The goal of this R21 EBRG project is to develop new optical methods to map high intensity focused ultrasound (HIFU) pressure ?elds. The methods would enable simple, fast, and low-cost in situ HIFU beam measurements, which are needed for quality assurance and safety in the clinic, and to accelerate the pace of research and development of new HIFU applications and technologies. An ideal beam mapping instrument would be low cost, capable of rapidly measuring relevant acoustic parameters of clinical HIFU systems in situ between treatments, and usable by nontechnical experts. Needle hydrophones are currently the gold standard tool for mapping HIFU pressure ?elds, but are poorly suited to the measurement task since they sample only one spatial location at a time, and most can only measure sub- therapeutic pressures. They can be translated in a water tank by a motion stage to produce spatially-resolved pressure maps, but this is a slow and cumbersome measurement that can take several hours to complete. The techniques proposed in this application could meet this clinical need and also provide a fast, ?exible, and spatially- resolved beam mapping instrument that would be invaluable for HIFU research since it would enable rapid val- idation and experimental designs that are currently infeasible, such as mapping pressure ?elds across multiple experimental variables. Standard optical schlieren imaging has a long history in 2D and 3D ultrasound pressure ?eld mapping but has conventionally been applied using sophisticated and expensive high-speed optical setups with limited ?eld-of-view, limited portability and high cost. The methods and devices proposed in this project are instead based on a newer schlieren technique called background oriented schlieren (BOS) imaging, and in their simplest form can be implemented using just a water tank, a tablet PC and a webcam. In essence, BOS trades the sophisticated optical setup for more sophisticated computation, which is a much cheaper commodity. The central innovation in this project is to use BOS imaging to quantitatively map continuous-wave HIFU pressure ?elds in 2D and 3D. The ?rst Aim is to develop portable hardware for BOS imaging and tomography, that can be used with a wide variety of HIFU systems in situ.
The second Aim i s to develop the mathematical theory underlying the BOS image formation process for HIFU beam mapping, which is different from conventional BOS imaging since the underlying refractive index ?eld is not static.
The third Aim i s to develop acquisition and reconstruction methods that produce quantitative spatially-resolved pressure ?eld maps, and validate those maps against simulations and optical hydrophone measurements of state-of-the-art HIFU systems. By developing and disseminating BOS hardware, theory, and methods for quantitative 2D and 3D HIFU beam mapping, this development project will lead to fast, simple and robust devices that can be widely adopted and even shipped with each clinical HIFU system for regular quality assurance and exposimetry measurements.
The ability to rapidly map high intensity focused ultrasound beams is critical to dosimetry, quality assurance, and safety in the clinic, and would accelerate the pace of research and development of new applications and technologies. This development project will address this unmet need by producing and disseminating new optical beam mapping methods and instruments that are fast, quantitative, portable, and inexpensive.
