# Laser Deflection Acoustic Field Quantification: A Non-Invasive Measurement Technique for Focused Ultrasound Field Characterization

## TL;DR

This paper introduces a non-invasive method called LDAQ to accurately measure high-pressure focused ultrasound fields, which is crucial for medical treatments like tumor ablation.

## Contribution

The novel contribution is the development of LDAQ, a non-invasive technique using laser deflection for high-precision acoustic field quantification.

## Key findings

- LDAQ results showed high consistency with hydrophone measurements and simulations in the focal zone.
- The RMSE between LDAQ and simulation was 0.1102, and between LDAQ and hydrophone was 0.1422.
- LDAQ enables non-invasive quantification of megapascal-level focused acoustic fields.

## Abstract

Focused ultrasound (FU) technology is extensively employed in clinical applications such as tumor ablation, Parkinson’s disease treatment, and neuropathic pain management. The safety and efficacy of FU therapy critically depend on the accurate quantification of the acoustic field, particularly the high-pressure distribution in focal region. To address the limitations of existing acoustic measurement techniques—including invasiveness, inability to measure high sound pressure, and system complexity—this study proposes a non-invasive method termed Laser Deflection Acoustic Field Quantification (LDAQ), based on the laser deflection principle. An experimental system was constructed utilizing the acousto-optic deflection effect, which incorporates precision displacement control, rotational scanning, and synchronized triggering. Through tomographic scanning, laser deflection images of the acoustic field were acquired at multiple orientations. An inversion algorithm using Radon transforms was proposed to reconstruct the refractive index gradient distributions from the variations of light intensity and spot displacement. An adaptive weighted fusion strategy was then employed to map these optical signals to the sound pressure field. To validate the LDAQ technique, an acoustic field generated by an FU transducer operating at 0.84 MHz was measured. The reconstructed results were compared with both hydrophone measurements and numerical simulations. The findings demonstrated high consistency among all three results within the focal zone. Full-field analysis yielded a root mean square error (RMSE) of 0.1102 between LDAQ and simulation, and an RMSE of 0.1422 between LDAQ and hydrophone measurements. These results confirm that LDAQ enables non-invasive and high-precision quantification of megapascal-level focused acoustic fields, offering a reliable methodology for acoustic field characterization to support FU treatment optimization and device standardization.