inflammation and infections. The collaboration of several nuclear medicine centers with a long experience in this field, as well as among different AIMN focus groups represents a further attempt in this direction. We hope that this document will be the basis for a "common nuclear physicians' language" throughout all the country.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40336-021-00445-w.

Diagnosis and Image-guided Therapy of Cardiac Left Ventricular Assist Device Infections

Due to limited availability of donor hearts, more and more end stage heart failure patients are dependent on left ventricular assist device (LVAD) as their destination therapy rather than the original intended use as a bridge for heart transplantation. While LVADs improve life expectancy in these patients, infection emerges as one of the major adverse events. Early and accurate localization of LVAD infection is critical, as it can significantly influence clinical management decisions and ultimately impact patient outcome. Although the International Society of Heart and Lung Transplantation has defined 3 categories for LVAD infection: (1) LVAD-specific infection, (2) LVAD-related infection, and (3) non-LVAD infection, there is still lack of standardized criteria for diagnosing these 3 types of LVAD infections. Morphologically based imaging tools such as transesophageal echocardiogram and cardiac computed tomography (CT) or CT angiogram have limited roles in diagnosing LVAD infections due to their nonspecific findings, often affected by significant streaking and beam hardening artifacts from the metal device. In contrast, ¹⁸F-fluorodeoxyglucose (FDG) Positron Emission Tomography (PET)/CT has repeatedly shown a high sensitivity and specificity for LVAD infection diagnosis, albeit in small number of subjects. Beyond its accuracy for detecting infection, FDG PET/CT can predict clinical outcome based on the location of LVAD infection. As a functional imaging tool, FDG PET/CT can demonstrate the extent and severity of LVAD infection, as well as infectious embolism and potential extra-cardiac source of infection, which are all critical for providing optimal patient care, justifying its judicious and precise use in the workup of LVAD infection.

Detection of Native and Prosthetic Valve Endocarditis: Incremental Attributes of Functional FDG PET/CT over Morphologic Imaging

PURPOSE OF REVIEW

The clinical and incremental value of functional imaging with ¹⁸F-fluorodeoxyglucose-positron emission tomography/computed tomography (FDG PET/CT) for the diagnosis and management of patients with suspected native and prosthetic valve infective endocarditis (IE).

RECENT FINDINGS

The diagnosis of IE is challenging because of the highly variable clinical presentations, especially in the case of prosthetic valve endocarditis (PVE). FDG PET/CT has been shown to play an important role for the diagnosis of PVE as a major Duke criterion. Whether FDG PET/CT could play a similar role in patients with suspected native valve endocarditis (NVE) is less well established. It is increasingly recognized that IE is a multisystem disorder, and identification of extra-cardiac manifestations on whole-body FDG PET/CT impacts management and prognosis of patients with IE. Finally, FDG PET/CT provides incremental prognostic value over other clinical and para-clinical parameters, enabling prediction of in-hospital mortality, IE recurrence, hospitalization, and new onset heart failure and embolic events. FDG PET/CT plays a key role in the investigation of patients with suspected IE, enabling detection of valvular infection and extra-cardiac manifestations of the infection which has important prognostic implications.

Comparison Between ESC and Duke Criteria for the Diagnosis of Prosthetic Valve Infective Endocarditis

OBJECTIVES

The primary objective was to assess the value of the European Society of Cardiology (ESC) criteria, including ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG-PET/CT) in prosthetic valve infective endocarditis (PVE). Secondary objectives were: 1) to assess the reproducibility of ¹⁸F-FDG-PET/CT; 2) to compare its diagnostic value with that of echocardiography; and 3) to assess the diagnostic value of the presence of a diffuse splenic uptake BACKGROUND: ¹⁸F-FDG PET/CT has been added as a major criterion in the ESC 2015 infective endocarditis (IE) guidelines, but the benefit of the ESC criteria has not been prospectively compared with the conventional Duke criteria.

METHODS

Between 2014 and 2017, 175 patients with suspected PVE were prospectively included in 3 French centers. After exclusion of patients with uninterpretable ¹⁸F-FDG PET/CT, 115 patients were evaluated, including 91 definite and 24 rejected IE, as defined by an expert consensus.

RESULTS

Cardiac uptake by ¹⁸F-FDG PET/CT was observed in 67 of 91 patients with definite PVE and 6 with rejected IE (sensitivity 73.6% [95% confidence interval (CI): 63.3% to 82.3%], specificity 75% [95% CI: 53.3% to 90.2%]). The ESC 2015 classification increased the sensitivity of Duke criteria from 57.1% (95% CI: 46.3% to 67.5%) to 83.5% (95% CI: 74.3% to 90.5%) (p < 0.001), but decreased its specificity from 95.8% (95% CI: 78.9% to 99.9%) to 70.8% (95% CI: 48.9% to 87.4%). Intraobserver reproducibility of ¹⁸F-FDG PET/CT was good (kappa = 0.84) but interobserver reproducibility was less satisfactory (kappa = 0.63). A diffuse splenic uptake was observed in 24 (20.3%) patients, including 23 (25.3%) of definite PVE, and only 1 (4.2%) rejected PVE (p = 0.024).

CONCLUSIONS

¹⁸F-FDG PET/CT is a useful diagnostic tool in suspected PVE, and explains the greater sensitivity of ESC criteria than Duke criteria. However, ¹⁸F-FDG PET/CT also presents with important limitations concerning its feasibility, specificity, and reproducibility. Our study describes for the first time a new endocarditis criterion, that is, the presence of a diffuse splenic uptake on ¹⁸F-FDG PET/CT.

Diagnostic imaging in infective endocarditis: a contemporary perspective

INTRODUCTION

Infective endocarditis (IE) remains a diagnostic challenge. Prompt diagnosis is essential for accurate risk stratification and appropriate therapeutic decisions and surgical management. In recent years, the use of multimodal imaging has had a transformative effect on the diagnostic approach of IE in selected patients.

AREAS COVERED

This review assesses published literature on different imaging modalities for the diagnosis of IE published between 1 January 2009 and 1 February 2020. We illustrate the diagnostic approach to IE with three clinical cases.

EXPERT OPINION

Novel approaches to imaging for cardiac and extracardiac complications improve and individualize diagnosis, management, and prognosis in patients with suspected IE. The use of multimodal imaging should be guided by a multidisciplinary group of medical providers that includes infectious disease specialists, radiologists, cardiologists, and cardiothoracic surgeons.

Methicillin-Resistant Staphylococcus aureus Prosthetic Valve Endocarditis: Pathophysiology, Epidemiology, Clinical Presentation, Diagnosis, and Management

Staphylococcus aureus prosthetic valve endocarditis (PVE) remains among the most morbid bacterial infections, with mortality estimates ranging from 40% to 80%. The proportion of PVE cases due to methicillin-resistant Staphylococcus aureus (MRSA) has grown in recent decades, to account for more than 15% of cases of S. aureus PVE and 6% of all cases of PVE. Because no large studies or clinical trials for PVE have been published, most guidelines on the diagnosis and management of MRSA PVE rely upon expert opinion and data from animal models or related conditions (e.g., coagulase-negative Staphylococcus infection). We performed a review of the literature on MRSA PVE to summarize data on pathogenic mechanisms and updates in epidemiology and therapeutic management and to inform diagnostic strategies and priority areas where additional clinical and laboratory data will be particularly useful to guide therapy. Major updates discussed in this review include novel diagnostics, indications for surgical management, the utility of aminoglycosides in medical therapy, and a review of newer antistaphylococcal agents used for the management of MRSA PVE.

Prosthetic valve endocarditis - A trouble or a challenge?

Prosthetic valve endocarditis (PVE) represents a rare and serious complication of valve replacement associated with high morbidity and mortality, which significantly differs from native valve endocarditis (NVE). There are two major problems: establishing diagnosis and treatment of PVE. Diagnosis in PVE is challenging and often requires several imaging methods besides standard microbiological analyzes. Transesophageal echocardiographic examination remains the widely used imaging technique in PVE diagnosis, but additional techniques such as computed tomography (CT) and ¹⁸F-fluodeoxyglucose positron emission tomography/CT are often necessary. Persistent fever, embolic complications, valve dehiscence, intracardial abscess, heart failure, as well as staphylococcal and fungal PVE require surgical treatment to avoid lethal outcome. The introduction of transcatheter valve implantations and devices significantly complicated the approach - diagnostic and therapeutic to PVE patients. Despite constantly increasing knowledge regarding pathogenesis and treatment of PVE, the optimal therapy remains a matter of debate. Additional studies are necessary to define therapeutic strategies for this potentially fatal complication.

Novel PET and Near Infrared Imaging Probes for the Specific Detection of Bacterial Infections Associated With Cardiac Devices

OBJECTIVES

The aim of this study was to develop imaging agents to detect early stage infections in implantable cardiac devices.

BACKGROUND

Bacteria ingest maltodextrins through the specific maltodextrin transporter. We developed probes conjugated with either a fluorescent dye (maltohexaose fluorescent dye probe [MDP]) or a F-18 (F18 fluoromaltohexaose) and determined their usefulness in a model of infections associated with implanted cardiac devices.

METHODS

Stainless steel mock-ups of medical devices were implanted subcutaneously in rats. On post-operative day 4, animals were injected with either Staphylococcus aureus around the mock-ups to induce a relatively mild infection or oil of turpentine to induce noninfectious inflammation. Animals with a sterile implant were used as control subjects. On post-operative day 6, either the MDP or F18 fluoromaltohexaose was injected intravenously, and the animals were scanned with the appropriate imaging device. Additional positron emission tomography imaging studies were performed with F18-fluorodeoxyglucose as a comparison of the specificity of our probes (n = 5 to 9 per group).

RESULTS

The accumulation of the MDP in the infected rats was significantly increased at 1 h after injection when compared with the control and noninfectious inflammation groups (intensity ratio 1.54 ± 0.07 vs. 1.26 ± 0.04 and 1.20 ± 0.05, respectively; p < 0.05) and persisted for more than 24 h. In positron emission tomography imaging, both F18 fluoromaltohexaose and F18 fluorodeoxyglucose significantly accumulated in the infected area 30 min after the injection (maximum standard uptake value ratio 4.43 ± 0.30 and 4.87 ± 0.28, respectively). In control rats, there was no accumulation of imaging probes near the device. In the noninfectious inflammation rats, no significant accumulation was observed with F18 fluoromaltohexaose, but F18 fluorodeoxyglucose accumulated in the mock-up area (maximum standard uptake value 2.53 ± 0.39 vs. 4.74 ± 0.46, respectively; p < 0.05).

CONCLUSIONS

Our results indicate that maltohexaose-based imaging probes are potentially useful for the specific and sensitive diagnosis of infections associated with implantable cardiac devices.

18F-FDG-PET/CT Imaging to Diagnose Septic Emboli and Mycotic Aneurysms in Patients with Endocarditis and Cardiac Device Infections

PURPOSE OF REVIEW

This review analyzes recent studies evaluating the diagnostic value of ¹⁸F-FDG-PET/CT for the detection of peripheral emboli and secondary infectious foci in patients with infective endocarditis and cardiac device infections.

RECENT FINDINGS

Detection of extracardiac septic localizations in patients with infective endocarditis and cardiac device infections is crucial, as it may impact the diagnosis, prognosis, and therapeutic management. Recent literature substantiated the clinical usefulness of ¹⁸F-FDG-PET/CT in this setting. ¹⁸F-FDG-PET/CT has proven its high diagnostic value for the detection of peripheral emboli in patients with infective endocarditis and cardiac device infections, substantially affecting patients' outcome and treatment. A multimodal approach, combining the high sensitivity of ¹⁸F-FDG-PET/CT with morphological imaging seems promising.

Usefulness of positron emission tomography/computed tomography in patients with valve-tube graft infection

Objective

Infection of valved aortic grafts is a rare entity whose diagnosis remains challenging. Positron emission tomography (PET)/CT has become a criterion for the diagnosis of infective endocarditis (IE) in prosthetic valves, but its role on ascending aortic graft infections remains unclear. This study aims to assess the diagnostic value of PET/CT in patients with valved aortic graft infection.

Methods

12 episodes with a valved aortic graft who had undergone a PET/CT due to suspicion of IE were prospectively included (group I) and compared with five controls free of infection who underwent PET/CT for other reasons (group II). Pathological uptake of 18F-fluorodeoxyglucose (FDG) and its pattern at the prosthetic valve and aortic graft were studied.

Results

Diagnosis of IE was confirmed in 9 out of 12 episodes of group I. 18F-FDG uptake was detectable in eight out of nine cases with a final diagnosis of IE. The most repeated pattern of uptake was homogeneous around the valve and heterogeneous around the tube. There was one false-negative study. Of the three patients in which IE was ruled out, there were two false positives and one true negative. In group II, there were three patients with a positive PET/CT study, two of them had active aortitis and the third was considered false positive.

Conclusions

18F-FDG PET/CT shows high sensitivity in the detection of infected aortic grafts. Thus, this technique should be considered in the diagnostic work-up of patients with suspicion of aortic graft infection. However, further validation of this approach is needed.

Construction and Evaluation of a Targeted Hyaluronic Acid Nanoparticle/Photosensitizer Complex for Cancer Photodynamic Therapy

Photodynamic therapy (PDT) is a novel treatment modality that is under intensive preclinical investigations for a variety of diseases, including cancer. Despite extensive studies in this area, selective and effective photodynamic agents that can specifically accumulate in tumors to reach a therapeutic concentration are limited. Although recent attempts have produced photosensitizers (PSs) complexed with various nanomaterials, the tedious preparation steps and poor tumor efficiency of therapy hamper their utilization. Here, we developed a CD44-targeted nanophotodynamic agent by physically encapsulating a photosensitizer, Ce6, into a hyaluronic acid nanoparticle (HANP), which was hereby denoted HANP/Ce6. Its physical features and capability for photodynamic therapy were characterized in vitro and in vivo. Systemic delivery of HANP/Ce6 resulted in its accumulation in a human colon cancer xenograft model. The tumor/muscle ratio reached 3.47 ± 0.46 at 4 h post injection, as confirmed by fluorescence imaging. Tumor growth after HANP/Ce6 treatment with laser irradiation (0.15 W/cm², 630 nm) was significantly inhibited by 9.61 ± 1.09-fold compared to that in tumor control groups, which showed no change in tumor growth. No apparent systemic and local toxic effects on the mice were observed. HANP/Ce6-mediated tumor growth inhibition was accessed and observed for the first time by ¹⁸F-fluoro-2-deoxy-d-glucose positron emission tomography as early as 1 day after treatment and persisted for 14 days within our treatment time window. In sum, our results highlight the imaging properties and therapeutic effects of the novel HANP/Ce6 theranostic nanoparticle for CD44-targeted PDT cancer therapy that may be potentially utilized in the clinic. This HANP system may also be applied for the delivery of other hydrophobic PSs, particularly those that could not be chemically modified.

Cardiac molecular imaging to track left ventricular remodeling in heart failure

Cardiac left ventricular (LV) remodeling is the final common pathway of most primary cardiovascular diseases that manifest clinically as heart failure (HF). The more advanced the systolic HF and LV dysfunction, the worse the prognosis. The knowledge of the molecular, cellular, and neurohormonal mechanisms that lead to myocardial dysfunction and symptomatic HF has expanded rapidly and has allowed sophisticated approaches to understanding and management of the disease. New therapeutic targets for pharmacologic intervention in HF have also been identified through discovery of novel cellular and molecular components of membrane-bound receptor-mediated intracellular signal transduction cascades. Despite all advances, however, the prognosis of systolic HF has remained poor in general. This is, at least in part, related to the (1) relatively late institution of treatment due to reliance on gross functional and structural abnormalities that define the "heart failure phenotype" clinically; (2) remarkable genetic-based interindividual variations in the contribution of each of the many molecular components of cardiac remodeling; and (3) inability to monitor the activity of individual pathways to cardiac remodeling in order to estimate the potential benefits of pharmacologic agents, monitor the need for dose titration, and minimize side effects. Imaging of the recognized ultrastructural components of cardiac remodeling can allow redefinition of heart failure based on its "molecular phenotype," and provide a guide to implementation of "personalized" and "evidence-based" evaluation, treatment, and longitudinal monitoring of the disease beyond what is currently available through randomized controlled clinical trials.

Increased aortic wall thickness on CT as a sign of prosthetic valve endocarditis

Background Increased wall thickness in the aortic root has been suggested as an early sign of prosthetic valve endocarditis (PVE). However, there are no previous studies on the aortic wall thickness after aortic valve replacement (AVR) or in patients with PVE. Purpose To identify a clinically useful cutoff value for aortic wall thickness to detect PVE. Material and Methods Chest computed tomography (CT) studies (n = 303) on patients with a prosthetic aortic valve were retrospectively analyzed. CT studies on patients without PVE (n = 260) were compared with CT studies on patients with definite PVE (n = 43). A receiver operator characteristic (ROC) analysis was performed. Results In non-PVE patients, the wall thickness during the first 3 months postoperatively (n = 70, 4.5 ± 1.7 mm) was increased compared to beyond 3 months postoperatively (n = 190, 3.2 ± 1.0 mm, P < 0.001). Beyond 3 months postoperatively, the wall thickness 95th percentile was 5.0 mm without signs of further decrease with time. The wall thickness in PVE patients was 6.8 ± 3.0 mm (n = 43). Beyond 3 months postoperatively, ROC analysis yielded an area under the curve of 0.89 (95% CI, 0.81-0.96). With a cutoff value of 5 mm the sensitivity was 67%, specificity 95%, positive likelihood ratio 14.1, and negative likelihood ratio 0.35 of increased wall thickness in detecting PVE. Conclusion In the early postoperative period after AVR, the aortic wall thickness is increased compared to the late postoperative period. After 3 months, the wall thickness has decreased and stabilized. Increased wall thickness (>5 mm) beyond 3 months postoperatively significantly increases the likelihood of PVE.

Alternative Cardiac Imaging Modalities to Echocardiography for the Diagnosis of Infective Endocarditis

Infective endocarditis (IE) is a life-threatening disease. Considered the gold standard for the diagnosis of IE, the modified Duke criteria rely on echocardiographic findings to satisfy its major criterion. Echocardiography is an invaluable tool in the evaluation of patients with suspected IE but suffers from certain limitations. For example, it cannot differentiate vegetation from clot, or between infected and noninfected vegetation, and may miss vegetation and periannular extensions in the presence of prosthetic material. Therefore, alternative cardiac imaging modalities are needed. Nuclear imaging, particularly ¹⁸F-fluorodesoxyglucose positron emission tomography-computed tomography (CT), is becoming increasingly popular in the evaluation of patients for IE and has shown promise in diagnosing valvular and device-related IE when echocardiography results were inconclusive. Other techniques such as radiolabeled leukocyte scintigraphy and single-photon emission computed tomography with or without CT are less well studied, however. Cardiac CT angiography is also evolving as a powerful supplementary tool to echocardiography for the detection of perivalvular complications of IE and for preoperative evaluation of coronary anatomy. The combination of cardiac CT angiography and echocardiography is superior to either test alone in the diagnosis of IE and its complications. Although brain magnetic resonance imaging may impact prognosis and clinical management by identifying cerebral emboli in patients with IE, the role of cardiac and abdominal magnetic resonance imaging is less clear. In conclusion, with these additional diagnostic tools at our disposal, the diagnosis of IE may be achieved in a more timely and accurate manner to secure better clinical outcomes.

Radionuclide Imaging Applications in Cardiomyopathies and Heart Failure

Multiple epidemiological factors including population aging and improved survival after acute coronary syndromes have contributed to a heart failure (HF) prevalence in the USA in epidemic proportions. In the absence of transplantation, HF remains a progressive disease with poor prognosis. The structural and functional abnormalities of the myocardium in HF can be assessed by various radionuclide imaging techniques. Radionuclide imaging may be uniquely suited to address several important clinical questions in HF such as identifying etiology and guiding the selection of patients for coronary revascularization. Newer approaches such as autonomic innervation imaging, phase analysis for synchrony assessment, and other molecular imaging techniques continue to expand the applications of radionuclide imaging in HF. In this manuscript, we review established and evolving applications of radionuclide imaging for the diagnosis, risk stratification, and management of HF.

Diagnostic value of imaging in infective endocarditis: a systematic review

Sensitivity and specificity of the modified Duke criteria for native valve endocarditis are both suboptimal, at approximately 80%. Diagnostic accuracy for intracardiac prosthetic material-related infection is even lower. Non-invasive imaging modalities could potentially improve diagnosis of infective endocarditis; however, their diagnostic value is unclear. We did a systematic literature review to critically appraise the evidence for the diagnostic performance of these imaging modalities, according to PRISMA and GRADE criteria. We searched PubMed, Embase, and Cochrane databases. 31 studies were included that presented original data on the performance of electrocardiogram (ECG)-gated multidetector CT angiography (MDCTA), ECG-gated MRI, ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET/CT, and leucocyte scintigraphy in diagnosis of native valve endocarditis, intracardiac prosthetic material-related infection, and extracardiac foci in adults. We consistently found positive albeit weak evidence for the diagnostic benefit of ¹⁸F-FDG PET/CT and MDCTA. We conclude that additional imaging techniques should be considered if infective endocarditis is suspected. We propose an evidence-based diagnostic work-up for infective endocarditis including these non-invasive techniques.

Radiopharmaceuticals in positron emission tomography: present situation and future perspectives

Positron emission tomography (PET) is an imaging technique that has grown greatly in recent years. PET is considered a fundamental tool in oncology, and it also has indications in other fields such as neurology and cardiology. Although ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) is the radiopharmaceutical most widely used in PET, the availability of new radiotracers has been a key element in the expansion of the use of PET. These new radiopharmaceuticals have made it possible to study different biological targets that are essential for obtaining greater knowledge and better characterization of different diseases and have thus contributed to the research and development of different therapeutic agents. This article provides a description of different PET radiopharmaceutical, structured according to their areas of application. Some of these radiotracers are already commercially available, whereas others are still under research or pending approval by regulatory bodies.

(18)F-FDG-PET Scanning Confirmed Infected Intracardiac Device-Leads with Abiotrophia defectiva

Abiotrophia species are relatively slow growing pathogens, which may be present as commensal flora. However, invasive infections are frequently reported, like endocarditis, septic arthritis, osteomyelitis, and many other types of infection. In this case report we describe a 65-year-old male patient with an intracardiac device- (ICD-) lead infection caused by Abiotrophia defectiva. Diagnosis was confirmed by ¹⁸F-FDG-PET scanning. This is remarkable, since Abiotrophia defectiva is a slow growing pathogen causing low-grade infections. This case demonstrates that although infection of ICD-leads cannot be excluded in case of ¹⁸F-FDG-PET-negative findings, positive findings are highly suggestive for infection.

Diagnosing pulmonic valve infective endocarditis with positron emission tomography-CT

Infective endocarditis (IE) affects the pulmonic valve in less than 2% of cases. Not only is pulmonary valve IE rare, it is also challenging to visualise with commonly used imaging modalities. In this vignette, we present a 50-year-old patient with a history of repaired Tetralogy of Fallot who underwent a prolonged hospitalisation and extensive work up for fever of unknown origin. Although we suspected IE as the source of his fevers, he had persistently negative transthoracic and transoesophageal echocardiograms. We were ultimately able to establish the diagnosis with the use of positron emission tomography-CT (PET-CT). Although PET-CT is not part of the traditional work up for IE, it can be a useful imaging modality when there is a high index of suspicion for IE with negative echocardiography findings.

Additional Heparin Preadministration Improves Cardiac Glucose Metabolism Suppression over Low-Carbohydrate Diet Alone in ¹⁸F-FDG PET Imaging

Adequate suppression of cardiac glucose metabolism increases the interpretability and diagnostic reliability of (18)F-FDG PET studies performed to detect cardiac inflammation and infection. There are no standardized guidelines, though prolonged fasting (>6 h), carbohydrate-restricted diets, fatty meals, and heparin loading all have been proposed. The aim of this study was to compare the 3 preparatory protocols used in our institution.

METHODS

(18)F-FDG PET scans were selected and grouped according to 3 preparatory protocols (50 consecutive scans per group): 6-h fast (group 1), low-carbohydrate diet plus 12-h fast (group 2), and low-carbohydrate diet plus 12-h fast plus intravenous heparin preadministration (50 IU/kg) (group 3). Consecutive scans were retrospectively included from time frames during which the particular protocol was used. Group 1 included oncologic indications, and groups 2 and 3 infection or inflammation detection. Cardiac segments for which inflammation or infection foci had been confirmed on other imaging modalities were excluded from the analysis. (18)F-FDG uptake in normal myocardium was scored according to a scale ranging from 0 (uptake less than that in left ventricle blood pool) to 4 (diffuse uptake greater than that in liver). Adequate suppression was defined as uptake less than that in liver and without any focus (scores 0-2).

RESULTS

Adequate suppression differed significantly between groups: 28% in group 1, 54% in group 2, and 88% in group 3 (P< 0.0001 for all comparisons).

CONCLUSION

Single-dose heparin administration before (18)F-FDG PET in addition to a low-carbohydrate diet significantly outperforms a low-carbohydrate diet alone in adequately suppressing cardiac glucose metabolism.

High performances of (18)F-fluorodeoxyglucose PET-CT in cardiac implantable device infections: A study of 40 patients

BACKGROUND

Cardiovascular implantable electronic devices (CIED) infections are life-threatening complications. The diagnosis can be difficult to establish. Our purpose is to evaluate the diagnostic value of (18)F-FDG PET.

METHODS

Forty patients who received work-up for suspected CIED infection were retrospectively included (group 1) and compared with 40 controls (group 2); CIED patients were referred for oncologic PET. PET-CT data were blindly assessed. Interpretation was based on visual analysis of both attenuation-corrected and non-corrected images and a semi-quantitative analysis was performed. The gold standard was bacteriological data of explanted devices or clinical follow-up for at least 1 year.

RESULTS

Infection was present in 18 out of 40 patients of group 1. Sensitivity, specificity, positive predictive value, and negative predictive value of PET-CT were 83%, 95%, 94%, and 88%, respectively. Accuracy was 90%. PET-CT revealed the presence of additional pathological hypermetabolic foci in 28% of cases. PET-CT was negative at implanted devices in all patients of group 2.

CONCLUSION

(18)F-FDG PET-CT is helpful in the work-up of suspected CIED infections. It is a potential tool to make the accurate diagnosis of CIED infection and to assess the extent of infection. The promising results in this indication need to be validated in a prospective multicenter study.