Model-based Reconstruction for Multi-Frequency Collimated Beam Ultrasound Systems

TL;DR

This paper introduces a novel multi-frequency model-based iterative reconstruction algorithm for collimated beam ultrasound systems, significantly improving imaging quality in complex multi-layered structures like geothermal wells.

Contribution

The paper develops a physics-based joint multi-frequency reconstruction method tailored for collimated ultrasound systems, addressing limitations of existing algorithms like SAFT.

Findings

Multi-frequency UMBIR outperforms SAFT and single-frequency methods in reconstruction quality.

The algorithm effectively models wave propagation and noise in heterogeneous layered media.

Experimental results validate the improved imaging performance of the proposed method.

Abstract

Collimated beam ultrasound systems are a technology for imaging inside multi-layered structures such as geothermal wells. These systems work by using a collimated narrow-band ultrasound transmitter that can penetrate through multiple layers of heterogeneous material. A series of measurements can then be made at multiple transmit frequencies. However, commonly used reconstruction algorithms such as Synthetic Aperture Focusing Technique (SAFT) tend to produce poor quality reconstructions for these systems both because they do not model collimated beam systems and they do not jointly reconstruct the multiple frequencies. In this paper, we propose a multi-frequency ultrasound model-based iterative reconstruction (UMBIR) algorithm designed for multi-frequency collimated beam ultrasound systems. The combined system targets reflective imaging of heterogeneous, multi-layered structures. For each transmitted frequency band, we introduce a physics-based forward model to accurately account for the propagation of the collimated narrow-band ultrasonic beam through the multi-layered media. We then show how the joint multi-frequency UMBIR reconstruction can be computed by modeling the direct arrival signals, detector noise, and incorporating a spatially varying image prior. Results using both simulated and experimental data indicate that multi-frequency UMBIR reconstruction yields much higher reconstruction quality than either single frequency UMBIR or SAFT.