Three-dimensional sonoelastography: principles and practices

Sonoelastography is an ultrasound imaging technique where low-amplitude, lo w-frequency shear waves (less than 0.1 mm displacement and less than 1 kHz frequency) are propagated through internal organs, while real-time Doppler techniques are used to image the resulting vibration pattern. When a discre te hard inhomogeneity, such as a tumour, is present within a region of soft tissue, a decrease in the vibration amplitude will occur at its location. This forms the basis for tumour detection using sonoelastography. For three -dimensional (3D) imaging the acquisition of sequential tomographic slices using this technique, combined with image segmentation, enables the reconst ruction, quantification and visualization of tumour volumes. Sonoelastograp hy and magnetic resonance images (MRI) of a tissue phantom containing a har d isoechoic inclusion are compared to evaluate the accuracy of this method. The tumour delineation from sonoelastography was found to have good agreem ent with the tumour from MRI except for a bleeding at one of its ends. Alth ough sonoelastography is still in an experimental phase, the principles beh ind this imaging modality are explained and some practical aspects of acqui ring sonoelastography images are described. Results from a 3D sonoelastogra phy reconstruction of a tissue mimicking phantom and an ex vivo whole prost ate specimen are presented.