OCT-Guided Surgery for Gliomas: Current Concept and Future Perspectives

Abstract

Optical coherence tomography (OCT) has been recently suggested as a promising method to obtain in vivo and real-time high-resolution images of tissue structure in brain tumor surgery. This review focuses on the basics of OCT imaging, types of OCT images and currently suggested OCT scanner devices and the results of their application in neurosurgery. OCT can assist in achieving intraoperative precision identification of tumor infiltration within surrounding brain parenchyma by using qualitative or quantitative OCT image analysis of scanned tissue. OCT is able to identify tumorous tissue and blood vessels detection during stereotactic biopsy procedures. The combination of OCT with traditional imaging such as MRI, ultrasound and 5-ALA fluorescence has the potential to increase the safety and accuracy of the resection. OCT can improve the extent of resection by offering the direct visualization of tumor with cellular resolution when using microscopic OCT contact probes. The theranostic implementation of OCT as a part of intelligent optical diagnosis and automated lesion localization and ablation could achieve high precision, automation and intelligence in brain tumor surgery. We present this review for the increase of knowledge and formation of critical opinion in the field of OCT implementation in brain tumor surgery.

Keywords: brain imaging; brain tumor; intraoperative imaging; minimally invasive theranostics; neurosurgical guidance; optical coherence tomography.

Figure 1

Different OCT devices are presented with corresponding types of OCT probes: (1) rigid curve-shaped (a1) and flexible (a2,a3) handheld probes for intraoperative use with portable OCT device (а5) and application during brain tumor removal (a4); (2) needle-like probe (b1,b2) for stereotactic biopsy providing 2D images; (3) operating microscope with integrated OCT system providing OCT imaging directly in oculars and on a small-sided screen* fixed close to the microscope ocular (c1,c2).

Figure 2

OCT data types in neuro-oncology: 2D OCT images of brain tissue obtained by OCT-integrated microscope (a) and portable CP OCT system with handled probe (b); based on attenuation coefficient color-coded map of border between white matter and glioma obtained by CP OCT device from human biopsy sample (c); OCTA images of cortex (d) and glioblastoma 101.6 in rat (e); 3D OCT image of border between white matter and glioma (f). WM—white matter. Scale bar is 1 mm in all images.

Figure 3

OCT signal (a3,b3) is formed by close-packed myelin fibers in white matter (a1–a3) and by a variety of cells, vascular proliferation and areas of necrosis (black dotted area) in glioblastoma demonstrated on histological images using hematoxylin and eosin staining (b1–b3). Scale bar is 1 mm in all images.

Figure 4

OCT imaging of cortex in vivo (a,b) using OCT-integrated microscope and handheld CP OCT probe, ex vivo (d) and color-coded OCT map of cortex based on the attenuation coefficient (e). The white arrows show a specific vertical striation arising from “shadows” of the blood vessels located just under the cortex surface (b), which disappear in the case of tumor infiltration of the cortex (c). The CP OCT image includes two parts: co-polarization (co) based on initial state of polarization after backscattering within the tissue and cross-polarization (cross) that determines any orthogonal polarization. Scale bar is 1 mm in all images.

Figure 5

Damage to myelinated fibers in the region of interest causes the decrease in attenuation coefficient values both in co- (Att(co)) and cross-polarizations (Att(cross)), which is reflected on color-coded optical maps—the bright colors (red, orange) of myelinated fibers change to pale blue of damaged myelin. * Me [Q1; Q3]–Me–median value; Q1 and Q3 are the values of the 25th and 75th percentile of the distribution.

Figure 6

Use of stereotactic OCT needle for identification of tumor within white matter (a1,a2) and blood vessels (b1–b6) in preclinical studies. Visualization of white matter (WM)—tumor border using OCT in a model of glioblastoma 101.8 grafted into the rat brain and surrounding brain structures (frontal section) and corresponding histology (a2). OCT visualization of blood vessels in normal human brain samples (post mortem samples); (b1,b2)—digital photographs of the samples; (b3,b4)—OCT images obtained using a needle system; (b5,b6)—corresponding histological images. The width of the lumen of blood vessels, measured on histological preparations: 650 μm (b3), 300 μm (blue arrow) and 125–150 μm (green arrows) (b4).