Research on the method of improving magnetoacoustic tomography quality based on liquid metal

Abstract

Background: Magnetoacoustic tomography with magnetic induction (MAT-MI) is a promising noninvasive, radiation-free imaging technique capable of millimeter-level spatial resolution for mapping tissue conductivity. However, its application to luminal tissues (e.g., digestive tract, vasculature) is significantly hindered by low image quality due to acoustic wave attenuation and inherent tissue properties.

Purpose: This study aimed to overcome the image quality limitation in MAT-MI imaging of luminal structures by utilizing liquid metal (LM) as a novel conductive contrast agent and implementing M-sequence coded excitation to enhance signal strength and acquisition efficiency.

Methods: The LM contrast agent used was a biocompatible Ga₆₇In_20.5Sn_12.5 alloy (σ = 3.1×10⁶ S/m). MAT-MI experiments were conducted on gel phantoms containing LM in various shapes and simulated luminal structures (PVC tubes, ex vivo mouse intestines), ex vivo mouse stomach tissues infused with LM or PBS (control), and in vivo mouse stomachs. The MAT-MI system employed 0.34 T static magnetic field, a pulsed excitation coil (1 MHz center frequency), and an ultrasound transducer. We applied M-sequence coded excitation (up to 31-bit) and processed the signals using pulse compression followed by filtered back-projection reconstruction. Safety was assessed via long-term biocompatibility studies, blood elemental analysis, and histological examination (H&E staining) of gastrointestinal tissues.

Results: Integrating LM into the imaging target greatly increased the MAT-MI signal intensity. In vivo imaging of mouse stomachs demonstrated an approximate 28 dB increase in image quality after LM infusion compared to pre-infusion imaging. LM enabled clear visualization within fine luminal structures (down to 0.5 mm inner diameter) in phantoms and ex vivo tissues. M-sequence coding further improved image clarity and reduced total imaging time by approximately 84% relative to single-pulse excitation (from 6360 s to 1020 s for comparable image quality). High-resolution imaging (approximately 2 mm spatial resolution) of LM distribution was achieved. The LM was safely excreted, with no significant toxicity observed in blood analysis or histology over 180 days.

Conclusions: LM proved to be an effective and safe contrast agent for MAT-MI, significantly enhancing image quality and enabling high-quality imaging of luminal tissues, including the first successful in vivo visualization of the stomach in a live animal model. Combined with M-sequence coded excitation, this approach overcomes key limitations of conventional MAT-MI and could broaden its diagnostic utility in cardiovascular and gastrointestinal imaging.

Keywords: M‐sequence; contrast agent; liquid metal; magnetoacoustic tomography.