Tc-99m ciprofloxacin imaging in acute cholecystitis

99m Tc-labeled antibiotics for infection diagnosis: Mechanism, action, and progress

Discovery of penicillin marked a turning point in the history of infection therapy which also led to the emergence of bacterial resistance. It is now 100 years to fight with ever-muted variants of pathogens by developing more and more antibiotics. Since 1987 to todate, no successful class of antibiotic was introduced; this three decade period is known as "the discovery void" period. While, the clinically approved antibiotics are gradually dying in front of bacterial resistance due to which bacterial infections are appearing leading cause of death and disability. Nuclear medicine imaging technique is the strongest modality to diagnose and follow-up of deep-seated and complicated infections. However, the selection of radiolabeled antimicrobial agents plays critical role in gaining sensitivity and specificity of the imaging results. This review comprises of two main sections; first section explains antibiotic targets, and second section explains the imaging efficacy of ^99m Tc-labeled antimicrobial agents against bacterial infection along with the emphasis on progress and update of ^99m Tc-labeled antibiotics as infection imaging probes. The review, in conclusion, could be an acceleration for radiopharmaceutical chemists for designing and developing ^99m Tc-labeled antimicrobial agents to improve infection imaging quality.

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.

Imaging bacteria with radiolabelled quinolones, cephalosporins and siderophores for imaging infection: a systematic review

Bacterial infections are still one of the main causes of patient morbidity and mortality worldwide. Nowadays, many imaging techniques, like computed tomography or magnetic resonance imaging, are used to identify inflammatory processes, but, although they recognize anatomical modifications, they cannot easily distinguish bacterial infective foci from non bacterial infections. In nuclear medicine, many efforts have been made to develop specific radiopharmaceuticals to discriminate infection from sterile inflammation. Several compounds (antimicrobial peptides, leukocytes, cytokines, antibiotics…) have been radiolabelled and tested in vitro and in vivo, but none proved to be highly specific for bacteria. Indeed factors, including the number and strain of bacteria, the infection site, and the host condition may affect the specificity of tested radiopharmaceuticals. Ciprofloxacin has been proposed and intensively studied because of its easy radiolabelling method, broad spectrum, and low cost, but at the same time it presents some problems such as low stability or the risk of antibiotic resistance. Therefore, in the present review studies with ciprofloxacin and other radiolabelled antibiotics as possible substitutes of ciprofloxacin are reported. Among them we can distinguish different classes, such as cephalosporins, fluoroquinolones, inhibitors of nucleic acid synthesis, inhibitors of bacterial cell wall synthesis and inhibitors of protein synthesis; then also others, like siderophores or maltodextrin-based probes, have been discussed as bacterial infection imaging agents. A systematic analysis was performed to report the main characteristics and differences of each antibiotic to provide an overview about the state of the art of imaging infection with radiolabelled antibiotics.

A systematic review and meta-analysis of diagnostic performance of imaging in acute cholecystitis

PURPOSE

To update previously summarized estimates of diagnostic accuracy for acute cholecystitis and to obtain summary estimates for more recently introduced modalities.

MATERIALS AND METHODS

A systematic search was performed in MEDLINE, EMBASE, Cochrane Library, and CINAHL databases up to March 2011 to identify studies about evaluation of imaging modalities in patients who were suspected of having acute cholecystitis. Inclusion criteria were explicit criteria for a positive test result, surgery and/or follow-up as the reference standard, and sufficient data to construct a 2 × 2 table. Studies about evaluation of predominantly acalculous cholecystitis in intensive care unit patients were excluded. Bivariate random-effects modeling was used to obtain summary estimates of sensitivity and specificity.

RESULTS

Fifty-seven studies were included, with evaluation of 5859 patients. Sensitivity of cholescintigraphy (96%; 95% confidence interval [CI]: 94%, 97%) was significantly higher than sensitivity of ultrasonography (US) (81%; 95% CI: 75%, 87%) and magnetic resonance (MR) imaging (85%; 95% CI: 66%, 95%). There were no significant differences in specificity among cholescintigraphy (90%; 95% CI: 86%, 93%), US (83%; 95% CI: 74%, 89%) and MR imaging (81%; 95% CI: 69%, 90%). Only one study about evaluation of computed tomography (CT) met the inclusion criteria; the reported sensitivity was 94% (95% CI: 73%, 99%) at a specificity of 59% (95% CI: 42%, 74%).

CONCLUSION

Cholescintigraphy has the highest diagnostic accuracy of all imaging modalities in detection of acute cholecystitis. The diagnostic accuracy of US has a substantial margin of error, comparable to that of MR imaging, while CT is still underevaluated.

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.