Kirk W. Finnis

Three-dimensional database of subcortical electrophysiology for image-guided stereotactic functional neurosurgery

We present a method of constructing a database of intraoperatively observed human subcortical electrophysiology. In this approach, patient electrophysiological data are standardized using a multiparameter coding system, annotated to their respective magnetic resonance images (MRIs), and nonlinearly registered to a high-resolution MRI reference brain. Once registered, we are able to demonstrate clustering of like interpatient physiologic responses within the thalamus, globus pallidus, subthalamic nucleus, and adjacent structures. These data may in turn be registered to a three-dimensional patient MRI within our image-guided visualization program enabling prior to surgery the delineation of surgical targets, anatomy with high probability of containing specific cell types, and functional borders. The functional data were obtained from 88 patients (106 procedures) via microelectrode recording and electrical stimulation performed during stereotactic neurosurgery at the London Health Sciences Centre. Advantages of this method include the use of nonlinear registration to accommodate for interpatient anatomical variability and the avoidance of digitized versions of printed atlases of anatomy as a common database coordinate system. The resulting database is expandable, easily searched using a graphical user interface, and provides a visual representation of functional organization within the deep brain.

A 3-Dimensional Database of Deep Brain Functional Anatomy, and Its Application to Image-Guided Neurosurgery

We describe a surgical planning environment that permits the determination or refinement of the location of a therapeutic neurosurgical intervention using information derived from an electrophysiological database. Such intraoperative stimulation-response and microelectrode recording data are generated from subcortical exploration performed as part of neurosurgical interventions at multiple centres. We have quantified and nonlinearly registered these intraoperative data, acquired from a large population of patients, to a reference brain imaging volume to create an electrophysiological database. This database can then be nonlinearly registered to future patient imaging volumes, enabling the delineation of surgical targets, cell types, and functional and anatomical borders prior to surgery. The user interface to our system allows the population-acquired physiology information to be accessed in a fully searchable format within a patient imaging volume. This system may be employed in both preoperative planning and intraoperative guidance of stereotactic neurosurgical procedures. We demonstrate preliminary results illustrating the use of this database approach to predict the optimum surgical site for creating thalamic lesions in the surgical treatment of Parkinson’s disease.

Application of a Population Based Electrophysiological Database to the Planning and Guidance of Deep Brain Stereotactic Neurosurgery

Stereotactic neurosurgery for movement disorders involves the accurate localization of functionally distinct nuclei deep within the brain. These surgical targets exist within anatomy appearing homogeneous on preoperative magnetic resonance images (MRIs) making direct radiographic localization impossible. We have developed a visualization-oriented searchable and expandable database of functional organization representing bilaterally the sensorimotor thalamus, pallidum, internal capsule, and subthalamic nucleus. Data were obtained through microelectrode recording and stimulation mapping routinely performed during 145 functional stereotactic procedures. Electrophysiologic data were standardized using a multi-parameter coding system and annotated to their respective MRIs at the appropriate position in patient stereotactic space. We have developed an intensity-based nonlinear registration algorithm to accommodate for normal anatomical variability that rapidly warps a patients volumetric MRI to an MRI average brain considered representative of the patient population. The annotated functional data are subsequently transformed into the average brain coordinate system using the displacement grids generated by the algorithm. When the database is searched, clustering of like inter-patient physiologic responses within target anatomy and adjacent structures is revealed. These data may in turn be registered to a preoperative MRI using a desktop computer enabling prior to surgery interactive delineation of surgical targets.

3D Functional Database of Subcortical Structures for Surgical Guidance in Image Guided Stereotactic Neurosurgery

Current techniques for deep brain stereotactic neurosurgery require identification of targets by preoperative imaging localization. Many critical structures targeted in this way (the thalamic nuclei) are functionally distinct but not discernable on magnetic resonance images. These structures are also surrounded by critical brain areas which must not be damaged by the surgical procedure. These factors make accurate localization of lesion targets crucial. Digitized anatomical atlases derived from histochemically stained brain specimens registered to patient MRI datasets aid in delineating targets but accuracy of registration withinhomogeneous anatomy remains questionable. To address this problem, we have designed a searchable and expandable database of functional organization for the sensorimotor thalamus, internal capsule, and internal pallidum from a population of patients (n=40). Data were obtained through microcellular recording, microstimulation, and macrostimulation mapping performed during stereotactic thalamotomies and pallidotomies. After registration of the database into standard stereotactic space, clustering of like physiological responses was noted in the internal capsule and sensorimotor thalamus and an articulated joint-based organization was observed in the internal pallidum. Furthermore, a clear delineation of the kinesthetic-paresthetic functional border was observed within the thalamus. When registered to a patient MRI within our image guided visualization platform, the database provides a visual representation of deep brain functional organization facilitating physiological exploration and preoperative planning.

Visualization and navigation system development and application for stereotactic deep-brain neurosurgeries

We present the development of a visualization and navigation system and its application in pre-operative planning and intra-operative guidance of stereotactic deep-brain neurosurgical procedures for the treatment of Parkinsons disease, chronic pain, and essential tremor. This system incorporates a variety of standardized functional and anatomical information, and is capable of non-rigid registration, interactive manipulation, and processing of clinical image data. The integration of a digitized and segmented brain atlas, an electrophysiological database, and collections of final surgical targets from previous patients facilitates the delineation of surgical targets and surrounding structures, as well as functional borders. We conducted studies to compare the surgical target locations identified by an experienced stereotactic neurosurgeon using multiple electrophysiological exploratory trajectories with those located by a non-expert using this system on 70 thalamotomy, pallidotomy, thalamic deep-brain stimulation (DBS), and subthalamic nucleus (STN) DBS procedures. The average displacement between the surgical target locations in both groups was 1.95 ± 0.86 mm, 1.83 ± 1.07 mm, 1.88 ± 0.89 mm and 1.61 ± 0.67 mm for each category of surgeries, respectively, indicating the potential value of our system in stereotactic deep-brain neurosurgical procedures, and demonstrating its capability for accurate surgical target initiation.

Development and application of functional databases for planning deep-brain neurosurgical procedures

This work presents the development and application of a visualization and navigation system for planning deep-brain neurosurgeries. This system, which incorporates a digitized and segmented brain atlas, an electrophysiological database, and collections of final surgical targets of previous patients, provides assistance for non-rigid registration, navigation, and reconstruction of clinical image data. The fusion of standardized anatomical and functional data, once registered to individual patient images, facilitates the delineation of surgical targets. Our preliminary studies compared the target locations identified by a non-expert using this system with those located by an experienced neurosurgeon using regular technique on 8 patients who had undergone subthalamic nucleus (STN) deep-brain stimulations (DBS). The average displacement between the surgical target locations in both groups was 0.58 mm +/- 0.49 mm, 0.70 mm +/- 0.37 mm, and 0.69 mm +/- 0.34 mm in x, y, and z directions respectively, indicating the capability of accurate surgical target initiation of our system, which has also shown promise in planning and guidance for other stereotactic deep-brain neurosurgical procedures.

A functional database for guidance of surgical and therapeutic procedures in the deep brain

Current techniques for stereotactic neurosurgery of the deep brain require identification of targets by preoperative image localization. These structures are also surrounded by critical brain areas which must not be damaged by the surgical procedure. We have designed and implemented a searchable and expandable database of functional organization for the sensorimotor thalamus, internal capsule, and internal pallidum from a population of over 70 patients. Data were obtained through microcellular recording, microstimulation, and macrostimulation mapping performed during stereotaetic thalamotomies and pallidotomies. These data may be in turn registered to a patient 3D MRI within our image guided visualization platform. This functional database, provides a visual representation of functional organization in the deep brain, facilitating physiological exploration and preoperative planning.

Subcortical physiology deformed into a patient-specific brain atlas for image-guided stereotaxy

Stereotactic neurosurgery for movement disorders involves the accurate localization of functionally distinct subcortical anatomy that appears homogeneous on magnetic resonance or computed tomographic images. To aid localization of these surgical targets on patient images, we have developed a visualization oriented searchable and expandable database of functional organization representing bilaterally the sensorimotor thalamus, pallidum, internal capsule, and subthalamic nucleus. Data were obtained through microelectrode recording and stimulation mapping routinely performed during 123 functional stereotactic procedures. Electrophysiologic data were standardized using a multi-parameter coding system and annotated to their respective MRIs at the appropriate position in patient stereotactic space. To accommodate for normal anatomical variability, we have developed an intensity-based nonlinear registration algorithm that rapidly warps a patients volumetric MRI to a high-resolution MRI average brain. The annotated functional data are subsequently transformed into the average brain coordinate system using the displacement grids generated by the algorithm. When the database is searched, clustering of like inter-patient physiologic responses within target anatomy and adjacent structures is revealed. These data may in turn be registered to a preoperative MRI using a desktop computer enabling prior to surgery interactive delineation of surgical targets. The database is expandable, fully searchable, and provides a visual 3D representation of subcortical functional organization.

Three-dimensional somatotopic organization and probabilistic mapping of motor responses from the human internal capsule

OBJECT The somatotopic organization of the motor fibers within the posterior limb of the internal capsule (IC) in humans remains unclear. Several electrophysiological atlases created from stimulation during stereotactic neurosurgery have suggested that there is considerable overlap between representations of body parts. Overlap reported in these studies may have been due to linear scaling methods applied to the data that were unable to account for individual anatomical variability. In the current work, the authors attempted to overcome these limitations by using a nonlinear registration technique to better understand the spatial location and extent of the body-part representations in the IC. METHODS Data were acquired during 30 cases of deep brain neurosurgery in which the IC was electrically stimulated to localize the ventrolateral nucleus for a subsequent thalamotomy or implantation of a thalamic deep brain stimulator. Motor responses from the tongue, face, arm, or leg were evoked in the IC and coded in the patients native MR imaging space. The tagged MR images were then nonlinearly registered to a high-resolution template MR image. This work resulted in a functional electrophysiological atlas demonstrating the locations of body-part representations in the posterior limb of the IC that takes individual anatomical variability into account. To further understand the spatial location and extent of the motor responses, the electrophysiological data points were transformed into 3D probability maps that describe the likelihood of obtaining motor responses in the posterior limb of the IC. RESULTS The analyses suggest a reliable face-anterior, arm-intermediate, and leg-posterior somatotopic organization in the posterior limb of the IC with little overlap between the body-part representations. CONCLUSIONS This probabilistic atlas of functional responses evoked by stimulating the posterior limb of the IC provides better understanding of the anatomical organization of descending motor fibers, can be used for indirect intraoperative confirmation of the location of the ventrolateral thalamus, and is applicable to clinical and research MR imaging studies requiring information on spatial organization of motor fibers at the thalamic level in the human brain.

A Method for Analysis of Electrophysiological Responses Obtained from the Motor Fibers of the Human Internal Capsule

During stereotactic surgery in the ventrolateral (VL) thalamic nucleus we localized the motor fibers of the internal capsule (IC) by electrophysiological stimulation. Knowledge of the location and motor somatotopy in the IC helps predict the boundaries of the VL. Although the somatotopy of the IC in individual patients is determined during their respective surgeries, quantitative analysis of somatotopic data from multiple subjects within a common magnetic resonance imaging (MRI) reference space has not been attempted. Here we describe a method for group analysis, in a single coordinate system, of responses obtained from the IC adjacent to the thalamus. We analyzed tongue, face, arm, and leg motor responses in 25 cases of thalamotomy. We used existing software to develop a three dimensional (3D) database of motor responses. Our preliminary analysis suggests a face-anterior to leg-posterior somototopic organization, with some overlap between adjacent representations.