Localization of the Subthalamic Nucleus: Optimization with Susceptibility-Weighted Phase MR Imaging

Sagittal, coronal, and axial T2-weighted images centered at the level of the STN. The ACPC line is defined on the sagittal image where the anterior and posterior commissures can be delineated and a line can be drawn through them as shown. The axial images are acquired parallel to the ACPC line, and the coronal images are perpendicular. The black lines on the sagittal and coronal images show the corresponding position and orientation of the axial image. The black line on the axial image shows the corresponding position on the coronal image. The relative orientation and borders of the RN, SN, and STN are outlined.

Magnitude (A), phase (B), and combined/venogram (C) images from the same SWI sequence acquisition. The STN, SN, and RN are most sharply delineated on the phase image.

Magnitude (A, D, G), phase (B, E, H), and combined/venogram (C, F, I) images are shown with an acceleration factor of 1 and TEs of 16.11 ms (A–C), 20.7 ms (D–F), and 25 ms (G–I). On phase images, the STN, SN, RN, globus pallidus (GP), and medial geniculate body (MG) are shown with greatest contrast at a TE of 25.3 ms but still can be well seen at a lower TE. On magnitude images, these structures are less well visualized than on phase images at all TEs and are not well visualized below a TE of 25.3 ms. The venogram images are intermediate to phase and magnitude images at all TEs.

Magnitude (A, D, G), phase (B, E, H), and combined/venogram (C, F, I) images are shown with acceleration factors of 1.8 (A–C), 1.5 (D–F), and 1 (D–F). At a TE of 25 ms, worse image quality is observed as the SENSE factor is increased, particularly on the magnitude images. The STN, SN, RN, globus pallidus (GP), superior colliculus (S), and medial geniculate body (MG) are seen best on the phase images at a SENSE of 1.0 but are relatively well depicted on phase maps at all SENSE factors. Magnitude images, in particular, show decreasing sharpness of the RN, STN, and SN at SENSE factors of 1.5 and 1.8.

High-quality SWI phase images (subject 7, TE = 20.71 ms, SENSE = 1) rated “good” or “excellent” for both visualization of the STN and delimitation of the STN from adjacent structures (most important, the SN). The STN are visualized on at least 6 images from inferior (A) to superior (F). The STN, SN, and RN are labeled on image B. Other structures of interest that are visible on phase imaging are also labeled on B and on some of the other images where they are well delineated, including the vascularized (v) and nonvascularized (n) portions of the RN, capsule of the RN (asterisk), crus cerebri (CC), fascicula nigrale (FN), globus pallidus (GP), superior colliculus (S), and medial geniculate body (MG).

3D axial SWI phase images were obtained with isotropic voxels (TE = 20 ms, SENSE = 1, voxel size = 0.7 × 0.7 × 0.7 mm, acquisition time = 6 minutes). Lines on the coronal images A and C correspond to section planes of axial images B and D, respectively, and vice versa. The RN, SN, and STN are encircled and labeled on each image and are each demonstrated in 2 planes.