Part II: ApplicationsMotor and Sensory Mapping
Section snippets
Clinical importance
The use of fMRI in the clinical setting benefits patients insomuch as it allows neurosurgeons to be aware of and to navigate the precise location of patient-specific eloquent cortices and any structural anomalies that may have developed from a tumor.2 This anatomic/functional preview facilitates the creation of more effective patient-specific treatment plans. Before the use of fMRI, the preoperative location of eloquent cortices and their relationship to the lesion was determined based on the
Neuroanatomic Review
A brief review of basic anatomy of the motor and sensory system facilitates the discussion of paradigm selection. The motor and sensory systems both have a topographic organization; in other words, motor and sensory functions are mapped to specific locations on the cortex.1 The foot and leg are represented along the interhemispheric fissure, the hand lateral to that of the foot and leg, and the tongue and face lateral to that of the hand (Fig. 2).
Voluntary movement is performed through a
Cortical plasticity/reorganization
fMRI can provide an insight into cortical plasticity/reorganization, a phenomenon that can add new layers of complexity to the analysis of fMRI data and to the planning and resection of brain lesions. Cortical reorganization is thought to occur when an area of the brain is no longer able to complete its function, which causes another area of the brain to attempt to compensate in an effort to maintain function.11, 31 Cortical reorganization is an area of intense investigation both in the basic
Analysis Overview
fMRI data analysis seeks to determine active areas through identification of voxels in the brain with statistically significant changes in blood oxygenation–level dependent (BOLD) signal from baseline to activation.11 The goal is to pinpoint voxels that show changes in signal related to the paradigm performed (the timing of the ON/OFF periods).11, 12 Surgeons can then consider the locations of such active areas when planning surgery. Signal changes, however, are very small, between 0.5% and
Artifacts and other pitfalls in clinical fMRI
Artifacts from various sources can affect the results of fMRI data. Unwanted movement can produce motion artifacts; such motion can include larger head or body movement or simple periodic fluctuations in heart rate and respiration (pulsatile artifact).12, 31 Often leading to false-negative/false-positive results, head motion can inadvertently move voxels of a high signal intensity to locations of low signal intensity.31 Patient comfort must also be ensured to minimize extra motion and
Current Research for Future Applications
Current research with fMRI is revealing exciting future applications for enhanced use in presurgical planning and areas of treatment/rehabilitation. With increased use and understanding of the technique, fMRI-guided presurgical planning concerning atypical anatomy13 (eg, disruptions caused by tumors and tumor neovasculature) will improve and become more reliable. In patients with gliosis, for example, in whom functional areas surrounding the lesion may be distorted due to mass effect,12
Summary
fMR is important to the understanding of brain function, structure, and mechanism as well as to the localization of critical motor, speech, and cognitive function. It has many advantages when compared with other methods of neuroimaging and functional mapping: it is noninvasive, it does not entail the use of radioactive isotopes, it is easily repeatable, and it has no known risks.2 Its use in presurgical mapping, such as locating motor, sensory, language, and/or memory functional areas in
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Cited by (16)
Functional magnetic resonance imaging
2022, Handbook of Neuro-Oncology NeuroimagingMethods of Analysis: Functional MRI for Presurgical Planning
2021, Neuroimaging Clinics of North AmericaCitation Excerpt :Since its discovery in the early 1990s, functional MRI (fMRI) has been used to study brain function and to advance clinical care.1,2
Patient Preparation and Paradigm Design in fMRI
2021, Neuroimaging Clinics of North AmericaCitation Excerpt :In the motor homunculus, the foot and leg motor areas are located along the interhemispheric fissure. The hand motor area is lateral to the foot motor area, and the tongue and face motor areas are lateral to the hand motor area.24–26 The SMA is composed of the pre-SMA and the SMA proper, the latter of which is involved in motor planning and also is known to support word articulation.24
Spatiotemporal mixed modeling of multi-subject task fMRI via method of moments
2016, NeuroImageCitation Excerpt :Mapping brain regions in individuals is important in clinical neuroimaging, and localization studies with task fMRI are increasingly used for pre-surgical mapping of motor and language areas in tumor and epileptic patients (Pillai, 2010). Task fMRI is a non-invasive technique that can be used in neuronavigational planning to allow the surgeon to minimize damage to brain tissue in the path of the tumor (Holodny et al., 2011). Subject-specific activation maps from fMRI can also be used to identify targets for transcranial magnetic stimulation (tMS) (Neggers et al., 2004; Wig et al., 2005) and for multifocal transcranial direct current stimulation (Ruffini et al., 2014).
Functional Magnetic Resonance Imaging
2016, Handbook of Neuro-Oncology Neuroimaging: Second Edition
The authors have nothing to disclose.