Enhanced Thermoacoustic Imaging System with Parallel Ultrasonic Velocity Measurement for Distinguishing Types of Microwave-Absorbing Anomalies

Microwave-absorbing suspicious objects (MASOs) found using microwave-induced thermoacoustic imaging (MTI) can be divided into two types—endogenous (such as tumors or hematoceles) and exogenous (such as calculi or foreign bodies). These have different microwave absorption or ultrasonic velocity than normal human tissue, so MTI is efficient in detecting these anomalies. However, the existing MTI techniques can only reflect morphological information, making it difficult to distinguish the type of each anomaly. In this paper, a newly enhanced MTI system composed of a multiple-element ring transducer and a parallel data acquisition system (DAS) is presented. By using ultrasonic velocity and microwave absorption measurements, where the ultrasonic velocity is mainly used as an additional parameter to reflect mechanical characteristics, the type of the detected anomaly can be identified. In our experiments, the MASO can be located through the absorption difference detected by MTI. Due to the use of multiple-element transducers and a parallel DAS, the raw data can be acquired within about 20 ms for a two-dimensional image. Additionally, the ultrasonic velocity of the MASO can be calculated from the time sequence diagram of ultrasound propagation with a maximum time error of 0.084 μs. Apart from distinguishing the type of the anomaly, the proposed ultrasonic velocity-assisted microwave-induced thermoacoustic imaging (US-MTI) system has other advantages, such as being noninvasive, and allowing rapid imaging and a large field of view, which make US-MTI a suitable modality for regular screening.