Biomedical subjects

Meng-Lin Li

Publications and source records attributed to Meng-Lin Li.

3 recordsLinked to original sources

PubMed2003

Adaptive imaging using the generalized coherence factor.

Sound-velocity inhomogeneities degrade both spatial and contrast resolutions. This paper proposes a new adaptive imaging technique that uses the generalized coherence factor (GCF) to reduce the focusing errors resulting from the sound-velocity inhomogeneities. The GCF is derived from the spatial spectrum of the received aperture data after proper receive delays have been applied. It is defined as the ratio of the spectral energy within a prespecified low-frequency range to the total energy. It is demonstrated that the low-frequency component of the spectrum corresponds to the coherent portion of the received data, and that the high-frequency component corresponds to the incoherent portion. Hence, the GCF reduces to the coherence factor defined in the literature if the prespecified low-frequency range is restricted to dc only. In addition, the GCF is also an index of the focusing quality and can be used as a weighting factor for the reconstructed image. The efficacy of the GCF technique is demonstrated for focusing errors resulting from the sound-velocity inhomogeneities. Simulations and real ultrasound data are used to evaluate the efficacy of the proposed GCF technique. The characteristics of the GCF, including the effects of the signal-to-noise ratio and the number of channels, are also discussed. The GCF technique also is compared with the correlation-based technique and the parallel adaptive receive compensation algorithm; the improvement in image quality obtained with the proposed technique rivals that of the latter technique. In the presence of a displaced phase screen, this proposed technique also outperforms the correlation-based technique. Computational complexity and implementation issues also are addressed.

Algorithms↗

PubMed2003

Improved Fourier-transform-based parallel receive beam formation.

A Fourier transform (FT)-based technique for forming parallel receive beams has been previously employed to increase the imaging frame rate in ultrasonic imaging. However, the image quality in FT-based parallel reconstruction is degraded because differences in range focusing delays are ignored and a wide transmit beam needs to be used. In this paper, an adaptive weighting technique based on a focusing-quality index is used to reduce the sidelobes of the FT-derived parallel receive beams. The focusing-quality index is derived from the spatial spectrum of the received aperture data after the receive delays have been applied. Since the spatial spectrum of the baseband aperture data is also used to approximate receive beams in FT-based parallel reconstruction, the adaptive weighting technique can be directly combined with the FT-based technique for forming parallel receive beams with only a slight increase in system complexity. Real ultrasound data are used to demonstrate the efficacy of the proposed technique on both wire targets and speckle-generating objects. The results clearly demonstrate the effectiveness in reducing the sidelobes. In addition, the image background noise is suppressed. The principles, experimental results, and the extension of the proposed technique to 3D ultrasound imaging are described in this paper.

Fourier Analysis↗

PubMed2002

Elastic modulus measurements of human liver and correlation with pathology.

Viral hepatitis causes fibrosis in the liver and may change mechanical properties of the liver. To evaluate the impact of fibrosis on elastic properties of human liver and to investigate potential benefits of ultrasonic elasticity imaging, 19 fresh human liver samples and 1 hepatic tumor (focal nodular hyperplasia) sample obtained during operations were studied. Simple 1-D estimates based on the cyclic compression-relaxation method were performed. Elastic modulus values were derived from the predetermined strain (controlled by a step motor system) and the stress values (measured by an electronic balance). Each specimen subsequently received histologic examination and a grade of liver fibrosis was scored from 0 to 5. Results show that the elastic modulus values were on the order of several hundreds to thousands of Pascals. The elastic modulus generally increased with the fibrosis grade, although some discrepancies existed at the middle grades of fibrosis (scores 1 to 3). The correlation between the fibrosis score and the elastic modulus was significant (p < 0.01) based on the statistical analysis using the Pearson correlation method. In addition, the relation between the elastic modulus and the fibrosis grade generally exhibited a quadratic trend. It was concluded that severity of fibrosis had a good correlation with stiffness of the liver. Results also indicated that the elasticity imaging of the liver may provide significant clinical values if the elastic modulus can be accurately measured.

Elasticity↗