A pre-treatment planning strategy for high-intensity focused ultrasound (HIFU) treatments

Abstract

Most operational protocols for HIFU procedures do not incorporate a pre-treatment planning stage comparable to the rigorous pre-treatment planning that is mandated for other modalities of radiation therapy. Ongoing studies investigating pre-treatment strategies that would improve the efficiency and effectiveness of HIFU treatments are complex in nature. Most are based on the incorporation of predictive phase-aberration corrections of propagation-path-specific phase changes. We have shown that the substantially simpler method of optimizing HIFU source placement in relation to layered tissue structures can have a significant effect on focal integrity, and that MRI scans and a wave-vector time-domain linear propagation model can potentially be used to plan for optimized source orientation.Five ex vivo bovine tissue specimens with heterogeneous tissue structures were each mounted in rigid frames with acoustic windows for HIFU transmission. A spherically-focused HIFU source (F 0 = 1.502 MHz, D = 100 mm, R c = 100 mm) was positioned to transmit though each specimen at pre-selected orientations, and the transmitted ultrasound pressure fields were scanned for a series of orientations, followed by a series of MRI scans. Ultrasound transmission simulations were performed and compared with experimental results.Analyses performed on the acoustic field scans to quantify the level of focal distortion [Distortion Index (DI) = 1-(the ratio between the acoustic energy within a focal zone and the total acoustic energy within the measured area] demonstrated that over the 5 specimens, at least an average of 7.3% (range 5.6% to 12.3%, SD = 2.8%) improvement in DI could be expected by source placement optimization. The accurate simulation of ultrasound propagation through heterogeneous tissue layers using MRI data was also achieved.

Patient‐Specific 3‐Dimensional Model for High‐Intensity Focused Ultrasound Treatment Through the Rib Cage

“…The model proposed in this study is not only a numeric model generated from patient data but also a physical prototyped model with the patient's anatomic structure and acoustic properties. Some challenges of HIFU therapy have been addressed by simulations using numeric models . Meanwhile, automated treatment‐planning software has been developed, as treatment planning has been considered as a time‐consuming task with great output variability .…”

“…Some challenges of HIFU therapy have been addressed by simulations using numeric models. 14,15,18,19 Meanwhile, automated treatment-planning software has been developed, as treatment planning has been considered as a timeconsuming task with great output variability. 37 However, experimental data are still necessary to validate and improve the parameters of the simulation.…”

“…Medical images have been used to generate 3‐dimensional (3D) numeric models for simulation in treatment planning, as treatment planning plays an important role in achieving a successful result of HIFU surgery. Numeric simulations with HIFU were performed to quantify the focal distortion, determine dosage parameters, reduce the overall treatment duration, and prevent damage to nontarget tissue for treatment planning . To reduce the deposition energy on ribs, medical images were applied to compute the deactivated elements of the transducer in HIFU focused through the rib cage .…”

“…Numeric simulations with HIFU were performed to quantify the focal distortion, determine dosage parameters, reduce the overall treatment duration, and prevent damage to nontarget tissue for treatment planning. [14][15][16] To reduce the deposition energy on ribs, medical images were applied to compute the deactivated elements of the transducer in HIFU focused through the rib cage. 10,11,17 Based on the relative position of the focus and the ribs, as identified from anatomic image data, elements that were covered by the shadow of the ribs were deactivated.…”

Portable Ultrasound Imaging of the Brain for Use in Forward Battlefield Areas

“…Utilizing ultrasound's superior ability to be customized, we will design a field whose wavefront is directed into a nearly-parallel beam only within the ROI using our previously-designed numerical projection technique, where the desired field is specified and then rapidly backward-propagated to the imaging transducer. [10], [11] In the present case this will include the effects of the skull bone [12]. Unlike algorithms that only focus ultrasound in a particular location [3], the method is devised to produce arbitrarily-shaped fields within the brain; in the present case a coherent wavefront within the ROI.…”