Decreased light attenuation in cerebral cortex during cerebral edema detected using optical coherence tomography

Abstract

Cerebral edema develops in response to a variety of conditions, including traumatic brain injury and stroke, and contributes to the poor prognosis associated with these injuries. This study examines the use of optical coherence tomography (OCT) for detecting cerebral edema in vivo. Three-dimensional imaging of an in vivo water intoxication model in mice was performed using a spectral-domain OCT system centered at 1300 nm. The change in attenuation coefficient was calculated and cerebral blood flow was analyzed using Doppler OCT techniques. We found that the average attenuation coefficient in the cerebral cortex decreased over time as edema progressed. The initial decrease began within minutes of inducing cerebral edema and a maximum decrease of 8% was observed by the end of the experiment. Additionally, cerebral blood flow slowed during late-stage edema. Analysis of local regions revealed the same trend at various locations in the brain, consistent with the global nature of the cerebral edema model used in this study. These results demonstrate that OCT is capable of detecting in vivo optical changes occurring due to cerebral edema and highlights the potential of OCT for precise spatiotemporal detection of cerebral edema.

Keywords: brain swelling; cerebral edema; optical coherence tomography.

Fig. 1

(a) Schematic of spectral domain optical coherence tomography (OCT) setup. Red arrows depict the optical beam scan pattern for three-dimensional 3-D imaging of sample. m: mirror, gm: galvanometer mounted mirror, gr: grating, lsc: line scan camera. (b) Two-dimensional OCT sagittal image of in vivo mouse brain. S: skull, CTX: cerebral cortex, CC: corpus callosum. $\text{Scale bar}=0.5\mathrm{mm}$. (c) 3-D volume of in vivo mouse brain rendered from OCT volumetric scan.

Fig. 2

(a) Sagittal optical coherence tomography (OCT) intensity image of in vivo mouse brain and (b) corresponding attenuation image. $\text{Scale bar}=0.5\mathrm{mm}$.

Fig. 3

Percent change of average attenuation coefficient in the cerebral cortex over time from in vivo cerebral edema mouse model. Arrow indicates IP water injection for water intoxication group. Error bars represent standard error for $n=3$.

Fig. 4

BWC measurements of right cerebral cortex quadrant. Error bars represent standard error.

Fig. 5

Attenuation depth profile from a small region of cerebral cortex. The gray line represents the values during baseline and the black line represents the same depth profile after water intoxication. The percent difference between the two profiles is shown by the red dotted line on the right $y$-axis. The average percent difference over the entire depth is $-12\%$.

Fig. 6

Rate of change in average attenuation coefficient during baseline, edema (postIP injection) and control experiments. Error bars represent the standard error.

Fig. 7

(a) MIP en face images of the cerebral vascular network created from DOCT volumetric data. The orientation is specified by the rostral (R) and midline (M) arrows. Time points (in minutes) are labeled in the bottom left corners. The red arrow indicates an area where capillaries became increasingly visible after IP injection compared to baseline. (b) Percent change in flow density as a function of time for water intoxication and control animals.

Fig. 8

Percent change of average attenuation coefficient in the cerebral cortex from three regions spanning (a) medial-lateral, (b) rostral caudal and (c) axial positions (ROIs shown in inset). Arrow indicates IP injection time point. Error bars represent standard error.

Fig. 9

Percent change in flow density as a function of time as measured in the three local ROI groups. Arrow indicates IP injection. Error bars represent standard error.