Date of Award
Fall 1993
Document Type
Thesis - Restricted
Degree Name
Master of Science (MS)
Department
Biomedical Engineering
Abstract
In medical ultrasound, the Doppler shift of a segment of acoustic pulses transmitted into the body is used to measure blood velocity. Since tissue and bone are much more echogenic than blood, the signal from these two components- collectively called the "wall signal"- must be removed before the blood signal can be processed for spectral display. Blood usually moves at higher velocities than tissue so its contribution to the "receive" echo is the higher frequencies; the wall signal is often removed with an analog high pass filter. With the wall signal removed, segments of Doppler data are analyzed with an FFT and displayed in a real-time, "waterfall format." In newer, time-multiplexing ultrasound machines, Doppler data segments are interrupted by data segments used for other types of imaging. See Figure 0-1. This presents a challenge to wall filter implementation; the discontinuity at the beginning of each Doppler segment causes the wall filter to "ring," polluting the Doppler data. On current ultrasound machines, the solution has been to wait for the filter transients to die down before doing Doppler spectral analysis. During transient die-down- up to 2mS [12] - information is lost, decreasing the time-precision of both imaging and blood velocity measurements. The subject of this thesis is the lessening of the effect of the wall filter ring, particularly in the case when the ultrasound data arrives in a digital format which is processed with a digital IIR filter.
Recommended Citation
Otterson, Scott, "Transient Reduction for Digital Wall Filters in Doppler Ultrasound" (1993). Master's Theses (1922-2009) Access restricted to Marquette Campus. 3798.
https://epublications.marquette.edu/theses/3798