Mapping drug-induced changes in cerebral R2∗ by Multiple Gradient Recalled Echo functional MRI

A Multiple Gradient Recalled Echo MRI sequence was used to map spatial and temporal changes in the rate of MR signal decay (R2∗) in response to L-3,4-dihydroxyphenylalanine (levodopa) in the striatal dopaminergic system of a rhesus monkey unilaterally lesioned with 4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP). R2∗ decreased significantly in the right (dopamine depleted) putamen and caudate following levodopa. More focal areas of smaller R2∗ decline were also observed in these structures in the left hemisphere. The observed spatial and temporal patterns of R2∗ change support the view that the method is monitoring changes in neural activity.