Current trends in intraoperative optical imaging for functional brain mapping and delineation of lesions of language cortex

Abstract

Resection of a cerebral arteriovenous malformation (AVM), epileptic focus, or glioma, ideally has a prerequisite of microscopic delineation of the lesion borders in relation to the normal gray and white matter that mediate critical functions. Currently, Wada testing and functional magnetic resonance imaging (fMRI) are used for preoperative mapping of critical function, whereas electrical stimulation mapping (ESM) is used for intraoperative mapping. For lesion delineation, MRI and positron emission tomography (PET) are used preoperatively, whereas microscopy and histological sectioning are used intraoperatively. However, for lesions near eloquent cortex, these imaging techniques may lack sufficient resolution to define the relationship between the lesion and language function, and thus not accurately determine which patients will benefit from neurosurgical resection of the lesion without iatrogenic aphasia.Optical techniques such as intraoperative optical imaging of intrinsic signals (iOIS) show great promise for the precise functional mapping of cortices, as well as delineation of the borders of AVMs, epileptic foci, and gliomas. Here we first review the physiology of neuroimaging, and then progress towards the validation and justification of using intraoperative optical techniques, especially in relation to neurosurgical planning of resection AVMs, epileptic foci, and gliomas near or in eloquent cortex. We conclude with a short description of potential novel intraoperative optical techniques.

Intraoperative optical imaging of intrinsic signals: a reliable method for visualizing stimulated functional brain areas during surgery

“…Most groups have used a filter in the wavelength range of 600-700 nm, at which the intrinsic signal is dominated by deoxyhemoglobin. 21 However, the amplitude of the imaged changes of the intrinsic signal was shown to be higher in the wavelength range sensitive to cerebral blood volume. 7 The resulting changes imaged with the presented IOI setup were about 0.8%, which correspond to the results reported in literature.…”

“…Depending on the wavelength used, the changes in either blood volume or oxygenation will dominate the detected signal. 21,32 Intraoperative optical imaging of intrinsic signals of the cortex in humans was first described in 1992 by Hag lund et al 10 Since then, the method has been used for functional imaging in patients with tumors and arteriovenous malformations. [1][2][3][4]6,15,18,20,23,24,27,31 The somatosensory cortex was identified by using electrical stimulation of peripheral nerves (for example, the median nerve and trigeminal nerve) 2,6,15,25,31 and mechanical stimulation.…”

Intraoperative optical imaging of functional brain areas for improved image-guided surgery

“…Awake patients performed different object-naming tasks to stimulate the speech areas (Broca and Wernicke areas) [3,13]. An active tongue movement performed by awake patients showed an activation of the motor cortex [15]. Also, epileptic foci were successfully detected by optical imaging [8,9].…”

“…In most imaging setups, this problem was solved using a transparent glass plate as a fixation gently pressed onto the surface of the brain [8,11,18,19,21]. Others used software algorithms that computed the displacements of the cortical surface [1,3,13,15]. Some setups triggered the image acquisition to respiration and heartbeat [2,28].…”

Separation of cortical arteries and veins in optical neurovascular imaging

“…While OIS imaging is a useful tool for functional brain imaging, it can obtain oxygen distribution information in vessels and tissues. 10 The di®erences in the concentration of oxygen-hemoglobin between arteries and veins could be used to di®erentiate arteries and veins.…”