Yapa A. B. D. Wickramasinghe

Fast algorithm to determine optical properties of a turbid medium from time-resolved measurements.

After analytical expressions for the time-resolved reflectance are introduced from the diffusion approximation under the three most commonly used boundary conditions, a novel algorithm is demonstrated for determining the reduced scattering and the absorption coefficients from time-resolved reflectance (or backscatter) measurements at two positions on the surface of biotissue. The algorithm is straightforward and fast and involves only some simple mathematical operations, avoiding complicated iterative nonlinear fitting to the time-resolved curve. The derived reduced scattering coefficient is not affected by whatever boundary condition is applied. The algorithm was verified with time-resolved data from the Monte Carlo model. Both a semi-infinite medium and a turbid slab medium were tested. In contrast to the nonlinear fitting method, this algorithm allows both the scattering and the absorption coefficients to be determined to a high accuracy.

Near infrared spectroscopy: Blood and tissue oxygenation in renal ischemia-reperfusion injury in rats

Near infrared spectroscopy was used to monitor blood (HbO2, Hb, and Hbtot) and tissue oxygenation (oxidized cyt aa3) of both left and right kidneys of ratsin vivo simultaneously, during either 45 or 80 minutes of left renal ischemia followed by 4.5 hours of reperfusion. Ischemia significantly reduced HbO2 (p< 0.0001) and increased Hb (p<0.05) concentration change in the left kidney compared with the right kidney (control). Reperfusion with oxygenated blood reached control levels after 1 hour. The rate of change in HbO2 (p<0.05) and Hbtot (p<0.05) concentration during reperfusion was dependent upon the duration of ischemia, being slower after the longer ischemic period of 80 minutes. The concentration change of oxidized cyt aa3 of the 80-minute ischemic group slowly increased compared with the stable redox state of the 45-minute ischemic group, during the latter stages of reperfusion (p<0.05). Near infrared spectroscopy is a promising new development that will enable the effects of interventional treatment upon ischemia and reperfusion injury to be studied.

Negative extrathoracic pressure ventilation — evaluation of the neck seal

The effect of the neck seal used in the application of negative extra-thoracic pressure ventilation was studied using near infrared spectroscopy. Changes in cerebral blood volume (CBV) were monitored during discontinuation of negative pressure and during removal of the neck seal. CBV increased by 0.17 ml 100 ml brain-1 (95% CI +0.0875 to +0.481) when negative pressure was discontinued. Removal of the neck seal had no significant effect on CBV. It is concluded that the neck seal does not cause significant jugular venous occlusion.

Analysis techniques for pulsatile components of cardiac near infra-red absorbance measurements

Introduction The ultimate aim of this project is to apply the proven technique of near infra-red spectroscopy (nirs) [1,2] to monitor myocardial oxygenation and metabolism. The aim of the initial work presented here was to identify a significant pulsatile component in near infra-red absorbance measurements. Analysis of pulsatile components is considered to offer a practicable method of isolating the myocardial readings from those due to surrounding tissue: the chest wall, ribs, blood in the heart chambers and vessels, etc.

Development Of Algorithms For Noninvasive, Neonatal Cerebral Monitoring Using Near Infra-red Spectroscopy

Absorption spectroscopy is an established technique to determine the concentration of a substance in a solution, and has now been extended to the determination of change in the concentration of oxygenated and deoxygenated haemoglobin and also that of the terminal member of the respiratory chain - cytochrome aa3, noninvasively in the neonatal head. The quantitation of these parameters, once found difficult, has now been achieved.