Imaging of focal inflammation with 99Tcm-labelled human polyclonal immunoglobulin G

Abstract

A 99Tcmm-based radiopharmaceutical for detecting focal inflammation would present several advantages over 67Ga citrate or 111In leucocytes, i.e. rapid availability in the acute clinical setting, superior images and a lower radiation burden. Recent reports have indicated success in localizing focal infection using 111In-labelled polyclonal IgG. This paper reports our initial experience in labelling polyclonal human IgG with 99Tcm using a modification of the carboxycarbonic anhydride method, and imaging with this new substance in a selection of clinical situations. Our preliminary observations in 38 patients suggest that: (1) In the early phase (at least the initial 20 min) the injected radiolabelled IgG behaves like a blood pool tracer. (2) The optimal imaging time is probably 6-8 h, beyond which there is insignificant increase in IgG localization and further 99Tcm decay reduces image quality. (3) 99Tcm IgG, or a metabolite carrying the 99Tcm, is excreted into the bowel, reducing the vaue of this tracer in detecting inflammatory bowel disease. (4) The scan is more sensitive in acute rather than chronic infections, and uptake of the tracer appears to correlate with the degree of the inflammatory reaction. This may be of clinical value in assessment of response to antimicrobial therapy. 99Tcmlabelled polyclonal IgG presents a new and attractive option which needs further evaluation in the detection of focal inflammation with radionuclides, with a sensitivity of 94.7% and specificity of 92.3% in this limited study group.