Effects of the method of drawing regions of interest on the differential diagnosis of extrapyramidal syndromes using I-123-iodolisuride SPET

Various parameters are currently used for the semi-quantitative assessment of dopamine D-2 receptors and differ according to the delineation of the st riatal region of interest (ROI) and the choice of the reference ROI. The ai m of this study was to assess the value of different ROI approaches in diff erentiating patients with normal or increased numbers of D-2 dopamine recep tors (group 1 = Parkinson's disease, n = 8) from patients with decreased do pamine D-2 receptors (group 2 = other extrapyramidal syndromes, n = 9) usin g I-123-iodolisuride SPET (ILIS-SPET). I-123-iodolisuride (190 +/- 31 MBq) and Tc-99(m)-ethyl cysteinate dimer (Tc-99(m)-ECD) perfusion SPET were perf ormed in the the same position, with a dual-headed gamera camera equipped w ith fan beam collimators. Both a geometric approach (ellipse, circle or rec tangle) and an anatomical approach using the CT scan and perfusion SPET as anatomical guides were used to draw striatal and reference ROIs. A total of 33 different parameters were calculated for each patient, indicating the r atio of counts between the striatal and reference ROIs (frontal, occipital cortex or cerebellum) and the asymmetry between the right and left striatum . More significant differences between group 1 and group 2 were found by us ing geometric ROIs than by using anatomical ROIs. The most discriminant rat ios were the caudate/occipital, caudate/frontal and striatum/occipital rati os (P = 0.001, P = 0.002, P = 0.003 respectively). A close correlation was found between the striatum/caudate and striatum/occipital ratios, but not b etween the striatum/frontal and striatum/occipital ratios or between the st riatum/frontal and striatum/caudate ratios. We conclude that the occipital cortex is the best reference for the semi-quantitative evaluation of dopami ne D-2 receptors as the frontal cortex could include some dopamine D-2 rece ptor-bound radioligand, and that the caudate/occipital ratio is an appropri ate parameter for differentiating Parkinson's disease from non-Parkinson ex trapyramidal syndrome by I-123- iodolisuride SPET. ((C) 1999 Lippincott Wil liams & Wilkins).