The current role of gallium imaging in infection

Ga complexes of 8-hydroxyquinoline-2-carboxylic acid: Chemical speciation and biological activity

The binding ability of 8-hydroxyquinoline-2-carboxylic acid (8-HQA) towards Ga3+ has been investigated by ISEH+ (Ion Selective Electrode, glass electrode) potentiometric and UV/Vis spectrophotometric titrations in KCl(aq) at I = 0.2 mol dm-3 and at T = 298.15 K. Further experiments were also performed adopting both the metal (with Fe3+ as competing cation) and ligand-competition approaches (with EDTA as competing ligand). Results gave evidence of the formation of the [Ga(8-HQA)]+, [Ga(8-HQA)(OH)], [Ga(8-HQA)(OH)2]- and [Ga(8-HQA)2]- species, the latter being so far the most stable, as also confirmed by ESI-MS analysis. Experiments were also designed to determine the stability constants of the [Ga(EDTA)]- and [Ga(EDTA)(OH)]2- in the above conditions. Due to the relevance of Ga3+ hydrolysis in aqueous systems, literature data on this topic were collected and critically analyzed, providing equations for the calculation of mononuclear Ga3+ hydrolysis constants at T = 298.15 K, in different ionic media, in the ionic strength range 0 < I / mol dm-3 ≤ 1.0. The synthesis and characterization (by ElectroSpray Ionization - Mass Spectrometry (ESI-MS), Attenuated Total Reflectance - Fourier-Transform Infrared Spectroscopy (ATR-FTIR) and ThermoGravimetric Analysis (TGA)) of Ga3+/8-HQA complexes were also performed, identifying [Ga(8-HQA)2]- as the main isolated species, even in the solid state. Finally, the potential effects of 8-HQA and Ga3+/8-HQA complex towards human microbiota exposed to ionizing radiation were evaluated (namely Actinomyces viscosus, Streptococcus mutans, Streptococcus sobrinus, Pseudomonas putida, Pseudomonas fluorescens and Escherichia coli), as well as their anti-proliferative and anti-inflammatory properties. A radioprotective effect of Ga3+/8-HQA complex was observed on Actinomyces viscosus, while showing a potential radiosensitizing effect against Streptococcus mutans and Streptococcus sobrinus. No cytotoxicity on RAW264.7 murine macrophage cells was observed, neither for the free ligand or Ga3+/8-HQA complex. Nevertheless, Ga3+/8-HQA complex highlighted potential anti-inflammatory properties.

A review of organic small-molecule fluorescent probes for the gallium(III) ion

Gallium metal and gallium compounds play significant roles in industry and medicine; however, their pollution and residue can pose potential risks to plants, animals and human health. Moreover, accurately detecting Ga3+ during tumor treatment holds great clinical significance. Therefore, it is crucial to reliably determine the content of Ga3+ in environmental and biological samples. Organic small-molecule fluorescent probe technology offers high selectivity and sensitivity, rapid detection speed, and non-destructive in situ bioimaging capabilities, making it an ideal approach for Ga3+ detection. The numerous reported probes for detecting Ga3+ highlight the immense application potential of fluorescent probes in this field. However, due to limited development of Ga3+-specific fluorescent probes thus far, several challenges associated with their design and development remain. This paper presents a comprehensive overview of the performance achieved by Ga3+ fluorescent probes, while addressing existing issues and proposing corresponding solutions. Additionally, future directions for developing highly efficient Ga3+ fluorescent probes are outlined as valuable guidance.

PET/CT and SPECT/CT for Infection in Joints and Bones: An Overview and Future Directions

Infections of the bones and joints, if misdiagnosed, may result in serious morbidity and even mortality. A prompt diagnosis followed by appropriate management may reduce the socioeconomic impact of bone and joint infections. Morphologic imaging such as ultrasound and plain radiographs form the first line investigations, however, in early infections findings may be negative or nonspecific. Nuclear medicine imaging techniques play a complementary role to morphologic imaging in the diagnosis of bone and joint infections. The availability of hybrid systems (SPECT/CT, SPECT/MRI, PET/CT or PET/MRI) offers improved specificity with ability to assess the extent of infection. Bone scans are useful as a gatekeeper wherein negative scans rule out sepsis with a good accuracy, however positive scans are nondiagnostic and more specific tracers should be considered. These include the use of labeled white blood cells and antigranulocyte antibodies. Various qualitative and quantitative interpretation criteria have been suggested to improve the specificity of the scans. PET has better image resolution and 18F-FDG is the major tracer for PET imaging with applications in oncology and inflammatory/infective disorders. It has demonstrated improved sensitivity over the SPECT based tracers, however, still suffers from lack of specificity. 18F-FDG PET has been used to monitor therapy in bone and joint infections. Other less studied, noncommercialized SPECT and PET tracers such as 111In-Biotin, 99mTc-Ubiquicidin, 18F-Na-Fluoride, 18F-labeled white blood cells and 124I-Fialuridine to name a few have shown great promise, however, their role in various bone and joint infections has not been established. Hybrid imaging with PET or PET/MRI offers huge potential for improving diagnostics in infections of the joints and bones.

The diagnostic conundrum in necrotizing otitis externa

Necrotizing otitis externa (NOE) is an aggressive and fast-evolving infection of the external auditory canal. Late diagnoses and untreated cases can lead to severe, even fatal consequences and so early diagnosis and treatment are paramount. NOE is a notoriously challenging diagnosis to make. It is therefore important to understand what diagnostic modalities are available and how otolaryngologists can use them to accurately treat such an aggressive disease. This review aims to evaluate the different diagnostic options available in NOE and discuss their advantages and limitations, thus, providing an up-to-date picture of the multimodal approach required in the diagnosis of this disease.

Radiosynthesis Standardization and Preclinical Assessment of the [68Ga]Ga-DOTA-Ubiquicidin29-41: A Translational Study Targeting Differential Diagnosis of Infectious Processes

Human bacterial infections significantly contribute to the increase in healthcare-related burdens. This scenario drives the study of novel techniques for the early and precise diagnosis of infectious processes. Some alternatives include Nuclear Medicine- and Molecular Imaging-based strategies. However, radiopharmaceuticals that are available for routine assessments are not specific to differentiating infectious from aseptic inflammatory processes. In this context, [68Ga]Ga-DOTA-Ubiquicidin29-41 was synthesized using an automated module and radiochemical; in vivo and in vitro studies were performed. The radiopharmaceutical remained stable in saline (up to 180 min) and in rodent serum (up to 120 min) with radiochemical purities > 99 and 95%, respectively. Partition coefficient and serum protein binding at 60 min were determined (-3.63 ± 0.17 and 44.06 ± 1.88%, respectively). Ex vivo biodistribution, as well as in vivo microPET/CT images in mice, showed rapid blood clearance with renal excretion and reduced uptake in other organs in Staphylococcus aureus-infected animals. Higher uptake was observed in the target as compared to the non-target tissue (p < 0.0001) at 60 min post administration. The presented in-human clinical case demonstrates uptake of the radiopharmaceutical by Staphyloccocus aureus bacteria. These results indicate the potential of [68Ga]Ga-DOTA-Ubiquicidin29-41 as a radiopharmaceutical that can be obtained in a hospital radiopharmacy for the diagnosis of infectious processes using PET/CT.

A Brief History of Nuclear Medicine Imaging of Infection

For nearly 50 years, nuclear medicine has played an important role in the diagnosis of infection. Gallium citrate Ga 67 was one of the first, if not the first, radionuclide used for this purpose. Unfavorable imaging characteristics, a lack of specificity, and the long interval (2-3 days) between administration and imaging spurred the search for alternatives. At the present time, gallium 67 citrate is used primarily for differentiating acute tubular necrosis from interstitial nephritis and as an alternative for indications including sarcoid, spondylodiscitis, and fever of unknown origin, when 18F-fluorodeoxyglucose (18F-FDG) is not available. The approval, in the mid-1980s, of techniques for in vitro labeling of leukocytes with indium-111 and technetium-99m that subsequently migrate to foci of infection was a significant advance in nuclear medicine imaging of infection and labeled leukocyte imaging still plays an important role in imaging of infection. There are significant disadvantages to in vitro labeled leukocyte imaging. Unfortunately, efforts devoted to developing in vivo leukocyte labeling methods have met with only limited success. Over the past 20 years 18F-FDG has established itself as a valuable imaging agent for musculoskeletal and cardiovascular infections, as well as sarcoidosis and fever of unknown origin. As useful as these agents are, their uptake is based on the host response to infection, not infection itself. Previous attempts at developing infection-specific agents, including radiolabeled antibiotics and vitamins, were limited by poor results and/or lack of availability, so investigators continue to focus on developing infection-specific nuclear medicine imaging agents.

Imaging of Spondylodiscitis: An Update

Spondylodiscitis is an infection of the vertebral body and/or intervertebral disc, which can also involve the epidural space, posterior elements, and paraspinal soft tissues. Due to high morbidity and mortality, prompt diagnosis and treatment of spondylodiscitis is critical. However, diagnosis can be challenging due to nonspecific signs and symptoms. Magnetic resonance imaging with and without contrast is the imaging modality of choice due to high sensitivity and specificity. Intravenous administration of gadolinium contrast can better demonstrate the extent of soft tissue and bone abscesses. However, magnetic resonance imaging is less useful in the evaluation of treatment response. When magnetic resonance imaging cannot be performed or is not diagnostic, radionuclide imaging is a useful alternative. Although bone scintigraphy frequently is used as a screening test, false negative results can occur early in the course of the infection and in the elderly. This test is not useful for detecting the soft tissue infections that often accompany or mimic spondylodiscitis. Gallium-67 citrate improves the specificity of the bone scan, can detect infection earlier than the bone scan, may be more sensitive, especially in elderly patients, and identifies accompanying soft tissue infection. Performing SPECT and SPECT/CT improve accuracy. The 2-3 day delay between radiopharmaceutical administration, poor image quality, and relatively high patient radiation dose are significant disadvantages of gallium-67. Furthermore gallium-67 is no longer as readily available as it once was. ¹⁸F-FDG imaging is the radionuclide test of choice for spondylodiscitis. The procedure, completed in one day, is sensitive, has a high negative predictive value, and reliably differentiates degenerative from infectious vertebral body end-plate abnormalities. ¹⁸F-FDG has outperformed bone and gallium-67 imaging in comparative studies. ¹⁸F-FDG may be able to provide an objective means for monitoring response to treatment. The potential of other agents for diagnosing spondylodiscitis has been studied. Although indium-111biotin accurately diagnoses spondylodiscitis, this radiopharmaceutical has never been commercially available. Gallium-68 citrate and ^99mTc-radiolabeled antimicrobial peptides have been investigated, but their role in the diagnosis of spondylodiscitis has not been established. Labeled leukocyte scintigraphy has no role in the diagnosis of spondylodiscitis.

A Comparative Case Study between Gallium-67 Citrate Scintigraphy and Gallium-68 Citrate Positron Emission Tomography-Computed Tomography in Bone Infection

Bone infections are a common problem, and early diagnosis and intervention can lead to better clinical outcomes and prognoses. Here, we compare the well-known tracers Gallium-67 (Ga-67) citrate versus Ga-68 citrate in the diagnosis of infections.

Cyclic Analogs of Desferrioxamine E Siderophore for 68Ga Nuclear Imaging: Coordination Chemistry and Biological Activity in Staphylococcus aureus

As multidrug-resistant bacteria are an emerging problem and threat to humanity, novel strategies for treatment and diagnostics are actively sought. We aim to utilize siderophores, iron-specific strong chelating agents produced by microbes, as gallium ion carriers for diagnosis, applying that Fe(III) can be successfully replaced by Ga(III) without losing biological properties of the investigated complex, which allows molecular imaging by positron emission tomography (PET). Here, we report synthesis, full solution chemistry, thermodynamic characterization, and the preliminary biological evaluation of biomimetic derivatives (FOX) of desferrioxamine E (FOXE) siderophore, radiolabeled with ⁶⁸Ga for possible applications in PET imaging of S. aureus. From a series of six biomimetic analogs, which differ from FOXE with cycle length and position of hydroxamic and amide groups, the highest Fe(III) and Ga(III) stability was determined for the most FOXE alike compounds–FOX 2-4 and FOX 2-5; we have also established the stability constant of the Ga-FOXE complex. For this purpose, spectroscopic and potentiometric titrations, together with the Fe(III)–Ga(III) competition method, were used. [⁶⁸Ga]Ga-FOXE derivatives uptake and microbial growth promotion studies conducted on S. aureus were efficient for compounds with a larger cavity, i.e., FOX 2-5, 2-6, and 3-5. Even though showing low uptake values, Fe-FOX 2-4 seems to be also a good Fe-source to support the growth of S. aureus. Overall, proposed derivatives may hold potential as inert and stable carrier agents for radioactive Ga(III) ions for diagnostic medical applications or interesting starting compounds for further modifications.

In this work, the authors have investigated a set of novel ferrioxamine E analogs as potential Ga-68 chelators and tools for infection imaging.

Calculations for the nuclear reaction cross-sections via α-particle induced reactions on 65Cu to produce impurity free 67Ga for medical applications

Diagnostics field is facilitated with advancements enacted in anatomic imaging (cross-sectional modalities). Radionuclide scans (imaging) escorted by ⁶⁷Ga are extensively beneficial in bone scintigraphy and recognition of prosthetic joint failure. Present work comprises the data concerning ⁶⁷Ga production via α-particle induced nuclear reactions, TTY (thick target yield) and impurity analysis. Experimental measurements regarding ⁶⁷Ga production are analyzed through a comparative study performed with calculations of theoretical model codes (TALYS-1.95, EMPIRE-3.2.3 and ALICE-IPPE). A data set of recommended cross-sections was generated and utilized to deduce TTY. The contribution of radionuclidic impurities is canvassed to suggest an energy region to produce impurity free ⁶⁷Ga for medical applications.

Radiological evaluation of postoperative osteomyelitis in long bones: Which is the best tool?

Currently, definitive diagnosis of osteomyelitis involves a combination of clinical signs, symptoms, laboratory tests, imaging modalities and cultures from blood, joint or body fluid. Imaging plays a critical role in the osteomyelitis diagnosis. Each of these tests incurs an additional cost to the patient or healthcare system and their use varies according to the preference of the healthcare professional and the healthcare setup. Imaging plays a critical role in the diagnosis and management of postoperative long bone osteomyelitis, with the aim of reducing long-term complications such as non-union, amputation and pathological fractures. In this review, we discuss the key findings on different radiological modalities and correlate them with disease pathophysiology. Currently, magnetic resonance imaging is the best available imaging modality due to its sensitivity in detecting early signs of long bone osteomyelitis and high soft tissue resolution. Other modalities such as radio-nuclear medicine, computed tomography and ultrasound have been proved to be useful in different clinical scenarios as described in this narrative review.

Nuclear Medicine Scans in Total Joint Replacement

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A 3-phase bone scan is a potential first-line nuclear medicine study for pain after total joint arthroplasty (TJA) when there is concern for periprosthetic joint infection or aseptic loosening.

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In patients who have a positive bone scintigraphy result and suspected infection of the joint, but where aspiration or other studies are inconclusive, labeled leukocyte scintigraphy with bone marrow imaging may be of benefit.

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Magnetic resonance imaging (MRI), while not a nuclear medicine study, also shows promise and has the advantage of providing information about the soft tissues around a total joint replacement.

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Radiotracer uptake patterns in scintigraphy are affected by the prosthesis (total knee arthroplasty [TKA] versus total hip arthroplasty [THA]) and the use of cement.

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Nuclear medicine scans may be ordered 1 year postoperatively but may have positive findings that are due to normal physiologic bone remodeling. Nuclear studies may be falsely positive for up to 2 years after TJA.

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Single-photon emission computed tomography (SPECT) combined with computed tomography (CT) (SPECT/CT), fluorine-18 fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)/CT, and MRI show promise; however, more studies are needed to better define their role in the diagnostic workup of pain after TJA.

Multivalent ions and biomolecules: Attempting a comprehensive perspective

Ions are ubiquitous in nature. They play a key role for many biological processes on the molecular scale, from molecular interactions, to mechanical properties, to folding, to self-organisation and assembly, to reaction equilibria, to signalling, to energy and material transport, to recognition etc. Going beyond monovalent ions to multivalent ions, the effects of the ions are frequently not only stronger (due to the obviously higher charge), but qualitatively different. A typical example is the process of binding of multivalent ions, such as Ca2+ , to a macromolecule and the consequences of this ion binding such as compaction, collapse, potential charge inversion and precipitation of the macromolecule. Here we review these effects and phenomena induced by multivalent ions for biological (macro)molecules, from the "atomistic/molecular" local picture of (potentially specific) interactions to the more global picture of phase behaviour including, e. g., crystallisation, phase separation, oligomerisation etc. Rather than attempting an encyclopedic list of systems, we rather aim for an embracing discussion using typical case studies. We try to cover predominantly three main classes: proteins, nucleic acids, and amphiphilic molecules including interface effects. We do not cover in detail, but make some comparisons to, ion channels, colloidal systems, and synthetic polymers. While there are obvious differences in the behaviour of, and the relevance of multivalent ions for, the three main classes of systems, we also point out analogies. Our attempt of a comprehensive discussion is guided by the idea that there are not only important differences and specific phenomena with regard to the effects of multivalent ions on the main systems, but also important similarities. We hope to bridge physico-chemical mechanisms, concepts of soft matter, and biological observations and connect the different communities further.

Nuclear Imaging of Bacterial Infection: The State of the Art and Future Directions

Increased mortality rates from infectious diseases is a growing public health concern. Successful management of acute bacterial infections requires early diagnosis and treatment, which are not always easy to achieve. Structural imaging techniques such as CT and MRI are often applied to this problem. However, these methods generally rely on secondary inflammatory changes and are frequently not specific to infection. The use of nuclear medicine techniques can add crucial complementary information, allowing visualization of infectious pathophysiology beyond morphologic imaging. This review will discuss the current structural and functional imaging techniques used for the diagnosis of bacterial infection and their roles in different clinical scenarios. We will also present several new radiotracers in development, with an emphasis on probes targeting bacteria-specific metabolism. As highlighted by the current coronavirus disease 2019 epidemic, caused by the novel severe acute respiratory syndrome coronavirus 2, similar thinking may apply in imaging viral pathogens; for this case, prominent effects on host proteins, most notably angiotensin-converting enzyme 2, might also provide worthwhile imaging targets.

Should scintigraphy be completely excluded from the diagnosis of periprosthetic joint infection?

AIM

To analyse the diagnostic performance of bone and leukocyte scintigraphy for periprosthetic joint infection before excluding the test from routine practice, and to analyse the possible benefit of bone marrow scintigraphy in inconclusive cases.

MATERIALS AND METHODS

From 2012 to 2018, all patients with a total hip or knee arthroplasty who had a bone and leukocyte scintigraphy performed and underwent revision surgery were included. Bone marrow scintigraphy was indicated only in cases in which bone and leukocyte scintigraphy were inconclusive. Diagnosis of periprosthetic joint infection was confirmed by positive intraoperative cultures after revision surgery.

RESULTS

A total of 105 patients were included. Eighteen patients had total hip arthroplasties (18.1%) and 86 had total knee arthroplasties (81.9%). Mean age was 74 years. Nineteen cases were diagnosed with a periprosthetic joint infection. Bone and leukocyte scintigraphy had 64% sensitivity and 97% specificity. Bone marrow scintigraphy increased sensitivity and specificity to 88% and 100%, respectively.

CONCLUSION

Bone and leukocyte scintigraphy possesses high sensitivity and specificity for the diagnosis of chronic periprosthetic joint infection. The additional use of bone marrow scintigraphy significantly increases diagnostic performance. For these reasons, bone scintigraphy is reserved for inconclusive cases of chronic periprosthetic joint infection.

Nuclear Medicine for the Orthopedic Foot and Ankle Surgeon

Nuclear medicine has been widely applied as a diagnostic tool for orthopedic foot and ankle pathology. Although its indications have diminished with improvements in and the availability of magnetic resonance imaging, nuclear medicine still has a significant and valuable role. The present article offers a comprehensive and current review of the most common nuclear imaging modalities for the orthopedic foot and ankle surgeon. Methods discussed include bone scintigraphy, gallium citrate scintigraphy, labeled-leukocyte scintigraphy, and single-photon emission computed tomography (SPECT). We review the indications and utility of these techniques as they pertain to specific foot and ankle conditions, including osteomyelitis, stress fractures, talar osteochondral lesions, complex regional pain syndrome, oncology, plantar fasciitis, and the painful total ankle arthroplasty. We conclude with a discussion of our approach to nuclear medicine with illustrative cases. Level of Evidence: Level V, expert opinion.

99mTc-radiolabeled Levofloxacin and micelles as infection and inflammation imaging agents

Easy and early detection of infection and inflammation is essential for early and effective treatment. In this study, PEGylated micelles were designed and both micelles and Levofloxacin were radiolabeled with 99mTcO4 - to develop potential radiotracers for detection of infection/inflammation. Radiolabeling efficiency, in vitro stability and bacterial binding of 99mTc-Levofloxacin and 99mTc-micelles were compared. The aim of this study is to formulate and compare 99mTc-Levofloxacin and 99mTc-micelles as infection and inflammation agents having different mechanisms for the accumulation at infection and inflammation site. PEGylated micelles were designed with a particle size of 80 ± 0.7 nm and proper characterization properties. High radiolabeling efficiency was achieved for 99mTc-Levofloxacin (96%) and 99mTc-micelles (87%). The radiolabeling efficiency was remained stable with some insignificant alterations for both radiotracers at 25 °C for 24 h. Although in vitro bacterial binding of 99mTc-levofloxacine was higher than 99mTc-micelles, 99mTc-micelles may also be evaluated potential agent due to long circulation and passive accumulation mechanisms at infection/inflammation site. Both radiopharmaceutical agents exhibit potential results in design, characterization, radiolabeling efficiency and in vitro bacterial binding point of view.

Radiotracer Development for Bacterial Imaging

Bacterial infections remain a major threat to humanity and are a leading cause of death and disability. Antimicrobial resistance has been declared as one of the top ten threats to human health by the World Health Organization, and new technologies are urgently needed for the early diagnosis and monitoring of deep-seated and complicated infections in hospitalized patients. This review summarizes the radiotracers as applied to imaging of bacterial infections. We summarize the recent progress in the development of pathogen-specific imaging and the application of radiotracers in understanding drug pharmacokinetics as well as the local biology at the infection sites. We also highlight the opportunities for medicinal chemists in radiotracer development for bacterial infections, with an emphasis on target selection and radiosynthetic approaches. Imaging of infections is an emerging field. Beyond clinical applications, these technologies could provide unique insights into disease pathogenesis and expedite bench-to-bedside translation of new therapeutics.

Molecular Imaging of Infection: The First 50 Years

Despite significant advances in the understanding of microorganisms and an increased availability of antimicrobial therapy, infection remains a major cause of morbidity and mortality. The diagnosis can be challenging and imaging studies often are used for confirmation and localization. For nearly 50 years, molecular imaging agents have played an important role in the diagnosis of infection. Gallium-67 citrate was perhaps the first molecular imaging agent used for diagnosing and localizing infection. Poor imaging characteristics, along with a lack of specificity, and the long (usually 48-72 hours) interval between administration and imaging motivated investigators to search for alternatives. Currently the role of ⁶⁷Ga is limited to differentiating acute tubular necrosis from interstitial nephritis and as an alternative to ¹⁸F-FDG for indications, such as sarcoid, spondylodiscitis, and fever of unknown origin, when the latter is not available. The development, in the mid-1970s, of techniques for radiolabeling leukocytes that subsequently migrate to foci of infection was a significant advance and labeled leukocyte imaging still has a preeminent role in molecular imaging of infection. There are significant disadvantages to in-vitro labeled leukocyte imaging. Efforts devoted to developing in-vivo leukocyte labeling methods, however, met with only limited success. Over the past 20 years ¹⁸F-FDG has established itself as the molecular imaging agent of choice for fever of unknown origin, vasculitis, sarcoid, and spondylodiscitis. As useful as these agents are, their uptake is based on the host response to infection, not infection itself. Previous attempts at developing infection specific agents, including radiolabeled antibiotics, antibiotics, and vitamins like biotin were limited by poor results and/or limited availability and so investigators continue to focus on developing infection specific molecular imaging agents. Initial results with radiolabeled nucleoside analogs, sugars, and amino acids, and a renewed interest in radiolabeled antibiotics for both diagnosis and monitoring treatment are exciting and hold great promise for the future.

Susceptibility of 99mTc-Ciprofloxacin for Common Infection Causing Bacterial Strains Isolated from Clinical Samples: an In Vitro and In Vivo Study

^99mTc-ciprofloxacin scintigraphy is useful in the detection of gram-positive and gram-negative bacterial infections and also for differentiating the infection from aseptic inflammation. However, due to growing bacterial resistance to antibiotics, the ^99mTc-ciprofloxacin no longer can be effective in broad-spectrum infection imaging as it is gradually losing specificity. In this study, we are presenting our findings regarding the in vitro and in vivo susceptibility of ^99mTc-ciprofloxacin for multi-drug-resistant Staphylococcus aurous, Escherichia coli, and Pseudomonas aeruginosa bacterial strains which were isolated from clinical samples. The results of radiosynthesis of ^99mTc-ciprofloxacin showed more the 95% radiochemical purity and less than 5% radioactive impurities. In vitro ^99mTc-ciprofloxacin susceptibility test showed that E. coli offered more resistant to ^99mTc-ciprofloxacin as compared to S. aurous and P. aeruginosa. In vivo study using bacterial infection induced rabbit model also revealed lowest uptake by E. coli lesion. The T/NT values were obtained 1.96 ± 0.15 in the case of E. coli; 2.81 ± 0.51 in the case of S. aurous; and 2.32 ± 0.66 in the case of P. aeruginosa at 4 h post-injection. The SPECT infection imaging of S. aurous, E. coli, and P. aeruginosa bacterial infection induced rabbit models also indicated the clear accumulation in S. aurous and P. aeruginosa lesions while negligible uptake by E. coli lesion further verify the in vitro and in vivo susceptibility profile. On the bases of the results obtained, the ^99mTc-ciprofloxacin showed selective and poor broad spectrum SPECT infection imaging.

Radiopharmaceutical tracers for cardiac imaging

Cardiovascular disease (CVD) is the leading cause of death and disease burden worldwide. Nuclear myocardial perfusion imaging with either single-photon emission computed tomography or positron emission tomography has been used extensively to perform diagnosis, monitor therapies, and predict cardiovascular events. Several radiopharmaceutical tracers have recently been developed to evaluate CVD by targeting myocardial perfusion, metabolism, innervation, and inflammation. This article reviews old and newer used in nuclear cardiac imaging.

The sensitivity and specificity of 99mTc-IgG radiotracer to differentiate infection lesions induced by Staphylococcus aureus and sterile inflammation lesions induced by carrageenan assay in rat's foot

Background

Detection and identification of infection from sterile inflammation foci has a crucial role in diagnosis and therapy of patients in clinical practice.

Objective

To assess the efficiency of labeled human polyclonal immunoglobulin with technetium 99m in order to detect septic or aseptic lesions which were induced in a rat model.

Methods

The freeze-dried IgG kits have been reconstituted by ^99mTc. The radio conjugate yield, radiochemical impurities and stability radio complex were performed by ITLC (Instant Thin Layer Chromatography) and Gel filtration assays. Twenty adult, male NMRI (Naval Medical Research Institute) rats were randomly divided into two groups equally. Infection was induced by Staphylococcus aureus and sterile inflammation created by Carrageenan test. All lesions were created in the rat’s foot. Then radioisotope investigations were undertaken.

Results

Labeling yield was approximately 98%. The radio complex showed good stability in normal saline. All affected feet could be easily visualized by imaging in qualitative study. The value of target to non-target ratio at the infection (n=10) and sterile inflammation (n=10) were 2.81±0.16 and 1.54±0.15 with p<0.007. Therefore, the radiotracer uptake at the septic lesions was significantly higher than the aseptic lesions.

Conclusion

Imaging with ^99mTc-IgG is highly sensitive to localized infection or inflammation foci. The increased accumulation of radiotracer at the infection versus inflammation foci may be helpful to interpret the image.

67Ga Scintigraphy for Assessment of Disease Severity and Treatment Response in Patients With Paracoccidioidomycosis

OBJECTIVE

The evaluation of therapy response of patients with deep mycosis is a major challenge. The aim of this study was to assess the severity of disease at admission and evaluate treatment response of patients with paracoccidioidomycosis using Ga scintigraphy.

SUBJECTS AND METHODS

Seventy-three patients with fully active disease were enrolled. A scoring system based on clinicoradiological and serological evaluation and Ga scan was devised. Pretherapy Ga score of 73 patients was compared with clinicoradiological and serological scores. A subgroup of 23 patients was followed up during treatment, and the rates of improvement of their clinicoradiological, serological, and Ga scores during treatment were compared at 3 time points (fully active phase, after clinical improvement, and clinically inactive disease).

RESULTS

The correlations between scores before therapy were statistically significant. Ga score correlated with clinical score (r = 0.47, P < 0.001). Serological score correlated with both Ga and clinical scores (r = 0.32, P = 0.006, and r = 0.25, P = 0.034, respectively). Concerning evaluation of therapy response, clinicoradiological, serological, and Ga scores decreased significantly after therapy (P < 0.001). Notably, Ga score was the single one to become negative in most patients at the end of treatment (20 of 23 patients compared with 7 on clinicoradiological evaluation and 10 on serology, P = 0.003).

CONCLUSIONS

In patients with paracoccidioidomycosis, pretherapy Ga scintigraphy correlates with disease severity. Serial Ga scans seem to be helpful in evaluating the response to therapy.

Pathogen-Specific Bacterial Imaging in Nuclear Medicine

When serious infections are suspected, patients are often treated empirically with broad-spectrum antibiotics while awaiting results that provide information on the bacterial class and species causing the infection, as well as drug susceptibilities. For deep-seated infections, these traditional diagnostic techniques often rely on tissue biopsies to obtain clinical samples which can be expensive, dangerous, and has the potential of sampling bias. Moreover, these procedures and results can take several days and may not always provide reliable information. This combination of time and effort required for proper antibiotic selection has become a barrier leading to indiscriminate broad-spectrum antibiotic use. Exposure to nosocomial infections and indiscriminate use of broad-spectrum antibiotics are responsible for promoting bacterial drug-resistance leading to substantial morbidity and mortality, especially in hospitalized and immunosuppressed patients. Therefore, early diagnosis of infection and targeted antibiotic treatments are urgently needed to reduce morbidity and mortality caused by bacterial infections worldwide. Reliable pathogen-specific bacterial imaging techniques have the potential to provide early diagnosis and guide antibiotic treatments.

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.

67Ga as a biosensor of iron needs in different organs: Study performed on male and female rats subjected to iron deficiency and exercise

The aim of the present study was to determine the iron needs in different organs and tissues using ⁶⁷Ga as a biosensor in males and females rats subjected to iron deficiency (ID) and voluntary exercise (EX). ⁶⁷Ga citrate was injected i.p. to female and male Wistar rats (n=5/sex/group). Groups: Control (sedentary conditions), Control+EX, ID and ID+EX. To determine the ⁶⁷Ga uptake, samples from the following regions of interest (ROIs) were extracted 12h post-injection: blood, liver, gonads, bone marrow, heart, adrenal glands, skeletal muscle, stomach, kidney, eyeball, sciatic nerve, small intestine and peritoneum. The total ⁶⁷Ga uptake was 412% higher in ID subjects than in control subjects, being 1011% higher in ID-males than ID-females. In ID-females, the ROIs with the greater ⁶⁷Ga uptake were blood, kidney and bone marrow, while in ID-males they were sciatic nerve, eyeball and adrenals, which demonstrates that the biodistribution differed between sexes in sedentary conditions but when subjected to EX, the biodistribution was similar in each sex group although females had a greater ⁶⁷Ga uptake. In ID+EX subjects, the ROIs that showed the highest uptake were sciatic nerve, eyeball and adrenal glands. Using ⁶⁷Ga as a biosensor, it is possible to identify the needs of iron that each organ requires to perform their functions in normal physiological conditions. In addition, a higher or lower ⁶⁷Ga uptake in a specific organ may indicate its malfunction or show damage.

The efficacy of 18F-FDG PET/CT and 67Ga SPECT/CT in diagnosing fever of unknown origin

OBJECTIVE

Fever of unknown origin (FUO) is a diagnostic challenge. This study aimed to assess the efficacy of fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) and gallium-67 single-photon emission computed tomography/computed tomography (⁶⁷Ga SPECT/CT) in diagnosing FUO.

METHODS

A total of 68 patients with FUO underwent ¹⁸F-FDG PET/CT and ⁶⁷Ga SPECT/CT from January 2013 through May 2016. Images were read independently. The imaging results were compared with the final diagnosis and categorized as helpful for diagnosis or non-contributory to diagnosis in the clinical setting. Associations between categorical variables were evaluated with the chi-square test or Fisher's exact test.

RESULTS

Ten of the 68 patients were excluded. An infectious underlying disease was found in 23 patients. A malignant disorder was the cause of FUO in 10 patients. Non-infectious inflammatory disease was found in 11 patients. Adrenal insufficiency was the cause of FUO in two patients. The cause of FUO was not found for 12 patients. A high false-positive rate of 44% (7/16) was observed for ¹⁸F-FDG PET/CT, while a high false-negative rate of 55% (23/42) was observed for ⁶⁷Ga SPECT/CT. ¹⁸F-FDG PET/CT studies depicted all ⁶⁷Ga-avid lesions. The sensitivity (79% vs. 45%) and clinical contribution (72% vs. 55%) of ¹⁸F-FDG PET/CT in diagnosing FUO were significantly higher than those of ⁶⁷Ga SPECT/CT (p<0.05).

CONCLUSIONS

On the basis of this study, the diagnostic performance of ¹⁸F-FDG PET/CT is superior to ⁶⁷Ga SPECT/CT in the work-up of patients with FUO. With its rapid results and superior sensitivity, ¹⁸F-FDG PET/CT may replace ⁶⁷Ga SPECT/CT where this technique is available.

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

The process of inflammation (with or without infection) forms part of essentially every major debilitating disease. Early detection and accurate distinction of inflammation from infection are important to optimize and individualize therapy. Nuclear medicine is ideally suited for the detection of pathologic changes early on and is able to target a magnitude of role players involved in the aforementioned processes. Hybrid modalities such as PET/CT and PET/MRI offer high spatial resolution that combines morphologic and pathophysiological changes and add various quantification possibilities that are preferable in these settings. It follows then that the development of PET radiopharmaceuticals is imperative to make use of these latest advances. Gallium-68 (Ga-68)-based tracers are exceptionally well suited to these indications, considering the year-round availability from a single generator, the relative cost-effectiveness, and relative ease of labeling. Over the past few years, the development of Ga-68-based tracers has understandably exploded with a recent growing interest in infection and inflammation imaging. This review aims to highlight some of the most important and interesting advances made with Ga-68-based PET/CT in the field of infection and inflammation imaging.

Concurrent Diffuse Pyelonephritis and Prostatitis: Discordant Findings on Sequential FDG PET/CT and 67Ga SPECT/CT Imaging

A 45-year-old man underwent FDG PET/CT for initial imaging evaluation of recurrent Escherichia coli urinary tract infections, which demonstrated no significant FDG uptake in either kidney and subtle FDG uptake in the right prostate lobe. Subsequent Ga SPECT/CT demonstrated abnormal intense gallium uptake throughout the right kidney and entire prostate gland, clearly discordant with PET/CT findings and consistent with unexpected concurrent pyelonephritis and prostatitis. Although FDG has effectively replaced Ga in everyday clinical practice, the current case serves as a reminder that there is still a role for Ga in the evaluation of genitourinary infections.

The therapeutic potential of iron-targeting gallium compounds in human disease: From basic research to clinical application

Gallium, group IIIa metal, shares certain chemical characteristics with iron which enable it to function as an iron mimetic that can disrupt iron-dependent tumor cell growth. Gallium may also display antimicrobial activity by disrupting iron homeostasis in certain bacteria and fungi. Gallium's action on iron homeostasis leads to inhibition of ribonucleotide reductase, mitochondrial function, and changes in proteins of iron transport and storage. In addition, gallium induces an increase in mitochondrial reactive oxygen species in cells which triggers downstream upregulation of metallothionein and hemoxygenase-1. Early clinical trials evaluated the efficacy of the simple gallium salts, gallium nitrate and gallium chloride. However, newer gallium-ligands such as Tris(8-quinolinolato)gallium(III) (KP46) and gallium maltolate have been developed and are undergoing clinical evaluation. Additional gallium-ligands that demonstrate antitumor activity in preclinical studies have emerged. Their mechanisms of action and their spectrum of antitumor activity may extend beyond the earlier generations of gallium compounds and warrant further investigation. This review will focus on the evolution and potential of gallium-based therapeutics.

The Accuracy of Imaging Techniques in the Assessment of Periprosthetic Hip Infection: A Systematic Review and Meta-Analysis

BACKGROUND

Various imaging techniques are used for excluding or confirming periprosthetic hip infection, but there is no consensus regarding the most accurate technique. The objective of this study was to determine the accuracy of current imaging modalities in diagnosing periprosthetic hip infection.

METHODS

A systematic review and meta-analysis of the literature was conducted with a comprehensive search of MEDLINE and Embase to identify clinical studies in which periprosthetic hip infection was investigated with different imaging modalities. The sensitivity and specificity of each imaging technique were determined and compared with the results of microbiological and histological analysis, intraoperative findings, and clinical follow-up of >6 months.

RESULTS

A total of 31 studies, published between 1988 and 2014, were included for meta-analysis, representing 1,753 hip prostheses. Quality assessment of the included studies identified low concerns with regard to external validity but more concerns with regard to internal validity including risk of bias (>50% of studies had insufficient information). No meta-analysis was performed for radiography, ultrasonography, computed tomography, and magnetic resonance imaging because of insufficient available clinical data. The pooled sensitivity and specificity were 88% (95% confidence interval [CI], 81% to 94%) and 92% (95% CI, 88% to 96%), respectively, for leukocyte scintigraphy; 86% (95% CI, 80% to 90%) and 93% (95% CI, 90% to 95%) for fluorodeoxyglucose positron emission tomography (FDG PET); 69% (95% CI, 58% to 79%) and 96% (95% CI, 93% to 98%) for combined leukocyte and bone marrow scintigraphy; 84% (95% CI, 70% to 93%) and 75% (95% CI, 66% to 82%) for antigranulocyte scintigraphy; and 80% (95% CI, 72% to 86%) and 69% (95% CI, 64% to 73%) for bone scintigraphy.

CONCLUSIONS

Of the currently used imaging techniques, leukocyte scintigraphy has satisfactory accuracy in confirming or excluding periprosthetic hip infection. Although not significantly different, combined leukocyte and bone marrow scintigraphy was the most specific imaging technique. FDG PET has an appropriate accuracy in confirming or excluding periprosthetic hip infection, but may not yet be the preferred imaging modality because of limited availability and relatively higher cost.

LEVEL OF EVIDENCE

Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Evaluation of a Novel Tc-99m Labelled Vitamin B12 Derivative for Targeting Escherichia coli and Staphylococcus aureus In Vitro and in an Experimental Foreign-Body Infection Model

Purpose

Vitamin B₁₂ (cyanocobalamin, Cbl) is accumulated by rapidly replicating prokaryotic and eukaryotic cells. We investigated the potential of a Tc-99m labelled Cbl derivative ([^99mTc]PAMA(4)-Cbl) for targeting infections caused by Escherichia coli and Staphylococcus aureus. In vitro binding assays were followed by biodistribution studies in a mouse model of foreign body infection.

Procedures

E. coli (ATCC 25922) and S. aureus (ATCC 43335) were used as test strains. [⁵⁷Co]Cbl, [⁶⁷Ga]citrate and [^99mTc]DTPA served as reference compounds. The in vitro competitive binding of [⁵⁷Co]Cbl or [^99mTc]PAMA(4)-Cbl, and unlabeled Cbl, to viable or killed bacteria, was evaluated at 37 and 4 °C. A cage mouse model of infection was used for biodistribution of intravenous [⁵⁷Co]Cbl and [^99mTc]PAMA(4)-Cbl in cage and dissected tissues of infected and non-infected mice.

Results

Maximum binding (mean ± SD) of [⁵⁷Co]Cbl to viable E. coli was 81.7 ± 2.6 % and to S. aureus 34.0 ± 6.7 %, at 37 °C; no binding occurred to heat-killed bacteria. Binding to both test strains was displaced by 100- to 1000-fold excess of unlabeled Cbl. The in vitro binding of [^99mTc]PAMA(4)-Cbl was 100-fold and 3-fold lower than the one of [⁵⁷Co]Cbl for E. coli and S. aureus, respectively. In vivo, [^99mTc]PAMA(4)-Cbl showed peak percentage of injected dose (% ID) values between 1.33 and 2.3, at 30 min post-injection (p.i.). Significantly higher retention occurred in cage fluids infected with S. aureus at 4 h and with E. coli at 8 h p.i. than in non-infected animals. Accumulation into infected cages was also higher than the one of [^99mTc]DTPA, which showed similar biodistribution in infected and sterile mice. [⁵⁷Co]Cbl gradually accumulated in cages with peaks % ID between 3.58 and 4.83 % achieved from 24 to 48 h. Discrimination for infection occurred only in E. coli-infected mice, at 72 h p.i. [⁶⁷Ga]citrate, which showed a gradual accumulation into cage fluids during 12 h, was discriminative for infection from 48 to 72 h p.i. (P < 0.05).

Conclusion

Cbl displayed rapid and specific in vitro binding to test strains. [^99mTc]PAMA(4)-Cbl was rapidly cleared from most tissues and discriminated between sterile and infected cages, being a promising candidate for imaging infections in humans.

Imaging for infection: from visualization of inflammation to visualization of microbes

BACKGROUND

With the development of high-resolution cross-sectional imaging, anatomic identification of most areas of infection has become routine. Imaging a site of infection allows for diagnosis and treatment. In the past, molecular imaging for infection involved mainly the use of radiolabeled leukocytes for functional targeting at infection sites. With the recent development of functional nuclear imaging, bacterial and viral metabolism can also be imaged directly for potential identification of early infection.

METHODS

Review of pertinent English-language literature.

RESULTS

Cross-sectional imaging is used routinely to identify and treat sources of infection in patients with fever, leukocytosis, or unexplained hemodynamic instability. Although ultrasound is preferred for the identification of biliary or hepatic sepsis, computed tomography (CT) has proved to be accurate for the identification and treatment of intra-abdominal fluid collections and abscesses. Biologic imaging is a non-invasive technique that identifies sites of infection in cases in which no definite abnormality is identified via cross-sectional imaging. This is made possible by imaging the accumulation of radioisotopes that have been attached to white blood cells or glucose. Biologic imaging is useful for the identification of anatomic sites where there is inflammation or high metabolic demand. However, a drawback of biologic imaging is that it is not specific for infection. Techniques that image microbes directly increase the specificity of imaging results significantly and can be used to quantify and track infectious processes. For example, radiolabeling of antimicrobial proteins and antibiotics is one technique that has been demonstrated to identify areas of infection accurately in animals but is not currently being used clinically in humans. With the advent of gene therapy, many researchers are inserting the herpes viral thymidine kinase gene into both viruses and bacteria. This allows for tracking of the infectious process by imaging the accumulation of radiolabeled thymidine analogues.

CONCLUSION

This review summarizes standard imaging for infection as it is currently practiced clinically. We will also explore the promising new methods of microbial imaging that are likely to become standards in clinical care in the near future.

A Novel Method for the Synthesis of (99m)Tc-Ofloxacin Kits Using D-Penicillamine as Coligand and Their Application as Infection Imaging Agent

The employment of radiopharmaceuticals is increasing nowadays for infection imaging and early execution of patients having infectious or inflammatory complaints. The main aim of this study was to discover a novel method for the labeling of ofloxacin with ^99mTc, optimization of labelling conditions to get higher percent yield, to assess kits radiochemical purity, in vitro stability, partition coefficient, protein binding, and intracellular accumulation in Pseudomonas aeruginosa, Salmonella typhi, and Escherichia coli in infected rabbits. Maximum labeling efficiency was achieved when 1.5 mg ofloxacin was labeled with 10–20 mCi sodium pertechnetate in the presence of 3 mg D-penicillamine, 75 μg SnCl₂. In vitro binding and biodistribution in Pseudomonas aeruginosa, Salmonella typhi, and Escherichia coli showed good results. This new complex is efficient for the imaging of infections caused by Gram-positive and Gram-negative bacteria.

The diagnostic role of (18)F fluorodeoxyglucose positron emission tomography in patients with fever of unknown origin

BACKGROUND

Identification of aetiology for fever of unknown origin (FUO) is challenging, due to the high rates of undiagnosed cases. The current diagnostic approach includes initially first-line procedures such as general examination and various laboratory tests and basic imaging techniques followed by second-line tests such as more advanced imaging techniques including (18)F fluorodeoxyglucose positron emission tomography (FDG PET) and tissue biopsies. If no diagnosis is obtained, more invasive measures may be in order such as liver biopsy and exploratory laparotomy.

MATERIALS AND METHODS

This review article is based on the relative published material found on MEDLINE and PubMed up to August 2014. We looked for the terms 'fever of unknown origin, FDG PET' in combination with 'cancer, infection and autoimmune disease'.

RESULTS

Several clinical studies have investigated the utility of the FDG PET during the diagnostic approach of FUO. Recent evidence suggests that FDG PET has the advantage of total body imaging and may depict all common causes of FUO such as infections, noninfectious inflammatory causes and tumours because they all exhibit glucose hypermetabolism. Depiction of an abnormal lesion on FDG PET could guide clinicians to the next diagnostic procedure (another imaging method, culture, biopsy or surgery) to establish the diagnosis.

CONCLUSIONS

Emerging evidence suggests that FDG PET, when available, may provide critical diagnostic information early during evaluation of FUO.

67Ga SPECT/CT of infected bladder stones and pyelitis

A 64-year-old male patient diagnosed with amyotrophic lateral sclerosis 2 years ago was admitted with fever and chills. The patient had complex medical history and several indwelling catheters/tubes in his body. To identify the infection focus, 67Ga whole-body scintigraphy and SPECT/CT were obtained. 67Ga whole-body scintigraphy demonstrated focal 67Ga uptake in the lower pelvic cavity and the right kidney. Additional Ga SPECT/CT images were obtained, and it enabled characterization of these uptakes as infection of bladder stones that result in pyelitis.

Fast and simple one-step preparation of ⁶⁸Ga citrate for routine clinical PET

The imaging of infectious and inflammatory diseases using gallium-67 (⁶⁷Ga) citrate scintigraphy has been a well-established diagnostic tool for decades. In recent times, interest has focused on PET using the short-lived positron emitting radioisotope ⁶⁸Ga. ⁶⁸Ga is not only more readily available, it also provides better quality images whose high resolution permits quantitative analyses, thus improving the management of patients suffering from infections or inflammation. The purpose of our study was to develop a fast and reliable synthesis protocol for the preparation of ⁶⁸Ga citrate under good manufacturing practice aspects without the use of organic solvents. A commercially available synthesis module was used to perform 10 syntheses with an average yield of 768 ± 31 MBq (mean ± SD) within 10 min; 92.04 ± 1.23% of the radioactivity was located in the product vial, and the rest on the cation exchange cartridge (7.48 ± 1.23%) and in the waste vial (0.47 ± 0.28%). The radiochemical purity of the product determined by instant thin-layer chromatography was greater than 99%. The products have been proven to be sterile and pyrogen-free. Variations were made in several critical synthesis parameters, and the results are presented herein. By eliminating the use of organic solvents, the previously required quality control testing of the final product by gas chromatography can be abandoned. This novel, high-yielding method allows for a more efficient synthesis of ⁶⁸Ga citrate with both shorter production time and high radiochemical purity.

SPECT/CT with a hybrid camera: a new imaging modality for the functional anatomical mapping of infections

Evaluation of: Bar-Shalom R, Yefremov N, Guralnik L et al. SPECT/CT using (67)Ga and (111)In-labeled leukocyte scintigraphy for diagnosis of infection. J. Nucl. Med. 47(4), 587-594 (2006). Labeled leukocytes and (67)Ga scan have been proved to be useful to image infectious and inflammatory processes. However, it is well known that nuclear imaging lacks precise anatomical landmarks. When highly specific tracers are used, the background activity may be too low to be used as a framework for spatial orientation. To overcome these drawbacks, the hybrid devices combining positron emission tomography/single photon emission computed tomography (SPECT) and computed tomography (CT) have been introduced, thereby providing a precise anatomical-functional correlation. The paper under evaluation highlights the emerging role of hybrid SPECT/CT to image infection with labeled leukocytes and (67)Ga. The authors suggest that fusion imaging can be of paramount value to locate the site of infection and to better define the extent of disease.

Radionuclide imaging of inflammation and infection in the acute care setting

Although infection may be suggested by signs and symptoms such as fever, pain, general malaise, and abnormal laboratory results, imaging tests often are used to confirm its presence. Morphologic imaging tests identify structural alterations of tissues or organs that result from a combination of microbial invasion and the inflammatory response of the host. Functional imaging studies use minute quantities of radioactive material, which are taken up directly by cells, tissues, and organs, or are attached to substances that subsequently migrate to the region of interest. Bone scintigraphy is extremely sensitive and can be positive within 2 days after the onset of symptoms. With an accuracy of more than 90%, 3-phase bone scintigraphy is the radionuclide procedure of choice for diagnosing osteomyelitis in unviolated bone. In patients with acute renal failure, gallium imaging facilitates the differentiation of acute interstitial nephritis from acute tubular necrosis. Gallium imaging also is useful in the evaluation of pulmonary infections and inflammation. Many opportunistic infections affect the lungs, and a normal gallium scan of the chest excludes infection with a high degree of certainty, especially when the chest x-ray is negative. In the human immunodeficiency virus positive patient, lymph node uptake usually is associated with mycobacterial disease or lymphoma. Focal pulmonary parenchymal uptake suggests bacterial pneumonia. Diffuse pulmonary uptake suggests an opportunistic pneumonia. Gallium imaging provides useful information about other acute respiratory conditions, including radiation pneumonitis and hypersensitivity pneumonitis. In vitro labeled leukocyte imaging with indium-111 and technetium-99m labeled leukocytes is useful in various acute care situations. The test facilitates the differentiation of normal postoperative changes from infection and is useful for diagnosing prosthetic vascular graft infection. In inflammatory bowel disease, labeled leukocyte imaging is useful for initial screening, monitoring treatment response, detecting recurrent disease, and evaluating patients with discordant physical presentation and laboratory test results. Labeled leukocyte imaging, combined with bone marrow scintigraphy accurately diagnoses complicating osteomyelitis. Fluorine-18-fluorodeoxyglucose, imaging is rapidly completed and provides high-resolution images. This test is especially valuable in patients with fever of unknown origin, patients in septic shock, and mechanically ventilated patients suspected of harboring infection. Fluorine-18-fluorodeoxyglucose imaging also shows promise in inflammatory bowel disease.

(99m) Tc-tricabonyl labeling of ofloxacin and its biological evaluation in Staphylococcus aureus as an infection imaging agent

Even in recent decades, one of the major causes of death and unhealthiness in the whole world is infection and inflammation. The use of radiopharmaceuticals is a powerful tool in managing the patients with infectious diseases. In this study, ofloxacin as a second-generation fluoroquinolone has been labeled with [(99m) Tc(CO)3 (H2 O)3 ](+) core to formulate a suitable infection imaging agent. Ofloxacin was radiolabeled with (99m) Tc using carbonyl core. Radioligand chemical analysis involved HPLC methods. Radioconjugate stability and lipophilicity were determined. Binding with Staphylococcus aureus and biodistribution in infected mice for labeled compound were studied. The radioligand was characterized by HPLC, and its radiochemical purity was more than 90%. In vitro stability studies have shown the complex was stable at least 6 h after labeling at room temperature. The n-octanol/water partition coefficient experiment exhibited logP = 1.52 ± 0.21 for (99m) Tc(CO)3 -ofloxacin. The complex showed specific binding to S. aureus. Biodistribution results showed that radioligand had high accumulation in the infected muscle in a mice (T/NT = 2.02 ± 0.12 at 4 h postinjection). On the basis of stability and infection site uptake ratio, suitability of this complex as a radiotracer for imaging of infections is recognized.