Comparison of thallium-201 uptake and retention indices for evaluation of brain lesions with SPECT.

Thallium-201 chloride single photon emission computed tomography ((201)TlCl SPECT) has been applied extensively for studies of human tumors. To assess which indices for (201)TlCl SPECT are most useful for diagnosing brain lesions, a total of 82 patients (98 images) with intracranial abnormalities were investigated. Seventy-six cases with abnormal (201)Tl uptake were evaluated in terms of six different (201)Tl uptake and retention indices: (1) average early (201)Tl uptake = Av.Le/Av.Be; (2) maximum early (201)Tl uptake = Mx.Le/Av.Be; (3)(201) Tl retention A = Av.Ld/Av.Le; (4) (201)Tl retention B = Mx.Ld/Mx.Le; (5) (201)Tl retention C = (Av.Ld/Av.Bd)/(Av.Le/Av.Be); (6) (201)Tl retention D = (Mx.Ld/Av.Bd)/(Mx.Le/Av.Be), where Av.Le and Mx.Le are average and maximum early counts for lesions, Av.Be and Av.Bd are average early and delayed counts for contralateral normal brains, and Av.Ld and Mx.Ld are average and maximum delayed counts for lesions. Comparison of patients with benign and malignant lesions did not demonstrate significant differences with any of the indices. However, low (I-II) and high (III-IV) grade astrocytomas varied in their average and maximum early (201)Tl uptake indices (both P = 0.0026). For patients with and without meningiomas, P values for indices of maximum early(201) Tl uptake and (201)Tl retention A and B were 0.0338, 0.0005, 0.0002, respectively. While comparison of patients with metastatic brain tumors and gliomas again showed no significant differences between the groups, the presence or absence of calcification was associated with significant variation in all the indices. With (201)TlCl-SPECT imaging, the average and maximum early (201)Tl uptake indices are appropriate for the assessment of tumor viability or malignancy, while (201)Tl retention indices (A,B) are useful for tumor differentiation, especially with meningiomas. Choice of suitable indices should enhance the utility of (201)TlCl-SPECT imaging in pre- and postoperative evaluation of intracranial lesions.