Abstract
Focused ultrasound (FUS) therapies induce therapeutic effects in localized tissues using either temperature elevations or mechanical stresses caused by an ultrasound wave. During an FUS therapy, it is crucial to continuously monitor the position of the FUS beam in order to correct for tissue motion and keep the focus within the target region. Toward the goal of achieving real-time monitoring for FUS therapies, we have developed a method for the real-time visualization of an FUS beam using ultrasonic backscatter. The intensity field of an FUS beam was reconstructed using backscatter from an FUS pulse received by an imaging array and then overlaid onto a B-mode image captured using the same imaging array. The FUS beam visualization allows one to monitor the position and extent of the FUS beam in the context of the surrounding medium. Variations in the scattering properties of the medium were corrected in the FUS beam reconstruction by normalizing based on the echogenicity of the coaligned B-mode image. On average, normalizing by echogenicity reduced the mean square error between FUS beam reconstructions in nonhomogeneous regions of a phantom and baseline homogeneous regions by 21.61. FUS beam visualizations were achieved, using a single diagnostic imaging array as both an FUS source and an imaging probe, in a tissue-mimicking phantom and a rat tumor in vivo with a frame rate of 25–30 frames/s.
Highlights
F OCUSED ultrasound (FUS) is a therapeutic modality with a broad range of clinical applications
While our method was not well-suited for quantitative measurements of FUS beam properties, it did provide real-time qualitative information on the beam position in the context of anatomical information provided by the registered B-mode image
We have presented a technique for the real-time visualization of an FUS beam using ultrasonic backscatter
Summary
F OCUSED ultrasound (FUS) is a therapeutic modality with a broad range of clinical applications. Notable examples of FUS therapy include the treatment of uterine fibroids [1], bone metastases [2], essential tremor [3], and prostate cancer [4]. There has been a multitude of clinical and preclinical studies exploring applications of FUS to the treatment of other diseases [5]–[9]. FUS therapies operate by noninvasively inducing biological effects in localized regions of tissue using a tightly focused ultrasound beam. Therapeutic effects are achieved through thermal or mechanical mechanisms. Thermal-based FUS therapies use ultrasonic energy to produce temperature elevations in well-defined regions, typically for the surgical ablation of Manuscript received July 15, 2020; accepted October 29, 2020.
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