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Biomedical subjects

Andrew G Parrent

Publications and source records attributed to Andrew G Parrent.

6 recordsLinked to original sources
PubMed2006

Segmentation of thalamic nuclei using a modified k-means clustering algorithm and high-resolution quantitative magnetic resonance imaging at 1.5 T.

Patient outcome in minimally invasive stereotactic neurosurgical procedures depends on the ability to accurately locate the desired functional region within the deep brain while avoiding the surrounding anatomy. Due to the lack of sufficient contrast within this region in pre-operatively acquired MR images, electrophysiological exploration and histological atlases are currently required to define the surgical target within the thalamus in the treatment of many motor-control disorders. In this paper we introduce a method for segmenting the individual thalamic nuclei based on high-resolution quantitative magnetic resonance images, providing improved target visualization. The method was tested using whole-brain T1 and T2 data acquired from four healthy individuals. Accuracy of the segmentation results was assessed by comparing the center-of-mass coordinates of the segmented nuclei, with coordinates obtained from a classic histological atlas registered to these images. Strong agreement was found, with an average Euclidean distance difference of less than 4.5 mm averaged across all nuclei and all individuals. Reproducibility of the method, determined by calculating the percent similarity of segmentation results derived from data acquired from repeated scan sessions, was greater than 85%. These results illustrate the ability to accurately and reliably segment the primary nuclei of the thalamus and suggest that the method may have utility in the study of individual nuclear regions in disease state as well as for planning deep-brain surgical procedures.

Adult↗
PubMed2006

Morbidity associated with the use of intracranial electrodes for epilepsy surgery.

BACKGROUND: Invasive monitoring for the investigation of medically intractable epilepsy may be associated with undesirable morbidity. We performed a review of our recent experience to determine the incidence of major complications. METHODS: We reviewed the clinical records of all patients who underwent invasive EEG monitoring at our institution between 2000 and 2004. RESULTS: One-hundred and sixteen patients (57 males, 59 females) with a mean age of 32 years of age underwent intracranial placement of electrodes for epilepsy surgery investigation. Subdural strips were placed in 115 patients with a mean of eight strips per patient. Subdural grids were inserted in 11 patients and depth electrodes in five. Fourteen of the 15 patients with grids or depth electrodes also had strips. Coverage was unilateral in 37 patients and bilateral in 79 patients. Electrodes were placed over the frontal lobe in 78 cases, temporal in 93, parietal in 24, and occipital in 27 patients. The average duration of investigation was 12.3 days (range 3-29). The evaluation led to the performance of a surgical resection in 85 patients (74%). Complications were seen in four patients with subdural strips (3%), and in two patients with grids (13%), characterized by clinical infection, intracranial hemorrhage, aseptic meningitis, transient neurological deficits, and status epilepticus. Mortality was nil. CONCLUSIONS: In comparison with previously published literature on the topic, the major complication rate in this group of patients appears to be low.

Adolescent↗
PubMed2006

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 Parkinson's 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.

Adult↗
PubMed2005

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.

Artificial Intelligence↗
PubMed2003

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.

Brain↗