Noninvasive in vivo imaging of brain specific absorption rate using thermoacoustic tomography

Abstract

Electromagnetic field-based diagnostic and therapeutic techniques are gradually becoming widespread in brain disease applications, but their associated safety assessment techniques still have limitations. Specific absorption rate (SAR), as a key parameter to measure the degree of tissue absorption of electromagnetic energy, and its accurate measurement is of great significance to guarantee the safety of electromagnetic diagnostic techniques. However, current dosimetry assessment system and magnetic resonance imaging (MRI) methods, which reflect SAR by measuring temperature rise, both face challenges in realizing noninvasive, accurate, and in vivo SAR mapping. In this work, a three-dimensional (3D) thermoacoustic imaging (3D-TAT) technique is proposed to perform noninvasive SAR measurements of deep tissues with hundred-micron accuracy by using passive ultrasound as an information carrier of the temperature rise of the tissues after absorbing the electromagnetic wave energy. The accuracy of SAR measurements with 3D-TAT is validated in a water pipe model, and its potential application in complex biological tissues is demonstrated in a mouse brain model. 3D-TAT provides a technological path for safety monitoring of electromagnetic techniques such as high-field strength magnetic resonance imaging (MRI) and microwave thermotherapy, which has a wide range of clinical and scientific applications.