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High intensity focused ultrasound with large aperture transducers: A MRI based focal point correction for tissue heterogeneity
Author(s) -
Mougenot Charles,
Tillander Matti,
Koskela Julius,
Köhler Max O.,
Moonen Chrit,
Ries Mario
Publication year - 2012
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3693051
Subject(s) - imaging phantom , aperture (computer memory) , transducer , focal point , phased array , ultrasound , biomedical engineering , optics , cardinal point , computer science , medicine , physics , acoustics , telecommunications , antenna (radio)
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 R² = 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.