I-123 ALPHA-METHYL TYROSINE SINGLE-PHOTON EMISSION TOMOGRAPHY OF CEREBRAL GLIOMAS - STANDARDIZED EVALUATION OF TUMOR UPTAKE AND EXTENT

Single-photon emission tomography (SPET) with the amino acid analogue L-3-[I-123]iodo-alpha-melhyl tyrosine (IMT) is helpful in the diagnosi s and monitoring of cerebral gliomas, Radiolabelled amino acids seem t o reflect tumour infiltration more specifically than conventional meth ods like magnetic resonance imaging and computed tomography. Automatic tumour delineation based on maximal tumour uptake may cause an overes timation of mean tumour uptake and an underestimation of tumour extens ion in tumours with circumscribed peaks. The aim of this study was to develop a program for tumour delineation and calculation of mean tumou r uptake which takes Into account the mean background activity and is thus optimised to the problem of tumour definition in IMT SPET. Using the frequency distribution of pixel intensities of the tomograms a pro gram was developed which automatically detects a reference brain regio n and draws an isocontour region around the tumour taking into account mean brain radioactivity. Tumour area and tumour/brain ratios were ca lculated. A three-compartment phantom was simulated to test the progra m. The program was applied to IMT SPET studies of 20 patients with cer ebral gliomas and was compared to the results of manual analysis by th ree different investigators. Activity ratios and chamber extension elf the phantom were correctly calculated by the automatic analysis. A me thod based on image maxima alone failed to determine chamber extension correctly. Manual region of interest analysis in patient studies resu lted in a mean inter-observer standard deviation of 8.7%+/-6.1% (range 2.7%-25.0%). The mean value of the results of the manual analysis sho wed a significant correlation to the results of the automatic analysis (r = 0.91, P<0.0001 for the uptake ratio; r = 0.87, P<0.0001 for the tumour area), We conclude that the algorithm proposed simplifies the c alculation of uptake ratios and may be used for observer-independent e valuation of IMT SPET studies, Three-dimensional tumour recognition an d transfer to co-registered morphological images based on this program may be useful for the planning of surgical and radiation treatment.