Diffusion tensor MRI of the healthy brachial plexus

<div><p>Introduction</p><p>Diffusion Tensor MRI (DT-MRI) is a promising tool for the evaluation of brachial plexus pathology. Therefore, we introduce and evaluate a fast DT-MRI protocol (8min33s scanning with 5–10 min postprocessing time) for the brachial plexus.</p><p>Materials and methods</p><p>Thirty healthy volunteers within three age-groups (18–35, 36–55, and > 56) received DT-MRI of the brachial-plexus twice. Means of fractional-anisotropy (FA), mean-diffusivity (MD), axial-diffusivity (AD), and radial-diffusivity (RD) for the individual roots and trunks were evaluated. A stepwise forward approach was applied to test for correlations with age, sex, body-mass-index (BMI), bodysurface, height, and bodyweight. Within-subject, intra-rater, and inter-rater repeatability were assessed using Bland-Altman analysis, coefficient of variation (CV), intraclass-correlation (ICC), and minimal detectable difference (MDD).</p><p>Results</p><p>No differences between sides and root levels were found. MD, AD, and RD correlated (<i>P</i> < 0.05) with bodyweight. Within-subject quantification proved repeatable with CVs for FA, MD, AD, and RD of 16%, 12%, 11%, and 14%, respectively.</p><p>Discussion</p><p>The DT-MRI protocol was fast and repeatable. Found correlations should be considered in future studies of brachial plexus pathology.</p></div

Scatterplots of diffusivity values as a function of bodyweight.

<p>Scatterplots of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) as function of bodyweight. Regression lines are linear fits for MD (P = 0.005), AD (P = 0.002), and RD (P = 0.013).</p

DT-MRI tractography.

<p>Representative example of a DT-MRI tractography dataset (64 years old male), including tractography color coded for fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD) and signal to noise (SNR). The bottom right image is a maximum intensity projection (MIP) of the brachial plexus neurography image (MR-Neurography) with superimposed fiber tracts of the postganglionic tissue only. The circles along the tracts indicate the sample sections which are color-coded for sample number.</p

Group characteristics.

<p>Group characteristics.</p

Diffusion and non-diffusion weighted images and segmentation.

<p>(A) DT-MRI with b-value = 0 in axial orientation. (B) DT-MRI with b-value = 800 s/mm² in axial orientation. (C) Sagittal view of DT-MRI with b-value = 0 in which the red circles indicate the region of interest (ROI) placements per root. (D) Coronal MR neurography image with visualization of the roots and trunks. (E) DT-MRI with b-value = 0 reconstructed in coronal orientation. (F) DT-MRI with b-value = 800 s/mm² reconstructed in coronal orientation.</p

Bland-Altman analysis of DT-MRI derived diffusion values.

<p>Bland-Altman analysis of DT-MRI derived diffusion values FA, MD, AD, and RD. (Column 1) Within-subject variability. Comparisons between the first and second scan session for the first observer. (Column 2) Intra-rater variability. Comparisons of the first scan session for the first observer who analyzed the data twice. (Column 3) Inter-rater variability. Comparisons of the first scan session between the first and second observer. (Column 4) Data of the first scan session analyzed for right-left differences. The top and bottom orange lines are the 95% confidence interval (CI) of the measurements. The middle orange line indicates the mean difference between the measurements.</p

DT-MRI values and repeatability indices.

<p>DT-MRI values and repeatability indices.</p

Diagnostic accuracy of MRI and ultrasound in chronic immune-mediated neuropathies

OBJECTIVE: To assess and compare the diagnostic performance of qualitative and (semi-)quantitative MRI and ultrasound for distinguishing chronic inflammatory demyelinating polyneuropathy (CIDP) and multifocal motor neuropathy (MMN) from segmental spinal muscular atrophy (sSMA). METHODS: Patients with CIDP (n = 13), MMN (n = 10), or sSMA (n = 12) and healthy volunteers (n = 30) were included. MRI of the brachial plexus, using short tau inversion recovery (STIR), nerve-specific T2-weighted (magnetic resonance neurography [MRN]), and diffusion tensor imaging (DTI) sequences, was evaluated. Furthermore, with ultrasound, cross-sectional areas of the nerves were evaluated. Three radiologists blinded for diagnosis qualitatively scored hypertrophy and increased signal intensity (STIR and MRN), and intraobserver and interobserver agreement was assessed. For the (semi-)quantitative modalities, group differences and receiver operator characteristics were calculated. RESULTS: Hypertrophy and increased signal intensity were found in all groups including healthy controls. Intraobserver and interobserver agreements varied considerably (intraclass correlation coefficients 0.00-0.811 and 0.101-0.491, respectively). DTI showed significant differences (p < 0.05) among CIDP, MMN, sSMA, and controls for fractional anisotropy, axial diffusivity, and radial diffusivity in the brachial plexus. Ultrasound showed significant differences in cross-sectional area (p < 0.05) among CIDP, MMN, and sSMA in upper arm and brachial plexus. For distinguishing immune-mediated neuropathies (CIDP and MMN) from sSMA, ultrasound yielded the highest area under the curve (0.870). CONCLUSION: Qualitative assessment of hypertrophy and signal hyperintensity on STIR or MRN is of limited value. DTI measures may discriminate among CIDP, MMN, and sSMA. Currently, ultrasound may be the most appropriate diagnostic imaging aid in the clinical setting