Non-invasive approaches to tissue bioenergetics.

It is clear that continuous light affords a very limited window of opportunity for quantitative spectrophotometry of brain tissue. However, the number of qualitative applications which are available exemplify how this extremely simple technique can be applied to important medical problems. The development of devices which can measure directly the oxygen saturation of the brain is more complicated yet affords the essential data necessary for clinical decisions on the degree of hypoxia which may be critical for neuronal survival. We can predict that such devices will be available for reliable operation shortly and will complement the existing continuous-light devices. The information from time- and frequency-domain equipment can be employed in two ways, either directly to give saturation of haemoglobin by the dual-wavelength algorithms or to provide path-length information continuously to the continuous-light devices, as many of these are commercially available and afford realistically only trend information. Thus, quantitative brain oximetry can be obtained from continuous light devices with the input of pathlength information from time- and frequency-domain systems.