Quantitative Susceptibility Atlas Construction in Montreal Neurological Institute Space: Towards Histological-consistent Iron-rich Deep Brain Nucleus Sub-region Identification

Iron-rich deep brain nuclei (DBN) of the human brain are involved in various motoric, emotional and cognitive brain functions. The abnormal iron alterations in the DBN are closely associated with multiple neurological and psychiatric diseases. Quantitative susceptibility mapping (QSM) provides the spatial distribution of tissue magnetic susceptibility in the human brain. Compared to traditional structural imaging, QSM has superiority for imaging the iron-rich DBN owing to the susceptibility difference existing between brain tissues. In this study, we construct a Montreal Neurological Institute (MNI) space unbiased QSM human brain atlas via group-wise registration from 100 healthy subjects aged 19-29 years. The atlas construction process is guided by hybrid images that fused from multi-modal Magnetic Resonance Images (MRI), thus named as Multi-modal-fused magnetic Susceptibility (MuSus-100) atlas. The high-quality susceptibility atlas provides extraordinary image contrast between iron-rich DBN with their surroundings. Parcellation maps of DBN and their sub-regions that are highly related to neurological and psychiatric pathology are then manually labeled based on the atlas set with the assistance of an image border-enhancement process. Especially, the bilateral thalamus is delineated into 64 detailed sub-regions referring to the Schaltenbrand and Wahren stereotactic atlas. To our best knowledge, the histological-consistent thalamic nucleus parcellation map is well defined for the first time in MNI space. Comparing with existing atlases emphasized on DBN parcellation, the newly proposed atlas outperforms on atlas-guided individual brain image DBN segmentation accuracy and robustness. Moreover, we apply the proposed DBN parcellation map to conduct detailed identification of the pathology-related iron content alterations in subcortical nuclei for Parkinson Disease (PD) patients. We envision that the MuSus-100 atlas could play a crucial role in improving the accuracy of DBN segmentation for the research of neurological and psychiatric disease progress and also be helpful for target planning in deep brain stimulation surgery

Validation of diffusion tensor imaging tractography to visualize the dentatorubrothalamic tract for surgical planning

OBJECTIVEThe dentatorubrothalamic tract (DRTT) has been suggested as the anatomical substrate for deep brain stimulation (DBS)–induced tremor alleviation. So far, little is known about how accurately and reliably tracking results correspond to the anatomical DRTT. The objective of this study was to systematically investigate and validate the results of different tractography approaches for surgical planning.METHODSThe authors retrospectively analyzed 4 methodological approaches for diffusion tensor imaging (DTI)–based fiber tracking using different regions of interest in 6 patients with essential tremor. Tracking results were analyzed and validated with reference to MRI-based anatomical landmarks, were projected onto the stereotactic atlas of Morel at 3 predetermined levels (vertical levels −3.6, −1.8, and 0 mm below the anterior commissure–posterior commissure line), and were correlated to clinical outcome.RESULTSThe 4 different methodologies for tracking the DRTT led to divergent results with respect to the MRI-based anatomical landmarks and when projected onto the stereotactic atlas of Morel. There was a statistically significant difference in the lateral and anteroposterior coordinates at the 3 vertical levels (p < 0.001, 2-way ANOVA). Different fractional anisotropy values ranging from 0.1 to 0.46 were required for anatomically plausible tracking results and led to varying degrees of success. Tracking results were not correlated to postoperative tremor reduction.CONCLUSIONSDifferent tracking methods can yield results with good anatomical approximation. The authors recommend using 3 regions of interest including the dentate nucleus of the cerebellum, the posterior subthalamic area, and the precentral gyrus to visualize the DRTT. Tracking results must be cautiously evaluated for anatomical plausibility and accuracy in each patient.

Subthalamic Nucleus Deep Brain Stimulation: An Invaluable Role for MER

Introduction:Subthalamic nucleus (STN) deep brain stimulation (DBS) is currently the main surgical procedure for medically refractory Parkinson's disease. The benefit of intra-operative microelectrode recording (MER) for the purpose of neurophysiological localization and mapping of the STN continues to be debated.Methods:A retrospective review of the charts and operative reports of all patients receiving STN DBS implantation for Parkinson's disease at our institution from January 2004 to March 2011 was done.Results:Data from 43 of 44 patients with Parkinson's disease treated with STN DBS were reviewed. The average number of tracts on the left was 2.4, versus 2.3 on the right. The average dorsal and ventral anatomical boundaries of the STN based on Schaltenbrand's Stereotactic Atlas were estimated to be at -5.0 mm above and +1.4 mm below target respectively. The average dorsal and ventral boundaries of the STN using MER were -2.6 mm above and +2.0 mm below target respectively. The average dorsal-ventral distance of the STN as predicted by Stereotactic Atlas was 6.4 mm, compared to 4.6 mm as determined by MER. MER demonstrated the average dorsal and ventral boundaries on the left side were -2.6 mm and +2.2 mm from target respectively, while the average dorsal and ventral boundaries on the right side were -2.5 mm and +1.8 mm from target respectively with MER.Conclusions:MER in STN DBS surgery demonstrated measurable difference between stereotactic atlas/MRI STN target and neurophysiologic STN localization.

The subthalamic nucleus at 3.0 Tesla: choice of optimal sequence and orientation for deep brain stimulation using a standard installation protocol

Object Reliable visualization of the subthalamic nucleus (STN) is indispensable for accurate placement of electrodes in deep brain stimulation (DBS) surgery for patients with Parkinson disease (PD). The aim of the study was to evaluate different promising new MRI methods at 3.0 T for preoperative visualization of the STN using a standard installation protocol. Methods Magnetic resonance imaging studies (T2-FLAIR, T1-MPRAGE, T2*-FLASH2D, T2-SPACE, and susceptibility-weighted imaging sequences) obtained in 9 healthy volunteers and in 1 patient with PD were acquired. Two neuroradiologists independently analyzed image quality and visualization of the STN using a 6-point scale. Interrater reliability, contrast-to-noise ratios, and signal-to-noise ratios for the STN were calculated. For illustration of the anatomical accuracy, coronal T2*-FLASH2D images were fused with the corresponding coronal section schema of the Schaltenbrand and Wahren stereotactic atlas. Results The STN was best and reliably visualized on T2*-FLASH2D imaging (in particular, the coronal view). No major artifacts in the STN were observed in any of the sequences. Susceptibility-weighted, T2-SPACE, and T2*-FLASH2D imaging provided significantly higher contrast-to-noise ratio values for the STN than standard T2-weighted imaging. Fusion of the coronal T2*-FLASH2D and the digitized coronal atlas view projected the STN clearly within the boundaries of the STN found in anatomical sections. Conclusions For 3.0-T MRI, T2*-FLASH2D (particularly the coronal view) provides optimal delineation of the STN using a standard installation protocol.