T 1 ρ mapping for the evaluation of high intensity focused ultrasound tumor treatment

Purpose This study was aimed to assess the effects of High Intensity Focused Ultrasound (HIFU) thermal ablation on tumor T 1ρ . Methods In vivo T 1ρ measurements of murine tumors at various spin‐lock amplitudes ( B 1 = 0–2000 Hz) were performed before ( n = 13), directly after ( n = 13) and 3 days ( n = 7) after HIFU treatment. T 2 maps were obtained from the measurements at B 1 = 0 Hz. Results Average tumor T 1ρ distributions at the different experimental time points showed a shift toward lower T 1ρ 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 T 1ρ (ΔT 1ρ ) as compared to baseline at 3 days after HIFU. At 3 days after treatment, ΔT 1ρ values at B 1 above 100 Hz were significantly lower (more negative) than at B 1 = 0 Hz (T 2 ). Conclusion Significant changes in tumor T 1ρ were observed after HIFU treatment. These T 1ρ changes were distinctly more pronounced than HIFU‐induced changes in T 2 . The results indicate that T 1ρ 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.