USE OF 201THALLIUM BRAIN SPECT, IMAGE REGISTRATION, AND SEMI-QUANTITATIVE ANALYSIS IN THE FOLLOW-UP OF BRAIN TUMORS

Abstract Objective: To assess the use of 201 Thallium SPECT and of Thallium (Tl) uptake indices in the detection and follow-up of cerebral tumors. Material and methods: Two-hundred eighty 201 Tl, 135 99m Tc-HMPAO scintigraphies and 280 MRI studies were acquired in 135 patients with cerebral tumors. Three types of Tl uptake indices were calculated by establishing the ratio of the lesion activity to an homologous ROI (I 1 ), the contralateral hemisphere (I 2 ), and the contralateral scalp (I 3 ). Intermodal co-registration between Tl-SPECT and MRI when used, was performed using Pietrzyk visual interactive method. Results: Tl uptake indices showed mean values of 2.0 ± 0.5 (I 1 ); 1.77 ± 0. 57 (I 2 ) and 1.11 ± 0.40 (I 3 ) in positive scans, and of 1.05 ± 0.22 (I 1 ), 0.88 ± 0.22 (I 2 ) and 0.50 ± 0.15 (I 3 ) in negative scans, respectively. A linear combination of the two less correlated indices lead to a more powerful discrimination between positive and negative studies. Longitudinal follow-up studies in the same patients showed good concordance between the index values and the course of the disease. Conclusion: The use of Tl uptake indices improves the accuracy of Tl-SPECT in the follow-up of brain tumors.