Positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging of macrophages in large vessel vasculitis: Current status and future prospects

Abstract

Macrophages are key players in the pathogenesis of large-vessel vasculitis (LVV) and may serve as a target for diagnostic imaging of LVV. The radiotracer, F-FDG has proven to be useful in the diagnosis of giant cell arteritis (GCA), a form of LVV. Although uptake ofF-FDG is high in activated macrophages, it is not a specific radiotracer as its uptake is high in any proliferating cell and other activated immune cells resulting in high non-specific background radioactivity especially in aging and atherosclerotic vessels which dramatically lowers the diagnostic accuracy. Evidence also exists that the sensitivity of F-FDG PET drops in patients upon glucocorticoid treatment. Therefore, there is a clinical need for more specific radiotracers in imaging GCA to improve diagnostic accuracy. Numerous clinically established and newly developed macrophage targeted radiotracers for oncological and inflammatory diseases can potentially be utilized for LVV imaging. These tracers are more target specific and therefore may provide lower background radioactivity, higher diagnostic accuracy and the ability to assess treatment effectiveness. However, current knowledge regarding macrophage subsets in LVV lesions is limited. Further understanding regarding macrophage subsets in vasculitis lesion is needed for better selection of tracers and new targets for tracer development. This review summarizes the development of macrophage targeted tracers in the last decade and the potential application of macrophage targeted tracers currently used in other inflammatory diseases in imaging LVV.

The utility of PET/CT in large vessel vasculitis

“…Accordingly, over the last twenty years, scientists have worked on developing macrophage targeted tracers 42 . As the field continues to evolve, we are likely to see PET/CT adapt new radiotracers with target specific biomarkers which, in the case of LVV, will highlight specific subsets of macrophages 43 . Moreover, as the use of theranostic radiopharmaceuticals advances, nuclear medicine may also provide a way to offer precision treatment of LVV 44 .…”

[18F]FDG Uptake in Adipose Tissue Is Not Related to Inflammation in Type 2 Diabetes Mellitus

“…This indicates again that [ 18 F]FDG uptake is at least not related to macrophage-driven AT inflammation. In order to evaluate AT macrophage infiltration, specific targeting of active macrophages, such as folate receptor-ß fluorescence imaging, or other markers which were independent of glucose metabolism are probably more accurate [42,43]. Besides, GLUT4 is the only insulin-dependent glucose transporter in AT [26].…”

Implementation and role of modern musculoskeletal imaging in rheumatological practice in member countries of EULAR

“…While PET, CT and MRI are generally operated and performed by radiologists; there are dedicated MRI (eg, extremity MRI) and micro-CT units in individual rheumatological centres solely under the control or catering specifically to the needs of rheumatology departments 6–8. In addition, there is a growing network of European centres performing research on the use of PET (both PET–MRI or PET–CT) in rheumatic diseases 9. Appropriate training is highly important to ensure skilled use and accurate interpretation of findings by rheumatologists.…”