Assessment of acute thermal damage volumes in muscle using magnetization-prepared 3D T2 -weighted imaging following MRI-guided high-intensity focused ultrasound therapy

J Magn Reson Imaging. 2017 Aug;46(2):354-364. doi: 10.1002/jmri.25605. Epub 2017 Jan 9.

Abstract

Purpose: To evaluate magnetization-prepared 3D T2 -weighted magnetic resonance imaging (MRI) measurements of acute tissue changes produced during ablative MR high-intensity focused ultrasound (MR-HIFU) exposures.

Materials and methods: A clinical MR-HIFU system (3T) was used to generate thermal lesions (n = 24) in the skeletal muscles of three pigs. T1 -weighted, 2D T2 -weighted, and magnetization-prepared 3D T2 -weighted sequences were acquired before and after therapy to evaluate tissue changes following ablation. Tissues were harvested shortly after imaging, fixed in formalin, and gross-sectioned. Select lesions were processed into whole-mount sections. Lesion dimensions for each imaging sequence (length, width) and for gross sections (diameter of lesion core and rim) were assessed by three physicists. Contrast-to-background ratio between lesions and surrounding muscle was compared.

Results: Lesion dimensions on T1 and 2D T2 -weighted imaging sequences were well correlated (R2 ∼0.7). The contrast-to-background ratio between lesion and surrounding muscle was 7.4 ± 2.4 for the magnetization-prepared sequence versus 1.7 ± 0.5 for a conventional 2D T2 -weighted acquisition, and 7.0 ± 2.9 for a contrast-enhanced T1 -weighted sequence. Compared with diameter measured on gross pathology, all imaging sequences overestimated the lesion core by 22-33%, and underestimated the lesion rim by 6-13%.

Conclusion: After MR-HIFU exposures, measurements of the acute thermal damage patterns in muscle using a magnetization-prepared 3D T2 -weighted imaging sequence correlate with 2D T2 -weighted and contrast-enhanced T1 -weighted imaging, and all agree well with histology. The magnetization-prepared sequence offers positive tissue contrast and does not require IV contrast agents, and may provide a noninvasive imaging evaluation of the region of acute thermal injury at multiple times during HIFU procedures.

Level of evidence: 1 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:354-364.

Keywords: HIFU; MRI; high-intensity focused ultrasound; preclinical; thermal ablation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Catheterization
  • Contrast Media
  • Extracorporeal Shockwave Therapy*
  • Female
  • Hot Temperature
  • Image Processing, Computer-Assisted
  • Imaging, Three-Dimensional
  • Magnetic Resonance Imaging*
  • Muscle, Skeletal / diagnostic imaging*
  • Necrosis
  • Oxygen
  • Signal-To-Noise Ratio
  • Swine

Substances

  • Contrast Media
  • Oxygen