The detection of many targets in ultrasonic images, such as low contrast liver and pancreatic tumors and breast carcinomas, is limited by a coherent noise phenomenon known as speckle. In coherent optical systems, studies have shown that speckle reduces perceived resolution by a factor of five to seven. Preliminary investigations indicate that the efficient incorporation of a speckle reduction technique known as spatial compounding into existing ultrasonic imaging systems will markedly increase these target's detectability. A second speckle reduction technique, frequency compounding, also holds promise although it has not been quantitatively studied. The major goals of this proposal are: (1) the measurement of ultrasonic image degradation due to speckle for a variety of target types, (2) the experimental determination of the maximal speckle reduction achievable by spatial compounding, frequency compounding, and the simultaneous use of these methods, and (3) an evaluation of the improvement of in vitro and in vivo target detectability due to the application of these speckle reduction techniques. Hardware implementations of spatial and frequency compounding systems will be incorporated into a phased array imaging system and careful measurements made of the speckle reduction obtainable by these methods. The results of these studies will form the basis for the design of real time ultrasonic imaging system with speckle reduction capabilities. This system will be subjected to in vitro and in vivo image quality tests. In vitro image evaluation experiments will involve contrast-detail studies involving human observers of tissue-mimicking targets of three types, two of which will be constructed specifically for this purpose. In vivo tests are designed to provide a preliminary demonstration of the improved clinical image quality resulting from compound imaging. These tests include trained observer studies of low contrast targets (e.g. kidney and adrenal gland structures) and high contrast targets (i.e. calcified pelvic and abdominal masses). It is anticipated that these studies will lead to the development of improved ultrasonic imaging systems.
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