A digital filtering technique has been developed for enhancement of two-dimensional ultrasonic images of the heart. The filtering is applied to the lateral axis normal to the direction of scanlines. The enhancement results from both filtering off-axis artifacts and interpolation within the scanning plane. Simple filters of this design have been implemented which significantly increase the quality of images. Theoretical considerations for development of such filters is also discussed.
Ultrasonic cardiac imaging is increasingly being used to assess cardiac function. The two factors which have contributed most to this increased use are the noninvasive nature of ultrasound and the development of real-time imaging systems. A major disadvantage, however, of the ultrasonic images is that the images have not had the clarity nor resultuion seen in angiographic images. Efforts to improve ultrasonic scanners have, therefore, been directed toward techniques to increase the geometric resolution of the images. A major source of the poor resolution is the finite dimensions of the ultrasonic pulse (I, 2). Typically, the axial length of the transmitted pulse for adult echocardiography is of the order of 2 mm and the lateral width of the pulse at the focal point is nominally between 4 and 8 mm. The effect of these dimensions can best be understood by visualizing the echo signal generated by scanning a single thin wire in a water bath. Figure is an example of the transducer output as it scans in a plane normal to the long axis of the phantom. As seen from the figure, a signal (even though reduced in amplitude) is received even when axis of 265