Proton resonance frequency shift‐weighted imaging for monitoring MR‐guided high‐intensity focused ultrasound transmissions

Abstract

Purpose: To combine temperature-related information of phase images and magnitude images acquired from an MR spoiled gradient echo sequence using a postprocessing method referred to as PRF-shift-weighted imaging (PRFSWI). Materials and Methods:Phase images are capable of detecting shifts in proton resonance frequency (PRF) caused by local changes in temperature. Magnitude images provide anatomical information for treatment planning and positioning as well as temperature-related contrast. We used PRFSWI to produce a phase-mask and performed multiplication on the magnitude image to increase temperature-related contrast.Results: Through MRI-guided focused ultrasound (MRIg-FUS) experiments (both ex vivo and in vivo), we determined that PRFSWI is capable of enhancing the contrast of a heated area even in the initial stages of transmitting high-intensity focused ultrasound energy. Conclusion:The PRFSWI images are sensitive to changes in temperature and display the heated spot directly in the magnitude images. Although the images do not provide quantitative data related to temperature, this method could be used as a complement to the phase temperature mapping method in the real-time monitoring of MRIgFUS experiments.

Magnetic resonance image-guided versus ultrasound-guided high-intensity focused ultrasound in the treatment of breast cancer

“…Because MRI guidance is sensitive to temperature, the focal spot can be identified with the MR thermometry technique[13],[14]. Thus, the operator can quickly determine the precision of the ablation in 3D space and obtain accurate information about tumor borders and the organs at risk, greatly improving the accuracy of ablation and avoiding damage to critical normal structures.…”

“…During the procedure, MRI can accurately monitor energy deposition. Thermometry based primarily on PRFS[13],[14] is a reliable method for the quantification of temperature changes in vivo , which can provide active feedback on the thermal exposure in lesions. Chen et al [13].…”

“…Thermometry based primarily on PRFS[13],[14] is a reliable method for the quantification of temperature changes in vivo , which can provide active feedback on the thermal exposure in lesions. Chen et al [13]. concluded that PRFS-weighted imaging was sensitive to temperature changes and could display the focal spot directly in the magnitude images.…”