Abstract
We present a method that allows for hybrid microwave-excited thermoacoustic and ultrasound (HMTAU) imaging without an additional ultrasound transmitting circuitry. The same microwave pulse is used to simultaneously generate thermoacoustic (TA) signals from the sample by the thermoacoustic effect, and ultrasound (US) signals from the piezoelectric transducer by the inverse piezoelectric effect. The same transducer collects the US signals reflected from the sample as a result of the US pulse (pulse-echo) and the TA signals as a result of the sample absorbing microwaves. Experiments are conducted to show how the microwave pulse-width significantly impacts the excitation efficiency of ultrasonic waves, which can reduce the requirement for microwave power. We found that the mechanical response of the US transducer to this transient expansion shows a maximum if the pulse-width of the microwave is close to half of the center period of the US transducer. We also use phantom experiments to demonstrate the complementary contrast mechanisms of the two modalities. The results obtained indicate that our method offers the potential of a low-cost dual-modality technique for noninvasive biomedical imaging.
Highlights
Microwave-induced thermoacoustic tomography (TAT) is widely used in biomedical imaging research because of its non-invasive, high resolution and high penetration depth.1–9 While TAT alone has been used for various biomedical applications, its combination with US has been exploited naturally given that a single transducer can commonly be used as the receiver for TAT and the transmitter/receiver for ultrasound (US), in addition to using US information to reduce distortion in TAT.10–14 Using different contrast mechanisms, hybrid microwave-excited thermoacoustic and ultrasound (HMTAU) imaging can simultaneously provide complementary and coregistered information on the dielectric and acoustic properties of tissue
Previous studies indicate that the realization of HMTAU requires a costly high peak power of microwave pulse, which limits its applications
A pulsed microwave generator was used to produce microwave pulses, which were delivered to the sample and transducer simultaneously through a home-made coaxial waveguide switch filled with castor oil
Summary
Microwave-induced thermoacoustic tomography (TAT) is widely used in biomedical imaging research because of its non-invasive, high resolution and high penetration depth. While TAT alone has been used for various biomedical applications, its combination with US has been exploited naturally given that a single transducer can commonly be used as the receiver for TAT and the transmitter/receiver for ultrasound (US), in addition to using US information to reduce distortion in TAT. Using different contrast mechanisms, hybrid microwave-excited thermoacoustic and ultrasound (HMTAU) imaging can simultaneously provide complementary and coregistered information on the dielectric and acoustic properties of tissue. Microwave-induced thermoacoustic tomography (TAT) is widely used in biomedical imaging research because of its non-invasive, high resolution and high penetration depth.. Hybrid microwave-excited thermoacoustic and ultrasound (HMTAU) imaging can simultaneously provide complementary and coregistered information on the dielectric and acoustic properties of tissue. The same transducer collects the US signals reflected from the sample as a result of the ultrasound pulse (pulse-echo), and the TA signals as a result of the sample absorbing microwaves. This method obtains temporally and spatially co-registered TAT/US images without increasing the complexity of the TAT imaging system. Previous studies indicate that the realization of HMTAU requires a costly high peak power (energy) of microwave pulse, which limits its applications. Here we show that
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