Effective R relaxation rate, derived from dual-contrast fast-spin-echo MRI, enables detection of hemisphere differences in iron level and dopamine function in Parkinson's disease and healthy individuals.

Background: Clinical estimates of brain iron concentration are achievable with quantitative transverse relaxation rate R, via time-consuming multiple spin-echo (SE) sequences. The objective of this study was to investigate whether quantitative iron-sensitive information may be derived from 3.0 T dual-contrast fast-spin-echo (FSE) sequences (typically employed in anatomical non-quantitative evaluations), as a routinely-collected alternative to evaluate iron levels in healthy (HC) and Parkinson's disease (PD) brains.

New Method: MRI 3.0 T FSE data from the Parkinson's Progression Markers Initiative (PPMI) (12 PD, 12 age- and gender-matched HC subjects) were cross-sectionally and longitudinally evaluated. A new measure, 'effective R', was calculated for bilateral subcortical grey matter (caudate nucleus, putamen, globus pallidus, red nucleus, substantia nigra). Linear regression analysis was performed to correlate 'effective R' with models of age-dependent brain iron concentration and striatal dopamine transporter (DaT) receptor binding ratio.

Results: Effective R was strongly correlated with estimated brain iron concentration. In PD, putaminal effective R difference was observed between the hemispheres contra-/ipsi-lateral to the predominantly symptomatic side at onset. This hemispheric difference was correlated with the putaminal DaT binding ratios in PD.

Comparison With Existing Method(s): Effective R, derived from rapid dual-contrast FSE sequences, showed viability as an alternative to R from SE sequences. Linear correlation of effective R with estimated iron concentration was comparable to documented iron-dependent R. The effective R correlation coefficient was consistent with theoretical R iron-dependence at 3.0 T.

Conclusions: Effective R has clinical potential as a fast quantitative method, as an alternative to R, to aid evaluation of brain iron levels and DaT function.