No abstract

18 F]dopa PET should provide an objective method of assessment of progression of disease that can be used in studies of progression and neuroprotection; at least two studies are already in progress using [ 18 F]dopa PET to examine the eVect of sparing levodopa (and substitution with a dopamine agonist) in early Parkinson's disease. We considered two explanations for the diVerence in the results of published studies; a diVerence in the clinical characteristics of the patients selected and a diVerence in PET methods.The aim of the present study was to examine the influence of diVering PET methods (specifically, larger total striatal regions of interest and quantification by ratio) on the measurement of the mean rate of progression and estimation of the preclinical period. We wished to examine the reproducibility and sensitivity of each method to establish the optimum method of assessing disease progression and duration of preclinical period with [ 18 F]dopa PET. In doing so we hoped to establish guidelines for the use of [ 18 F]dopa PET in therapeutic trials. By increasing our previous group of 17 patients to 32 we hoped to exclude the possibility that our previous group were atypical in their rate of progression. This larger group would also allow us to examine further the influence of duration, severity, and clinical presentation (with or without tremor) on the rate of progression of disease. Methods RECRUITMENT AND CLINICAL ASSESSMENTThirty two patients (mean age 58 (13) years, mean duration of symptoms 39 (SD 33)