SPECT was performed 90 to 120 minutes after injection of 150 MBq IPT. After reconstruction by filtered backprojection transverse slices corrected for attentuation were realigned parallel to the AC-PC line. For semiquantitative evaluation of specific (I-123)IPT binding ratios beween striatum, caudate, putamen, and background regions were calculated. Specific uptake ratios were defined as mean counts per pixel in the respective region of interest minus mean counts in a background region divided by the mean counts in the background region. The uptake ratios obtained in the patient studies and in age matched controls are listed in the table. The increased IPT binding in the left putamen in the 1996 study is most probably due to an artefact caused by a spot of high background activity accidentally located around the putamenal region of interest in this investigation.