Three dimensional medical ultrasonic imaging in biomedical applications

In this thesis, it is planned to acquire ultrasonic data from own hardware and to process it in a personal computer system. The main aim in this study, is to reconstruct a volume of biological tissues, specially human organs, by using two dimensional slice images. The thesis consists of hardware, that produces ultrasonic signals and receives the echoes, and related software, that processes the ultrasonic data. The hardware parts of this study should have special properties. High speed and low noise devices are required for excitating the piezos at high voltages (up to 350 Volts) with narrow impulses (about 2 usee). For this purpose, fast and high voltage FET type switches are used to generate vibration on the piezoelectrics. Echoes from biological medium are received by transmitter-receiver diode switch structures. Subdevices, such as dc-dc converter that is used to generate 350 V from 12 V dc, far region gain curcuit, echo receiver-amplifier, 8031 microcontroller based timing and synchronizing circuit were realized considering high speed and noisiness conditions. After acquiring the ultrasonic echoes, a prototype card for PC to interface with analog devices is designed and ultrasonic data is acquired by using this IIcircuit. This card can be called as a "7 Bits Data Acquisition Card", which can work in nanoseconds when DMA (Direct Memory Access) is used. Because of using assembler routines in which it is possible to get a 7 bit data in only 1 jisec, therefore, we can get 200 samples in one frame which is about 200 jj,sec. Those 7 bits data is saved in memory and processed as 256X256 pixel images called "Slices", then, reconstructed as 3-D Images called "Volume". After that point, several digital signal processing algorithms like smoothing and thresholding are used. During processing operations, C++ programming language is used for being the most effective language. Effective means firstly fast, then having high level functions and finally, reachable to Machine Codes and Internal Registers. Program can acquire ultrasonic data through prototype card and process and show the images considering data characteristics. We used two image modes for ultrasound: One of them is M-Mode that is based on stimulating only one direction, and showing only time dependent changes at that direction, which are used imaging heart valves in motion and etc. The second is B-Mode, which shows us a slice cut of the media under examine. The final two and three dimensional images are given at the end of the research. When this results are investigated, it can be said that we have realized most of the things desired at the beginning of this thesis.