Gallium-68 PET: A Powerful Generator-based Alternative to Infection and Inflammation Imaging

89Zr-leukocyte labelling for cell trafficking: in vitro and preclinical investigations

BACKGROUND

The non-invasive imaging of leukocyte trafficking to assess inflammatory areas and monitor immunotherapy is currently generating great interest. There is a need to develop more robust cell labelling and imaging approaches to track living cells. Positron emission tomography (PET), a highly sensitive molecular imaging technique, allows precise signals to be produced from radiolabelled moieties. Here, we developed a novel leukocyte labelling approach with the PET radioisotope zirconium-89 (89Zr, half-life of 78.4 h). Experiments were carried out using human leukocytes, freshly isolated from whole human blood.

RESULTS

The 89Zr-leukocyte labelling efficiency ranged from 46 to 87% after 30-60 min. Radioactivity concentrations of labelled cells were up to 0.28 MBq/1 million cells. Systemically administered 89Zr-labelled leukocytes produced high-contrast murine PET images at 1 h-5 days post injection. Murine biodistribution data showed that cells primarily distributed to the lung, liver, and spleen at 1 h post injection, and are then gradually trafficked to liver and spleen over 5 days. Histological analysis demonstrated that exogenously 89Zr-labelled human leukocytes were present in the lung, liver, and spleen at 1 h post injection. However, intravenously injected free [89Zr]Zr4+ ion showed retention only in the bone with no radioactivity in the lung at 5 days post injection, which implied good stability of radiolabelled leukocytes in vivo.

CONCLUSIONS

Our study presents a stable and generic radiolabelling technique to track leukocytes with PET imaging and shows great potential for further applications in inflammatory cell and other types of cell trafficking studies.

A decade of ubiquicidin development for PET imaging of infection: A systematic review

BACKGROUND

Ubiquicidin is a peptide fragment with selective binding to negatively charged bacterial cell membranes. Besides its earlier labelling with gamma emitting radionuclides, it has been labelled with Positron Emission Tomography (PET) radionuclides in the last decade for imaging infection and distinguishing infectious disease from sterile inflammation. This systematic review aims to evaluate the technology readiness level of PET based ubiquicidin radiopharmaceuticals.

METHODS

Two independent researchers reviewed all articles and abstracts pertaining ubiquicidin and PET imaging that are currently available. Scopus, Google Scholar and PubMed/Medline were used in the search. Upon completion of the literature search all articles and abstracts were evaluated and duplicates were excluded. All non-PET articles as well as review articles without new data were deemed ineligible.

RESULTS

From a total of 17 papers and 10 abstracts the studies were grouped into development, preclinical and clinical studies. Development was published in 15/17 (88%) publications and 6/10 (60%) abstracts, preclinical applications in 9/17 (53%) publications and 1/10 (10%) of abstracts. Finally, clinical studies made up 6/17 (35%) of full publications and 4/10 (40%) of the available abstracts. Development results were the most abundant. All the findings in the different areas of development of ubiquicidin as PET radiopharmaceutical are summarized in this paper.

CONCLUSION

Labelling procedures are generally uncomplicated and relatively fast and there are indications of adequate product stability. The production of PET radiopharmaceuticals based on UBI will therefore not be a barrier for clinical introduction of this technology. Systematization and unification of criteria for preclinical imaging and larger clinical trials are needed to ensure the translation of this radiopharmaceutical into the clinic. Therefore a conclusion with regards to the clinical relevance of ubiquicidin based PET is not yet possible.

PET/CT features of a novel gallium-68 labelled hypoxia seeking agent in patients diagnosed with tuberculosis: a proof-of-concept study

INTRODUCTION

Positron emission tomography/computed tomography (PET/CT) in infection and inflammation has yielded promising results across a range of radiopharmaceuticals. In particular, PET/CT imaging of tuberculosis (TB) allows for a better understanding of this complex disease by providing insights into molecular processes within the TB microenvironment. TB lesions are hypoxic with research primarily focussed on cellular processes occurring under hypoxic stress. With the development of hypoxia seeking PET/CT radiopharmaceuticals, that can be labelled in-house using a germanium-68/gallium-68 (68Ge/68Ga) generator, a proof-of-concept for imaging hypoxia in TB is presented.

METHODS

Ten patients diagnosed with TB underwent whole-body PET/CT imaging, 60-90 min after intravenous administration of 74-185 MBq (2-5 mCi) 68Ga-nitroimidazole. No oral or intravenous contrast was administered. Images were visually and semiquantitatively assessed for abnormal 68Ga-uptake in the lungs.

RESULTS

A total of 28 lesions demonstrating hypoxic uptake were identified. Low- to moderate-uptake was seen in nodules, areas of consolidation and cavitation as well as effusions. The mean standard uptake value (SUVmean) of the lesions was 0.47 (IQR, 0.32-0.82) and SUVmax was 0.71 (IQR, 0.41-1.11). The lesion to muscle ratio (median, 1.70; IQR, 1.15-2.31) was higher than both the left ventricular and the aorta lesion to blood ratios.

CONCLUSION

Moving towards the development of unique host-directed therapies (HDT), modulation of oxygen levels may improve therapeutic outcome by reprogramming TB lesions to overcome hypoxia. This proof-of-concept study suggests that hypoxia in TB lesions can be imaged and quantified using 68Ga-nitroimidazole PET/CT. Subsequently, hypoxic load can be estimated to inform personalised treatment plans of patients diagnosed with TB.

68Ga-labeled dendrimer-entrapped gold nanoparticles for PET/CT dual-modality imaging and immunotherapy of tumors

The design and fabrication of nanoplatforms with both nuclear medical imaging and therapeutic functions remain challenging in current precision nanomedicine. Herein, we report the design of a novel nanoplatform based on glucose-modified dendrimer-entrapped gold nanoparticles (Au DENPs) labeled with radionuclide ⁶⁸Ga and incorporated with cytosine-guanine (CpG) oligonucleotide for positron emission tomography (PET)/computed tomography (CT) dual-mode imaging and immunotherapy of tumors. In this study, generation 5 poly(amidoamine) (PAMAM) dendrimers were first modified to have 8.2 DOTA and 7.3 polyethylene glycol with the other end functionalized with 2-amino-2-deoxy-D-glucose (DG) for each dendrimer, entrapped with Au NPs, and then radiolabeled with ⁶⁸Ga through the DOTA chelation. The synthesized DG-Au DENPs have good cytocompatibility, targeting specificity toward cancer cells expressing glucose transporters, and the ability to be labeled by ⁶⁸Ga with great labeling efficiency (≥85%) and stability (≥95%). After being loaded with CpG, the formed DG-Au DENPs/CpG polyplexes were proven to be used for tumor dual-mode PET/CT imaging and immunotherapy by effectively maturing dendritic cells to initiate a T cell-based antitumor immune response in vivo. Compared with the DG-free polyplexes, the developed DG-Au DENPs/CpG polyplexes show a much more sensitive imaging effect and better inhibition effect of tumors. These findings demonstrate a unique design of ⁶⁸Ga-labeled DG-Au DENPs, a promising theranostic nanoplatform that may be extended to tackle different tumor types.

Malignant External Otitis in a Patient With Diabetes Mellitus: Comparison of Bone Scan SPECT/CT and 68Ga-Citrate PET/CT

ABSTRACT

We reported a 66-year-old woman with malignant external otitis who was referred to our department for evaluation of disease extension. Both 99mTc-MDP bone SPECT/CT and 68Ga-citrate PET/CT were done for the patient. Both studies showed concordant areas of increased uptake in the petrous bone. In addition, 68Ga-citrate PET/CT showed soft tissue infection in the nasopharyngeal wall. Our case showed the potential of 68Ga-citrate PET/CT for evaluation of malignant external otitis.

Cold Kit Labeling: The Future of 68Ga Radiopharmaceuticals?

Over the last couple of decades, gallium-68 (68Ga) has gained a formidable interest for PET molecular imaging of various conditions, from cancer to infection, through cardiac pathologies or neuropathies. It has gained routine use, with successful radiopharmaceuticals such as somatostatin analogs ([68Ga]Ga-DOTATOC and [68Ga]GaDOTATATE) for neuroendocrine tumors, and PSMA ligands for prostate cancer. It represents a major clinical impact, particularly in the context of theranostics, coupled with their 177Lu-labeled counterparts. Beside those, a bunch of new 68Ga-labeled molecules are in the preclinical and clinical pipelines, with some of them showing great promise for patient care. Increasing clinical demand and regulatory issues have led to the development of automated procedures for the production of 68Ga radiopharmaceuticals. However, the widespread use of these radiopharmaceuticals may rely on simple and efficient radiolabeling methods, undemanding in terms of equipment and infrastructure. To make them technically and economically accessible to the medical community and its patients, it appears mandatory to develop a procedure similar to the well-established kit-based 99mTc chemistry. Already available commercial kits for the production of 68Ga radiopharmaceuticals have demonstrated the feasibility of using such an approach, thus paving the way for more kit-based 68Ga radiopharmaceuticals to be developed. This article discusses the development of 68Ga cold kit radiopharmacy, including technical issues, and regulatory aspects.

Fully Automated Macro- and Microfluidic Production of [68Ga]Ga-Citrate on mAIO® and iMiDEVTM Modules

⁶⁸Ga-radionuclide has gained importance due to its availability via ⁶⁸Ge/⁶⁸Ga generator or cyclotron production, therefore increasing the number of ⁶⁸Ga-based PET radiopharmaceuticals available in clinical practice. [⁶⁸Ga]Ga-citrate PET has been shown to be prominent for detection of inflammation/infection of the musculoskeletal, gastrointestinal, respiratory, and cardiovascular systems. Automation and comparison between conventional and microfluidic production of [⁶⁸Ga]Ga-citrate was performed using miniAllInOne^® (Trasis) and iMiDEV™ (PMB-Alcen) synthetic modules. Fully automated procedures were elaborated for cGMP production of tracer. In order to facilitate the tracer approval as a radiopharmaceutical for clinical use, a new method for radiochemical identity determination by HPLC analysis to complement standard TLC radiochemical purity measurement was developed. The results showed higher radiochemical yields when using MCX cartridge on the conventional module mAIO^®, while a PS-H+ cation exchanger was shown to be preferred for integration into the microfluidic cassette of iMiDEV™ module. In this study, the fully automated radiosynthesis of [⁶⁸Ga]Ga-citrate using different synthesizers demonstrated reliable and reproducible radiochemical yields. In order to demonstrate the applicability of [⁶⁸Ga]Ga-citrate, in vitro and in vivo studies were performed showing similar characteristics of the tracer obtained using macro- and microfluidic ways of production.

Tuberculosis: Role of Nuclear Medicine and Molecular Imaging With Potential Impact of Neutrophil-Specific Tracers

With Tuberculosis (TB) affecting millions of people worldwide, novel imaging modalities and tools, particularly nuclear medicine and molecular imaging, have grown with greater interest to assess the biology of the tuberculous granuloma and evolution thereof. Much early work has been performed at the pre-clinical level using gamma single photon emission computed tomography (SPECT) agents exploiting certain characteristics of Mycobacterium tuberculosis (MTb). Both antituberculous SPECT and positron emission tomography (PET) agents have been utilised to characterise MTb. Other PET tracers have been utilised to help to characterise the biology of MTb (including Gallium-68-labelled radiopharmaceuticals). Of all the tracers, 2-[¹⁸F]FDG has been studied extensively over the last two decades in many aspects of the treatment paradigm of TB: at diagnosis, staging, response assessment, restaging, and in potentially predicting the outcome of patients with latent TB infection. Its lower specificity in being able to distinguish different inflammatory cell types in the granuloma has garnered interest in reviewing more specific agents that can portend prognostic implications in the management of MTb. With the neutrophil being a cell type that portends this poorer prognosis, imaging this cell type may be able to answer more accurately questions relating to the tuberculous granuloma transmissivity and may help in characterising patients who may be at risk of developing active TB. The formyl peptide receptor 1(FPR1) expressed by neutrophils is a key marker in this process and is a potential target to characterise these areas. The pre-clinical work regarding the role of radiolabelled N-cinnamoyl –F-(D) L – F – (D) –L F (cFLFLF) (which is an antagonist for FPR1) using Technetium 99m-labelled conjugates and more recently radiolabelled with Gallium-68 and Copper 64 is discussed. It is the hope that further work with this tracer may accelerate its potential to be utilised in responding to many of the current diagnostic dilemmas and challenges in TB management, thereby making the tracer a translatable option in routine clinical care.

Advances in Radiopharmaceutical Sciences for Vascular Inflammation Imaging: Focus on Clinical Applications

Biomedical imaging technologies offer identification of several anatomic and molecular features of disease pathogenesis. Molecular imaging techniques to assess cellular processes in vivo have been useful in advancing our understanding of several vascular inflammatory diseases. For the non-invasive molecular imaging of vascular inflammation, nuclear medicine constitutes one of the best imaging modalities, thanks to its high sensitivity for the detection of probes in tissues. 2-[¹⁸F]fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) is currently the most widely used radiopharmaceutical for molecular imaging of vascular inflammatory diseases such as atherosclerosis and large-vessel vasculitis. The combination of [¹⁸F]FDG and positron emission tomography (PET) imaging has become a powerful tool to identify and monitor non-invasively inflammatory activities over time but suffers from several limitations including a lack of specificity and avid background in different localizations. The use of novel radiotracers may help to better understand the underlying pathophysiological processes and overcome some limitations of [¹⁸F]FDG PET for the imaging of vascular inflammation. This review examines how [¹⁸F]FDG PET has given us deeper insight into the role of inflammation in different vascular pathologies progression and discusses perspectives for alternative radiopharmaceuticals that could provide a more specific and simple identification of pathologies where vascular inflammation is implicated. Use of these novel PET tracers could lead to a better understanding of underlying disease mechanisms and help inform the identification and stratification of patients for newly emerging immune-modulatory therapies. Future research is needed to realize the true clinical translational value of PET imaging in vascular inflammatory diseases.

[68Ga]Ga-4HMSA a promising new PET tracer for imaging inflammation

BACKGROUND

Imaging diagnosis of inflammation has been challenging for many years. Inflammation imaging agents commonly used in nuclear medicine, such as [⁶⁷Ga]Ga-citrate and 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) showed some limitations. The identification of a radiotracer with high specificity and low radiation dose is clinically important. With the commercialization of ⁶⁸Ge/⁶⁸Ga generators and the high ⁶⁸Ga cyclotron production capacity, the study of ⁶⁸Ga-based tracer for inflammation has increased and shown good potential. In the present work, we report the synthesis of 4HMSA, a new acyclic chelator, and its first investigation for ⁶⁸Ga complexation and as a new positron emission tomography (PET) imaging agent of inflammation in comparison to [⁶⁸Ga]Ga-citrate.

RESULTS

The present experimental studies have shown that the novel [⁶⁸Ga]Ga-4HMSA is stable allowing imaging of inflammation in a preclinical model of adjuvant- and pathogen-based inflammation involving intraplantar injection of complete Freund's adjuvant (CFA). We also found that [⁶⁸Ga]Ga-4HMSA displayed similar uptakes in the inflamed paw than [⁶⁸Ga]Ga-citrate, which are superior compared to those of contralateral (non-injected) paws at days 1-3 from PET imaging. [⁶⁸Ga]Ga-citrate accumulated in the upper body of the animal such as the liver, lungs and the heart, whereas the [⁶⁸Ga]Ga-4HMSA revealed low uptakes in the majority of the organs and was cleared relatively rapidly from blood circulation through the kidneys and bladder.

CONCLUSION

The results highlight the potential of [⁶⁸Ga]Ga-4HMSA as an interesting alternative to [⁶⁸Ga]Ga-citrate for inflammation imaging by PET. The new PET tracer also offers additional advantages than [⁶⁸Ga]Ga-citrate in term of dosimetry and lower overall background activity.

Pathophysiology and Molecular Imaging of Diabetic Foot Infections

Diabetic foot infection is the leading cause of non-traumatic lower limb amputations worldwide. In addition, diabetes mellitus and sequela of the disease are increasing in prevalence. In 2017, 9.4% of Americans were diagnosed with diabetes mellitus (DM). The growing pervasiveness and financial implications of diabetic foot infection (DFI) indicate an acute need for improved clinical assessment and treatment. Complex pathophysiology and suboptimal specificity of current non-invasive imaging modalities have made diagnosis and treatment response challenging. Current anatomical and molecular clinical imaging strategies have mainly targeted the host's immune responses rather than the unique metabolism of the invading microorganism. Advances in imaging have the potential to reduce the impact of these problems and improve the assessment of DFI, particularly in distinguishing infection of soft tissue alone from osteomyelitis (OM). This review presents a summary of the known pathophysiology of DFI, the molecular basis of current and emerging diagnostic imaging techniques, and the mechanistic links of these imaging techniques to the pathophysiology of diabetic foot infections.

Pathophysiology and Molecular Imaging of Diabetic Foot Infections

Diabetic foot infection is the leading cause of non-traumatic lower limb amputations worldwide. In addition, diabetes mellitus and sequela of the disease are increasing in prevalence. In 2017, 9.4% of Americans were diagnosed with diabetes mellitus (DM). The growing pervasiveness and financial implications of diabetic foot infection (DFI) indicate an acute need for improved clinical assessment and treatment. Complex pathophysiology and suboptimal specificity of current non-invasive imaging modalities have made diagnosis and treatment response challenging. Current anatomical and molecular clinical imaging strategies have mainly targeted the host's immune responses rather than the unique metabolism of the invading microorganism. Advances in imaging have the potential to reduce the impact of these problems and improve the assessment of DFI, particularly in distinguishing infection of soft tissue alone from osteomyelitis (OM). This review presents a summary of the known pathophysiology of DFI, the molecular basis of current and emerging diagnostic imaging techniques, and the mechanistic links of these imaging techniques to the pathophysiology of diabetic foot infections.

Medical Imaging in the Diagnosis of Schistosomiasis: A Review

Schistosomiasis is one of the most important parasitic diseases and it is endemic in tropical and subtropical areas. Clinical and laboratory data are fundamental for the diagnosis of schistosomiasis, but diagnostic imaging techniques such as x-rays, ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography/computed tomography (PET/CT) may be helpful in the evaluation of disease severity and complications. In this context, the aim of this review is to explore the actual role of diagnostic imaging in the diagnosis of schistosomiasis, underlining advantages and drawbacks providing information about the utilization of diagnostic imaging techniques in this context. Furthermore, we aim to provide a useful guide regarding imaging features of schistosomiasis for radiology and nuclear medicine physicians of non-endemic countries: in fact, in the last years non-endemic countries have experienced important flows of migrants from endemic areas, therefore it is not uncommon to face cases of this disease in daily practice.

Physiological Animal Imaging with 68Ga-Citrate

BACKGROUND

Gallium-68 is an ideal research and hospital-based PET radioisotope. The uptake mechanism of Gallium citrate is a combination of specific and non-specific processes, for example, vasodilatation, increased vascular permeability, plasma transferrin binding and lactoferrin and siderophores.

OBJECTIVE

In this study, by applying the ⁶⁸Ge/⁶⁸Ga generator product, a simple technique for the synthesis and quality control of 68Ga-citrate was introduced and was followed by preliminary animal studies.

METHODS

The synthesis of ⁶⁸Ga-citrate was performed with a cationic method using the Scintomics automated synthesis system (Scintomics GmbH GRP module 4V). Since the standard procedure for quality control (QC) was not available, the definition of chemical and radiochemical purity of ⁶⁸Ga-citrate was carried out according to the ICH Q2(R1) guideline. The standard QC tests were analysed with Scintomics 8100 radio-HPLC system equipped with a radioactivity detector. In this study, a New Zealand rabbit weighing 2520 g was used for PET/CT images.

RESULTS

⁶⁸Ga-citrate synthesis was performed by a cationic method without using organic solvents. The labelling efficiency was found to be >98%. The HPLC method used to assess the radiochemical purity of ⁶⁸Ga -citrate was validated as rapid, accurate and reproducible enough to apply it to patients safely. The physiological distribution of ⁶⁸Ga-citrate was investigated in a healthy rabbit. The blood pool, liver, spleen, kidneys and growth plates were the most common sites of ⁶⁸Ga-citrate involvement.

Sensing Living Bacteria in Vivo Using d-Alanine-Derived 11C Radiotracers

Incorporation of d-amino acids into peptidoglycan is a unique metabolic feature of bacteria. Since d-amino acids are not metabolic substrates in most mammalian tissues, this difference can be exploited to detect living bacteria in vivo. Given the prevalence of d-alanine in peptidoglycan muropeptides, as well as its role in several antibiotic mechanisms, we targeted this amino acid for positron emission tomography (PET) radiotracer development. d-[3-11C]Alanine and the dipeptide d-[3-11C]alanyl-d-alanine were synthesized via asymmetric alkylation of glycine-derived Schiff-base precursors with [11C]methyl iodide in the presence of a cinchonidinium phase-transfer catalyst. In cell experiments, both tracers showed accumulation by a wide variety of both Gram-positive and Gram-negative pathogens including Staphylococcus aureus and Pseudomonas aeruginosa. In a mouse model of acute bacterial myositis, d-[3-11C]alanine was accumulated by living microorganisms but was not taken up in areas of sterile inflammation. When compared to existing clinical nuclear imaging tools, specifically 2-deoxy-2-[18F]fluoro-d-glucose and a gallium citrate radiotracer, d-alanine showed more bacteria-specific uptake. Decreased d-[3-11C]alanine uptake was also observed in antibiotic-sensitive microbes after antimicrobial therapy, when compared to that in resistant organisms. Finally, prominent uptake of d-[3-11C]alanine uptake was seen in rodent models of discitis-osteomyelitis and P. aeruginosa pneumonia. These data provide strong justification for clinical translation of d-[3-11C]alanine to address a number of important human infections.

PET/CT Imaging in Soft Tissue Infection and Inflammation-An Update

Nuclear medicine procedures, including Ga-67 and labeled leucocyte SPECT/CT as well as PET/CT using 18F-FDG and recently Ga-68 tracers, have found extensive applications in the assessment of infectious and inflammatory processes in general and in soft tissues in particular. Recent published data focus on summarizing the available imaging information with the purpose of providing the referring clinicians with optimized evidence based results. Guidelines and/or recommendations of clinical societies have incorporated nuclear medicine tests (using both labeled leucocytes and FDG) in their suggested work-up for evaluation of infective endocarditis and in certain patients with suspected vascular graft infections. Joint guidelines of the European and American nuclear medicine societies include fever of unknown origin, sarcoidosis, and vasculitis among the major clinical indications that will benefit from nuclear medicine procedures, specifically from FDG PET/CT. Limitations and pitfalls for the use of radiotracers in assessment of infection and inflammation can be related to patient conditions (eg, diabetes mellitus), or to the biodistribution of a specific radiopharmaceutical. Limited presently available data on the use of functional and/or metabolic monitoring of response to infectious and inflammatory processes to treatment and with respect to the effect of drugs such as antibiotics and glucocorticoids on the imaging patterns of these patients need further confirmation.

Pediatric Musculoskeletal Imaging: The Indications for and Applications of PET/Computed Tomography

The use of PET/computed tomography (CT) for the evaluation and management of children, adolescents, and young adults continues to expand. The principal tracer used is 18F-fluorodeoxyglucose and the principal indication is oncology, particularly musculoskeletal neoplasms. The purpose of this article is to review the common applications of PET/CT for imaging of musculoskeletal issues in pediatrics and to introduce the use of PET/CT for nononcologic issues, such as infectious/inflammatory disorders, and review the use of 18F-sodium fluoride in trauma and sports-related injuries.

[11C]Para-Aminobenzoic Acid: A Positron Emission Tomography Tracer Targeting Bacteria-Specific Metabolism

Imaging studies are frequently used to support the clinical diagnosis of infection. These techniques include computed tomography (CT) and magnetic resonance imaging (MRI) for structural information and single photon emission computed tomography (SPECT) or positron emission tomography (PET) for metabolic data. However, frequently, there is significant overlap in the imaging appearance of infectious and noninfectious entities using these tools. To address this concern, recent approaches have targeted bacteria-specific metabolic pathways. For example, radiolabeled sugars derived from sorbitol and maltose have been investigated as PET radiotracers, since these are efficiently incorporated into bacteria but are poor substrates for mammalian cells. We have previously shown that para-aminobenzoic acid (PABA) is an excellent candidate for development as a bacteria-specific imaging tracer as it is rapidly accumulated by a wide range of pathogenic bacteria, including metabolically quiescent bacteria and clinical strains, but not by mammalian cells. Therefore, in this study, we developed an efficient radiosynthesis for [11C]PABA, investigated its accumulation into Escherichia coli and Staphylococcus aureus laboratory strains in vitro, and showed that it can distinguish between infection and sterile inflammation in a murine model of acute bacterial infection.

99mTc-HMPAO-leukocyte scintigraphy for diagnosis and therapy monitoring of skull base osteomyelitis

Objective

Skull base osteomyelitis (SBO) is a rare but life‐threatening disease observed in elderly diabetic patients, with high risk of recurrence and difficult therapeutic management. The diagnosis is ascertained from a set of clinical, biological, and imaging findings. CT and MRI allow initial diagnosis, but are not accurate to affirm healing at the end of therapy. 99mTc‐HMPAO‐Leucocyte Scintigraphy (LS) is highly sensitive and specific for the detection of infection. The aim of this study was to evaluate LS i) for initial diagnosis, and ii) to confirm healing at the end of antibiotherapy in SBO.

Study design

We retrospectively reviewed from November 2011 to September 2015 all patients with confirmed SBO who underwent LS twice, at diagnosis and at the end of antibiotic therapy in our nuclear medicine department (n = 27).

Methods

Clinical, biological, CT, LS, and follow‐up data were recorded in all patients. LS images (planar and tomographic performed 4 hours and 24 hours after intravenous injection of autologous Tc‐99m‐HMPAO‐leucocytes) were visually assessed and quantified.

Results

At initial diagnosis, 25 of 27 patients had a positive LS. At the end of antibiotic therapy (3 ± 1 months duration), 26 of 27 patients had a negative LS. During subsequent follow‐up (= or >6 months), the disease recurred in four patients including three with a negative postantibiotherapy LS scan.

Conclusion

In this retrospective study, LS was powerful for initial diagnostic of SBO and for healing assessment at the end of antibiotic therapy. We conclude it is a useful technique for therapeutic monitoring of SBO.

Level of Evidence

4

A Comparative 68Ga-Citrate and 68Ga-Chloride PET/CT Imaging of Staphylococcus aureus Osteomyelitis in the Rat Tibia

There may be some differences in the in vivo behavior of ⁶⁸Ga-chloride and ⁶⁸Ga-citrate leading to different accumulation profiles. This study compared ⁶⁸Ga-citrate and ⁶⁸Ga-chloride PET/CT imaging under standardized experimental models. Methods. Diffuse Staphylococcus aureus tibial osteomyelitis and uncomplicated bone healing rat models were used (n = 32). Two weeks after surgery, PET/CT imaging was performed on consecutive days using ⁶⁸Ga-citrate or ⁶⁸Ga-chloride, and tissue accumulation was confirmed by ex vivo analysis. In addition, peripheral quantitative computed tomography and conventional radiography were performed. Osteomyelitis was verified by microbiological analysis and specimens were also processed for histomorphometry. Results. In PET/CT imaging, the SUV_max of ⁶⁸Ga-chloride and ⁶⁸Ga-citrate in the osteomyelitic tibias (3.6 ± 1.4 and 4.7 ± 1.5, resp.) were significantly higher (P = 0.0019 and P = 0.0020, resp.) than in the uncomplicated bone healing (2.7 ± 0.44 and 2.5 ± 0.49, resp.). In osteomyelitic tibias, the SUV_max of ⁶⁸Ga-citrate was significantly higher than the uptake of ⁶⁸Ga-chloride (P = 0.0017). In animals with uncomplicated bone healing, no difference in the SUV_max of ⁶⁸Ga-chloride or ⁶⁸Ga-citrate was seen in the operated tibias. Conclusions. This study further corroborates the use of ⁶⁸Ga-citrate for PET imaging of osteomyelitis.

Prospective of 68Ga Radionuclide Contribution to the Development of Imaging Agents for Infection and Inflammation

During the last decade, the utilization of ⁶⁸Ga for the development of imaging agents has increased considerably with the leading position in the oncology. The imaging of infection and inflammation is lagging despite strong unmet medical needs. This review presents the potential routes for the development of ⁶⁸Ga-based agents for the imaging and quantification of infection and inflammation in various diseases and connection of the diagnosis to the treatment for the individualized patient management.

Tuberculosis

Tuberculosis (TB) is currently the world's leading cause of infectious mortality. Imaging plays an important role in the management of this disease. The complex immune response of the human body to Mycobacterium tuberculosis results in a wide array of clinical manifestations, making clinical and radiological diagnosis challenging. ¹⁸F-FDG-PET/CT is very sensitive in the early detection of TB in most parts of the body; however, the lack of specificity is a major limitation. ¹⁸F-FDG-PET/CT images the whole body and provides a pre-therapeutic metabolic map of the infection, enabling clinicians to accurately assess the burden of disease. It enables the most appropriate site of biopsy to be selected, stages the infection, and detects disease in previously unknown sites. ¹⁸F-FDG-PET/CT has recently been shown to be able to identify a subset of patients with latent TB infection who have subclinical disease. Lung inflammation as detected by ¹⁸F-FDG-PET/CT has shown promising signs that it may be a useful predictor of progression from latent to active infection. A number of studies have identified imaging features that might improve the specificity of ¹⁸F-FDG-PET/CT at some sites of extrapulmonary TB. Other PET tracers have also been investigated for their use in TB, with some promising results. The potential role and future perspectives of PET/CT in imaging TB is considered. Literature abounds on the very important role of ¹⁸F-FDG-PET/CT in assessing therapy response in TB. The use of ¹⁸F-FDG for monitoring response to treatment is addressed in a separate review.

Metabolic Imaging of Infection

Metabolic imaging has come to occupy a prominent place in the diagnosis and management of microbial infection. Molecular probes available for infection imaging have undergone a rapid evolution starting with nonspecific agents that accumulate similarly in infection, sterile inflammation, and neoplastic tissue and then extending to more targeted probes that seek to identify specific microbial species. This focus review describes the metabolic and molecular imaging techniques currently available for clinical use in infection imaging and those that have demonstrated promising results in preclinical studies with the potential for clinical applications.