The efficacy of technetium-99m ciprofloxacin (Infecton) imaging in suspected orthopaedic infection: a comparison with sequential bone/gallium imaging

Application of Nuclear Medicine Techniques in Musculoskeletal Infection: Current Trends and Future Prospects

Nuclear medicine has become an indispensable discipline in the diagnosis and management of musculoskeletal infections. Radionuclide tests serve as a valuable diagnostic tool for patients suspected of having osteomyelitis, spondylodiscitis, or prosthetic joint infections. The choice of the most suitable imaging modality depends on various factors, including the affected area, potential extra osseous involvement, or the impact of previous bone/joint conditions. This review provides an update on the use of conventional radionuclide imaging tests and recent advancements in fusion imaging scans for the differential diagnosis of musculoskeletal infections. Furthermore, it examines the role of radionuclide scans in monitoring treatment responses and explores current trends in their application. We anticipate that this update will be of significant interest to internists, rheumatologists, radiologists, orthopedic surgeons, rehabilitation physicians, and other specialists involved in musculoskeletal pathology.

Recent Progress in the Molecular Imaging of Tumor-Treating Bacteria

Bacterial cancer therapy (BCT) approaches have been extensively investigated because bacteria can show unique features of strong tropism for cancer, proliferation inside tumors, and antitumor immunity, while bacteria are also possible agents for drug delivery. Despite the rapidly increasing number of preclinical studies using BCT to overcome the limitations of conventional cancer treatments, very few BCT studies have advanced to clinical trials. In patients undergoing BCT, the precise localization and quantification of bacterial density in different body locations is important; however, most clinical trials have used subjective clinical signs and invasive sampling to confirm bacterial colonization. There is therefore a need to improve the visualization of bacterial densities using noninvasive and repetitive in vivo imaging techniques that can facilitate the clinical translation of BCT. In vivo optical imaging techniques using bioluminescence and fluorescence, which are extensively employed to image the therapeutic process of BCT in small animal research, are hard to apply to the human body because of their low penetrative power. Thus, new imaging techniques need to be developed for clinical trials. In this review, we provide an overview of the various in vivo bacteria-specific imaging techniques available for visualizing tumor-treating bacteria in BCT studies.

Evaluation of Musculoskeletal and Pulmonary Bacterial Infections With [124I]FIAU PET/CT

PURPOSE

Imaging is limited in the evaluation of bacterial infection. Direct imaging of in situ bacteria holds promise for noninvasive diagnosis. We investigated the ability of a bacterial thymidine kinase inhibitor ([124I]FIAU) to image pulmonary and musculoskeletal infections.

METHODS

Thirty-three patients were prospectively accrued: 16 with suspected musculoskeletal infection, 14 with suspected pulmonary infection, and 3 with known rheumatoid arthritis without infection. Thirty-one patients were imaged with [124I]FIAU PET/CT and 28 with [18F]FDG PET/CT. Patient histories were reviewed by an experienced clinician with subspecialty training in infectious diseases and were determined to be positive, equivocal, or negative for infection.

RESULTS

Sensitivity, specificity, positive-predictive value, negative-predictive value, and accuracy of [124I]FIAU PET/CT for diagnosing infection were estimated as 7.7% to 25.0%, 0.0%, 50%, 0.0%, and 20.0% to 71.4% for musculoskeletal infections and incalculable-100.0%, 51.7% to 72.7%, 0.0% to 50.0%, 100.0%, and 57.1% to 78.6% for pulmonary infections, respectively. The parameters for [18F]FDG PET/CT were 75.0% to 92.3%, 0.0%, 23.1% to 92.3%, 0.0%, and 21.4% to 85.7%, respectively, for musculoskeletal infections and incalculable to 100.0%, 0.0%, 0.0% to 18.2%, incalculable, and 0.0% to 18.2% for pulmonary infections, respectively.

CONCLUSIONS

The high number of patients with equivocal clinical findings prevented definitive conclusions from being made regarding the diagnostic efficacy of [124I]FIAU. Future studies using microbiology to rigorously define infection in patients and PET radiotracers optimized for image quality are needed.

Ciprofloxacin: from infection therapy to molecular imaging

Diagnosis of deep-seated bacterial infection remains a serious medical challenge. The situation is becoming more severe with the increasing prevalence of bacteria that are resistant to multiple antibiotic classes. Early efforts to develop imaging agents for infection, such as technetium-99m (^99mTc) labeled leukocytes, were encouraging, but they failed to differentiate between bacterial infection and sterile inflammation. Other diagnostic techniques, such as ultrasonography, magnetic resonance imaging, and computed tomography, also fail to distinguish between bacterial infection and sterile inflammation. In an attempt to bypass these problems, the potent, broad-spectrum antibiotic ciprofloxacin was labeled with ^99mTc to image bacterial infection. Initial results were encouraging, but excitement declined when controversial results were reported. Subsequent radiolabeling of ciprofloxacin with ^99mTc using tricarbonyl and nitrido core, fluorine and rhenium couldn't produce robust infection imaging agent and remained in discussion. The issue of developing a robust probe can be approached by reviewing the broad-spectrum activity of ciprofloxacin, labeling strategies, potential for imaging infection, and structure-activity (specificity) relationships. In this review we discuss ways to accelerate efforts to improve the specificity of ciprofloxacin-based imaging.

Fluoroquinolones as imaging agents for bacterial infection

Diagnosis of deep-seated bacterial infection is difficult, as neither standard anatomical imaging nor radiolabeled, autologous leukocytes distinguish sterile inflammation from infection. Two recent imaging efforts are receiving attention: (1) radioactive derivatives of sorbitol show good specificity with Gram-negative bacterial infections, and (2) success in combining anatomical and functional imaging for cancer diagnosis has rekindled interest in 99mTc-fluoroquinolone-based imaging. With the latter, computed tomography (CT) would be combined with single-photon-emission-computed tomography (SPECT) to detect 99mTc-fluoroquinolone-bacterial interactions. The present minireview provides a framework for advancing fluoroquinolone-based imaging by identifying gaps in our understanding of the process. One issue is the reliance of 99mTc labeling on the reduction of sodium pertechnetate, which can lead to colloid formation and loss of specificity. Specificity problems may be reduced by altering the quinolone structure (for example, switching from ciprofloxacin to sitafloxacin). Another issue is the uncharacterized nature of 99mTc-ciprofloxacin binding to, or sequestration in, bacteria: specific interactions with DNA gyrase, an intracellular fluoroquinolone target, are unlikely. Labeling with 68Ga rather than 99mTc enables detection by positron emission tomography, but with similar biological uncertainties. Replacing the C6-F of the fluoroquinolone with 18F provides an alternative to pertechnetate and gallium that may lead to imaging based on drug interactions with gyrase. Gyrase-based imaging requires knowledge of fluoroquinolone action, which we update. We conclude that quinolone-based probes show promise for the diagnosis of infection, but improvements in specificity and sensitivity are needed. These improvements include the optimization of the quinolone structure; such chemistry efforts can be accelerated by refining microbiological assays.

Utility of 18F sodium fluoride PET/CT imaging in the evaluation of postoperative pain following surgical spine fusion

STUDY DESIGN

A retrospective case review of patients who underwent 18F sodium fluoride PET/CT imaging of the spine with postoperative pain following vertebral fusion.

OBJECTIVE

To determine the benefit of 18F sodium fluoride PET/CT imaging in the diagnosis of persistent pain in the postoperative spine. The diagnosis of pain generators in the postoperative spine has proven to be a diagnostic challenge. The conventional radiologic evaluation of persistent pain after spine surgery with the use of plain radiographs, MRI, and CT can often fall short of diagnosis in the complex patient. 18F sodium fluoride PET/CT imaging is an alternative tool to accurately identify a patient's source of pain in the difficult patient.

METHODS

This retrospective study looked at 25 adult patients who had undergone 18F sodium fluoride PET/CT imaging. All patients had persistent or recurrent back pain over the course of a 15-month period after having undergone spinal fusion surgery. All patients had inconclusive dedicated MRI. The clinical accuracy of PET/CT in identifying the pain generator and contribution to altering the decision making process was compared to the use of CT scan alone.

RESULTS

Of the 25 patients studied, 17 patients had increased uptake on the 18F sodium fluoride PET/CT fusion images. There was a high-level correlation of radiotracer uptake to the patients' pain generator. Overall 88% of the studies were considered beneficial with either PET/CT altering the clinical diagnosis and treatment plan of the patient or confirming unnecessary surgery.

CONCLUSION

18F sodium fluoride PET/CT proves to be a useful tool in the diagnosis of complex spine pathology of the postoperative patients. In varied cases, a high correlation of metabolic activity to the source of the patient's pain was observed.

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.

FDG PET for diagnosing infection in hip and knee prostheses: prospective study in 221 prostheses and subgroup comparison with combined (111)In-labeled leukocyte/(99m)Tc-sulfur colloid bone marrow imaging in 88 prostheses

PURPOSE

This study aims to assess and compare the value of FDG PET with combined In-labeled leukocyte/Tc-sulfur colloid bone marrow (WBC/BM) imaging for diagnosing infection in hip and knee prostheses.

METHODS

In this prospective study, patients with painful hip or knee arthroplasty, who were scheduled to undergo clinical and diagnostic evaluation for prosthesis revision, were included. They have been studied by using FDG PET and WBC/BM scan. This study was institutional review board approved and Health Insurance Portability and Accountability Act compliant. All patients provided written informed consent.

RESULTS

A total of 134 hip and 87 knee prostheses, suspected of being either infected or noninfectious loosening, were evaluated. All 221 prostheses underwent FDG PET, whereas both WBC/BM imaging and FDG PET were performed in 88 prostheses. The initial analysis of data from the WBC/BM images demonstrated somewhat suboptimal results compared with those of FDG PET scans on 88 patients. In addition, some patients were not willing to undergo both procedures and therefore participate in this study. Therefore, a decision was made to eliminate WBC/BM imaging from the procedures for the remainder of this research study. This decision was reached partly because of the significant radiation dose delivered from labeled WBC and safety issues related to preparing these labeled cells. Final diagnosis was based on microbiological examinations of the surgical specimens in 125 prostheses and joint aspirations combined with the clinical follow-up of 6 months or more in 86 prostheses. The sensitivity, specificity, positive predictive value, and negative predictive value of FDG PET in hip prostheses were 81.8%, 93.1%, 79.4%, and 94.0%, respectively, and in knee prostheses were 94.7%, 88.2%, 69.2%, and 98.4%, respectively. The sensitivity, specificity, positive predictive value, and negative predictive value of WBC/BM imaging in hip prostheses were 38.5%, 95.7%, 71.4%, and 84.6%, respectively, and in knee prostheses were 33.3%, 88.5%, 25.0%, and 92.0%, respectively. In those cases that underwent both FDG PET and WBC/BM imaging, there was a trend (P = 0.0625) toward a higher sensitivity for FDG PET in hip prostheses, whereas other comparisons did not show any significant differences between the 2 imaging modalities.

CONCLUSIONS

Based on this study, the diagnostic performance of FDG PET scan in detecting infection in painful hip and knee prostheses is optimal for routine clinical application. Considering the complexity and costs of WBC/BM imaging and related safety issues associated with this preparation, FDG PET seems to be an appropriate alternative for assessing these patients.

Past and Present Scenario of Imaging Infection and Inflammation: A Nuclear Medicine Perspective

Nuclear medicine techniques provide potential non-invasive tools for imaging infections and inflammations in the body in a precise way. These techniques are further exploited by the use of radiopharmaceuticals in conjunction with imaging tests such as scintigraphy and positron emission tomography. Improved agents for targeting infection exploit the specific accumulation of radiolabeled compounds to understand the pathophysiologic changes involved in the inflammatory process and correlate them with other chronic illnesses. In the recent past, a wide variety of radiopharmaceuticals have been developed, broadly classified as specific radiopharmaceuticals and nonspecific radiopharmaceuticals. New developments in positron emission (leveraging 18F and 18fluorodeoxyglucose) and heterocyclic/peptide chemistry and radiochemistry are resulting in unique agents with high specific activity. Various approaches to visualizing infection and inflammation are presented in this review, in an integral manner, that give a clear view of the existing radiopharmaceuticals in clinical practice and those under development.

Antimicrobial peptides as infection imaging agents: better than radiolabeled antibiotics

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

The value of successive Infecton scans in assessing the presence of chronic bone and joint infection and in predicting its evolution after treatment and after a prolonged follow-up

OBJECTIVE

Our objective was to monitor the evolution of bone and/or joint infections with the aid of successive radiolabelled ciprofloxacin (Infecton) scans during antimicrobial treatment and to compare the results of an Infecton scan at the end of therapy with the respective results of clinical evaluation, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) in predicting resolution or recurrence of infection after a long period of posttreatment follow-up.

METHODS

Thirty-three patients with documented bone and/or joint infection were subjected to successive Infecton scans on two or three visits. Infecton scans were evaluated visually and scored accordingly. Clinical evaluation was scored by the referring clinicians. ESR and CRP values were evaluated independently. A minimum of 2-year free-of-infection follow-up after discontinuation of the antibiotic treatment served as a measure of successful antimicrobial therapy and nonrecurrence of infection. Statistics included survival analysis (Cox regression).

RESULTS

During follow-up, five patients in the study presented with recurrence, and three died as a result of an irrelevant cause. The remaining patients were followed up for a median of 108 months (range 97-132 months) without any signs of recurrence of infection. Recurrence of infection was 4.2 times more likely to occur in patients with positive Infecton scans [hazard ratio (HR): 4.2, confidence intervals 95%: 1.39-12.67, P=0.011]. Infecton had the highest sensitivity (83.3%), accuracy (69.69%) and negative predictive value (94.74%), whereas CRP had the highest specificity (76.92%).

CONCLUSION

Infecton scintigraphy proved to be more sensitive and accurate and had a higher negative predictive value compared with clinical evaluation, ESR and CRP in predicting infection resolution or recurrence in patients with chronic bone and joint infections.

Tc-99m Ciprofloxacin SPECT of Pulmonary Tuberculosis

PURPOSE

Tc-99m ciprofloxacin is available for imaging infection. However, there has been no study on employing single photon emission computed tomography (SPECT) with using Tc-99m ciprofloxacin to image active pulmonary tuberculosis. Therefore, we conducted this study to assess the efficacy of Tc-99m ciprofloxacin SPECT for imaging active pulmonary tuberculosis.

METHODS

Twenty-one participants were enrolled in this prospective study. They were divided into two groups according to the clinical and radiological assessment. Group one (Gr. 1) consisted of five normal volunteers and six patients with inactive pulmonary tuberculosis. Group two (Gr. 2) consisted of ten patients with active pulmonary tuberculosis. SPECT was performed 3 h after injecting 555 MBq (15 mCi) of Tc-99m ciprofloxacin. The findings of Tc-99m ciprofloxacin SPECT were interpreted by a nuclear medicine specialist and then the results were analyzed according to the patients' clinical and radiological classifications.

RESULTS

The results of Tc-99m ciprofloxacin SPECT were as follows: eight true-positive cases, ten true-negative cases, one false-positive case and two false-negative cases. The sensitivity and specificity was 80.0% and 90.9%, respectively. The positive predictive value was 88.9% and the negative predictive value was 83.3%.

CONCLUSIONS

Tc-99m ciprofloxacin SPECT is feasible for imaging active pulmonary tuberculosis. It is a useful nuclear-imaging method for discriminating between the active and inactive tuberculosis states in patients with a past medical history of pulmonary tuberculosis.

Clinical evaluation of antimicrobial peptide [(99m)Tc/Tricine/HYNIC(0)]ubiquicidin 29-41 as a human-specific infection imaging agent

INTRODUCTION

Ubiquicidin (UBI) 29-41 is a cationic synthetic antimicrobial peptide fragment that binds preferentially with the anionic microbial cell membrane at the site of infection. This study was conducted to evaluate the potentiality of [(99m)Tc/Tricine/HYNIC(0)]UBI 29-41 prepared from lyophilized kits as an infection imaging agent in humans.

METHODS

Seven patients (5 males and 2 females; mean age=55 years; age range=35-75 years) with suspected bone or soft-tissue infections participated in this study. [(99m)Tc/Tricine/HYNIC]UBI 29-41, corresponding to activity in the range 555-740 MBq added to 40 mug of peptide obtained from instant freeze-dried kit formulations with radiochemical purities >95%, was injected intravenously. A 45-min dynamic study was followed by spot views of the suspected region of infection (target) and a corresponding normal area (nontarget). Whole-body anterior and posterior images were also acquired at 30, 60 and 120 min after injection. True- or false-positive or true- or false-negative images were interpreted upon bacterial culture, radiography, clinical tests and bone scanning.

RESULTS

The biodistribution of [(99m)Tc/Tricine/HYNIC]UBI 29-41 in patients showed rapid accumulation of activity in the kidneys in the first 30 min after injection that gradually declined and accumulated in the urinary bladder. There were positive findings in five studies and negative findings in two. Findings were subsequently confirmed to be true positive or negative. Images showed minimal accumulation in nontarget tissues, with an average target/nontarget ratio of 2.10+/-0.33 in positive lesions at 30 min.

CONCLUSION

Given its favorable clinical characteristics, [(99m)Tc/Tricine/HYNIC]UBI 29-41 shows promise as a tracer for infection imaging that allows early diagnosis (30 min) of infection.

Efficacy of indigenously developed single vial kit preparation of 99mTc-ciprofloxacin in the detection of bacterial infection: an Indian experience

OBJECTIVE

To investigate the diagnostic efficacy of indigenously developed single vial kit preparation of Tc-ciprofloxacin (Diagnobact) for the detection of orthopedic infections.

METHODS

Seventy-seven patients [25 with clinical suspicion of diabetic foot osteomyelitis (DFOM), 25 with orthopedic device-related infection (ODRI) and 27 with tubercular bone infection] underwent three-phase Tc-methylenediphosphonate bone scintigraphy followed by static Tc-ciprofloxacin imaging at 1, 4 and 24 h. Imaging (anterior and posterior views) was performed under a dual-head gamma-camera using a low-energy, high-resolution, parallel-hole collimator. The lesion-to-background ratio (LBR) of the radiotracer was calculated on the static isotime Tc-ciprofloxacin images using semiquantitative analysis. Scintigraphic (Diagnobact) results were compared with the histopathological and/or culture/PCR analysis as a gold standard.

RESULTS

The mean LBR of the radiotracer (Tc-ciprofloxacin) in the positive scans (n=29; 16 ODRI, 13 DFOM) was > or =2.0 at 1 h postinjection and remained consistent till 24 h. In contrast, the mean LBR in the negative scans (n=21; 12 DFOM, nine ODRI) was < or =1.5 at 1 h and declined significantly (P<0.05) at 24 h. The observed trend in the mean LBR in positive (n=18) and negative (n=9) scans for tubercular osteomyelitis was identical to that seen in the nontubercular bacterial infections.

CONCLUSION

The management protocol for patients with suspected bony infection may include a three-phase bone scan followed by Tc-ciprofloxacin scan. An LBR of > or =2.0 at 1 h that remained consistent till 24 h on Tc-ciprofloxacin scan is indicative of active bacterial infection. However, resistance to ciprofloxacin at the bacterial cell membrane may be a limitation of this technique.

Diagnosis of mandibular osteomyelitis in probable coexisting tumor recurrence: role of Tc-99m ciprofloxacin imaging

We demonstrate the use of Tc-99m ciprofloxacin imaging in a follow-up case of squamous cell carcinoma of the tongue post hemi-mandibulectomy with clinical suspicion of local recurrence of osteomyelitis. On Tc-99m ciprofloxacin scan, we observed a focus of sharply increasing radiotracer concentration in the left side of the mandible after 24 hours, indicating active bacterial infection. Histopathologic analysis revealed no evidence of local recurrence, whereas the culture examination showed bacterial growth sensitive to ciprofloxacin. A follow-up Tc-99m ciprofloxacin scan after debridement and 8 weeks of antibiotic treatment showed no focus of tracer concentration in the region of the mandible.

An imaging analysis of (99m)Tc-UBI (29-41) uptake in S. aureus infected thighs of rabbits on ciprofloxacin treatment

PURPOSE

The uptake of (99m)Tc-UBI (29-41) was evaluated at sites of bacterial infections in rabbits before and after treatment with ciprofloxacin.

METHODS

Staphylococcus aureus susceptible to ciprofloxacin was used to induce a focal infection in each rabbit of group 1 (G1), group 2 (G2), and group 3 (G3) with 2 x 10(4), 2 x 10(6), and 2 x 10(8) colony forming units (CFU), respectively. After 24 h, images of infected thighs (target: T) and contralateral thighs (nontarget: NT) were acquired. Animals then received ciprofloxacin intramuscularly for 5 days followed by imaging on the third and fifth days. The control group 4 (G4) was imaged at days 1, 3, and 5 under the same acquisition parameters. Group 5 (G5) was employed to study biodistribution of the peptide.

RESULTS

Increases in (T/NT) ratios in G1, G2, and G3 were observed from 5 min onwards with maximum values at 60 min. G3 revealed the highest accumulation of the peptide. Growth of the same strain of S. aureus on blood agar medium was visualized after fine needle aspiration. After ciprofloxacin treatment, the images for G1-G3 resulted in significantly decreased (P < 0.05) T/NT values on the third and fifth days that correlated with reduction in number of viable bacteria. No significant difference (P < 0.05) in left to right thigh ratios in the control group (G4) was observed. Biodistribution of the peptide showed rapid removal of tracer from circulation through the kidneys.

CONCLUSIONS

( 99m ) Tc-UBI (29-41) accumulation directly correlates with the number of viable bacteria. This infection localization agent can be utilized for monitoring efficacy and duration of antibiotic treatment.

New imaging tools for the diagnosis of infection

Infection imaging became widespread in 1971 with the release of 67Ga citrate. Multiphase skeletal scintigraphy and radiolabeled white blood cells (WBCs) have since become the most widespread clinically used agents for the imaging of infection. A wide variety of other radiolabeled probes are under investigation, based on antibodies, cytokines, assorted proteins and other molecules, alone or in various combinations. However, these latter agents, with a few exceptions, are not routinely used clinically. Radiolabeled ciprofloxacin represents the first attempt to develop an infection-specific imaging agent (most infection-imaging probes localized nonspecifically to inflammation as well), but it has not proven superior to radiolabeled WBCs or 18F-fluoro-deoxy-glucose (FDG) PET. Because of the ability to combine exquisite anatomic detail with focal uptake of 18F-FDG, PET–computed tomography has achieved great success in the detection and localization of infection, including in clinically adverse conditions. Despite these advances, at this time an infection-specific imaging agent does not exist.

Evaluation of 99mTc-UBI 29-41 scintigraphy for specific detection of experimental Staphylococcus aureus prosthetic joint infections

PURPOSE

(99m)Tc-UBI 29-41 (UBI), an antimicrobial peptide, specifically targets bacteria. We tested the ability of UBI to discriminate between infected and uninfected prosthetic joints using a rabbit model previously validated.

METHODS

Left knee arthroplasty was performed on 20 New Zealand rabbits, then 10(7) cfu of S. aureus (n = 12) or sterile saline (n = 8) was injected into the joint. On days 9 and 20 after surgery, planar UBI scintigraphy was performed in six infected and four uninfected rabbits, 1 h and 4 h p.i. (150 MBq), on a gamma camera. Operated-to-normal knee activity ratio (ONKR) was calculated on each scintigram. Then, after sacrifice, tissue samples of both knees were counted in a gamma counter.

RESULTS

One rabbit injected with sterile saline had cutaneous infection at sacrifice and was excluded from analysis. ONKR was higher in infected than in uninfected animals 4 h p.i. 20 days after surgery: 1.75 +/- 0.48 vs 1.13 +/- 0.11, p = 0.04. From 1 h to 4 h p.i., ONKR increased in 9/12 infected and 0/7 uninfected animals. According to UBI uptake intensity and kinetics, scintigraphy was truly positive in all infected cases on day 9 and in four of six infected cases on day 20. It was truly negative in two of three sterile inflamed prosthetic knees on day 9, and in all cases on day 20. Biodistribution studies revealed increased UBI uptake in periprosthetic tissues in all animals 9 days after surgery, and only in infected animals on day 20.

CONCLUSION

In this experimental study, (99m)Tc-UBI 29-41 scintigraphy permitted the early detection of acute prosthetic joint infection, and exclusion of infection in chronic sterile prosthetic joint inflammation.

Optimized scintigraphic evaluation of infection and inflammation: role of single-photon emission computed tomography/computed tomography fusion imaging

Gallium-67 citrate and radiolabeled white blood cells have become standard inflammation/infection-seeking agents whereas other agents, such as (99m)Tc diphosphonates, commonly are used to infer an infectious process. These radiopharmaceuticals reflect physiologic and pathologic function rather than anatomical abnormality. In the clinical setting, it is often necessary to correlate these functional studies with anatomical imaging. The advent of single-photon emission computed tomography, as well as positron emission tomography, provides tomographic images for direct correlation to anatomic modalities such as computed tomography and magnetic resonance imaging. The methods by which these functional and anatomic imaging modalities are correlated include side-by-side, software, and hardware fusion. Clinically, fusion imaging has been applied primarily to oncologic and neurologic applications. The literature supports the premise that multimodality fusion would increase the specificity of the physiologic modality and increase the sensitivity of the anatomic modality. Our institution uses software fusion to aid in the diagnosis of infection and inflammation. Through case vignettes, we illustrate applications for single-photon emission computed tomography/computed tomography fusion for the diagnosis of infection and inflammation in multiple organ systems.

Synthesis and evaluation of fluorine-18 labelled compounds for imaging of bacterial infections with pet

Syntheses of no carrier added (n.c.a.) 6-fluoro-1,4-dihydro-1-cyclopropyl-4-oxo-7-[4-[18F]fluoro-phenacyl-1-piperacinyl]-chinolincarboxylic acid ([18F]COPCA) and n.c.a. 4-[18F]fluoro-benzoyl-ubiquicidin 29-41 ([18F]UBI 29-41) are described. [18F]COPCA was synthesised within 120 min with a radiochemical yield of 9-12%. [18F]UBI 29-41 was synthesised within 150 min with a radiochemical yield of 15-20%. Both compounds had a specific activity of more than 35 GBq/micromol. The biological activity was verified by measuring its binding to Staphylococcus aureus bacteria. Specific binding was found for [18F]UBI 29-41 (12-17%), whereas no specific binding for [18F]COPCA was found.

99mTechnetium-ciprofloxacin scintigraphy for the evaluation of spinal infections: a preliminary report

Currently available laboratory and imaging tests have limitations diagnosing and following patients with spinal infections. We evaluated 17 Technetium-99m labeled ciprofloxacin scintigraphy studies in 11 patients who had the diagnosis of a spinal infection based on the Centers for Disease Control and Prevention criteria. Three of the 17 studies were performed in three patients within 2 months from the onset of the symptoms. All of these three studies showed increased uptake of the radiopharmaceutical in the area of the spinal infection. Fourteen studies were performed during the followup period (from 210 to 690 days after the onset of symptoms) in nine patients with spinal infections. Ten of the 14 studies performed in five patients with an active spine infection showed positive results while the patients had evidence for active spinal infection at the time of the testing. Four studies were performed during the followup period in four patients who at the time of the nuclear imaging testing had no symptoms, signs, or laboratory or other imaging evidence for active infection. All four studies showed negative results. The results of this preliminary study show that scintigraphy with 99mTc-ciprofloxacin may be useful in the diagnosis of active spinal infections.

LEVEL OF EVIDENCE

Diagnostic study, level II-1 (Testing of previously developed diagnostic criteria on consecutive patients [with universally applied reference "gold" standard]). Please see Guidelines for Authors for a complete description of levels of evidence.

Diagnosis and Treatment of Septic Arthritis

Septic arthritis (SA) is a common orthopedic condition encountered in horses that are presented to equine veterinarians. Successful out-come is dependent on prompt and thorough evaluation and treatment. This article briefly reviews the pathophysiology, outlines diagnostics, describes treatment options and prognostics, and discusses current research in diagnosis and treatment of SA.

(99M)Tc-ciprofloxacin in imaging of clinical infections in camelids and a goat

(99M)Tc-ciprofloxacin was used to image five adult camelids and a juvenile goat with clinical and/or radiographic signs of infection. (99m)Tc-ciprofloxacin (range 10-33 MBq/kg) was injected intravenously and a series of 2-min static images were acquired at 1- and 4-h postinjection. At 24-h postinjection, 5-min static images were acquired. Only the skull or abdomen was imaged in the adults; the whole body was imaged in the goat. The quality of the 1-, 4-, and 24-h studies was evaluated subjectively. Normal and abnormal areas of (99m)Tc-ciprofloxacin uptake were recorded and subjectively graded as mild, moderate or intense. Image quality was best 4-h postinjection. Twenty-four-hour images were poor because of insufficient radioactivity. (99m)Tc-ciprofloxacin imaging resulted in true positive or true negative scans in four of six animals. Two false-negative studies occurred. Intense (99m)Tc-cirofloxacin activity was seen in the lungs and urinary bladder, moderate/intense activity in the kidneys, and mild activity in the physes/epiphyses, liver and intermittently in the gastrointestinal tract. The normal distribution of (99m)Tc-ciprofloxacin in camelids/small ruminants differed from people. Further studies to determine the sensitivity and specificity of infection detection using (99m)Tc-ciprofloxacin in animals are warranted.

Technetium-99m ciprofloxacin imaging in the diagnosis of postsurgical bony infection and evaluation of the response to antibiotic therapy: A case report

The use of radiolabelled antibiotics is fast emerging as a promising diagnostic test for the detection of infective lesions, because of their specific binding to the bacterial component. Ciprofloxacin is a broad-spectrum antibiotic that has been used as a radiolabelled antibiotic in both the diagnosis of infections in rabbits and in clinical trials on humans. The diagnosis of skeletal microbial infections remains a challenge, especially in orthopaedic patients with implants. We present a case report of a patient with undiagnosed and unrelenting pain in the lower third of the left leg, which had persisted for 6 months. A novel scintigraphy, which was developed in-house using a 99mTC ciprofloxacin single vial kit, was used for diagnosing the active bacterial infection. A 99mTC methylene diphosphonate bone scan was also performed to locate precisely the site of the lesion. Gradually increasing concentrations of both the radiotracers confirmed the presence of active bacterial infection in the distal third of the left tibia. Follow-up scanning after antibiotic therapy showed the disappearance of the pooling of 99mTC ciprofloxacin, indicating a good response. Therefore, 99mTC ciprofloxacin has good diagnostic and prognostic applications in deep-seated covert skeletal microbial infections. However, the persistence of a focal concentration detected by the 99mTC methylene diphosphonate scan was attributed to the inflammatory and not the infective pathology.

Suspected disk space infection with negative microbiological tests—report of eight cases and comparison with documented pyogenic discitis

Few data are available on patients with suspected noniatrogenic pyogenic discitis but negative microbiological tests.

OBJECTIVES

To compare the features, treatment, and outcomes in patients with suspected versus microbiologically documented noniatrogenic pyogenic discitis.

PATIENTS

A retrospective chart review identified eight patients with suspected noniatrogenic pyogenic discitis managed at our institution over a 15-year period. Eighteen age- and sex-matched patients with microbiologically documented noniatrogenic pyogenic discitis managed at our institution during the same period served as controls.

RESULTS

The eight cases had a longer time to diagnosis, a greater risk of abscess formation or epidural infection, and a smaller number of cutaneous portals of entry, as compared to the controls. None of the cases had evidence of endocarditis or diabetes mellitus. Infection at another site preceded the discitis in half the cases. Empirical treatment with two antimicrobials (usually a fluoroquinolone with a beta-lactam or fosfomycin) ensured a full recovery in all eight cases, with no relapses or long-term recurrences, whereas relapses occurred in three of the 18 controls treated with antibiotics selected by antibiotic susceptibility testing.

CONCLUSION

Noniatrogenic pyogenic discitis with negative microbiological studies is associated with distinctive clinical features consistent with smoldering infection. The outcome is favorable under empirical two-drug antimicrobial therapy, usually including a fluoroquinolone given by the intravenous route.

Management of osteomyelitis

Osteomyelitis is an infection of the medullary or cortical bone that is becoming more difficult to cure with the increasing prevalence of methicillin- and vancomycin-resistant organisms. This article discusses the etiology of osteomyelitis and the effectiveness of various treatment options.

99mTc ciprofloxacin imaging for the diagnosis of infection in the postoperative spine

BACKGROUND

The non-invasive assessment of postoperative spinal infections can pose a substantial diagnostic challenge, especially in the presence of orthopaedic devices. In contrast to white blood cell scanning, which is of limited use in the spine, the low uptake of 99mTc ciprofloxacin into normal bone marrow, combined with its claimed bacterial specificity, makes it, theoretically, an ideal candidate for evaluating postoperative spinal infections.

AIM

This study aimed to evaluate 99mTc ciprofloxacin planar and single photon emission tomography (SPET) imaging in relation to microbiological diagnosis in the postoperative spine.

METHODS

Only patients with a microbiologically confirmed diagnosis were included in this analysis. Planar imaging was performed at 1, 3 and 24 h, and SPET was performed at 3 h post-injection of 370 MBq 99mTc ciprofloxacin. Images were scored by two independent, certified, nuclear medicine physicians, blinded for the final diagnosis.

RESULTS

Within the first 22 consecutive patients with microbiological diagnosis, there were nine deep infections. Sensitivity, specificity and accuracy at visual scoring were, respectively, 67%, 77%, 73% (1 h), 78%, 69%, 73% (3 h), and 56%, 92%, 77% (24 h) for planar imaging, and 100%, 54%, and 73% for SPET.

CONCLUSION

In contrast to white blood cell scanning, SPET with Tc ciprofloxacin is sensitive in evaluating infections in the postoperative spine. Sensitivity is higher for SPET than for planar imaging. However, the results presented prove that its specificity is limited, especially in patients who have recently (< 6 months) undergone surgery. Taken this limitation into account, we advise planar and SPET imaging at 3 h post-injection and at an interval of at least 6 months after surgery to minimize the chance for false positives.

Applications of fluorodeoxyglucose positron emission tomography in the diagnosis of infection

The purpose of this study was to assess the accuracy of fluorodeoxyglucose positron emission tomography (FDG PET) in diagnosing infection in a large population of patients and in a variety of clinical circumstances where the performance of conventional imaging modalities has been questioned. We retrospectively analysed 167 FDG PET scans obtained to evaluate 175 anatomical sites for the presence of infection. The major indications for the scans were (1) complicated orthopaedic hardware (n=97), (2) chronic osteomyelitis (n=56), and (3) other (n=14: six fever of unknown origin, three vascular grafts, and five soft tissue). We assessed the overall diagnostic accuracy of FDG PET for each of these indications. In addition, we further analysed this modality's effectiveness by grouping the scans into specific clinical situations. A final diagnosis was made on the basis of surgical pathology and clinical follow-up for a minimum of 6 months. The overall accuracy of FDG PET in evaluating orthopaedic hardware was 96.2% for hip prosthesis, 81% for knee prosthesis, and 100% in 15 patients with other orthopaedic devices. Among the patients in our sample suspected of having chronic osteomyelitis, the accuracy was 91.2%. FDG PET was inaccurate in three cases of fever of unknown origin and accurate in all vascular graft and soft tissue infections. In 49 patients with a clinically apparent soft-tissue infection, FDG PET was able to detect or exclude underlying osteomyelitis with an accuracy of 92.3%. Among the 23 patients who had recent orthopaedic procedures, FDG PET imaging was accurate in 87% of cases. It is concluded that FDG PET is a highly effective imaging modality in the assessment of patients with suspected infection.

Prosthetic joint infections: bane of orthopedists, challenge for infectious disease specialists

Prosthetic joint infections (PJIs) occur in approximately 1.5%-2.5% of all primary hip or knee arthroplasties. The mortality rate attributed to PJIs may be as high as 2.5%. Substantial morbidity is associated with a loss of mobility, although this is temporary. The costs associated with a single episode of PJI are approximately $50,000 per episode, exclusive of lost wages. Risk factors that increase the occurrence of PJI include revision arthroplasty, time in the operating room, postoperative surgical site infection, and malignancy. Pain is the most consistent symptom. Staphylococcus species are the most common organisms isolated from PJI sites. Two-stage revision is superior to single-stage revision or to debridement with prosthesis retention. Long-term antibiotic suppression and/or arthrodesis are useful for patients too frail to undergo extensive surgery. Using an optimal approach, recurrent infection occurs in <10% of previously infected joints.

The value of (18)FDG-PET for the detection of infected hip prosthesis

We compared the accuracy of fluorine-18 labelled 2-fluoro-2-deoxy- d-glucose positron emission tomography ((18)FDG PET) with that of technetium-99m hexamethylpropylene amine oxime leucocyte scintigraphy (LS) in the detection of infected hip prosthesis. Seventeen patients with a hip prosthesis suspected for infection were prospectively included and underwent (99m)Tc-methylene diphosphonate bone scintigraphy (BS), LS and an (18)FDG-PET scan within a 2-week period. Seven volunteers with ten asymptomatic hip prostheses were used as a control group and underwent BS and an (18)FDG-PET scan. Bacteriology of samples obtained by surgery or by needle aspiration and/or clinical follow-up for up to 6 months were used as the gold standard. Planar images of BS and LS (4 and 24 h p.i.) were acquired, followed by single-photon emission tomography (SPET) LS images (after 4 h). These images were scored as positive or negative by two experienced readers. The (18)FDG-PET scans of the patients were compared with the tracer distribution pattern in the asymptomatic control group and with BS. A phantom study was performed in order to identify artefacts. For this purpose, three different attenuation correction methods were tested. The combined analysis of the planar BS and LS resulted in a 75% sensitivity and a 78% specificity. The SPET LS images showed a better lesion contrast, resulting in an 88% sensitivity and a 100% specificity, while 24-h planar images were of no additional value. The analysis of PET images alone resulted in an 88% sensitivity and a 78% specificity. The combination of (18)FDG-PET and BS images resulted in an 88% sensitivity and a 67% specificity. Given the presence of small errors near the edge of the metal, which can induce significant artefacts in the corrected emission image, we decided to use the data without attenuation correction. In this preliminary study, (18)FDG-PET scans alone showed the same sensitivity as combined BS and LS, although the specificity was slightly lower.