[Difference of thallium-201 kinetics between VX-2 tumors and inflammatory lesions in rabbits]

To evaluate the difference of thallium-201 chloride (201Tl) kinetics between malignant tumors and inflammatory lesions, 201Tl scintigraphy was performed in the 30 rabbits with variable sized VX-2 tumors; and in the 27 rabbits with variable sized inflammatory lesions induced by turpentine oil and the solution of auto-feces. The degree of 201Tl uptake was expressed as the count ratios of the lesions over the contralateral normal muscle tissue, and the early uptake ratio (1 min after the injection) and the delayed uptake ratio (30 min) were acquired. The retention index derived from these ratios was used to assess the degree of 201Tl washout from the lesions. When dividing both the tumors and inflammatory lesions into the large lesions (more than 40 mm in diameter) and smaller ones, different 201Tl kinetics according to the size of the lesions were demonstrated. In the small lesions, the VX-2 tumors showed higher early and delayed uptake ratios and a faster washout than the inflammatory lesions. In contrast, in the large lesions, both the early and delayed uptake ratios were not significantly different; however, the retention index in the tumors was higher compared to the inflammatory lesions. Thus, our animal study indicates that 201Tl kinetics are different according to the size of the tumor and inflammatory lesions, and that in the small lesions the higher tumor uptake compared to the inflammatory lesions may be available to differentiate. However, in the large sized lesions, assessment of the 201Tl washout from the lesions is necessary for differentiation.