A comparison of 18F-dopa PET and inversion recovery MRI in the diagnosis of Parkinson’s disease

Objective: To quantify structural changes in the substantia nigra of patients with PD with inversion recovery MRI and to compare these with striatal dopaminergic function measured with 18F-dopa PET. Methods: The authors studied 10 patients with PD and eight age-matched control subjects with a combination of MR sequences previously reported to be sensitive to nigral cell loss. Striatal regions of interest were defined on T1-weighted MRI coregistered to 18F-dopa PET in all subjects. Results: Discriminant function analysis of the quantified MR nigral signal correctly classified 83% of the combined PD patient/control group; three of 10 PD cases were incorrectly classified as “normal” (Wilks’ λ = 0.724, p > 0.05). Discriminant function analysis correctly classified 100% of PD patients and control subjects with 18F-dopa PET based on mean caudate and putamen Ki values (Wilks’ λ = 0.065, p < 0.001). Correlations between mean putamen Ki and rostral and caudal nigral MR signal changes and mean caudate Ki and caudal nigral MR signal changes were found (r = −0.76, −0.69, −0.80, p < 0.05). Conclusion: 18F-dopa PET is more reliable than inversion recovery MRI in discriminating patients with moderately severe PD from normal subjects. However, the structural changes detected within the substantia nigra of patients with PD found using inversion recovery MRI correlate with measures of striatal dopaminergic function using 18F-dopa PET.