4T1 tumors with central necrosis exhibit significant T1-enhancement.

<p>Difference between pre- and post-contrast R1 relaxation rates (ΔR1 relaxation rates) of 4T1 tumors, PymT tumors as well as skeletal muscle. Data are displayed as mean data of six tumors in each group and standard deviations. Insert shows ΔR1 data of 4T1 tumor core versus periphery at 24 hours. Tumor ΔR1 data at 60 minutes and 24 hours post contrast are significantly different from baseline values (p<0.05).