Comparison of 3T and 7T susceptibility-weighted angiography of the substantia nigra in diagnosing Parkinson disease

Abstract

Background and purpose: Standard neuroimaging fails in defining the anatomy of the substantia nigra and has a marginal role in the diagnosis of Parkinson disease. Recently 7T MR target imaging of the substantia nigra has been useful in diagnosing Parkinson disease. We performed a comparative study to evaluate whether susceptibility-weighted angiography can diagnose Parkinson disease with a 3T scanner.

Materials and methods: Fourteen patients with Parkinson disease and 13 healthy subjects underwent MR imaging examination at 3T and 7T by using susceptibility-weighted angiography. Two expert blinded observers and 1 neuroradiology fellow evaluated the 3T and 7T images of the sample to identify substantia nigra abnormalities indicative of Parkinson disease. Diagnostic accuracy and intra- and interobserver agreement were calculated separately for 3T and 7T acquisitions.

Results: Susceptibility-weighted angiography 7T MR imaging can diagnose Parkinson disease with a mean sensitivity of 93%, specificity of 100%, and diagnostic accuracy of 96%. 3T MR imaging diagnosed Parkinson disease with a mean sensitivity of 79%, specificity of 94%, and diagnostic accuracy of 86%. Intraobserver and interobserver agreement was excellent at 7T. At 3T, intraobserver agreement was excellent for experts, and interobserver agreement ranged between good and excellent. The less expert reader obtained a diagnostic accuracy of 89% at 3T.

Conclusions: Susceptibility-weighted angiography images obtained at 3T and 7T differentiate controls from patients with Parkinson disease with a higher diagnostic accuracy at 7T. The capability of 3T in diagnosing Parkinson disease might encourage its use in clinical practice. The use of the more accurate 7T should be supported by a dedicated cost-effectiveness study.

© 2015 by American Journal of Neuroradiology.

Figures

Fig 1.

SWAN-targeted axial image of the midbrain in a healthy subject evaluated at 3T (right column) and at 7T (left column). The trilaminar organization of the SN at level II (upper row) and the nigrosome formation at level I (lower row) are clearly shown with 3T and 7T magnets. Levels I and II of image acquisition are represented by white and gray lines in the scout image. On 7T images, we overlaid a diagram of the trilaminar structure of the SN derived by anatomic atlases. The diagnostic accuracy is elevated for both high- and ultra-high-field-strength magnets. cp indicates cerebral peduncle; PBN, parabrachial nucleus; RRF, retrorubral field; scp, superior cerebellar peduncle; SNcv, substantia nigra pars compacta ventralis; SNcd, substantia nigra pars compacta dorsalis; SNr, substantia nigra pars reticularis; VTA, ventral tegmental area; R, red nucleus.

Fig 2.

SWAN-targeted axial image of the midbrain in a healthy subject evaluated at 3T (right) and 7T (left). The nigrosome formation appreciable at 7T is interpreted as lost at 3T, generating a false-positive.

Fig 3.

SWAN-targeted axial image of the midbrain in a patient with PD evaluated at 3T (right) and 7T (left). The nigrosome formation seems recognizable in the left SN. On the right SN, the nigrosome formation is lost at 7T, while at 3T the slight hyperintense component (arrow) has been erroneously interpreted as a nigrosome, leading to a false-negative finding.