Application of Phased Array Radar Theory to Ultrasonic Linear Array Medical Imaging System

Basic principle of ultrasound medical imaging is a direct adaptation of that of phased array radar. Modern ultrasound scanners use large either linear or phased array of piezoelectric (PZT, for instance) transducers. Designing electronic beam-forming network for ultrasound pulsed echo system is thus very much similar to the adaptive antenna array system design in a different modality. When ultrasound propagates through human tissue layers having different acoustic impedance at each tissue layer interface it gives an echo. The attenuation coefficient , speed, viscosity, density, compressibility and other acoustic parameters of the medium directly control the characteristics of the back scattered components that is received by the same transducer utilized in transmitting the ultrasound signal. The interaction of ultrasound with human tissue, thus, is a multi parameter one being capable of delivering more information about the medium. As a result while with X-rays we get only a shadow image of the system, with ultrasound we get more detailed image of different tissues. However, it is necessary to pursue R&D work in each block of the ultrasound pulse echo imager to improve the image quality. Making Improvements in adaptive beam forming algorithms is one of such efforts. Authors in this paper first introduce the subject through a brief survey of the devices utilized and technique involved, and then describe the simulation of a delay-sum digital beam-former of a linear ultrasound array imaging system. Simulation has been performed for 8-, 16-, and 64-element linear transducer array. A near-real situation has been effected in the simulation by taking a pulse modulated 2MHz sinusoidal signal. Effect of modulating pulse width on directivity and amplitude of the side lobes have been studied and results presented. INTRODUCTION Quality of an ultrasound medical image depends largely on the transmit/receive probe used that normally is a piezoelectric transducer. This entails that a large portion of historical development of diagnostics is captured by the history of development of the transducer technology that includes material research, understanding of the physics of wave and its propagation through fluid and solid and particularly through tissue media. The complexity of the interaction of ultrasound with human tissue is resulted because of the composition of the media. It is highly inhomogeneous, non-linear and anisotropic. It is embedded with different types of tissue types, namely, hard, soft, softer etc. some example being, bone, muscle, blood, fat and so on. During interactions of ultrasound with such a …