201T1-chloride uptake ratios in differentiating benign from malignant lesions: recommendations for ratio calculations and interpretation.

Thallium-201 (201T1) chloride ratios have been used to differentiate benign from malignant lesions in bones and soft tissues, brain, breast, lungs and thyroid. Different values of these ratios have been reported by various authors. The need to standardize the methods for calculating thallium ratios is discussed in this paper. The difference between calculating the ratios using planar and single photon emission tomography (SPET) images is presented in two patients who had metastatic bone lesions to the lower femoral condyle from non-Hodgkin's lymphoma and to the iliac bone from breast carcinoma. In our experience, it is more reliable to calculate the thallium ratios from SPET images whenever possible.