Temperature measurement error reduction for MRI-guided HIFU treatment

Abstract

Purpose: We present a method to remove the temperature measurement errors due to the movement of the ultrasound applicator during MRI-guided high-intensity focused ultrasound (MRgHIFU) treatment.

Methods: MR thermometry, based on proton resonance frequency (PRF) shift, can provide high accuracy and temporal resolution of MR temperature imaging for tumour treatment by MRgHIFU. However, the challenge is that the movement of the ultrasound applicator causes temperature measurement errors due to the magnetic susceptibility of the applicator. In a clinical environment the applicator has to be moved to cover the whole tumour volume, even in the case of a phased array ultrasound applicator. With conventional PRF shift-based phase mapping method, a reference image must be repetitively acquired as the ultrasound applicator is repositioned and tissue cooling down time must be inserted before a new reference scan. Therefore, the treatment workflow becomes complex and time consuming. In this paper we propose a method to reduce temperature measurement error by compensating the ultrasound applicator susceptibility through a pre-measured or calculated magnetic field distribution of the applicator.

Results: The large temperature measurement error shown around the ultrasound focal region can be significantly reduced by compensating the ultrasound applicator-induced delta magnetic field. Accurate temperature maps can be obtained when the ultrasound applicator is repositioned without repetitively acquiring new reference images.

Conclusions: The reference image can be repetitively used for the temperature imaging when the ultrasound applicator is repositioned. Therefore, the treatment workflow is simplified resulting in a reduction in total treatment time.

• MR thermometry
• focused ultrasound
• susceptibility
• HIFU