**8. Future prospects and novel agents**

The future for infection imaging looks promising with the search for an ideal agent still on. There has been a progression in the development of leukocytes labelled in-vitro by F-18 FDG. Moreover, leukocytes labelled with Copper-64 (Cu-64) are being studied. Radiolabelled antibiotics are also in vogue. The theoretical reasoning for radiolabelled antibiotics would be that such would incorporate into and metabolized by bacteria, thereby, making it possible to localize the site of infection. Tc-99m Ciprofloxacin has been studied, some results published with regards to its use in post-operative infections, however, this did not go into routine clinical practice due to conflicting data. Tc-99m labelled anti-microbial peptides are also being studied including Tc-99m labelled recombinant human betadefensin-3 that exerts bactericidal effects on gram positive and gram negative bacteria as well as some yeasts, and Tc-99m ubiquicidin whose uptake is related to number of viable bacteria. Most recently (Lupetti et al., 2011) in a review have mentioned radiolabelled antimicrobial peptides, fluconazole and chitin targeting agents that have been studied to image fungal infection in mice. There is a limitation of difficulty in differentiating bacterial and fungal infections. However, radiolabelled fluconazole has the ability to distinguish Candida albicans infection from bacterial infections/sterile inflammation.

Tc-99m ubiquicidin (Tc-99m UBI29-41), Tc-99m labelled lactoferrin (hLF1-11), Tc-99m fluconazole and I-123 labelled chitinase are being further studied at the moment. Tc-99m UBI29-41 was clinically tested in trial setting as human infection imaging agent (Akhtar et al., 2005) with promising results. They suggested an optimal imaging time of 30 minutes post injection for this agent. Another team (Salber et al., 2008) assessed and compared Tc-99m ubiquicidin and F-18 ubiquicidin autoradiography to anti-Staphylococcus aureus immunofluorescence in rat muscles abscesses. However, most recently, (Assadi et al., 2011) assessed the diagnostic accuracy of Tc-99m UBI29-41 scintigraphy for osteomyelitis making a comparison to Tc-99m MDP Bone scan and MR imaging. The authors concluded that for fast imaging with high accuracy, Tc-99m UBI29-41 is suitable for detection of osteomyelitis. In this most recent study the accuracy for Tc-99m UBI29-41 for detection of infection was observed to be 100% as compared to 90% for Tc-99m MDP bone scan. MR imaging was done in more than half of these cases and showed an accuracy of 75% for detecting osteomyelitis. Further in another most recent preliminary study by (Nazari et al., 2011) evaluated the role and ability of Tc-99m UBI29-41 to assess response to antibiotic therapy in orthopedic infections with quantitative analysis. With these recent encouraging reports, Tc-99m UBI29- 41 seems a novel agent of the future for infection imaging.

N-formyl products (fMLF or fMLP) labelled with Tc-99m are also being studied in rabbits for localization of infection. Tc-99m labelled Interleukin-8 (IL-8) seems another promising agent for the future as after initial animal model experiments it has been tried in humans with promising initial results.
