Research On Ultra Wide Band Electromagnetic Pulse Source Based On Thermoacoustic Imaging

Microwave-induced thermoacoustic imaging(MITAI)combines the advantages of microwave imaging and ultrasound imaging,which has excellent penetration depth,high contrast and imaging resolution.So it is a new noninvasive medical imaging method which has a good prospects for development and wide application potential.First,MITAI uses pulsed microwaves as excitation source to irradiate tissue.Then,the tissue absorbs microwave energy and further induce thermoelastic expansion to generate ultrasound waves;Finally,ultrasound waves as the information carrier,combined with an reconstruction algorithm to recover thermoacoustic image which reflects microwave absorption distributions.MITAI can be used in studying the dielectric properties distribution of tissue,based on microwave absorbing discrepancies under different physiological and pathological of biological tissues.MITAI can realize medical detection with non-invasive,high resolution and high contrast.Although MITAI has good penetration and high imaging resolution,the resolution remains to be further improved.Now,due to the conversion efficiency of TA wave is low,lead to microwave excitation source power is high,causing potential thermal damage of tissue.The pulse width of traditional thermoacoustic imaging(TAI)is sub-microsecond,generated energy density of several mJ/cm2,imaging resolution reaching the level of millimeter.With TAI developing towards clinical application,effectively improving the conversion efficiency of TA wave and imaging resolution,decreasing the microwave radiation dose are key factors.Research found that the compressed pulse width of pulse excitation source can effectively improve the imaging resolution,also can significantly increase TA wave conversion efficiency and reduce thermal damage.Through the above analysis,this paper presents a TAI technique based on ultra-wideband(UWB)electromagnetic pulse source.The pulse power source used in this study can produce 10 ns ultra-short pulse microwave signals.According to the theory of TAI,several reconstruction algorithms commonly used in TAI are described.In this paper,the TAI system based on UWB electromagnetic pulse source is designed and built.The imaging capability of the system is studied by phantom and biological tissue imaging.The imaging range of the system is studied by different layers of marker array.The effect of environmental factors on the image quality was studied.The method of improving the energy coupling efficiency in MITAI was explored by copper plate reflection experiment.The influence of hardware and equipment on the system performance was studied by comparing different amplifiers and different types of transducers.The research of this paper makes the TAI technology based on UWB electromagnetic pulse source a key step for clinical application,and gives strong technical support.