Thallium-201 versus technetium-99m-MIBI SPECT in evaluation of childhood brain tumors: a within-subject comparison

We previously found that 201TI SPECT is a highly specific agent for detection of metabolic activity of childhood brain tumors. To compare the relative diagnostic accuracy of 201TI and a technetium-based tumor-avid agent, we have obtained SPECT in 19 children using 201TI (37-111 MBq) followed immediately by 99mTc-methoxyisobutylisonitrile (MIBI) (370-740 MBq) intravenously. Moderate to intense focal uptake of both tracers characterized true positive cases (n = 6). Lesion boundaries were better defined by MIBI. Uptake of MIBI by choroid plexus occurred despite pretreatment with potassium perchlorate (6 mg/kg) and complicated interpretation of deep/paraventricular lesions. Preliminary assessment indicated sensitivity approximately 67% (TI and MIBI); specificity approximately 91% (TI); approximately 100% (MIBI). Two tumors (medulloblastoma, dysgerminoma) were TI/MIBI nonavid. Semi-quantitative assessment of tracer uptake was made using a ratio of radioactivity in tumor-containing areas compared to uninvolved brain. Ratio values were (mean +/- s.d.) 7.88 +/- 7.70 (TI) and 27.1 +/- 36.41 (MIBI). The spectrum of tumor avidity is similar for TI and MIBI. Clearer identification of boundaries by MIBI may be an advantage in applications, e.g., radiotherapy port planning.