Discerning infection from inflammation: A new PET/CT technique

Antimicrobial peptide PET/CT imaging with gallium-68 appears to break through previous roadblocks in differentiating infections and sterile inflammatory processes, according to a study published Jan. 16 in the Journal of Nuclear Medicine.

Thomas Ebenhan, of the department of nuclear medicine at the University of Pretoria and Steve Biko Academic Hospital, Pretoria, South Africa, and colleagues evaluated a molecular imaging tracer combining the gallium-68 radiolabeled antimicrobial peptide UBI29-41 with 1,4,7-triazacy-clononane-triacetic acid (NOTA) with preclinical PET/CT to determine if the tracer could tell the difference between muscular Staphylococcusaureus infections and inflammation. Results showed that the tracer highlighted areas of bacterial infection but was only weakly localized in areas of sterile inflammation.

Infection imaging is commonly carried out with Ga-67 citrate and leukocytes, which has been used with some success as a radioligand for infection, but this and other tracers often do not clearly differentiate between physiological processes of infection and inflammation. This complicates diagnoses and erodes the effectiveness of imaging.  

“To determine the correct course of treatment, clinicians need to be able to discriminate between sites of sterile inflammation and those that are infected by pathogenic microorganisms,” wrote Ebenhan et al. “Sites that are infected appear, at least superficially, similar to sites that are inflamed due to other reasons, such as trauma, ischemia, or the presence of foreign bodies such as implants or neoplasm.”

For this study, static PET/CT imaging was staggered at varying time intervals following injection. Standardized uptake value ratios for infected and inflamed tissues were approximately 2.9 after at 5 minutes, 2.9 at 30 minutes, 3.5 at 60 minutes and 3.8 at 90 minutes after injection.

“The findings propose this compound to be an excellent first-line PET/CT tracer to allow the distinguishing of infection from inflammation,” the authors wrote.

The Ga-68 radiolabeled peptide tracer is thought to be an improvement compared to other molecular imaging methods in part due to gallium-68’s superior pharmacokinetics. Further research is required to validate this technique in human studies.