Diffuse Correlation Spectroscopy to Assess Cerebral Blood Flow in a Mouse Model

Overview

In this video, we demonstrate the diffuse correlation spectroscopy technique to measure cerebral blood flow in a mouse model of mild traumatic brain injury.

Protocol

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board

1. Assessment of cerebral blood flow with diffuse correlation spectroscopy

1. DCS data acquisition
   1. Remove hair on the scalp. Because DCS works best in the absence of hair, it is necessary to remove fur on the head prior to the start of experiments. Typically, hair removal is done 1-3 days prior to the start of the study.
      1. Induce mice with 4.5% isoflurane in 100% oxygen for 45 seconds and maintain with 1-2% isoflurane in 100% oxygen.
      2. Shave the head between the eyes and the ears. Then, use depilatory cream to remove fur on the head as in Figure 1.
      3. Allow the animal to recover from anesthesia on a warming pad and then return to the cage.
   2. Measure cerebral blood flow with DCS. To minimize motion artifacts during measurement, study mice under brief isoflurane anesthesia.
      NOTE: Visually monitor respiration and toe pinch response throughout measurements and adjust isoflurane concentration as needed to ensure consistent depth of anesthesia. Significant variations in the depth of anesthesia could alter blood flow given the known vasomodulatory effects of isoflurane.
      1. Induce with 4.5% isoflurane in 100% oxygen for 45 seconds, and then maintain with 1.0-1.75% isoflurane in 100% oxygen. Confirm sufficient depth of anesthesia by the absence of a toe pinch response and normal respiration (between ~60-80 breaths per minute).
      2. After a 2 min period of stabilization, gently rest the DCS sensor over the right hemisphere such that the top edge of the optical sensor lines up with the back of the eye and the side of the sensor lines up along the midline (Figure 1). Cup a hand over the sensor to shield it from room light. Acquire 5 seconds of data (1 Hz acquisition).
      3. Reposition the sensor over the left hemisphere, and acquire 5 seconds of data.
      4. Repeat 3 times/hemisphere to account for local heterogeneities under the tissue surface.
   3. Recovery
      1. Remove the mouse from anesthesia and place it on a warming pad.
      2. After the mouse regains its righting reflex return it to the cage.

Representative Results

Figure 1: Measurement of cerebral blood flow by Diffuse Correlation Spectroscopy. (A) An optical sensor is gently manually held over the right hemisphere to measure blood flow in an anesthetized mouse. (B) Representative sensor placement on the right hemisphere. The outline of the sensor is represented as a dashed black rectangle, and the location of the source and detector fibers are in red and blue circles, respectively. The sensor is placed such that the short edge of the sensor lines up with the back of the eye and the long edge of the sensor aligns with the midline.

Materials

Name	Company	Catalog Number	Comments
Depilatory cream	Amazon	Nair
DiH2O	VWR	VWRL0200-1000
Hardware Autocorrelator Board	www.correlator.com	Flex05-8ch
Isoflurane 250 mL	MED-VET INTERNATIONAL	RXISO-250
Kimwipe (11.2 x 21.3 cm)	VWR	21905-026
Laboratory vortex mixer	VWR	10153-838
LabView	National Instruments	LabVIEW
Luminex 200, HTS, FLEXMAP 3D, or MAGPIX with xPONENT software	Luminex Corporation
R Programming Language
RStudio	www.rstudio.com
Sonicator
1 m acrylic guide tube	McMaster-Carr	49035K85
4 photon counting avalanche photodiode	Perkin-Elmer	SPCM-AQ4C-IO
400 um multimode source fiber	Thorlabs Inc.	FT-400-EMT
54 g bolt	Ace Hardware		0.95 cm basic body diameter, 2 cm head diameter, 10.2 cm length
780 nm single mode detector fiber	Thorlabs Inc.	780HP
852 nm long-coherence length laser	TOPTICA Photonics	iBeam smart