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

Abstract

Thallium-201 chloride single photon emission computed tomography (201TlCl SPECT) has been applied extensively for studies of human tumors. To assess which indices for 201TlCl 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 201Tl uptake were evaluated in terms of six different 201Tl uptake and retention indices: (1) average early 201Tl uptake=Av.Le/Av.Be; (2) maximum early 201Tl uptake=Mx.Le/Av.Be; (3)201 Tl retention A=Av.Ld/Av.Le; (4) 201Tl retention B=Mx.Ld/Mx.Le; (5) 201Tl retention C=(Av.Ld/Av.Bd)/(Av.Le/Av.Be); (6) 201Tl 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 201Tl uptake indices (bothP =0.0026). For patients with and without meningiomas, P values for indices of maximum early201 Tl uptake and 201Tl 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 201TlCl-SPECT imaging, the average and maximum early 201Tl uptake indices are appropriate for the assessment of tumor viability or malignancy, while 201Tl retention indices (A,B) are useful for tumor differentiation, especially with meningiomas. Choice of suitable indices should enhance the utility of 201TlCl-SPECT imaging in pre- and postoperative evaluation of intracranial lesions.