Usefulness of quantitative susceptibility mapping for the diagnosis of Parkinson disease.

Y Murakami,A Ogasawara,T Sato,Y Wang,S Ide,T Uozumi,K Futatsuya,Y Korogi,T Liu,I Ueda,S Tsuji,J Moriya,K Watanabe,K Okada,S Kakeda

doi:10.3174/ajnr.a4260

Abstract

Quantitative susceptibility mapping allows overcoming several nonlocal restrictions of susceptibility-weighted and phase imaging and enables quantification of magnetic susceptibility. We compared the diagnostic accuracy of quantitative susceptibility mapping and R2* (1/T2*) mapping to discriminate between patients with Parkinson disease and controls. For 21 patients with Parkinson disease and 21 age- and sex-matched controls, 2 radiologists measured the quantitative susceptibility mapping values and R2* values in 6 brain structures (the thalamus, putamen, caudate nucleus, pallidum, substantia nigra, and red nucleus). The quantitative susceptibility mapping values and R2* values of the substantia nigra were significantly higher in patients with Parkinson disease (P < .01); measurements in other brain regions did not differ significantly between patients and controls. For the discrimination of patients with Parkinson disease from controls, receiver operating characteristic analysis suggested that the optimal cutoff values for the substantia nigra, based on the Youden Index, were >0.210 for quantitative susceptibility mapping and >28.8 for R2*. The sensitivity, specificity, and accuracy of quantitative susceptibility mapping were 90% (19 of 21), 86% (18 of 21), and 88% (37 of 42), respectively; for R2* mapping, they were 81% (17 of 21), 52% (11 of 21), and 67% (28 of 42). Pair-wise comparisons showed that the areas under the receiver operating characteristic curves were significantly larger for quantitative susceptibility mapping than for R2* mapping (0.91 versus 0.69, P < .05). Quantitative susceptibility mapping showed higher diagnostic performance than R2* mapping for the discrimination between patients with Parkinson disease and controls.

Highlights

BACKGROUND AND PURPOSEQuantitative susceptibility mapping allows overcoming several nonlocal restrictions of susceptibilityweighted and phase imaging and enables quantification of magnetic susceptibility
There has been substantial interest in in vivo MR imaging of increased nigral iron content,[2,3] a pathophysiologic feature involved in the selective dopaminergic neurodegeneration of the substantia nigra in patients with Parkinson disease (PD).[4]
In this study, the quantitative susceptibility mapping (QSM) values and R2* values of the substantia nigra were significantly higher in patients with PD, the analyses of the volume of the substantia nigra showed no significant difference between the patients with PD and controls

Summary

Methods

For 21 patients with Parkinson disease and 21 age- and sex-matched controls, 2 radiologists measured the quantitative susceptibility mapping values and R2* values in 6 brain structures (the thalamus, putamen, caudate nucleus, pallidum, substantia nigra, and red nucleus). QSM was reconstructed from the complex data obtained during the gradient-echo sequence by using the morphology enabled dipole inversion technique.[19] After the complex multiecho MR images were saved, a nonlinear fitting was performed to estimate the magnetic field inhomogeneity, followed by a magnitude-guided phase unwrapping.[20] The background field was further removed by applying the projection to the dipole fields method.[26] the remaining tissue field was inverted to generate a susceptibility map by using the morphology enabled dipole inversion method.[20] An empirically determined regularization parameter of 1000 was consistently applied to all cases. All 11 echoes were used with weightings proportional to their signal-to-noise ratios for reconstructing QSM and R2*.27,28 R2* mapping was reconstructed from the magnitude gradient-echo data with a monoexponential fit by using the log-linear method

Results

Discussion

Conclusion