Intraoperative optical intrinsic signal imaging: a clinical tool for functional brain mapping

Abstract

<jats:p>Optical imaging of intrinsic signals (OIS) is a well-established neuroimaging modality by which functional cortical activity is mapped by detecting activity-related changes in cortical light reflectance. Light reflectance changes are detected by a charged-coupled device camera that captures images of the exposed cortex both at rest and during activity. Although to date OIS has only been used for research purposes, intraoperative OIS (iOIS) holds promise as a clinical mapping tool. In general, iOIS demonstrates good spatial correlation with electrocortical stimulation mapping (ECSM) and other electrophysiological modalities. Additionally, iOIS offers high spatial resolution (in microns), does not make contact with the surface of the brain, and introduces no potentially harmful compounds. Moreover, mapping is relatively rapid.</jats:p> <jats:p>The authors review the potential contribution of iOIS to the intraoperative environment. Specifically, they review iOIS methodology, discuss signal origin, compare OIS with other functional mapping modalities, and explain its potential benefits and limitations. They propose that iOIS may, in the future, be used in conjunction with ECSM to improve the resolution and accuracy of intraoperative mapping, decrease total time of intraoperative mapping, and possibly improve neurological outcomes. Additional studies will be required to quantify the sensitivity and specificity of optical maps relative to ECSM before it can be implemented clinically.</jats:p>

Laser Doppler imaging for intraoperative human brain mapping

“…The use of optical intrinsic signal imaging (OIS) for intraoperative brain mapping was pioneered by (Haglund et al, 1992) producing functional maps of high temporal resolution but requiring a glass plate to be in contact with the cortex (to minimize movement related artefacts) and several task repetitions to achieve a reliable signal to noise ratio. Intraoperative OIS has been developed further to incorporate image alignment and analysis, NeuroImage 44 (2009) Contents lists available at ScienceDirect NeuroImage j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / y n i m g mostly eliminating the need for a glass plate (Pouratian et al, 2002a(Pouratian et al, , 2003 and has provided many advances in high resolution brain mapping as well as understanding of local hemodynamics. Methods based on Laser Doppler provide another possibility, our work has derived from a CMOS-based Laser Doppler Imager (LDI) which has been designed and constructed to fit on a standard surgical microscope.…”

Intraoperative Human Functional Brain Mapping Using Optical Intrinsic Signal Imaging

“…The most beneficial combinations usually involve compensating for limitations of one technique with another, or concurrently measuring different aspects of the same response to better understand its physiological basis. For example, combined OISI-fMRI studies have also contributed to our knowledge of the etiology of these signals [101,[130][131]. The recent development of a system that allows simultaneous fMRI and OIS spectroscopy [132] promises to further this endeavor.…”

“…Spread may also be related to imprecise physiological coupling of neuronal activity, metabolism, and perfusion. The sensitivity, specificity, positive predictive value, and negative predictive value of intraoperative OISI relative to ESM as a gold standard have not been fully quantified [101][102], and such quantification will be essential to the broadening of intraoperative OISI as a fundamental clinical tool.…”

“…The recent development of a system that allows simultaneous fMRI and OIS spectroscopy [132] promises to further this endeavor. This combination has also been used to test the clinical utility of intraoperative human OISI for neurosurgical guidance by comparing intraoperative OISI maps with pre-surgical fMRI maps [101,[130][131].…”

Optical Intraoperative Measurement of Function in the Human Brain

“…Functional mapping using optical imaging has been investigated for some time, however has not developed sufficiently clinical application. The problems limiting its application as identified in [3] include the limited signal to noise (SNR) principally due to the variation of the signal with pulse and respiratory rate and registration difficulties due to patient movement. This project has developed techniques to overcome these problems.…”