Deconvolution in medical ultrasonics: practical considerations

Deconvolution can, in principle, enhance the spatial resolution of specular reflectors in medical ultrasonic imaging but, in practice, the resolution improvement offered is offset by the introduction of undesirable artefacts. In this study, several problems related to deconvolution were identified and practical suggestions for minimising artefacts were made. These include: fitting a three-dimensional surface to experimentally measured beam profiles in order to take into account the depth-dependence of the point spread function (PSF); adaptive detail-preserving noise filtering as a preprocessing tool in order to improve the quality of the data and reduce the speckle enhancement artefact; a histogram modification procedure in order to overcome the problems of ringing, over- and undershooting. Processing of a large number of A-scan data obtained from tissue-mimicking phantoms and the abdomens of normal volunteers demonstrated the efficiency of these techniques in reducing artefacts. The performance of deconvolution in terms of resolution improvement was satisfactory when data from resolution test objects were processed but poor with abdominal scans. This difference in performance raises the question as to how similar the PSF in tissue is to the experimentally measured PSF in water or even a tissue-mimicking material.