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Biomedical subjects

L N Bohs

Publications and source records attributed to L N Bohs.

5 recordsLinked to original sources
PubMed1992

Phase aberration correction using echo signals from moving targets. I: Description and theory.

Inhomogeneous acoustic velocity in human tissue introduces phase aberration in ultrasonic imaging systems and degrades image quality. A novel technique that employs echo signals from moving diffuse targets, such as flowing blood, as an image quality factor to compensate for phase aberration is described. Such signals can be obtained by subtracting the images of two consecutive target interrogations. The fundamental statistics of the quality factor and other related parameters are developed to provide a theoretical basis for the technique.

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PubMed1992

Phase aberration correction using echo signals from moving targets. II: Experimental system and results.

A method for correcting errors due to near-field tissue inhomogeneities in phased array ultrasound images is evaluated experimentally. The method uses the brightness of a moving speckle-generating target, such as blood, as a quality factor to correct for unknown phase aberrations. A real time experimental system utilizing the technique has been constructed and is described. Initial results from in vitro studies using a flow phantom are compared to theoretical predictions. The results indicate that the technique can provide significant improvements in image quality when imaging through aberrating media, and may find application in clinical imaging through skull and fatty layers.

Algorithms↗
PubMed1991

A novel method for angle independent ultrasonic imaging of blood flow and tissue motion.

Tracking the speckle patterns produced by moving targets has been shown effective for angle independent imaging of blood flow and tissue motion. While speckle tracking overcomes major limitations of Doppler-based flow imaging, the computational complexity of commonly used cross correlation algorithms currently limits it to off-line studies. A much simpler algorithm for angle independent motion imaging is described in this paper. This method requires only one absolute difference operation per pixel, compared to eight operations for normalized cross correlation. Quantitative studies using speckle-generating targets translated by fixed amounts both axially and laterally indicate that the technique tracks moving speckle as accurately as correlation. Color flow images generated from clinical blood and liver data highlight the success of the technique for tracking both large and small motions in two dimensions. The algorithm's suitability for implementation in digital hardware makes possible the development of clinical instruments for angle independent ultrasonic imaging of blood flow and tissue motion in real time.

Algorithms↗