Functional Magnetic Resonance Imaging for Brain Mapping in Neuro
Functional Magnetic Resonance Imaging for Brain Mapping in Neuro
One of the most pertinent applications of the principle primum non nocere (first do no harm) is in the optimization of neurosurgical procedures for patients with resectable lesions. The gold standard for identifying eloquent areas of the brain to be avoided in resections is direct cortical stimulation and somatosensory evoked potential monitoring, which is itself an invasive, cumbersome and difficult technique for mapping these areas. Functional magnetic resonance imaging shows great promise as a viable noninvasive alternative to invasive mapping as well as significant current clinical utility in cases in which it cannot yet fully supplant cortical stimulation methods. Ongoing work is directed toward overcoming technical limitations, improved mapping of complex functions such as language and memory, and mapping of white matter tracts.
The goal of modern neurosurgery is to improve the survival rates and quality of life of patients with surgically treatable intracranial lesions. It is known, however, that tumor progression and survival in cases of malignant intracranial tumors is contingent on the extent of tumor removal. The protection of functions potentially at risk during surgery is facilitated by functional mapping of critical eloquent areas. The gold standards for mapping eloquent areas of the brain are invasive cortical stimulation and somatosensory evoked potential monitoring.
A number of secondary physiological changes occur as a result of neuronal activity in the brain. Measurable changes such as glucose utilization led to the development of functional mapping with FDG-PET. It was also found that another of these changes, local differences in oxygen use, could be demonstrated and localized using MR imaging, which led to the development of BOLD fMR imaging. The introduction of frameless intraoperative neuronavigation systems such as StealthStation (Medtronic, Boulder, CO) or Vector Vision (BrainLab AG, Heimstetten, Germany) has allowed the precise coregistration and transfer of fMR imaging data into the surgical field. Understandably, however, the acceptance of MR imaging by neurobiologists in the investigation of neurophysiological functions of the human cerebral cortex was quick relative to its acceptance as a clinical tool by neurosurgeons; the stakes are obviously different. Although the status of fMR imaging currently is investigational; it is an evolving technology that shows both future promise and present-day utility. In some instances, it has been used successfully in lieu of invasive mapping tools. Indeed, in certain cases, evidence exists that fMR imaging mapping may be more appropriate than cortical stimulation. Its shortcomings can be categorized into the following two broad categories: 1) technical, which will be at the very least partially overcome by ongoing technical advancement; and 2) neuroscientific understanding in general, which otherwise applies to all modalities of brain mapping (including direct cortical stimulation and somatosensory evoked potential monitoring). When not used as an outright substitute for invasive mapping, fMR imaging has a well-documented adjunctive role in optimizing surgical procedures and outcomes that belie its investigational status.
One of the most pertinent applications of the principle primum non nocere (first do no harm) is in the optimization of neurosurgical procedures for patients with resectable lesions. The gold standard for identifying eloquent areas of the brain to be avoided in resections is direct cortical stimulation and somatosensory evoked potential monitoring, which is itself an invasive, cumbersome and difficult technique for mapping these areas. Functional magnetic resonance imaging shows great promise as a viable noninvasive alternative to invasive mapping as well as significant current clinical utility in cases in which it cannot yet fully supplant cortical stimulation methods. Ongoing work is directed toward overcoming technical limitations, improved mapping of complex functions such as language and memory, and mapping of white matter tracts.
The goal of modern neurosurgery is to improve the survival rates and quality of life of patients with surgically treatable intracranial lesions. It is known, however, that tumor progression and survival in cases of malignant intracranial tumors is contingent on the extent of tumor removal. The protection of functions potentially at risk during surgery is facilitated by functional mapping of critical eloquent areas. The gold standards for mapping eloquent areas of the brain are invasive cortical stimulation and somatosensory evoked potential monitoring.
A number of secondary physiological changes occur as a result of neuronal activity in the brain. Measurable changes such as glucose utilization led to the development of functional mapping with FDG-PET. It was also found that another of these changes, local differences in oxygen use, could be demonstrated and localized using MR imaging, which led to the development of BOLD fMR imaging. The introduction of frameless intraoperative neuronavigation systems such as StealthStation (Medtronic, Boulder, CO) or Vector Vision (BrainLab AG, Heimstetten, Germany) has allowed the precise coregistration and transfer of fMR imaging data into the surgical field. Understandably, however, the acceptance of MR imaging by neurobiologists in the investigation of neurophysiological functions of the human cerebral cortex was quick relative to its acceptance as a clinical tool by neurosurgeons; the stakes are obviously different. Although the status of fMR imaging currently is investigational; it is an evolving technology that shows both future promise and present-day utility. In some instances, it has been used successfully in lieu of invasive mapping tools. Indeed, in certain cases, evidence exists that fMR imaging mapping may be more appropriate than cortical stimulation. Its shortcomings can be categorized into the following two broad categories: 1) technical, which will be at the very least partially overcome by ongoing technical advancement; and 2) neuroscientific understanding in general, which otherwise applies to all modalities of brain mapping (including direct cortical stimulation and somatosensory evoked potential monitoring). When not used as an outright substitute for invasive mapping, fMR imaging has a well-documented adjunctive role in optimizing surgical procedures and outcomes that belie its investigational status.
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