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Dissertation
Pulse elongation and deconvolution processing for the signal-to-noise ratio improvement in medical ultrasonic imaging
Doctor of Philosophy (Ph.D.), Drexel University
Jun 1997
DOI:
https://doi.org/10.17918/00000840
Abstract
The purpose of this research was to improve the signal-to-noise ratio (SNR) of an ultrasound image and concurrently minimize the instantaneous peak pressure amplitude of the interrogating ultrasound wave. It is well known that the SNR of a medical ultrasonic imaging system can be improved by increasing the pulse duration of the transmitted waveform. However, the elongated waveform leads to deterioration in image quality by introducing blurring effects. To restore the original image quality a novel approach based on a modified pulse compression technique was developed. The novelty of the approach presented here is the combination of pulse elongation with optimal inverse filtering or deconvolution. The advantage of this method over other pulse compression techniques is the simultaneous minimization of electronic noise and range sidelobes. The deconvolution is implemented as a modified Wiener filter since the standard Wiener filter is inadequate in removing sidelobes. The question of how the excitation waveform should be elongated was addressed and an analytical expression for the optimal power spectrum of the excitation signal was derived. It is demonstrated that due to corner points in the optimized spectrum the desired time waveform is not realizable. Therefore, several numerical methods were investigated for their ability to find optimized waveforms with additional constraints on waveform amplitude and duration. It is shown that the numerical solutions approach the analytical solution for increasing pulse lengths. An experimental system has been built to verify the results of the analytical and numerical methods. The system is based on a commercial ultrasound scanner with appropriate modifications to the transmitting and receiving electronics. The system allows for real time image acquisition and off line signal processing. The results of in-vitro and in-vivo images including liver, gallbladder and kidney are presented side-by-side with those obtained using a conventional ultrasound scanner. The imaging results clearly evidence that improvement in the signal-to-noise ratio is feasible without increasing the peak pressure amplitudes of the transmitted waveforms. Implications for improved safety of ultrasound diagnostic devices are pointed out. Also, fundamental limitations of the approach are summarized and possible future improvements are suggested.
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Details
- Title
- Pulse elongation and deconvolution processing for the signal-to-noise ratio improvement in medical ultrasonic imaging
- Creators
- Bruno H. Haider
- Contributors
- Peter Andreas Lewin (Advisor) - Drexel University, School of Biomedical Engineering, Science, and Health Systems
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xi, 131 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Biomedical Engineering and Science Institute (1970-1997); Drexel University
- Other Identifier
- 991014970313704721