Refractive Index by Reconstruction: Use to Improve Compound B-Scan Resolution
Reconstructions of two-dimensional distributions of acoustic speed were utilized to correct digitized compound B-scan images for aberrations caused by inhomogeneous refractive index. Profiles of propagation’delays of acoustic pulses obtained during compound transmission scanning at 60 angles of view separated by 6° were used to reconstruct the distribution of acoustic speeds within a 64 × 64 element grid in the scan plane within which 8 to 16 digitized B-scans were obtained for views separated by 22.5° or less. Each B-scan contained 1000 to 1300 pulses, digitized at 10 or 20 megasamples/s. Values of calculated acoustic speed within those elements of the reconstruction grid which were intersected by the locus of each pulse trajectory were utilized to map the temporal sequence of echoes within each echo signal into the correct spatial sequence of echoes within the B-scan image. Straight line approximations to the loci of the acoustic beams were used. The set of corrected B-scans were summed to obtain high resolution compound B-scans of 128 × 128 or 256 × 256 picture elements. This method seems particularly suited to breast imaging although enhance. ment of abdominal scans may be possible as well.
KeywordsArrival Time Refraction Index Acoustic Velocity Point Reflector Acoustic Speed
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