(A) study on performance improvements in the ultrasound B-scan system

Abstract

The ultrasound B-scan system is the most successful imaging system in the field of diagnostic ultrasound and nondestructive testing. The B-scan system offers real time tomographic imaging at relatively low cost and does not produce any harmful effects to the patient. The B-scan is, in principal, a map of the backscattering efficiency from every point in the imaging volume. But a conventional B-scan system can provide only a crude approximation to a backscattered image due to (a) diffraction effect (b) non-linear propagation effect (c) B-scan system artifact. The major limiting factor on the use of the B-scan system is the poor resolution, especially along the lateral direction caused by a finite transducer aperture size. To improve the resolution, a number of studys have been reported to date including linear inverse filtering, non-linear filtering, transducer design, and focusing methods. Perhaps, dynamic focusing may be the most practical approach in real time imaging. The non-linear propagation effects can alter the backscattering efficiency estimation in a B-scan system. To get a quantitative B-scan image, all the phenomena that can alter the efficiency estimation should be taken into account. The propagation effects encountered in a diagnostic ultrasound are: inhomogeneous attention, beam softening by frequency dependent attention, and different velocity distribution in tissue. The B-scan system also changes the image estimation. In a digital sector scanner, a number of artifacts occurs during the coordinate transformation, known as scan conversion. The reduction of the artifact is very difficult because of the real time requirement. In this thesis, we propose several new methods to improve the B-scan performance. In part I, a new focusing method, to be called the sampled delay focusing (SDF), is proposed to improve the B-scan resolution. In SDF, sampling-sum process can replace the conventional delay-sum-sampling process, and thus the analog delay lines a...