Optimized 3D magnetization-prepared rapid acquisition of gradient echo: identification of thalamus substructures at 3T

Abstract

Background and purpose: Because the substructures of the thalamus are not visible on standard T1- and T2-weighted MR images, planning of deep brain stimulation implantation relies on stereotactic atlas coordinates. The goal of the present work was to test whether an optimized 3D MPRAGE protocol can depict thalamus substructures.

Materials and methods: After optimization of the TI to maximize contrast between gray matter and white matter, 6 healthy subjects were scanned at 3T with the optimized 3D MPRAGE. The results were compared with stereotactic atlases, and 2 expert readers trained in thalamic anatomy identified the 4 large thalamic nuclei groups.

Results: There was a high agreement between the different atlases and the resulting MR images. The 4 large thalamic nuclei groups (anterior, lateral, medial, posterior) could be detected reliably. The inter-reader consistency on the size and location was 75%-92%.

Conclusions: The optimized 3D MPRAGE protocol improves contrast in the thalamus, and the 4 large thalamic nuclei groups can be identified with high inter-reader agreement.

Fig 1.

Comparison of the normal MPRAGE protocol (left and middle image, different windowing) with the optimized MPRAGE protocol (right).

Fig 2.

Comparison of the normal MPRAGE protocol (top row) with the optimized protocol (bottom row) in different section orientations. Contrast in both images was chosen for an optimal depiction of thalamus substructures. Adjacent anatomic structures have been labeled. cc indicates corpus callosum; fx, fornix; R, red nucleus; LV, lateral ventricles; C, caudate nucleus; Pu, putamen; IC, internal capsule; GP, globus pallidus.

Fig 3.

Axial myelin stain (middle) from the Schaltenbrand and Wahren atlas,¹⁷ taken it from plate 54, located 6.5 mm above Reil's plane, and a corresponding inverted gray-scale image from one of the subjects located 8 mm above Reil's plane (right). For anatomic reference, a schematic drawing adapted from the overlay of the Schaltenbrand and Wahren atlas is shown on the left. The boundaries of the thalamus have been delineated in all images with a thin black line. The white arrow marks the anteroventral nucleus, which can be clearly delineated as a hyperintense structure. The CM (marked by an asterisk) is clearly distinguishable from the surrounding structures. The anatomic structures belonging to the 4 thalamic nuclei groups used in this work have been colored (blue, anterior; red, medial; green, lateral; yellow, posterior).

Fig 4.

Parasagittal myelin stain (middle) from the Schaltenbrand and Wahren atlas, taken from plate 44, located 5.5 mm lateral to the midline and a corresponding inverted gray-scale image from one of the subjects, located 6.2 mm lateral to the midline (right). The boundaries of the thalamus have been delineated in all images with a thin black line. The white star marks the CM, which can be clearly localized. The bright structure (black star) close to the MTT is a vessel. For anatomic reference, a schematic drawing adapted from the overlay of the Schaltenbrand and Wahren atlas is shown on the left. The anatomic structures belonging to the 4 thalamic nuclei groups used in this work have been colored (blue, anterior; red, medial; green, lateral).

Fig 5.

An axial section of the optimized MPRAGE. Note that not only the 4 large nucleus groups (middle image) but also the further substructures can be identified. Medial to the MD, a hyperintense structure is also visible (dashed line depicts border), which is most likely the superficial medial nucleus not described in the Morel atlas. In the lateral nucleus group, only thin bands of white matter can be used to distinguish the different parts. The MTT is clearly visible as a hyperintense spot between the anteroventral nucleus (AV), central medial nucleus (CeM), and ventral anterior nucleus (VA). CL indicates central lateral nucleus; VLa, ventral lateral anterior nucleus; VLp, ventral lateral posterior nucleus; VPL, ventral posterior lateral nucleus; LP, lateral posterior nucleus; PuM, medial pulvinar.

Fig 6.

Optimized MPRAGE (bottom row) and nucleus groups in axial sections parallel to the ACPC line (from left to right: apical to caudal sections; position given in millimeters relative to the ACPC line) selected by the first and second readers (top row, light and dark gray lines).