201Thallium SPECT; accuracy in astrocytoma diagnosis and treatment evaluation

Sammanfattning: The aims of the studies included in this thesis were:• to investigate the reliability of 201thallium single photon emission computed tomography (201Tl SPECT) for preoperative diagnosis and histological staging of malignant astrocytomas in comparison with CT; • to develop a method for quantification of cerebral thallium uptake, and to evaluate the quantitative measurement in comparison with CT, for astrocytoma treatment follow-up purposes; • to compare quantitative 201Tl SPECT and proton magnetic resonance spectroscopy (1H-MRS) with conventional MR imaging for astrocytoma monitoring, and to evaluate associations between change of morphological tumour characteristics during treatment and changes of cerebral thallium uptake and metabolic ratios. Results and conclusions:• High 201Tl-index, calculated as a ratio comparing tumour uptake to uptake in the contralateral hemisphere, is an indicator of highly malignant astrocytoma. Differentiation between the high-grade astrocytomas, the low-grade astrocytomas, and infectious lesions is only partial, with an overlap of 201Tl-indexes between these groups. High-grade astrocytomas that do not show contrast enhancement on CT, and astrocytomas with central necrosis and moderate ring-enhancement, tend to be underestimated when evaluated by 201Tl-index calculation. 201Tl SPECT is not a reliable method for non-invasive tumour staging among the group of highly malignant astrocytomas. • Quantification of cerebral 201Tl-uptake, defining the volume of viable tumour tissue, is a new method for astrocytoma chemotherapy monitoring. Results suggest that the method provides prognostic information, and information of treatment efficacy, at an earlier stage than CT. • We did not find a higher accuracy of quantitative 201Tl SPECT than of MR for monitoring purposes and our results indicated that treatment induced MR changes were interrelated with 201Tl-uptake variations. • Multi-voxel 1H-MRS was difficult to apply for astrocytoma treatment monitoring, due to the anatomical and histological heterogeneity of astrocytomas.