T1 ρ mapping for the evaluation of high intensity focused ultrasound tumor treatment.

Abstract

This study was aimed to assess the effects of High Intensity Focused Ultrasound (HIFU) thermal ablation on tumor T1ρ . In vivo T1ρ measurements of murine tumors at various spin-lock amplitudes (B1 = 0-2000 Hz) were performed before (n = 13), directly after (n = 13) and 3 days (n = 7) after HIFU treatment. T2 maps were obtained from the measurements at B1 = 0 Hz. Average tumor T1ρ distributions at the different experimental time points showed a shift toward lower T1ρ values after HIFU for all spin-lock amplitudes, which became larger with increasing spin-lock amplitude at 3 days after treatment. Statistical analysis confirmed a significant effect of spin-lock amplitude on the average change in T1ρ (ΔT1ρ ) as compared to baseline at 3 days after HIFU. At 3 days after treatment, ΔT1ρ values at B1 above 100 Hz were significantly lower (more negative) than at B1 = 0 Hz (T2 ). Significant changes in tumor T1ρ were observed after HIFU treatment. These T1ρ changes were distinctly more pronounced than HIFU-induced changes in T2 . The results indicate that T1ρ imaging is sensitive to HIFU-induced tissue changes and may thus be a suitable MR method for the evaluation of HIFU treatment. Magn Reson Med 73:1593-1601, 2015. © 2014 Wiley Periodicals, Inc.