Cecil Cheung

Diffuse Optical Tomography of Cerebral Blood Flow, Oxygenation, and Metabolism in Rat during Focal Ischemia

Diffuse optical tomography (DOT) is an attractive approach for evaluating stroke physiology. It provides hemodynamic and metabolic imaging with unique potential for continuous noninvasive bedside imaging in humans. To date there have been few quantitative spatial-temporal studies of stroke pathophysiology based on diffuse optical signatures. The authors report DOT images of hemodynamic and metabolic contrasts using a rat middle cerebral artery occlusion (MCAO) stroke model. This study used a novel DOT device that concurrently obtains coregistered images of relative cerebral blood volume (rCBV), tissue-averaged hemoglobin oxygen saturation (Sto2), and relative cerebral blood flow (rCBF). The authors demonstrate how these hemodynamic measures can be synthesized to calculate an index of the oxygen extraction fraction (OEF) and the cerebral metabolic rate of oxygen consumption (CMRo2). Temporary (60-minute) MCAO was performed on five rats. Ischemic changes, averaged over the 60 minutes of occlusion, were as follows: rCBF = 0.42 ± 0.04, rCBV = 1.02 ± 0.04, ΔSto2 = −11 ± 2%, rOEF = 1.39 ± 0.06 and rCMRo2 = 0.59 ± 0.07. Although rOEF increased in response to decreased blood flow, rCMRo2 decreased. The sensitivity of this method of DOT analysis is discussed in terms of assumptions about baseline physiology, and the diffuse optical results are compared with positron emission tomography, magnetic resonance imaging, and histology observations in the literature.

In vivo cerebrovascular measurement combining diffuse near-infrared absorption and correlation spectroscopies

We combine two near-infrared diffuse optical techniques to study variations of blood flow, haemoglobin concentration, and blood oxygen saturation in the functioning rat brain. Diffuse correlation spectroscopy (or flowmetry) monitors changes in the cerebral blood flow, without the use of the principles of tracer clearance, by measuring the optical phase-shifts caused by moving blood cells. Near-infrared absorption spectroscopy concurrently measures tissue absorption at two wavelengths to determine haemoglobin concentration and blood oxygen saturation in this same tissue volume. This optical probe is non-invasive and was employed through the intact skull. The utility of the technique is demonstrated in vivo by measuring the temporal changes in the regional vascular dynamics of rat brain during hypercapnia. Temporal and spatial variations of cerebral blood flow, haemoglobin concentration and blood oxygen saturation during hypercapnia are compared with other measurements in the literature, and a quantitative analysis demonstrating the self-consistency of our combined observations of vascular response is presented.

Diffuse Optical Measurement of Hemoglobin and Cerebral Blood Flow in Rat Brain During Hypercapnia, Hypoxia and Cardiac Arrest

We have demonstrated the ability to concurrently measure relative changes in cerebral blood flow, hemoglobin concentration, and hemoglobin oxygenation with a single non-contact, non-invasive instrument. Our measurements from rat hypercapnia, hypoxia and cardiac arrest models are in reasonable agreement with the literature, and offer the possibility for further growth and quantification. The optical techniques used in this study are attractive also because they enable experimenters to measure vascular response of deep tissues. The new instrument and concept may also be applicable to human studies especially in infants and neonates permitting noninvasive monitoring of cerebral hemodynamics and oxygen (see [4] and [2] for examples of NIR spectroscopy).

Correlation properties of multiple scattered light: implication to coherent diagnostics of burned skin

Modeling of skin burns has been performed in this study. Autocorrelation functions of intensity fluctuations of scattered light were measured for two-layered turbid media. The first layer served as a model for motionless scatterers (optically inhomogeneous gel film) whereas the second one simulated dynamic light scattering (Brownian motion of intralipid particles in aqueous suspension). This medium was used as a model of skin burns. A theory related quasi-elastic light scattering measurements to cutaneous blood flow was used. The dependencies of statistical properties of Doppler signal on the properties of burned skin as well as on the velocity of cutaneous blood flow have been investigated. Theoretical predictions have been verified by measurements both of dynamic and stationary light scattering in model media.

Refractive index matching of tissue components as a new technology for correlation and diffusing-photon spectroscopy and imaging

The refractive index matching of components of highly scattering tissue has a strong influence on its transmittance and reflectance what can be considered as a new tool for imaging within relatively thick tissues. We present experimental data on various solutions, gels and oils influence on optical properties of in vivo human eye and in vivo human skin. The dynamics of tissue optical properties depending on matter diffusion rate within tissue is studied. The possible application of refractive index matching effect for diffusing-photon imaging is discussed.

Time-dependent speckle contrast measurements for blood microcirculation monitoring

Features of the speckle patterns formation due to the laser light propagation in multiple scattering systems which influence on the accuracy of measurement of the scattering system dynamic parameters by means of statistical analysis of the time-averaged spatial speckle intensity fluctuations have been studied experimentally. Two different experimental techniques have been used: photon correlation spectroscopy and contrast analysis for time-averaged speckle patterns similar to LASCA method. Results of in-vivo experiments as well as experiments with model scattering media (water solution of Intralipid) are presented. Recommendations about the choose of appropriate data processing algorithms as well as about calibration technique for time-averaged speckle technique are discussed.

Near-infrared blood flow and oxygenation measurement in deep tissues

Summary form only given. By combining the diffuse photon-density wave method and diffuse correlation method into one probe, we can measure local blood flow and hemoglobin oxygenation changes in an organ or tumor as functions of treatment or stimulation.

Arm cuff experiment: correlation between f/d and cw light scattering

Concurrently the measurement of autocorrelation function of the light backscattering from the forearm and phase and amplitude changes of the phase modulated photon diffusion wave has been acquired in the arm cuff experiment. Dynamical performances with the varying blood pressure are presented and analyzed.

Dynamic light scattering in turbid media: deep tissue flow imaging

By extending the technique of dynamic light scattering from single light scattering to high order multiple scattering, we are able to measure the dynamics of a turbid medium averaged over some deep scattering volume. One biological application is to measure blood flow in deep tissues like the brain. Furthermore, by moving the light source and detector positions to cover an extended area, we are able to reconstruct images of the dynamics.