Biomedical microwave-induced thermoacoustic imaging

Abstract

Microwave-induced thermoacoustic imaging (MTAI) has emerged as a potential biomedical imaging modality with over 20-year growth. MTAI typically employs pulsed microwave as the pumping source, and detects the microwave-induced ultrasound wave via acoustic transducers. Therefore, it features high acoustic resolution, rich electromagnetic contrast, and large imaging depth. Benefiting from these unique advantages, MTAI has been extensively applied to various fields including pathology, biology, material and medicine. Till now, MTAI has been deployed for a wide range of biomedical applications, including cancer diagnosis, joint evaluation, brain investigation and endoscopy. This paper provides a comprehensive review on (1) essential physics (endogenous/exogenous contrast mechanisms, penetration depth and resolution), (2) hardware configurations and software implementations (excitation source, antenna, ultrasound detector and image recovery algorithm), (3) animal studies and clinical applications, and (4) future directions.

Microwave-induced thermoacoustic imaging for biomedical applications

“…In actuality, various systematic factors that affect PSF can degrade spatial resolution. Among these systematic factors, electromagnetic pulse width and the spectra response of the ultrasonic transducer are two primary deciding factors for resolution, other factors such as the aperture of a UST and sampling frequency (refer to the Nyquist criterion) also affects resolution [94]. Due to the insufficiently short pulse width of the microwave source, the limiting resolution of TA imaging is limited by thermal and stress confinement.…”

Quantitative Reconstruction of Dielectric Properties Based on Deep-Learning-Enabled Microwave-Induced Thermoacoustic Tomography

“…where S( r , t) = σ ( r )| E( r , t)| 2 /2ρ( r ) = A( r )I (t) represents the specific absorption rate (SAR) [34], U 0 is the spatial region, in which SAR or A( r ) is nonzero, r 0 is an arbitrary spatial location in U 0 , β (K −1 ) denotes the thermal expansion coefficient, ρ (kg • m −3 ) denotes the mass density, C p (J • K −1 • kg −1 ) denotes the specific heat capacity, c (m • s −1 ) denotes the speed of sound, and σ (S • m −1 ) denotes the conductivity.…”

“…MITAT essentially leverages the dielectric contrast in a biological sample and recovers an image, referred to as thermoacoustic (TA) image, of the sample's microwave power absorption distribution [32], [33]. MITAT can also be applied to quantitatively reconstruct permittivity and conductivity distributions in a sample [2], [3], [4], which are directly related to the power absorption distribution [34]. However, the quality and accuracy of the reconstructed dielectric property still need to be improved, especially for inhomogeneous biological samples [35].…”

RPCA-based thermoacoustic imaging for microwave ablation monitoring

“…Indeed, the principle of TAI is similar to PA, with the key difference being the excitation source: TAI uses microwaves and PA uses light. By combining the high contrast of microwave imaging with the high resolution of the US, TAI provides a unique advantage [13] , [14] .…”