Imaging hypoxia and blood flow in normal tissues.

Abstract

Oxygen deficiencies in normal tissue are assumed to be rare. This assumption is based upon detailed and time-tested mathematical and physiological models (for reviews see Oxygen Transport to Tissue Series). The input parameters to such models require detailed estimates of various circulatory and tissue properties: blood flow, distribution, oxygenation and pH; tissue cellularity, respiration rate and oxygen diffusion constant. Many of these parameters are only available in a global sense; thus there have been many experimental approaches to the assessment of tissue oxygenation. These include measurements by invasive devices such as microelectrodes. More recently, non-invasive techniques have been introduced, such as phosphorescence decay of blood-born dyes activated by short light pulses (Rumsey et al., 1988; Lo et al., 1996) and EPR of carbon particles (Vahidi et al., 1994). The former technique, introduced by Dr David Wilson, has the dual advantages of accurate temporal and spatial resolution (see reports this conference). One indirect method of tissue oxygen assessment utilizes the known oxygen-dependence of cellular radiation response - cells with oxygen tensions below about 20mm of Hg become progressively more radiation resistant. By measuring the radiation response of stem cells in the skin, investigators have concluded that some degree of hypoxia exists in this tissue (Douglas et al, 1975).