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Intraoperative Optical Imaging
Source: 2001;(7):173-192.
Author: Toga AW, Pouratian N.
Abstract:
Intraoperative mapping provides an unparalleled opportunity to examine the basic physiology of the functioning human brain. At the same time, intraoperative mapping poses unique challenges for the acquisition, analysis and interpretation that are over and above those issues that are part of any other intact in vivo brain mapping. These include the operating room environment, time constraints, spatial resolution, the status of the brain under anesthesia or performance during awake protocols, a dynamic cortical geometry and other considerations. Despite these challenges, intraoperative brain mapping provides extraordinary opportunities to examine brain function unencumbered by other tissues. Tremendous insights into language and sensory and motor representations have been achieved as a result of the advantages of intraoperative investigation. With the advent of intraoperative optical imaging, the opportunity exists to study brain function and physiology with greater spatial resolution, temporal resolution, and sensitivity than previously possible. In this chapter, we will discuss the methodology of intraoperative optical imaging of intrinsic signals and address how this imaging modality overcomes many of the challenges presented by the operating room environment. Haglund et al., were the first to observe optical signals in humans, reporting activity-related changes in cortical light reflectance during seizure and cognitive tasks. [1] This was a landmark paper as it demonstrated the use of optical methods in humans, which up until this point had been employed only in monkeys, cats and rodents. Since then, there have been reports describing the evolution of optical signals in the human cortex [2], the mapping of primary sensory and motor cortices [3], and the delineation of language cortices within [4] and across languages [5]. Although optical signals can be measured using either intrinsic signals, dyes that are restricted to physiological compartments, such as intravascular dyes [6, 7], or dyes that are sensitive to physiological events, such as oxygen-dependent phosphorescence quenching dyes [8], only intrinsic signal changes have been reported in humans. Optical signals can also be detected which are specific to pathological tissue, such as tumors, by using tracers specific to tissue properties or even metabolic rates [9]. In terms of clinical utility, the most obvious benefits of intraoperative optical imaging are obtained when it is used to map “eloquent” cortices (i.e. language, sensory, motor, or visual areas) that are adjacent to or involved in pathology. This allows maximal surgical resection of pathological tissue while leaving “eloquent” cortices intact. These eloquent regions provide the opportunity to utilize simple activation protocols compatible with an operating room environment or in the case of passive stimulation, the ability to create functional maps in anesthetized patients. This chapter surveys the development and methodology of intraoperative optical imaging of intrinsic signals. We include comparisons between pre- and intra-operative maps along with methods to equate them in space. We also review how intraoperative OIS (iOIS) has been applied to address questions of basic physiology and cognitive function. Finally, we comment on the potential use of iOIS as a clinical brain mapping tool for neurosurgical guidance.
Source: 2001;(7):173-192.
Author: Toga AW, Pouratian N.
Abstract:
Intraoperative mapping provides an unparalleled opportunity to examine the basic physiology of the functioning human brain. At the same time, intraoperative mapping poses unique challenges for the acquisition, analysis and interpretation that are over and above those issues that are part of any other intact in vivo brain mapping. These include the operating room environment, time constraints, spatial resolution, the status of the brain under anesthesia or performance during awake protocols, a dynamic cortical geometry and other considerations. Despite these challenges, intraoperative brain mapping provides extraordinary opportunities to examine brain function unencumbered by other tissues. Tremendous insights into language and sensory and motor representations have been achieved as a result of the advantages of intraoperative investigation. With the advent of intraoperative optical imaging, the opportunity exists to study brain function and physiology with greater spatial resolution, temporal resolution, and sensitivity than previously possible. In this chapter, we will discuss the methodology of intraoperative optical imaging of intrinsic signals and address how this imaging modality overcomes many of the challenges presented by the operating room environment. Haglund et al., were the first to observe optical signals in humans, reporting activity-related changes in cortical light reflectance during seizure and cognitive tasks. [1] This was a landmark paper as it demonstrated the use of optical methods in humans, which up until this point had been employed only in monkeys, cats and rodents. Since then, there have been reports describing the evolution of optical signals in the human cortex [2], the mapping of primary sensory and motor cortices [3], and the delineation of language cortices within [4] and across languages [5]. Although optical signals can be measured using either intrinsic signals, dyes that are restricted to physiological compartments, such as intravascular dyes [6, 7], or dyes that are sensitive to physiological events, such as oxygen-dependent phosphorescence quenching dyes [8], only intrinsic signal changes have been reported in humans. Optical signals can also be detected which are specific to pathological tissue, such as tumors, by using tracers specific to tissue properties or even metabolic rates [9]. In terms of clinical utility, the most obvious benefits of intraoperative optical imaging are obtained when it is used to map “eloquent” cortices (i.e. language, sensory, motor, or visual areas) that are adjacent to or involved in pathology. This allows maximal surgical resection of pathological tissue while leaving “eloquent” cortices intact. These eloquent regions provide the opportunity to utilize simple activation protocols compatible with an operating room environment or in the case of passive stimulation, the ability to create functional maps in anesthetized patients. This chapter surveys the development and methodology of intraoperative optical imaging of intrinsic signals. We include comparisons between pre- and intra-operative maps along with methods to equate them in space. We also review how intraoperative OIS (iOIS) has been applied to address questions of basic physiology and cognitive function. Finally, we comment on the potential use of iOIS as a clinical brain mapping tool for neurosurgical guidance.