Photoacoustic imaging and microwave-thermoacoustic imaging are innovative hybrid imaging techniques that have experienced rapid development in recent years. Photoacoustic imaging is based on the photoacoustic effect. When the laser pulses (the width of the laser pulse is usually several nanoseconds to tens of nanoseconds) irradiate the biological tissue, the absorbers in the tissue absorb the optical energy and then induce the instantaneous rise in temperature, and radiate the thermal energy in the form of mechanical energy, i.e. ultrasound signals. We can detect the ultrasound signals with ultrasound transducer and recover the absorption information of the absorbers in the tissue with different imaging algorithms. Photoacoustic imaging integrates the merit of high contrast of optical imaging and high imaging depth of ultrasound imaging. If the excitation source of the photoacoustic imaging is changed into the microwave (the width of the microwave pulse is usually from tens of nanoseconds to hundreds of nanoseconds), that is called thermoacoustic imaging, which can provide high-resolution imaging and imaging depth of more than ten centimeters. Meanwhile, photoacoustic imaging and thermoacoustic imaging have high molecular specificity and have already been widely used in the research of physics, chemistry, and biomedicine.