Alternative Nuclear Imaging Tools for Infection Imaging.

PURPOSE OF REVIEW: Cardiovascular infections are serious disease associated with high morbidity and mortality. Their diagnosis is challenging, requiring a proper management for a prompt recognition of the clinical manifestations, and a multidisciplinary approach involving cardiologists, cardiothoracic surgeons, infectious diseases specialist, imagers, and microbiologists. Imaging plays a central role in the diagnostic workout, including molecular imaging techniques. In this setting, two different strategies might be used to image infections: the first is based on the use of agents targeting the microorganism responsible for the infection. Alternatively, we can target the components of the pathophysiological changes of the inflammatory process and/or the host response to the infectious pathogen can be considered. Understanding the strength and limitations of each strategy is crucial to select the most appropriate imaging tool. RECENT FINDINGS: Currently, multislice computed tomography (MSCT) and nuclear imaging (18F-fluorodeoxyglucose positron emission tomography/computed tomography, and leucocyte scintigraphy) are part of the diagnostic strategies. The main role of nuclear medicine imaging (PET/CT and SPECT/CT) is the confirmation of valve/CIED involvement and/or associated perivalvular infection and the detection of distant septic embolism. Proper patients' preparation, imaging acquisition, and reconstruction as well as imaging reading are crucial to maximize the diagnostic information. In this manuscript, we described the use of molecular imaging techniques, in particular WBC imaging, in patients with infective endocarditis, cardiovascular implantable electronic device infections, and infections of composite aortic graft, underlying the strength and limitations of such approached as compared to the other imaging modalities.

Retrospective Study Comparing WBC scan and 18F-FDG PET/CT in Patients with Suspected Prosthetic Vascular Graft Infection.

OBJECTIVES: Prosthetic vascular graft infections (PVGIs) are associated with high mortality rates. To improve treatment outcome, an early and definite diagnosis is critical, and current diagnostic criteria are often insufficient. The accuracy of 2-deoxy-2-[fluorine-18]-fluoro-d-glucose positron emission tomography integrated with computed tomography (18F-FDG PET/CT) and white blood cell (WBC) scan for the diagnosis of PVGI were compared. METHODS: A retrospective single centre study was conducted on patients undergoing WBC scan and 18F-FDG PET/CT for a suspected PVGI between April 2013 and June 2016 at the Bordeaux University Hospital, France. The diagnostic value of both imaging tests was assessed for all grafts, using receiver operating characteristic (ROC) curve analysis. Images were independently interpreted by two nuclear medicine physicians blinded to the patients' clinical and other imaging data. RESULTS: Thirty-nine patients were included, of whom 15 had PVGI. Antibiotic treatment was started before nuclear imaging for 16 patients, including nine patients with a PVGI. The 96 grafts of these patients were analysed, and 19 were infected. The diagnostic value of the WBC scan was significantly higher than 18F-FDG PET/CT (ROC AUC = 0.902, 95% CI 0.824-0.980, and 0.759, CI 95% (0.659-0.858), respectively, p = .0071). Interobserver agreement was good for 18F-FDG PET/CT and excellent for WBC scan (kappa value of 0.76, 95% CI 0.62-0.9, and 0.97, 95% CI 0.92-1, respectively). Only one patient had a false negative 18F-FDG PET/CT result under antibiotic therapy. CONCLUSION: The WBC scan has a better diagnostic value than 18F-FDG PET/CT for PVGI diagnosis.

Development and evaluation of a radiolabelling agent for white blood cell scans.

Radiolabelled autologous leukocytes have been used for the clinical diagnosis of inflammation and infection. To develop a stable and efficient radiopharmaceutical for labelling leukocytes, we prepared a novel radioiodinated cell-penetrating peptide, 125I-TAT, using a bi-functional linker. 125I-TAT was stable for two days under three different temperature conditions of -20 °C, 4 °C, and 40 °C, with its radiochemical purity remaining over 99%. Iodinated TAT was non-toxic to leukocytes with an IC50 value of over 100 µM. The labelling efficiency of 125I-TAT using 1ｘ107 cells ranged from 27% to 53% when the three leukocyte cell lines were pre-treated with DMSO. This is comparable to the labelling efficiency recommended by the guideline for conventional labelling agents using 2ｘ108 cells. Radioiodinated cell-penetrating peptide may be an improved radiopharmaceutical for white blood cell scans by further optimization.

An 82-year-old man with a prosthetic aortic valve and multimicrobial bacteremia.

The patient is an 82-year-old male with a past medical history of aortic valve replacement who presented to the emergency department after a fall. He developed atrial fibrillation with a rapid ventricular response and non-ST-segment-elevation myocardial infarction, leading to hospitalization. During hospital admission, the patient complained of midline thoracic back pain, and an extensive evaluation for this complaint revealed discitis and osteomyelitis with epidural abscess near the T7 and T8 vertebrae that did not result in neurological deficits and required no surgical intervention. A total of 2 blood cultures were reported positive for Actinomyces naeslundii, Streptococcus mitis, Streptococcus oralis, and Abiotrophia defectiva. A transesophageal echocardiogram showed a small vegetation on the aortic prosthetic valve with probable small vegetation on the mitral valve. He was prescribed ceftriaxone intravenously for 12 weeks, followed by amoxicillin 2 g orally twice a day for at least 12 months. A. naeslundii is not commonly known to cause infective endocarditis, whereas S. mitis, S. oralis, and A. defectiva have been reported to do so. One previous case of A. naeslundii was reported to cause prosthetic valve endocarditis as a single infectious agent. To our knowledge, this is the first case report for A. naeslundii as part of multimicrobial bacteremia leading to endocarditis, discitis, and osteomyelitis.

Indium-111 labeled leukocyte accumulation in extremity soft tissue sarcoma.

Nuclear medicine labeled leukocyte whole-body scintigraphy is commonly used to identify a source of infection in a patient with fever of unknown origin. White blood cells can also localize to other sites of inflammation, including sometimes tumors. A patient with a large myxofibrosarcoma in his left forearm was scanned due to chronic low-grade fever and persistent leukocytosis. This case demonstrates focal white blood cell activity in an extremity soft tissue sarcoma.