CLINICALSCIENCES

technique for imaging the distribution of gases labeled with oxygen-I 5 (Tip 122 sec). Jones et al. (3), and later in more detail Subramanyam et al. (4), suggested a theoretical treatment, applicable to the brain, for ob taming regional oxygen extraction from data obtained by this technique. Their treatment did not include oxygen utilization capability. Another study used the steady state technique to monitor changes in tumor and sur rounding tissues caused by radiation therapy (5,6). This study gave empirical evidence for an oxygen-utilization interpretation of the observed changes based upon the suggestion that tissues exchanging water slowly may not require correction for either water clearance or recir culation