CHANGES IN T-2-ASTERISK-WEIGHTED IMAGES DURING HYPEROXIA DIFFERENTIATE TUMORS FROM NORMAL TISSUE

Experiments were performed to determine whether changes in T-2-weight ed MR images during and after hyperoxia differentiate tumors from norm al tissue. Mammary adenocarcinomas implanted in the right hind limbs o f rats were studied. Gradient echo images were obtained at 2 Tesla wit h an evolution time of 20 ms and a recycle time of 1 s. Breathing gas was either air or 100% O-2. Significant increases in image intensity w ere observed in tumor centers and rims during hyperoxia while much sma ller changes were detected in the surrounding muscle. The relaxation r ate (1/T-2) in tumors decreased during hyperoxia by an average of 2.5 +/- 1.0 s(-1), while in muscle the average change was an increase of 0.6 +/- 2.1 s(-1). The largest decreases in relaxation rate were detec ted in non-necrotic tumor regions with relatively low density of blood vessels. Immediately following hyperoxia significant decreases in int ensity were detected in tumors while much smaller decreases were detec ted in the surrounding muscle.