Marieke van Rosmalen

Diagnostic value of quantitative assessment of brachial plexus MRI in chronic inflammatory neuropathies 59 4 Nerve root measurements on MRI data We measured cervical nerve root sizes in coronal and sagittal planes, using PACS IDS7 21.1.2 (Sectra AB, Linköping, Sweden). We used the distance tool to measure diameters (mm) of nerve roots in coronal MIP images. Nerve root diameter was measured perpendicular on the center lines of the nerve roots, bilaterally in root C5, C6 and C7 at two predetermined anatomical sites: directly next to the ganglion (G 0 ) and 1 cm distal from the ganglion (G 1 ). In addition, we used the cross-cursor tool to identify the corresponding sites of these measurements on the sagittal 3D TSE SPIR, and measured cross sectional area (mm 2 ) in the sagittal plane using the area tool, which is a manual tracer, resulting in 24 measurements in total per subject (duration 3-5 minutes per subject, Figure 4.1 ). Zoom magnification was standardized to 1x for all images. As anatomic variability in the brachial plexus is common, and may be even more present in more distal parts, 16 we decided to not perform measurements when individual nerve roots merged, divided or showed other anatomical variances. We also did not perform measurements when image quality was poor. To determine intrarater reliability, one rater (MVR) performed all measurements twice in two sessions with an interval of 1 month between the first and second session. To determine interrater reliability a second rater (AG) scored a random sample of 20 MRI scans from our data set. Both raters were blinded to clinical status. Figure 4.1 Example of nerve root measurements in coronal and sagittal planes. Method of measurements in coronal (upper) and sagittal (lower) planes. Coronal measurements in maximum intensity projection images (A) using 1x zoom (B) and callipers placed in nerve root C5 (red), C6 (green) and C7 (yellow) next to the ganglion (blue arrow) and 1 cm distal of the ganglion (C). Sagittal measurements in T2 weighted fat-suppressed images using a cross-cursor to identify corresponding measurement sites (D) and 1x zoom (E). Measurements were then performed at these corresponding measurement sites (F, G). R = right; L = left; A = anterior; P = posterior.