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National Center for Image Guided Therapy

Functional MRI for Neurosurgical Planning

Figure 1: Example subject’s language maps resulting from task-free (resting-state and movie-watching) and task-based fMRI paradigms. The ICA-derived language-related components from task-free scans identify similar language areas as that from the language task-based activation map.

The NCIGT fMRI studies have focused on developing a novel and reliable task-free paradigm for mapping critical language areas for surgical planning. Instead of performing series of language tasks, patients will only need to rest or watch a movie clip while the BOLD signals are acquired. This will lead to an easy to perform and administer paradigm for pre-surgical language mapping with fMRI. In this effort, we have investigated two task-free paradigms, resting-state and movie-watching conditions, based on functional connectivity MRI (fcMRI) approaches. Using a seed-based fcMRI method, we confirmed the feasibility of assessing language-dominant hemisphere with task-free fMRIs (Tie et al., 2010a). Using a data-driven independent component analysis (ICA) method, we have generated spatial templates of language networks that can be used in patient study to identify language-related components from task-free fMRIs (Tie et al., 2010b) (Figure 1).

A collaborative project with MIT aims at developing a method called functional geometry alignment (FGA) for registering neuroanatomy by matching a spectral embedding of the functional connectivity patterns of two fMRI volumes (Langs et al., 2010a, 2010b). Initial experiments with the language system indicate that the proposed method yields improved functional correspondences across subjects. This advantage is pronounced for subjects with tumors that affect the language areas and thus cause spatial re-configuration of the functional regions (Figure 2).

Figure 2: Mapping a region by functional geometry alignment: a reference subject (first column) aligned to a tumor patient (second and third columns, the tumor is shown in blue). The green region in the healthy subject is mapped to the red region by the proposed functional registration and to the yellow region by anatomical registration. Note that the functional alignment places the region narrowly around the tumor location, while the anatomical registration result intersects with the tumor. The slice of the anatomical scan with the tumor and the zoomed visualization of the registration results (fourth column) is also shown.
Automated classification of fMRI data employing trial-based imagery tasks: The exclusively task-specific ROIs obtained from the two sessions (1st and 2nd) for five subjects (S1-S5; the p-value was different depending on the outcome of optimization. The six mental tasks (with corresponding acronyms) were (1) right-hand motor imagery (RH), (2) left-hand motor imagery (LH), (3) right foot motor imagery (RF), (4) mental calculation (MC), (5) internal speech generation (IS), and (6) visual imagery (VI).

To advance surgical planning, the Neurosurgery Core of the NCIGT along with its fellow Cores is investigating and refining preoperative fMRI and diffusion tensor imaging (DTI) - two methods of analyzing MRI images to reveal aspects about the functional activity of the brain through blood perfusion and about its anatomical complexity based on an understanding of tissue with respect to water diffusion. Because they use MR images, fMRI and DTI are non-invasive methods of mapping eloquent cortical areas and critical white matter structures that can be used to assess these areas in relationship to a tumor or other pathological neural manifestations. Such functional and anatomical information is crucial to understanding an individual's brain to best plan for surgery, especially when the activity of the brain is shifting over time if areas have become compromised. To optimize surgical planning and performance, a neurosurgical team needs as much functional and anatomical information on an individual patient's brain as possible to understand its unique aspects and configurations.

The NCIGT continues to add to the collective knowledge base of what is understood about the functional activities and characteristics of the brain through fMRI. A focus of NCIGT researchers is applying software techniques to fMRI data and comparing data from normal subjects to those with brain tumors or epilepsy to pinpoint language function to improve surgical planning.

Neurosurgical researchers are working on a study of overt language function through multimodal functional mappings using fMRI, MEG, and DTI across the same subjects. This effort will result in comprehensive mappings useful for the image guided surgical resection of lesions near critical language centers of the brain. To date, researchers have designed and tested fMRI protocols for a comparative study of music and language dissociations in the temporal lobe. fMRI findings, combined with intraoperative data collected by our collaborators from BWH, evidenced a singing and speech network that is separately distributed in the right and left temporal lobes, respectively. Such understandings will be useful in therapies aimed at helping otherwise aphasic patients to use singing as a form of overt communication.

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