Biomedical subjects
E Konofagou
Publications and source records attributed to E Konofagou.
Elastographic imaging of the normal canine prostate in vitro.
Elastography has been shown to be successful in mapping the relative mechanical attributes of normal as well as abnormal tissues. In this study, the histological characteristics of freshly excised normal canine prostates were used to explain consistently depicted elastographic features. The elastograms of the transverse cross-sections across the urethra demonstrated a consistent symmetry of the gland as well as clear anatomic structures. These include a central portion of the gland surrounding the urethra and a peripheral gland. The central gland was consistently softer than the peripheral gland. At the level of the verumontanum, depicted as a small stiff ridge, the lumen of the urethra was consistently demonstrated as an inverted soft 'u' or 'v' shaped area. The network of branching-fibrous connective tissue septa was depicted by the elastogram as linear features, which converged on the urethra. In the anterior side of the gland, the fibromuscular stroma was seen as a circumscribed hard tissue. In the sagittal view, the elastogram suggested a stiff peripheral zone surrounding a softer central zone, which is traversed by the urethra depicted as soft tissue.
Elastography: ultrasonic estimation and imaging of the elastic properties of tissues.
The basic principles of using sonographic techniques for imaging the elastic properties of tissues are described, with particular emphasis on elastography. After some preliminaries that describe some basic tissue stiffness measurements and some contrast transfer limitations of strain images are presented, four types of elastograms are described, which include axial strain, lateral strain, modulus and Poisson's ratio elastograms. The strain filter formalism and its utility in understanding the noise performance of the elastographic process is then given, as well as its use for various image improvements. After discussing some main classes of elastographic artefacts, the paper concludes with recent results of tissue elastography in vitro and in vivo.
A new elastographic method for estimation and imaging of lateral displacements, lateral strains, corrected axial strains and Poisson's ratios in tissues.
A major disadvantage of the current practice of elastography is that only the axial component of the strain is estimated. The lateral and elevational components are basically disregarded, yet they corrupt the axial strain estimation by inducing decorrelation noise. In this paper, we describe a new weighted interpolation method operating between neighboring RF A-lines for high precision tracking of the lateral displacement. Due to this high lateral-tracking precision, quality lateral elastograms are generated that display the lateral component of the strain tensor. These precision lateral-displacement estimates allow a fine correction for the lateral decorrelation that corrupts the axial estimation. Finally, by dividing the lateral elastogram by the axial elastogram, we are able to produce a new image that displays the distribution of Poisson's ratios in the tissue. Results are presented from finite-element simulations and phantoms as well as in vitro and in vivo experiments.
Reduction of stress nonuniformities by apodization of compressor displacement in elastography.
Elastography is a method for imaging the elastic properties of compliant tissues that produces gray-scale strain or elasticity images called elastograms. The method is based on external tissue compression, with ultrasonic detection of local target displacements and subsequent computation of strain profiles along the compression axis. The internal strain variations are a result of the tissue elasticity variations and the applied deformation or compression. A number of mechanical artifacts that appear in elastograms have been identified. One such artifact appears as the result of a nonuniform stress distribution under the compressors used, including darkening (low stress) of the central region and brightening (high stress) of the peripheral regions under the compressor. On an elastogram, these areas may be misinterpreted as being respectively harder and softer than the rest of the target. In this article, a displacement apodization method for the minimization of this artifact is discussed, and its effects are studied using finite element simulations. When the isometric compression of standard elastography was replaced by an apodized displacement profile calculated from reciprocity conditions, a significant improvement in stress uniformity under the compressor was achieved.