**9. Conclusion**

92 12 Chapters on Nuclear Medicine

therefore, differentiation between active and structural but indolent alterations following surgery or other interventions is difficult to differentiate and these modalities are generally of limited value in detecting early disease regardless of the cause. In evaluation of infectious process CT scans may assist in the assessment of disruption of the bony cortex and softtissue involvement. Furthermore, CT may also reveal edema, intra-osseous fistula and

CT is better suited for an evaluation of cortical bone, whereas MR imaging is more useful for the evaluation of internal architecture of structures such as the bone marrow, muscles, tendons, ligaments, cartilage etc. MR imaging has high accuracy in the acute osteomyelitis evaluation and detection primarily delineating adjacent soft tissue infection; particularly when no prior alterations in osseous or soft structure are present. However, in patients who have undergone previous surgical intervention, MR imaging may not be able to clearly distinguish signal abnormality secondary to bone marrow edema or enhancement related to a reactive phenomenon and that related to infection. Similarly, the diagnostic accuracies of both CT and MR imaging to evaluate osteomyelitis generally decrease in the presence of

MR imaging has a higher sensitivity and specificity than plain films and CT. Further findings become positive earlier in the disease process with MR than with plain films. MR imaging is particularly better at depicting bone marrow abnormalities with sensitivity of 82%-100% and specificity of 75%-95%. Vertebral osteomyelitis is one condition where MR has a characteristic pattern of confluent vertebral body and disk involvement; the diagnostic accuracy in such cases amount to 90%. MR imaging findings in osteomyelitis usually are related to the replacement of marrow fat with water secondary to edema, exudate, hyperemia, and bone ischemia. Findings include the following: decreased signal intensity in the involved bone on T1-weighted images, increased signal intensity in the involved bone on T2-weighted image, and increased signal intensity in the involved bone on short-tau inversion recovery (STIR) images. A decreased intensity on T1-weighted images with no change on T2-weighted images may indicate surgical or post-traumatic scarring of bone marrow. The MR imaging limitations are primarily due to the reason that findings of osteomyelitis are nonspecific, and similar changes may occur as a result of fractures, tumours, and a number of various intramedullary or juxtamedullary processes that result in

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

cortical defects that lead to soft tissue sinus tracts.

metallic implants due to streak and susceptibility artefacts.

bone marrow edema.

**8. Future prospects and novel agents** 

Radionuclide imaging plays a significant role in infection detection and localization. Currently the selection of infection imaging agent depends upon the availability and local expertise especially in cases of labelling leukocytes which require time consuming labelling procedures. SPECT-CT provides essential anatomical localization especially in cases of vertebral osteomyelitis, diabetic foot, and infected prosthesis, cardiovascular, abdominal and pulmonary infections. Gallium scintigraphy can be replaced with FDG PET where available. FDG PET is a preferred procedure of choice for pyrexia of unknown origin, vasculitis, sarcoidosis, infected grafts and inflammatory bowel disease, moreover quantitative FDG PET analysis appears another promising further advance. Finally, with the progress in hybrid imaging the diagnostic power of conventional scintigraphy in detection and localization of infection has greatly augmented and the development of newer infection seeking agents pave the way for improved patient management in future.
