Quantitative T-1 rho magnetic resonance imaging of RIF-1 tumors in vivo: Detection of early response to cyclophosphamide therapy

This study compares two potential magnetic resonance imaging (MRI) indices for noninvasive early detection of tumor response to chemotherapy: the spin -lattice relaxation in the rotating frame (T-1P) and the transverse relaxat ion time (T-2). Measurements of these relaxation parameters were performed on a s.c. murine radiation-induced fibrosarcoma (RIF-1) model before and af ter cyclophosphamide treatment. The number of pixels exhibiting T-1P values longer than controls in viable regions of the tumor increased significantl y as early as 18 h after drug administration and remained elevated up to 36 h after treatment (P < 0.005). Although a trend of increasing T(2)s relati ve to controls was noted in viable regions of the tumor 36 h after treatmen t, the changes were not statistically significant. Histological examination indicated a decrease in mitotic index that paralleled the changes in TIP. We conclude that TIP measurements may be useful for noninvasive monitoring of early response of tumors to chemotherapy.