The role of nuclear medicine in infection and inflammation

Insights into Peptidoglycan-Targeting Radiotracers for Imaging Bacterial Infections: Updates, Challenges, and Future Perspectives

The unique structural architecture of the peptidoglycan allows for the stratification of bacteria as either Gram-negative or Gram-positive, which makes bacterial cells distinguishable from mammalian cells. This classification has received attention as a potential target for diagnostic and therapeutic purposes. Bacteria's ability to metabolically integrate peptidoglycan precursors during cell wall biosynthesis and recycling offers an opportunity to target and image pathogens in their biological state. This Review explores the peptidoglycan biosynthesis for bacteria-specific targeting for infection imaging. Current and potential radiolabeled peptidoglycan precursors for bacterial infection imaging, their development status, and their performance in vitro and/or in vivo are highlighted. We conclude by providing our thoughts on how to shape this area of research for future clinical translation.

Metal-binding cyclodextrins: Synthesis and complexation with Zn2+ and Ga3+ cations towards antimicrobial applications

Highly resistant bacteria producing metallo-β-lactamases (MBLs) to evade β-lactam antibiotics, constitute a major cause of life-threatening infections world-wide. MBLs exert their hydrolytic action via Zn2+ cations in their active center. Presently, there are no approved drugs to target MBLs and combat the associated antimicrobial resistance (AMR). Towards this issue, we have prepared a family of cyclodextrins substituted with iminodiacetic acid (IDA) on their narrow side, while the wider side is either unmodified or per-2,3-O-methylated. The molecules form strong coordination complexes with Zn2+ or Ga3+ cations in aqueous solution. Free and metal-complexed compounds have been thoroughly characterized regarding structures, pH-dependent ionization states, distribution of species in solution, pKa values and metal-binding constants. At neutral pH the multi-anionic hosts bind up to four Zn2+ or Ga3+ cations. In vitro, 50 μΜ of the compounds achieve complete re-sensitization of MBL-producing Gram-negative clinical bacterial strains resistant to the carbapenems imipenem and meropenem. Moreover, the radioactive complex [67Ga]Ga-β-IDACYD prepared, displays high radiochemical purity, sufficient stability both overtime and in the presence of human plasma apo-transferrin, thus providing an invaluable tool for future biodistribution and pharmacokinetic studies of β-IDACYDin vivo, prerequisites for the development of therapeutic protocols.

Inflammation scintigraphy imaging through a novel antimicrobial peptide labeled with technetium-99m in an animal model

PURPOSE

Antimicrobial peptides (AMPs), due to their biological properties, have great potential for radiopharmaceutical development. In this research, a new antimicrobial peptide, derived from a 21-residue antimicrobial peptide microcinJ25 (MccJ25), was utilized to diagnose inflamed sites in mice bodies after labeling with [^99mTc]Tc.

MATERIALS AND METHODS

An antimicrobial peptide derivative was connected with an efficient chelator, hydrazinonicotinamide, and then labeled with [^99mTc]Tc. The binding of labeled microcinJ25 conjugate to lymphocyte was investigated in vitro. Turpentine oil-induced inflammation uptake and tissue distribution were assessed through the animal pattern. Detector scanning was done through scintigraphy post injection of [^99mTc]Tc-radiopeptide within different time points.

RESULTS

High radiochemical purity (>98%) was obtained for [^99mTc]Tc-radiopeptide. Lymphocyte binding assessment showed specific cell binding. Binding Inhibition was observed when additional unlabeled conjugate was used. In in vivo biological distribution studies, the uptake for inflamed tissue was 1.52 ± 0.12%ID/g. The inflammation site was visualized by scintigraphy imaging at 1 up to 2 hours.

CONCLUSION

Based on our results this new designed [^99mTc]Tc-radiopeptide was able to detect inflammation sites early and with high resolution, and could be considered a promising diagnostic candidate in inflammatory diseases.

PET/CT for Early Detection of COVID-19 Pneumonia: Diffuse Fluorodeoxyglucose Uptake in the Lungs without any Additional Changes in a Patient with Breast Cancer

Coronavirus disease-2019 (COVID-19), which causes infections in the upper and lower respiratory tract, became a pandemic shortly after it was first diagnosed in Wuhan city, China. Many people are affected with high mortality rates and severe respiratory distress syndrome. During this pandemic, all physicians paid attention to the findings of COVID-19. Suggestive findings in ¹⁸fluorine-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) were characterized as increased ¹⁸F-FDG uptake in bilateral peripheral consolidative areas and ground glass opacities. We aimed to show diffuse FDG uptake in PET images with indefinable lesions in CT as a suspicious finding for early COVID-19.

Design, Preparation, and Evaluation of a Novel 99mTcN Complex of Ciprofloxacin Xanthate as a Potential Bacterial Infection Imaging Agent

In order to seek novel technetium-99m bacterial infection imaging agents, a ciprofloxacin xanthate (CPF2XT) was synthesized and radiolabeled with [^99mTcN]²⁺ core to obtain the ^99mTcN-CPF2XT complex, which exhibited high radiochemical purity, hydrophilicity, and good stability in vitro. The bacteria binding assay indicated that ^99mTcN-CPF2XT had specificity to bacteria. A study of biodistribution in mice showed that ^99mTcN-CPF2XT had a higher uptake in bacterial infection tissues than in turpentine-induced abscesses, indicating that it could distinguish bacterial infection from sterile inflammation. Compared to ^99mTcN-CPFXDTC, the abscess/blood and abscess/muscle ratios of ^99mTcN-CPF2XT were higher and the uptakes of ^99mTcN-CPF2XT in the liver and lung were obviously decreased. The results suggested that ^99mTcN-CPF2XT would be a potential bacterial infection imaging agent.

CAR Chase: Where Do Engineered Cells Go in Humans?

Chimeric antigen receptor (CAR) - and T-cell receptor (TCR) - modified T-cells are rapidly emerging as a viable treatment option for cancer patients. While initial clinical trials for these CAR T cells showed response rates of over 90% in some cases, retrospective studies have revealed a wide variability in patient responses as well as a significant proportion of patients relapsing after an initial response. In addition, patients often have severe adverse reactions to this therapy (e.g., cytokine release and neurologic syndromes). As a result, much research is still needed to be able to predict both therapeutic outcomes and possible toxicities. Furthermore, little success has been seen in treating solid tumors with engineered T cells and uncovering modes of failure is a topic of much research. Finally, little is known about the T cells' pharmacokinetics after infusion into the patient, as standard methods of tracking the cells analyze peripheral blood and tumor biopsies - both of which lack spatiotemporal information. Herein, we propose that reporter gene-based imaging of engineered T cells in humans would be tremendously valuable in elucidating the fate of the transplanted T cells and would greatly facilitate clinical translation of new CAR and TCR technologies. Currently, there are no FDA-approved reporter genes and few methods have advanced to human studies. Herein, we outline current reporter gene approaches to track engineered cells in vivo, analyze why current reporter genes have not progressed into the clinic, and propose "rules" for designing a widely applicable reporter gene for use in humans.

Current Applications for Nuclear Medicine Imaging in Pulmonary Disease

Purpose of Review

The main goal of the article is to familiarize the reader with commonly and uncommonly used nuclear medicine procedures that can significantly contribute to improved patient care. The article presents examples of specific modality utilization in the chest including assessment of lung ventilation and perfusion, imaging options for broad range of infectious and inflammatory processes, and selected aspects of oncologic imaging. In addition, rapidly developing new techniques utilizing molecular imaging are discussed.

Recent Findings

The article describes nuclear medicine imaging modalities including gamma camera, SPECT, PET, and hybrid imaging (SPECT/CT, PET/CT, and PET/MR) in the context of established and emerging clinical applications. Areas of potential future development in nuclear medicine are discussed with emphasis on molecular imaging and implementation of new targeted tracers used in diagnostics and therapeutics (theranostics).

Summary

Nuclear medicine and molecular imaging provide many unique and novel options for the diagnosis and treatment of pulmonary diseases. This article reviews current applications for nuclear medicine and molecular imaging and selected future applications for radiopharmaceuticals and targeted molecular imaging techniques.

Diagnostic accuracy of 18F-FDG-PET in abdominal sepsis in rats

Purpose

The objective of this study was to investigate the accuracy of 18F-FDG-PET in the diagnosis of multibacterial abdominal sepsis by cecum ligation and puncture (CLP) in rats.

Methods

Adult Wistar rats ( Rattus norvegicus ), weighing 227±35g, were allocated into a sepsis group by CLP (n=10) and sham group (n=10). 18F-FDG-PET using microPET was performed on all rats after 24 hours.

Results

All animals survived for postoperative 24h. The abdomen/liver ratio of the standardized uptake value (SUV) percentage was significantly higher in the sepsis group than in the sham (p=0.004). The ROC curve showed an accuracy of 18F-FDG-PET to detect abdominal sepsis of 88.9% (p=0.001), sensitivity of 90% and specificity of 88.9%. When a cut-off point of 79% of the ratio between the SUV on the abdominal region and liver was established, the sensitivity was 90%, specificity of 88.9%; positive and negative predictive values of 90.0% and 88.9%, respectively.

Conclusions

The diagnostic accuracy of 18F-FDG-PET in rats with abdominal sepsis was significantly high. It was also demonstrated the predictive ability of the abdomen/liver SUV ratio to diagnose abdominal sepsis. These findings may have implications for the clinical setting, locating septic foci with PETscan.

Accuracy of Oral 67Gallium Citrate Scintigraphy in assessment of inflammatory activity of Crohn's disease

AIM

The main goal in Crohn´s disease (CD) is a sustained suppression of inflammatory activity associated with mucosa healing in endoscopic evaluation. During clinical routine, there are small numbers of good markers to monitor inflammatory activity under treatment. We postulated that Oral ⁶⁷Gallium Citrate Scintigraphy is able to mark inflammatory disease in mucosa and deep inflammation in CD, when used in oral form.

OBJECTIVE

Measure the accuracy of Oral ⁶⁷Gallium Citrate Scintigraphy in intestinal inflammatory activity of Crohn´s disease.

PATIENTS AND METHODS

In a prospective consecutive cross-sectional study from January 2018 to June 2019, the ileocolonic region of 32 patients with CD were studied by dividing into four regions of interest (ROI) from the ileum to the rectum. A total of 128 intestinal segments were analyzed in cluster data. Accuracy values of Oral ⁶⁷Gallium Scintigraphy and colonoscopy tests were evaluated with the histological reference test. Values of the respective receiver operating characteristic (ROC) curves were obtained  and compared. The reliability between the tests was evaluated by Kappa statistical with the segment-level analyses using variance adjustments. All statistical analyses were performed with a test significance level of 0.05.

RESULTS

The study population included 32 patients with CD (10 men, 22 women; average age 39 years). Disease time was five years on average. Anti-TNFs treatment was found in 71%. The most found phenotype of the Montreal classification was L3. Differences in ROC curves for colonoscopy (0.94) and Oral ⁶⁷Ga Scintigraphy (0.96) did not show significant value (p = 0.32). The sensitivity of scintigraphy to detect intestinal inflammatory activity in CD was 64%, specificity of 96% and accuracy of 84%. A high agreement was found between oral scintigraphy and histological measurements with kappa = 0.64.

CONCLUSIONS

Oral ⁶⁷Ga Scintigraphy had similar accuracy and agreement compared to colonoscopy in the identification of inflammatory activity in Crohn´s Disease. This new approach may be useful and less invasive for long term follow-ups.

Diagnosis of peripheral bone and prosthetic joint infections: overview on the consensus documents by the EANM, EBJIS, and ESR (with ESCMID endorsement)

OBJECTIVES

Peripheral bone infection (PBI) and prosthetic joint infection (PJI) are two different infectious conditions of the musculoskeletal system. They have in common to be quite challenging to be diagnosed and no clear diagnostic flowchart has been established. Thus, a conjoined initiative on these two topics has been initiated by the European Society of Radiology (ESR), the European Association of Nuclear Medicine (EANM), the European Bone and Joint Infection Society (EBJIS), and the European Society of Clinical Microbiology and Infectious Diseases (ESCMID). The purpose of this work is to provide an overview on the two consensus documents on PBI and PJI that originated by the conjoined work of the ESR, EANM, and EBJIS (with ESCMID endorsement).

METHODS AND RESULTS

After literature search, a list of 18 statements for PBI and 25 statements for PJI were drafted in consensus on the most debated diagnostic challenges on these two topics, with emphasis on imaging.

CONCLUSIONS

Overall, white blood cell scintigraphy and magnetic resonance imaging have individually demonstrated the highest diagnostic performance over other imaging modalities for the diagnosis of PBI and PJI. However, the choice of which advanced diagnostic modality to use first depends on several factors, such as the benefit for the patient, local experience of imaging specialists, costs, and availability. Since robust, comparative studies among most tests do not exist, the proposed flowcharts are based not only on existing literature but also on the opinion of multiple experts involved on these topics.

KEY POINTS

• For peripheral bone infection and prosthetic joint infection, white blood cell and magnetic resonance imaging have individually demonstrated the highest diagnostic performance over other imaging modalities. • Two evidence- and expert-based diagnostic flowcharts involving variable combination of laboratory tests, biopsy methods, and radiological and nuclear medicine imaging modalities are proposed by a multi-society expert panel. • Clinical application of these flowcharts depends on several factors, such as the benefit for the patient, local experience, costs, and availability.

Radiosynthesis and pre-clinical evaluation of [68Ga] labeled antimicrobial peptide fragment GF-17 as a potential infection imaging PET radiotracer

The antimicrobial peptide fragment GF-17 was synthesized in-house and conjugated with DOTA and measured molecular mass of DOTA-GF-17 conjugate was 2489 Da. The peptide conjugate was purified and labeled with [⁶⁸Ga]. The best radiolabeling efficiency (95.0%) of [⁶⁸Ga]DOTA-GF-17 was achieved at pH 4 with peptide conjugate amount of 20.0 nmol with 30 min of heating at 95 °C. The product remained stable for up to 3 h. The plasma protein binding and lipophilicity for [⁶⁸Ga]DOTA-GF-17 were 80.98% and -3.12 respectively. The uptake studies with [⁶⁸Ga]DOTA- GF-17 in S.aureus and P.aeruginosa bacterial strains demonstrated binding of 69.08% and 43.69% respectively. The animal bio-distribution and PET imaging studies were in agreement showing similar pattern for organs' tracer distribution and renal excretion. The tracer had rapid blood clearance and uptake in bone marrow and muscles was very low. The highest uptake of [⁶⁸Ga]DOTA-GF-17 was observed at 45 min and 120 min in S.aureus and P.aeruginosa infections respectively. [⁶⁸Ga]DOTA-GF-17 could be a promising PET tracer and holds a great scope for taking the product further to perform extensive PET studies in animal infection (using gram negative/positive strains) models to prove the diagnostic utility of this novel PET tracer for futuristic clinical applications.

Consensus document for the diagnosis of peripheral bone infection in adults: a joint paper by the EANM, EBJIS, and ESR (with ESCMID endorsement)

INTRODUCTION

In adults with a suspicion of peripheral bone infection, evidence-based guidelines in choosing the most accurate diagnostic strategy are lacking.

AIM AND METHODS

To provide an evidence-based, multidisciplinary consensus document on the diagnostic management of adult patients with PBIs, we performed a systematic review of relevant infectious, microbiological, orthopedic, radiological, and nuclear medicine literature. Delegates from four European societies (European Bone and Joint Infection Society, European Society of Microbiology and Infectious Diseases, European Society or Radiology, and European Association of Nuclear Medicine) defined clinical questions to be addressed, thoroughly reviewed the literature pertinent to each of the questions, and thereby evaluated the diagnostic accuracy of each diagnostic technique. Inclusion of the papers per statement was based on a PICO (Population/problem - Intervention/indicator - Comparator - Outcome) question following the strategy reported by the Oxford Centre for Evidence-based Medicine. For each statement, the level of evidence was graded according to the 2011 review of the Oxford Centre for Evidence-based Medicine. All approved statements were addressed taking into consideration the available diagnostic procedures, patient acceptance, tolerability, complications, and costs in Europe. Finally, a commonly agreed-upon diagnostic flowchart was developed.

Differentiating Disease Flare From Infection: A Common Problem in Rheumatology. Do 18F-FDG PET/CT Scans and Novel Biomarkers Hold The Answer?

PURPOSE OF REVIEW

Fever is common within rheumatology but it is often challenging to identify its source. To do so correctly is paramount in patients with an underlying inflammatory condition receiving immunosuppressive therapy. This review article looks at the available evidence and merits of both 18F-fluoro-deoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) scans and new proposed biomarkers in determining the cause of fever within rheumatology.

RECENT FINDINGS

18F-FDG PET/CT scans are already an established tool in the detection and diagnosis of malignancy and are emerging for use in fever of unknown origin. More recently, they have been used to identify rheumatological causes of fever such as large vessel vasculitis and adult-onset Still's disease. Within these conditions, biomarkers such as procalcitonin and presepsin may help to differentiate endogenous from exogenous pyrogens. 18F-FDG PET/CT scanning shows promise in locating the source of pyrogens and may be superior to other conventional forms of imaging. As evidence and test availability increases, its use is likely to become commonplace in the diagnostic work-up of fever. Once a source is located, selected biomarkers may be used to confirm a cause.

Delayed diagnosis of extrapulmonary tuberculosis presenting as fever of unknown origin in an intermediate-burden country

Background

Tuberculosis (TB), especially extrapulmonary tuberculosis (EPTB), is an important cause of fever of unknown origin (FUO) in TB-burdened areas. Little information is known about patients with EPTB with clinical features presenting as FUO and about the factor of delaying the diagnosis.

Methods

We retrospectively analyzed EPTB patients who were referred with FUO at 3 university-affiliated hospitals over 8 years (2010–2017). The subjects were assigned to groups of early diagnosis and delayed diagnosis within 3 days of an initial comprehensive evaluation from the referral. Clinical and laboratory variables were compared between the groups.

Results

A total of 95 patients with febrile EPTB were included. Localizing symptoms and/or signs suggestive of anatomy were identified in 62.1% of the patients. Concurrent lung involvement by TB was presented by 49.5% (47/95) of the patients, and only 23.4% of them showed typical findings of pulmonary TB on simple chest X-ray. Most of the patients showed abnormal lesions on cross-sectional CT (98.9%) and MRI (100%). The clinical variables and blood test results of patients were not significantly different between the two groups. The less typical imaging finding of EPTB on CT (38.5% vs. 79.0%) and MRI (37.5% vs. 79.0%) in the delayed diagnosis group was a risk factor for delayed diagnosis.

Conclusion

Febrile EPTB referred as FUO showed nonspecific clinical manifestations. The active application of cross-sectional imaging tests according to clinical clues or randomly in the absence of local manifestations, combined with invasive diagnostic approaches even for atypical presentations may lead to an earlier diagnosis of febrile EPTB.

The role of regulatory T cells, interleukin-10 and in vivo scintigraphy in autoimmune and idiopathic diseases - Therapeutic perspectives and prognosis

Previous studies have demonstrated the expression of the CD25 marker on the surface of naturally occurring T cells (Tregs) of mice, which have a self-reactive cellular profile. Recently, expression of other markers that aid in the identification of these cells has been detected in lymphocyte subtypes of individuals suffering of autoimmune and idiopathic diseases, including: CD25, CTLA-4 (cytotoxic T-lymphocyte antigen 4), HLA-DR (human leukocyte antigen) and Interleukin 10 (IL-10), opening new perspectives for a better understanding of an association between such receptors present on the cell surface and the prognosis of autoimmune diseases. The role of these molecules has already been described in the literature for the modulation of the inflammatory response in infectious and parasitic diseases. Thus, the function, phenotype and frequency of expression of the a-chain receptor of IL-2 (CD25) and IL-10 in lymphocyte subtypes were investigated. Murine models have been used to demonstrate a possible correlation between the expression of the CD25 marker (on the surface of CD4 lymphocytes) and the control of self-tolerance mechanisms. These studies provided support for the presentation of a review of the role of cells expressing IL-2, IL-10, HLA-DR and CTLA-4 receptors in the monitoring of immunosuppression in diseases classified as autoimmune, providing perspectives for understanding peripheral regulation mechanisms and the pathophysiology of these diseases in humans. In addition, a therapeutic approach based on the manipulation of the phenotype of these cells and ways of scintigraphically monitoring the manifestations of these diseases by labeling their receptors is discussed as a perspective. In this paper, we have included the description of experiments in ex vivo regulation of IL-10 and synthesis of thio-sugars and poly-sugars to produce radiopharmaceuticals for monitoring inflammation. These experiments may yield benefits for the treatment and prognosis of autoimmune diseases.

Targeting Cardiovascular Implant Infection: Multimodality and Molecular Imaging

Owing to their success in clinical practice, the prevalence of cardiovascular implants is continuously increasing. Implant infection is a relevant complication but remains a diagnostic challenge because echocardiography as a first-line test may be limited. Accordingly, a multimodality approach is increasingly used for diagnostic workup and supported by recent guidelines. As reviewed here, computed tomography and nuclear imaging provide incremental diagnostic value and may be combined in a single hybrid imaging session using positron emission tomography/computed tomography or single photon emission computed tomography/computed tomography. Molecular or cellular imaging helps to overcome the limitations of morphological imaging in implants. Larger-scale clinical studies, earlier application in the time course of diagnosis, monitoring of therapy success, technical advances, and novel radiopharmaceuticals will all contribute to sustained growth of advanced infection-targeted imaging in cardiovascular medicine.

New pathogen-specific immunoPET/MR tracer for molecular imaging of a systemic bacterial infection

The specific and rapid detection of Enterobacteriaceae, the most frequent cause of gram-negative bacterial infections in humans, remains a major challenge. We developed a non-invasive method to rapidly detect systemic Yersinia enterocolitica infections using immunoPET (antibody-targeted positron emission tomography) with [64Cu]NODAGA-labeled Yersinia-specific polyclonal antibodies targeting the outer membrane protein YadA. In contrast to the tracer [18F]FDG, [64Cu]NODAGA-YadA uptake co-localized in a dose dependent manner with bacterial lesions of Yersinia-infected mice, as detected by magnetic resonance (MR) imaging. This was accompanied by elevated uptake of [64Cu]NODAGA-YadA in infected tissues, in ex vivo biodistribution studies, whereas reduced uptake was observed following blocking with unlabeled anti-YadA antibody. We show, for the first time, a bacteria-specific, antibody-based, in vivo imaging method for the diagnosis of a Gram-negative enterobacterial infection as a proof of concept, which may provide new insights into pathogen-host interactions.

Synthesis, in vitro evaluation, and 68 Ga-radiolabeling of CDP1 toward PET/CT imaging of bacterial infection

Bacterial infections are a major concern in the human health sector due to poor diagnosis and development of multidrug-resistant strains. PET/CT provides a means for the non-invasive detection and localization of the infectious foci; however, the radiotracers available are either cumbersome to prepare or their exact contribution toward the imaging is not yet established. Human antimicrobial peptides are of interest for development as PET radiotracers as they are an integral component of the immune system, non-immunogenic toward the recipient, and show selectivity toward pathogens such as bacteria. Herein we report on the potential of LL37, a human cathelicidin antimicrobial peptide, as a radiotracer for bacterial imaging. Bifunctional chelator 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid was utilized to functionalize the antimicrobial peptide, which in turn was capable of chelating gallium. The synthesized ^nat Ga-CDP1 showed bacterial selectivity and low affinity toward hepatic cells, which are favorable characteristics for further preclinical application.

Using Nuclear Medicine Imaging Wisely in Diagnosing Infectious Diseases

In recent years, there has been an increasing emphasis on efficient and accurate diagnostic testing, exemplified by the American Board of Internal Medicine’s “Choosing Wisely” campaign. Nuclear imaging studies can provide early and accurate diagnoses of many infectious disease syndromes, particularly in complex cases where the differential remains broad.

This review paper offers clinicians a rational, evidence-based guide to approaching nuclear medicine tests, using an example case of methicillin-sensitive Staphylococcus aureus (MSSA) bacteremia in a patient with multiple potential sources. Fluorodeoxyglucose-positron emission tomography (FDG-PET) with computed tomography (CT) and sulfur colloid imaging with tagged white blood cell (WBC) scanning offer the most promise in facilitating rapid and accurate diagnoses of endovascular graft infections, vertebral osteomyelitis (V-OM), diabetic foot infections, and prosthetic joint infections (PJIs). However, radiologists at different institutions may have varying degrees of expertise with these modalities.

Regardless, infectious disease consultants would benefit from knowing what nuclear medicine tests to order when considering patients with complex infectious disease syndromes.

The Positron Emission Tomography Tracer 3'-Deoxy-3'-[18F]Fluorothymidine ([18F]FLT) Is Not Suitable to Detect Tissue Proliferation Induced by Systemic Yersinia enterocolitica Infection in Mice

Most frequently, gram-negative bacterial infections in humans are caused by Enterobacteriaceae and remain a major challenge in medical diagnostics. We non-invasively imaged moderate and severe systemic Yersinia enterocolitica infections in mice using the positron emission tomography (PET) tracer 3’-deoxy-3’-[¹⁸F]fluorothymidine ([¹⁸F]FLT), which is a marker of proliferation, and compared the in vivo results to the ex vivo biodistributions, bacterial loads, and histologies of the corresponding organs. Y. enterocolitica infection is detectable with histology using H&E staining and immunohistochemistry for Ki 67. [¹⁸F]FLT revealed only background uptake in the spleen, which is the main manifestation site of systemic Y. enterocolitica-infected mice. The uptake was independent of the infection dose. Antibody-based thymidine kinase 1 (Tk-1) staining confirmed the negative [¹⁸F]FLT-PET data. Histological alterations of spleen tissue, observed via Ki 67-antibody-based staining, can not be detected by [¹⁸F]FLT-PET in this model. Thus, the proliferation marker [¹⁸F]FLT is not a suitable tracer for the diagnosis of systemic Y. enterocolitica infection in the C57BL/6 animal model of yersiniosis.

Fever of unknown origin (FUO) revised

Fever of unknown origin (FUO) was originally characterised in 1961 by Petersdorf and Beeson as a disease condition of temperature exceeding 38.3 °C on at least three occasions over a period of at least three weeks, with no diagnosis made despite one week of inpatient investigation. However, since underlying diseases are often reported for classical FUO, these presentations may not be considered to be of “unknown origin”. Rather, the aetiology of prolonged fever may resolve, or not resolve. The definition of fever with unresolved cause (true FUO) is difficult, as it is a moving target, given the constant advancement of imaging and biomarker analysis. Therefore, the prevalence of fever with unresolved cause (FUO) is unknown.

In this review, we report such a case of prolonged fever, which initially has presented as classical FUO, and discuss current literature. Furthermore, we will give an outlook, how a prospective study on FUO will allow to solve outstanding issues like the utility of different diagnostic investigations, and the types and prevalence of various underlying diseases.

An Overview of Infections Associated With Soft Tissue Facial Fillers: Identification, Prevention, and Treatment

PURPOSE

The purpose of this study was to provide an overview of infections associated with facial soft tissue fillers.

MATERIALS AND METHODS

A literature review was performed which evaluated infections associated with facial soft tissue fillers.

RESULTS

Infection rates with soft tissue fillers are low and are estimated at 0.04 to 0.2%. Most of these infections arise when skin contaminants infiltrate the injection site at the time of injection. These infections can occur early, up to several days after treatment, or delayed, occurring weeks to years after treatment. Reactions vary based on the filler absorbability and duration. Early recognition and treatment are important factors in managing our cosmetic surgery patients.

CONCLUSION

Although facial fillers are safe and predictable, infections can still occur. Oral and maxillofacial surgeons need to be able to prevent, recognize, and properly manage infections related to these popular injections.

99mTc-MIBI Lung Scintigraphy in the Assessment of Pulmonary Involvement in Interstitial Lung Disease and Its Comparison With Pulmonary Function Tests and High-Resolution Computed Tomography: A Preliminary Study

The differentiation of active inflammatory processes from an inactive form of the disease is of great value in the management of interstitial lung disease (ILD). The aim of this investigation was to assess the efficacy of 99mTc-methoxy-isobutyl-isonitrile (99mTc-MIBI) scans in distinguishing the severity of the disease compared to radiological and clinical parameters.In total, 19 known cases of ILD were included in this study and were followed up for 1 year. Five patients without lung disease were considered as the control group. The patients underwent pulmonary function tests (PFTs) and high-resolution computed tomography scans, followed by 99mTc-MIBI scanning. The 99mTc-MIBI scans were analyzed either qualitatively (subjectively) or semiquantitatively.All 19 ILD patients demonstrated a strong increase in 99mTc-MIBI uptake in the lungs compared to the control group. The 99mTc-MIBI scan scores were higher in the patient group in both the early phase (0.24[0.19-0.31] vs 0.11[0.10-0.15], P < 0.05) and the delayed phase (0.15[0.09-0.27] vs 0.04[0.01-0.09], P < 0.05) compared with the control group. A positive correlation was detected between the 99mTc-MIBI scan and the high-resolution computed tomography (HRCT) scores (Spearman's correlation coefficient = 0.65, P < 0.02) in the early phase but not in the delayed phase in patients (P > 0.14). The 99mTc-MIBI scan scores were not significantly correlated with the PFT findings (P > 0.05). In total, 5 patients died and 14 patients were still alive over the 1-year follow-up period. There was also a significant difference between the uptake intensity of 99mTc-MIBI and the outcome in the early phase (dead: 0.32[0.29-0.43] vs alive: 0.21[0.18-0.24], P < 0.05) and delayed phase (dead: 0.27[0.22-0.28] vs alive: 0.10[0.07-0.19], P < 0.05).The washout rate was ~40 min starting from 20 min up to 60 min and this rate was significantly different in our 2 study groups (ILD: 46.61[15.61-50.39] vs NL: 70.91[27.09-116.36], P = 0.04).The present study demonstrated that 99mTc-MIBI lung scans might distinguish the severity of pulmonary involvement in early views, which were well correlated with HRCT findings. These results also revealed that 99mTc-MIBI lung scans might be used as a complement to other diagnostic and clinical examinations in terms of functional information in ILD; however, further investigations are strongly required.

The value of 18-FDG PET/CT in the diagnosis and management of implant-related infections of the tibia: a case series

BACKGROUND

Positron emission tomography (PET) combined with Computerised Tomography (CT) is gaining ground in clinical settings due to its added value of combined metabolic and anatomical imaging. PET/CT has shown promising results in diagnosing both acute and chronic infection of the axial and appendicular skeleton. PET imaging has an advantage in patients with metallic implants because FDG uptake, in contrast to magnetic resonance imaging (MRI) and standard computed tomography (CT), is not hampered by metallic artifacts. The role of PET/CT in the evaluation of implant-related infections involving the tibia in particular has not been thoroughly studied.

PURPOSE

To investigate the usefulness of 18-FDG PET/CT in the diagnosis and treatment of implant-related infections of the tibia following osteosynthesis.

METHODS

We reviewed 10 patients who underwent internal fixation to the tibia following trauma (4 open fractures, 6 closed fractures) and presented later with clinical signs of a possible implant-related infection. In evaluating the patients we used standard work-up methods (standard radiographs, lab tests) as well as advanced imaging techniques (PET/CT) in order to confirm the diagnosis and decide upon the preferred treatment. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were then calculated for PET/CTs ability to predict presence of infection using intraoperative cultures as the gold standard.

RESULTS

PET/CT validated our working diagnosis 9 out of 10 patients. In particular, it helped distinguish between: infected nonunion (n=4), aseptic nonunion (n=1), soft tissue infection (n=2) and chronic osteomyelitis (n=3). The overall sensitivity and specificity of PET/CT for identifying an osseous infection were 85.7% and 100%, respectively. The PPV and NPV were 100% and 75%, respectively.

CONCLUSION

PET/CT is a promising imaging modality that can aid in the work up of patients with suspected implant-related infections of the tibia following osteosynthesis, and may be used as a supportive measure in clinical decision making.

[(18)F]FDG-6-P as a novel in vivo tool for imaging staphylococcal infections

BACKGROUND

Management of infection is a major clinical problem. Staphylococcus aureus is a Gram-positive bacterium which colonises approximately one third of the adult human population. Staphylococcal infections can be life-threatening and are frequently complicated by multi-antibiotic resistant strains including methicillin-resistant S. aureus (MRSA). Fluorodeoxyglucose ([(18)F]FDG) imaging has been used to identify infection sites; however, it is unable to distinguish between sterile inflammation and bacterial load. We have modified [(18)F]FDG by phosphorylation, producing [(18)F]FDG-6-P to facilitate specific uptake and accumulation by S. aureus through hexose phosphate transporters, which are not present in mammalian cell membranes. This approach leads to the specific uptake of the radiopharmaceutical into the bacteria and not the sites of sterile inflammation.

METHODS

[(18)F]FDG-6-P was synthesised from [(18)F]FDG. Yield, purity and stability were confirmed by RP-HPLC and iTLC. The specificity of [(18)F]FDG-6-P for the bacterial universal hexose phosphate transporter (UHPT) was confirmed with S. aureus and mammalian cell assays in vitro. Whole body biodistribution and accumulation of [(18)F]FDG-6-P at the sites of bioluminescent staphylococcal infection were established in a murine foreign body infection model.

RESULTS

In vitro validation assays demonstrated that [(18)F]FDG-6-P was stable and specifically transported into S. aureus but not mammalian cells. [(18)F]FDG-6-P was elevated at the sites of S. aureus infection in vivo compared to uninfected controls; however, the increase in signal was not significant and unexpectedly, the whole-body biodistribution of [(18)F]FDG-6-P was similar to that of [(18)F]FDG.

CONCLUSIONS

Despite conclusive in vitro validation, [(18)F]FDG-6-P did not behave as predicted in vivo. However at the site of known infection, [(18)F]FDG-6-P levels were elevated compared with uninfected controls, providing a higher signal-to-noise ratio. The bacterial UHPT can transport hexose phosphates other than glucose, and therefore alternative sugars may show differential biodistribution and provide a means for specific bacterial detection.

Seeing stem cells at work in vivo

Stem cell based-therapies are novel therapeutic strategies that hold key for developing new treatments for diseases conditions with very few or no cures. Although there has been an increase in the number of clinical trials involving stem cell-based therapies in the last few years, the long-term risks and benefits of these therapies are still unknown. Detailed in vivo studies are needed to monitor the fate of transplanted cells, including their distribution, differentiation, and longevity over time. Advancements in non-invasive cellular imaging techniques to track engrafted cells in real-time present a powerful tool for determining the efficacy of stem cell-based therapies. In this review, we describe the latest approaches to stem cell labeling and tracking using different imaging modalities.

Clinical utility of indium 111-labeled white blood cell scintigraphy for evaluation of suspected infection

We assessed the clinical utility of indium 111–labeled white blood cell scans at our tertiary referral center from 2005 to 2011. Overall, scans meaningfully impacted clinical care <50% of the time. Scan utility was greater for suspected vascular graft infections or osteomyelitis.

Background

 We sought to characterize the clinical utility of indium 111 (¹¹¹In)–labeled white blood cell (WBC) scans by indication, to identify patient populations who might benefit most from this imaging modality.

Methods

 Medical records for all patients who underwent ¹¹¹In-labeled WBC scans at our tertiary referral center from 2005 to 2011 were reviewed. Scan indication, results, and final diagnosis were assessed independently by 2 infectious disease physicians. Reviewers also categorized the clinical utility of each scan as helpful vs not helpful with diagnosis and/or management according to prespecified criteria. Cases for which clinical utility could not be determined were excluded from the utility assessment.

Results

 One hundred thirty-seven scans were included in this analysis; clinical utility could be determined in 132 (96%) cases. The annual number of scans decreased throughout the study period, from 26 in 2005 to 13 in 2011. Forty-one (30%) scans were positive, and 85 (62%) patients were ultimately determined to have an infection. Of the evaluable scans, 63 (48%) scans were deemed clinically useful. Clinical utility varied by scan indication: ¹¹¹In-labeled WBC scans were more helpful for indications of osteomyelitis (35/50, 70% useful) or vascular access infection (10/15, 67% useful), and less helpful for evaluation of fever of unknown origin (12/35, 34% useful).

Conclusions

 ¹¹¹In-labeled WBC scans were useful for patient care less than half of the time at our center. Targeted ordering of these scans for indications in which they have greater utility, such as suspected osteomyelitis and vascular access infections, may optimize test utilization.

Antimicrobial peptides: their role as infection-selective tracers for molecular imaging

Antimicrobial peptides (AMPs) are a heterogeneous class of compounds found in a variety of organisms including humans and, so far, hundreds of these structures have been isolated and characterised. They can be described as natural microbicide, selectively cytotoxic to bacteria, whilst showing minimal cytotoxicity towards the mammalian cells of the host organism. They act by their relatively strong electrostatic attraction to the negatively charged bacterial cells and a relatively weak interaction to the eukaryote host cells. The ability of these peptides to accumulate at sites of infection combined with the minimal host's cytotoxicity motivated for this review to highlight the role and the usefulness of AMPs for PET with emphasis on their mechanism of action and the different interactions with the bacterial cell. These details are key information for their selective properties. We also describe the strategy, design, and utilization of these peptides as potential radiopharmaceuticals as their combination with nuclear medicine modalities such as SPECT or PET would allow noninvasive whole-body examination for detection of occult infection causing, for example, fever of unknown origin.

Regional Cerebral Blood-Flow with 99mTc-ECD Brain Perfusion SPECT in Landau-Kleffner Syndrome: Report of Two Cases

Landau-Kleffner syndrome (LKS) is a rare childhood disorder characterized by acquired aphasia and epilepsy. 99mTc-ECD SPECT imaging was performed in two right-handed children with LKS. A relative decrease in perfusion was found in the left frontal-temporal cortices of both patients as well as in the left and right parietal cortices of one patient with aphasia, without clinical epilepsy. The degree of regional cerebral perfusion impairment did not correlate with the severity of the clinical and EEG abnormalities, but the area of hypoperfusion was compatible with the speech area of the brain. Overall, although asymmetrical temporoparietal perfusion appears as a common finding in LKS, SPECT findings in LKS alone cannot elucidate the pathogenic features of the disorder in the brain. Here, we present two cases of LKS in which we investigated SPECT perfusion scans.

Cell based therapies for ischemic stroke: from basic science to bedside

Cell therapy is emerging as a viable therapy to restore neurological function after stroke. Many types of stem/progenitor cells from different sources have been explored for their feasibility and efficacy for the treatment of stroke. Transplanted cells not only have the potential to replace the lost circuitry, but also produce growth and trophic factors, or stimulate the release of such factors from host brain cells, thereby enhancing endogenous brain repair processes. Although stem/progenitor cells have shown a promising role in ischemic stroke in experimental studies as well as initial clinical pilot studies, cellular therapy is still at an early stage in humans. Many critical issues need to be addressed including the therapeutic time window, cell type selection, delivery route, and in vivo monitoring of their migration pattern. This review attempts to provide a comprehensive synopsis of preclinical evidence and clinical experience of various donor cell types, their restorative mechanisms, delivery routes, imaging strategies, future prospects and challenges for translating cell therapies as a neurorestorative regimen in clinical applications.

Antimicrobial peptides as infection imaging agents: better than radiolabeled antibiotics

Nuclear medicine imaging techniques offer whole body imaging for localization of number and site of infective foci inspite of limitation of spatial resolution. The innate human immune system contains a large member of important elements including antimicrobial peptides to combat any form of infection. However, development of antibiotics against bacteria progressed rapidly and gained popularity over antimicrobial peptides but even powerful antimicrobials failed to reduce morbidity and mortality due to emergence of mutant strains of bacteria resulting in antimicrobial resistance. Differentiation between infection and inflammation using radiolabeled compounds with nuclear medicine techniques has always been a dilemma which is still to be resolved. Starting from nonspecific tracers to specific radiolabeled tracers, the question is still unanswered. Specific radiolabeled tracers included antibiotics and antimicrobial peptides which bind directly to the bacteria for efficient localization with advanced nuclear medicine equipments. However, there are merits and demerits attributed to each. In the current paper, radiolabeled antibiotics and radiolabeled peptides for infection localization have been discussed starting with the background of primitive nonspecific tracers. Radiolabeled antimicrobial peptides have certain merits compared with labeled antibiotics which make them superior agents for localization of infective focus.

High prevalence of upper urinary tract involvement detected by 111indium-oxine leukocyte scintigraphy in patients with candiduria

The purpose of this investigation was to assess the prevalence of upper urinary tract involvement in patients with candiduria by means of (111)indium-oxine-labeled leukocyte scintigraphy. An observational cohort study of patients with confirmed candiduria was conducted in an acute-care teaching hospital in Spain from March 2006 through February 2009. An (111)In-labeled leukocyte scan was performed in order to assess the upper urinary tract involvement. A series of non-matched patients without candiduria nor bacteriuria undergoing scintigraphy to exclude infections in other sites than the urinary tract was also studied. Demographics, baseline illness, and clinical data were recorded. Candiduria was detected in 428 patients, and scintigraphy was performed in 35 of these patients. Twenty-nine patients without candiduria nor bacteriuria were also studied. Positive renal scintigraphy was documented in 24 (68%) patients with confirmed candiduria and in 3 (10%) patients without candiduria (p < 0.005). Renal uptake was not associated with a higher mortality nor with re-admissions. Subclinical pyelonephritis could be more frequent in patients with candiduria than it has been previously considered.

Role of gallium-67 scintigraphy in the evaluation of occult sepsis in the medical ICU

Patients in intensive care units (ICUs) frequently have multiple infections or persistent fever despite management. The aim of this study was to evaluate the diagnostic contribution of gallium-67 scintigraphy in ICU patients with suspected occult sepsis. One hundred and seventeen patients (>18 years) who had undergone gallium-67 scintigraphy in the ICU of our medical center over a 3-year period were retrospectively reviewed and analyzed. Patients were categorized into Group 1 (n = 84), those with a known infectious source, but who still had persistent fever or sepsis despite antibiotic treatment or abscess drainage; or Group 2 (n = 33), those without an evident infectious source after clinical, physical, and imaging studies. Among the 117 patients, 19 (16.2%) had a new diagnosis. In Group 1, 12 patients (14%) had a new infection, including pneumonia (4 patients), bed sore infection (2 patients), pulmonary tuberculosis (2 patients), leg cellulitis (1 patient), psoas muscle abscess (1 patient), osteomyelitis (1 patient), and infective endocarditis (1 patient). In Group 2, seven patients (21.2%) had a new infectious source, including septic arthritis (3 patients), osteomyelitis (2 patients), neck abscess (1 patient), and cholecystitis (1 patient). Significant differences were not observed between patients with positive and negative findings on gallium-67 scintigraphy in characteristics, underlying diseases, laboratory data, and outcomes. Gallium-67 scintigraphy helped to detect new or additional infectious sites, particularly bone, joint, and soft tissues. However, differences in hospital stay and mortality were not observed between patients with positive and negative findings.

Feasibility of treating irradiated bone with intramedullary delivered autologous mesenchymal stem cells

Background. We aimed to explore (i) the short-term retention of intramedullary implanted mesenchymal stem cells BMSCs and (ii) their impact on the bone blood flow and metabolism in a rat model of hindlimb irradiation. Methods. Three months after 30 Gy irradiation, fourteen animals were referred into 2 groups: a sham-operated group (n = 6) and a treated group (n = 8) in which ¹¹¹In-labelled BMSCs (2 × 10⁶ cells) were injected in irradiated tibias. Bone blood flow and metabolism were assessed by serial ^99mTc-HDP scintigraphy and 1-wk cell retention by recordings of ^99mTc/¹¹¹In activities. Results. The amount of intramedullary implanted BMSCs was of 70% at 2 H, 40% at 48 H, and 38% at 168 H. Bone blood flow and bone metabolism were significantly increased during the first week after cell transplantation, but these effects were found to reduce at 2-mo followup. Conclusion. Short-term cell retention produced concomitant enhancement in irradiated bone blood flow and metabolism.

A unique finding on gallium-67 scintigraphy: widespread fatal skin manifestations of Pseudomonas sepsis

We report a case of a 25-year-old woman presented with neutropenic fever after chemotherapy for the relapse of acute biphenotypic leukemia. Gallium-67 scintigraphy for the detection of infectious foci demonstrated a unique pattern of numerous foci with intense and varying-sized radioactivity spreading throughout the body. The subsequent skin biopsy and culture proved Pseudomonas infection. Therefore, this unique image, in combination with clinical information, was compatible with cutaneous manifestations of Pseudomonas sepsis. Eventually, the patient died of uncontrolled systemic infection despite the aggressive antibiotic treatment. This case reminded clinicians and nuclear medicine physicians to notice the potentially fatal finding on gallium-67 scan.