INTRODUCTION
Ultrasound imaging is the most extensively used non-ionized progressing demonstrative instrument in clinical applications because of its comfort to utilize and low radiation.
The main focuses of current SA research in are to improve the nature of pictures, to build the casing rate and to diminish power utilization. GPU is appropriate for constant applications yet with high force utilization.
Field Programmable Gate Array (FPGA) has gained popularity for the design based on rapid prototype technology. It can provide an optimized hardware choice suitable for SA algorithm. Compared with ordinary sequential scanning method applied to medical ultrasound, Synthetic aperture (SA) method had been developed for radar systems in the 1950s to reconstruct of high resolution image from successive transmission and reception position ,By the simulation and comparing with the result obtained by the Graphics Processing Unit (GPU), the current design demonstrates the feasibility of implementing the real time high resolution ultrasound imaging.
DESCRIPTION OF SA ALGORITHM
SA strategy communicates point source firings from various sidelong positions component by component at every outflow. Each terminating's heartbeat echoes from the medium are procured over all components in the accepting opening. The got information is utilized to produce one low goal picture (LRI). Consequently high goal picture (HRI) is procured through recursive summation of LRIs.The algorithm consists of three main steps as follows.
A. Analytic signal conversion
The insightful sign change is the initial phase in LRI arrangement. For the got reverberation of every emanation, the sign is first gone through Hilbert change to acquire the complex segments in the logical sign. Consequently, the got reverberation is changed into the pixel esteems for 2D picture.
B. Beamforming
In SA imaging, the delayed beam formation for each pixel requires the calculation of its time-of-flight,which is determined by the geometric distance from the transmitting source, to the pixel position, and back to the receive element position .With the total propagation time, we can get the weight the data point , adjacent analytic data.
C. Recursive compounding
Eventually, all low resolution images obtained from different transmit positions are combined linearly and a high resolution image can be obtained. SA algorithm, the Step A is used to
convert the receiving elements acquired signal into analytic
signal and then, Step B uses the propagating time of the
ultrasound pulse together with the analytic signal obtained in
Step A to reconstruct the LRIs for each transmitting element. At long last, Step C consolidates all LRIs into a HRI directly
ALGORITHM IMPLEMENTATION IN FPGA
It is found that the algorithm of SA imaging can be implemented in parallel structure to save computation time. In FPGA is mainly responsible for parallel processing the SA algorithm and a computer in charge of handling the preliminary non computational intense processing and the auxiliary functions such as I/O data to the FPGA, image storage, and User Interface. Then, a line accumulator applies different apodization weights to the signal received from different element arrays (usually Hanning window), which can suppress the sidelobe effectively and increase contrast in ultrasound imaging while the width of main lobe is increasing.
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