Imaging of immunocompromised patients: focus on fungal-specific PET tracers.

The global population of immunocompromised patients is growing, accompanied by a rising incidence of opportunistic infections. Among these, invasive mold infections are associated with substantial morbidity and mortality, in part because of delayed diagnosis. Although current diagnostic methods have improved, they are still limited by lack of specificity, invasiveness, or both. Recently, several novel noninvasive, pathogen-specific PET imaging ligands have been developed and evaluated. Among them, [18F]-fluorocellobiose, a carbohydrate-based metabolic tracer, has demonstrated high specificity for live cellulolytic mold infections, including Aspergillus spp. It also shows promise for treatment monitoring and can be readily synthesized enzymatically from [18F]-fluorodeoxyglucose. ImmunoPET approaches targeting fungal cell wall components are likewise highly promising as panfungal ligands and may be further optimized through antibody engineering strategies to enhance target binding, functionality and pharmacokinetic properties. These newer PET ligands have the potential to overcome the limited specificity of [18F]-FDG, allowing more accurate localization of infectious lesions and, importantly, differentiation between invasive fungal infections and other types of pathogens. Such advances are especially significant for this vulnerable patient population, in whom rapid and accurate diagnosis can have major prognostic implications.