The Research On Application And Performance Of Chirp Excitation In High Frequency Ultrasonic System

With the rapid growth of technological level in software,electronics and materials science,ultrasonic medical imaging technology got great development in the recent years.It obtained the extremely widespread application in the human body detection of soft tissue and cardiovascular organ blood dynamics because of its high real-time performance,low cost,displaying methods of diversity etc.HFUS(High frequency ultrasound system)whose central excitation frequency is higher than 15MHz is a branch of medical ultrasound imaging system.It is widely used including but not limited to ophthalmology UBM,dermatology clinic,nondestructive testing experiments with small animals,intravascular Ultrasound and Ultrasound endoscope,etc.HFUS got perfect resolution and image quality because of its high frequency,but sacrificed its penetration depth a lot.Aiming to the problem,this article will apply coded excitation technique to HFUS,in an effort to provide better penetration depth for HFUS on the basis of high resolution.In order to contrast advantages and disadvantages between conventional pulse excitation and chirp modulated excitation,we designed experimental system which consist of FPGA chip,MD2133,AD7982 and imaging program.Using the system,we can realize the traditional pulse and chirp modulated excitation?process RF signals and got figures of wires?phantom and tissue in four excitation modes(30 MHZ chirp,30 MHZ pulse,60 MHZ chirp,60 MHZ pulse).Then resolution,penetration depth,CNR of four excitation modes were calculated based on these ultrasonic images.The results shows that although the axial resolution of chirp modulated excitation got worse beacause of longer emmision time compared to conventioanal pulse excitation,the pennetration increased by 50%and lateral resoluition?CNR got a obviously improvement.These performance optimization have a positive clinical sigificance for the diagnosis of ophthalmology disease,cardiovascular disease,skin diseases,etc.