Rapid rotational magneto-acousto-electrical tomography with filtered back-projection algorithm based on plane waves

Abstract

Magneto-acousto-electrical tomography (MAET) is designed to produce conductivity images with high spatial resolution for a conducting object. In a previous study, for an irregular conductor, transverse scanning and rotational methods with a focus transducer were combined to collect complete electrical information. This kind of method, however, is time-consuming because of the transverse scanning procedure. In this study, we proposed a novel imaging method based on plane ultrasound waves and a new aspect of projection in rotational MAET. In the proposed method, we achieved the projection in each rotation angle by using plane waves rather than mechanical scanning of the focus waves along the transverse direction. Thus, the imaging time was significantly saved. To verify the proposed method, we derived a measurement formula containing a lateral integration, which built the relationship between the measurement formula and the projection under each rotation angle. Next, we constructed two different numerical models to compute magneto-acousto-electrical signals by using a finite element method and reconstructed the corresponding conductivity parameter images based on a filtered back-projection algorithm. Then, simulated signals under different signal-to-ratios (6, 20, 40, and 60 dB) were generated to test the performance of the proposed algorithm. To improve the image quality, we further analysed the influence of the filters and the frequency scaling factors embedded in the filtered back-projection algorithm. Moreover, we computed the L2 norm of the error in case of different frequency scaling factors and measurement noises. Finally, we conducted a phantom experiment with a 64-element linear phased array transducer (center frequency of 2.7 MHz) and reconstructed the conductivity parameter images of the circular phantom with an elliptical hole. The experimental results demonstrated the feasibility and time-efficiency of the proposed rapid rotational MAET.

General principle and optimization of magneto‐acousto‐electrical tomography based on image distortion evaluation

“…In the literatures published by Sun et al 32,36 . the conductivity boundaries of MAET images were reconstructed with improved SNR and spatial resolution through the rotary‐scanning measurement around two elliptical models within 180° using a focused transducer.…”

“…Whereas, the practical implementation is still limited by the reduced imaging stability and measurement speed introduced by too many rotations. Moreover, the selected rotation angle step in previous studies 32,36 based on vast numerical simulations is also lack of physical basis. Thus, the measurement efficiency and the imaging quality of MAET can be improved greatly by optimizing the rotation angle step based on the distortion evaluation of B-mode MAE imaging.…”

“…By rotating the object in one circle, N B-mode MAE images can be reconstructed. Finally, by further introducing the rotation matrix to B-mode images with the linear interpolation algorithm, 36 the MAET image can be calculated by…”

Weighted Radon transforms of vector fields, with applications to magnetoacoustoelectric tomography

“…Indeed, if electrodes and the object are held in a fixed position, there are very few directions from which the transducer can send sound waves into the object without illuminating the electrodes, which generates strong spurious elecrtic pulses that overwhelm the usefull signal. Thus, researchers are investigating a different approach to data acquisition [25,26], which assumes that object is rotated while the electrodes are kept stationary. Equivalently, one can keep the object fixed, and rotate the electrodes and transducer(s).…”

A Review on the Coupled Method of Using the Magnetic and Acoustic Fields for Biological Tissue Imaging

“…Furthermore, this team analyzed the effect of the number of excitation pulses and the ultrasonic excitation frequency on the longitudinal and vertical resolution of the MAET system and obtained images of the conductivity parameters of isolated pork under optimal experimental conditions [52] . To reconstruct conductivity images of irregular objects, this team proposed an approach with multi-angle scanning, and the relationship between the reconstruction error and number of angles was also presented, demonstrating that an optimal reconstruction can be achieved at 12 angles [53][54] . The team also conducted the Baker encoding excitation system, and achieved isolated tissue imaging [55] .…”