Improved Visibility of the Subthalamic Nucleus on High-Resolution Stereotactic MR Imaging by Added Susceptibility (T2*) Contrast Using Multiple Gradient Echoes

Abstract

SUMMARY:Reliable identification of the subthalamic nucleus (STN) is a critical step in deep brain stimulation for Parkinson disease but difficult on T1-weighted stereotactic MR imaging. By simultaneous imaging of multiple gradient echoes, susceptibility contrast is added to conventional T1-weighted high-resolution MR image. Thus, the visibility of the STN is enhanced on a second colocalized dataset by exploiting the sensitivity of the T2*-relaxation to local iron deposits. The feasibility is underpinned by quantitative measurements on healthy adults.A n established neurosurgical therapy for Parkinson disease is to place electrodes for deep brain stimulation within the subthalamic nucleus (STN).1 Reliable identification of the anatomic borders of the STN is thus a critical step in stereotactic procedures.2,3 T2-weighted MR imaging showing the iron-rich structures as hypointensities has been suggested as additional information to the poor contrast of the STN on T1-weighted highresolution 3D MR imaging. 4,5 Exploiting the increased sensitivity of T2* to local iron deposits, a multigradient echo fast low-angle shot (FLASH) technique 6 is proposed to visualize the STN. This 3D MR technique enables simultaneous acquisition of T1-weighted images for stereotactic use and images with superimposed T2* contrast to localize the STN. TechniqueThe feasibility study was carried out on 16 healthy adults (8 men; age range, 23-31 years; mean age, 26 years) on a 3T MR system (Magnetom Trio; Siemens Medical Solutions, Erlangen, Germany) using an 8-channel phased-array head coil (MR Imaging Devices, Waukesha, Wis). Written informed consent as supervised by the local ethical committee was obtained.A multi-echo FLASH sequence (TR, 30 ms; flip angle, 20°) provided primarily T1-weighted 3D datasets of 0.95-mm isotropic resolution (FOV ϭ 243 mm; 176 sagittal partitions with 6/8 partial Fourier sampling in phase and section directions; 7:09 minutes). Eight gradient-echoes (TE ϭ 2.2/5.2/8.2/11.2/14.2/17.2/20.2/23.2 ms; bandwidth/pixel ϭ 370 Hz) provided additional T2*-weighted contrast increasing with TE. For comparison, multisection turbo spinecho images (TSE; 29 contiguous 2-mm axial sections; effective TE, 119 ms; TR, 3900 ms) were also obtained.The data were transferred to a stereotactic workstation (Sofamore Danek Stealth Station; Medtronic, Minneapolis, Minn) for coregistration of images with the Schaltenbrand-Wahren atlas.7 For quantitative comparison, T2* was determined in the STN and the reticulate formation by a region-of-interest analysis in 1 subject. ResultsThe T2*-signal intensity decay was markedly faster in the area of the STN than in the surrounding tissue. Figure 1 shows representative curve fits to the STN and the reference region of the reticulate formation. This corresponded with a contrast of approximately 25% at the longest TE. Thus, both STNs could be identified in all 16 of the subjects even when motion artifacts impaired the delineation (2 subjects). Figure 2 shows the midbrain region, where the solely T1-weighted...

Three-dimensional SPACE fluid-attenuated inversion recovery at 3 T to improve subthalamic nucleus lead placement for deep brain stimulation in Parkinson's disease: from preclinical to clinical studies

“…T2WI is the gold standard for STN imaging at 1.5 T. 11 However, T2WI may be altered by higher spatial distortions at higher magnetic fields. 3 The 3D-SPACE-FLAIR sequence at 3 T provided a good delineation of STN in clinical-compatible acquisition-time durations, because it is less sensitive to susceptibility artifacts and less sensitive to geometrical distortion artifacts than T2WI sequences at 3 T, and it constitutes convenient imaging for stereotactic procedures at 3 T. 24 Potential geometric distortions at 3 T were evaluated as minimal by comparison with NHP histology.…”

Automated Optimization of Subcortical Cerebral MR Imaging−Atlas Coregistration for Improved Postoperative Electrode Localization in Deep Brain Stimulation

“…Because the similarity function of the registration procedure is based on structural information, accuracy of normalization will improve with optimized MR imaging sequences, with an improved contrast-to-noise ratio specific for the STN 52 or GPi. Recently, fast short time inversion-recovery images were shown to provide better differences in signal intensity between the STN and the substantia nigra and offered improved visibility of the inferior margin of the STN when compared with FSE T2-weighted MR imaging sequences, which provide better visibility of all other margins of the STN.…”

Neuroimaging and Deep Brain Stimulation

“…58 Other authors compared the location of the STN as obtained by direct localization at 3T with a computer-aided atlas-based procedure for automatic STN identification and showed that there was good agreement between the direct identification of the STN at 3T and the automatically identified structures. 65 More recently a multi-gradient-echo fast low-angle shot technique to visualize the STN, 66 exploiting the increased sensitivity of T2* to local iron deposits, has been used. This 3D MR imaging technique enables simultaneous acquisition of T1-weighted images for stereotactic use and images with superimposed T2* contrast to localize the STN.…”