High intensity focused ultrasound with large aperture transducers: A MRI based focal point correction for tissue heterogeneity

Charles Mougenot, Matti Tillander, Julius Koskela, Max O. Köhler, Chrit Moonen, Mario Ries

Research output: Contribution to journalArticlepeer-review

29 Citations (Scopus)

Abstract

Purpose: The risk of undesired tissue damage to thoracic cage, heart, and lung during MR guided HIFU ablations of breast cancer can be greatly reduced if a phased array transducer design with a lateral beam direction is used in combination with a large aperture. The disadvantage is an increased sensitivity to focus aberrations due to tissue heterogeneity. Here, the authors propose to restore the focal coherence by using a matched aperture phase correction, which is based on a noninvasively obtained tissue model. Methods: The method combines high resolution MRI with ultrasound wave measurements of different tissue types to determine a phase correction, which compensates focal point aberrations caused by tissue heterogeneity. 3D segmentation of tissue is used to quantify the relative proportion of each tissue type along a line running from the center of each element of the phased array to the target focal point. Results: For tissue types with a celerity difference of 3, the proposed method allows to quantify the phase aberration with an accuracy of 6° ± 20° and a correlation factor R 0.95. Using the refocusing method for a complex heterogeneous phantom resulted in 95 of the maximal pressure, whereas only 70 of the maximal pressure is obtained in absence of any phase correction. Conclusions: Since the proposed refocusing algorithm is compatible with a standard interventional preplanning and requires only a minimal amount of processing, it presents a promising approach to compensate for aberration in heterogeneous tissues such as the human breast.

Original languageEnglish
Pages (from-to)1936-1945
Number of pages10
JournalMedical Physics
Volume39
Issue number4
DOIs
Publication statusPublished - Apr 2012
Externally publishedYes

Keywords

  • high intensity focused ultrasound
  • MRI
  • refocusing
  • tissue heterogeneity

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