[BIC-announce] Mallar Chakravarty - Ph.D. defense, Monday,

[Jennifer Chew, Ms.]

M. Mallar Chakravarty

 Ph.D. ORAL DEFENSE

DEPARTMENT OF BIOMEDICAL ENGINEERING

Date:               Monday, December 3rd, 2007 
Time:               3:30 P.M.
Location:           MNI (The Montreal Neurological Institute and Hospital
                    3801 University Street)
                    De Granpré Communications Center

 Title:             Image- processing of MRI for measuring brain injury, repair and degeneration in patients with 					multiple sclerosis

 Abstract:

Planning functional neurosurgical procedures to minimize the symptoms of movement disorders requires the accurate localization of small subcortical structures for the creation of lesions (in the thalamus or the globus pallidus) or the implantation of deep brain stimulating electrodes (in structures such as the thalamus, globus pallidus, and the subthalamic nucleus). Standard computed tomography (CT) and magnetic resonance imaging techniques (MRI) have limited signal, resolution, and contrast in subcortical regions, thereby complicating target localization. Modern imaging and image processing techniques have demonstrated that targets are better identified using digital atlases which can be customized to each patients unique anatomy. In this thesis, multi-modal techniques for targeting subcortical nuclei in neurosurgical interventions are presented. 

 

Chapter 3 describes the development of a new atlas of the subcortical 

anatomy developed from a set of manually segmented high-resolution serial histological data using novel reconstruction techniques. The atlas was warped to fit a high-resolution, high-contrast MRI template and all versions of the atlas can be viewed in register to allow enhanced visualization of the subcortical anatomy and contains 105 structures. To accurately target subcortical structures on pre-operative MRI data, the atlas must be customized to each patient. Chapter 4 contains a validation of warping techniques for atlas-to-patient warping. An overlap metric is used to compare the atlas definition of three subcortical structures with a silver standard derived from the agreement of manual segmentations of five manual raters. A functional validation was also performed to compare the coordinates locations of positive intra-operative stimulations and the atlas definition of the sensory thalamus. The anatomical validation criteria was also used to compare two linear, two piecewise linear, and four nonlinear registration based atlas warping techniques using four different evaluation metrics in Chapter 5. 

 

To further enhance visualization and account for somatotopic differences between subjects, fMRI vibrotactile somatosensory stimulation techniques were developed. The construction, testing, and validation of an MRI compatible vibrotactile stimulator is presented in Chapter 6. In Chapter 7 this stimulator is used to show that activations of the somatosensory pathway including sensory thalamus can be reliably achieved at 1.5 and 3.0T. 

The techniques proposed in this thesis will have immediate clinical imapact, as studies confirm the correlation between target localization and identification with improved outcome.

 

Jennifer Chew

McConnell Brain Imaging Centre

MNI - WB317

3801 University Street

Montreal, Qc  H3A 2B4

Telephone:  514-398-8554

Fax:  514-398-2975