3D-sonography - Transparent presentation of volumetric scans

The 3-D presentation of organs, tumors and tissue structures up to now was only applied to CT and MR. In both procedures sequences of parallel two-dimensional slices are acquired. By means of digital image processing this information can be reconstructed into three-dimensional presentations. A main disadvantage of the described procedures is a long acquisition time and, with respect to CT, the application of ionizing radiation. Both methods are very complex, expensive and not readily available. Sonography with its well known advantages like fast handling, maximum patient safety and vast availability shows the best potential as a basis for 3D-presentation. The 3-D images presented are acquired with standard transducers. The position of the array during examination is registered by a computer. For this, two standard magnetic remote localizers are fixed on the array to measure the transducer's position in space. To scan the patient the operator manually moves the hand-held transducer while the remote localizer monitors its movement. This approach allows the operator to move the transducer without constraints in the usual manner. The digitally stored 3-D ultrasound information is presented by transparent projection or by reconstruction of oblique two-dimensional slices through the 3-D object. Position and direction of these reconstructed slices are defined by means of an interactive user interface. The object under investigation can be viewed through sequential slides. Orientation and step width are user selectable. In many applications, however, the spacial presentation of the complete three-dimensional information can establish a much higher diagnostic value. The spatial presentation on the system monitor is computed by projection of all grey scale pixels from the three-dimensional raw data set. By presenting a coordinated sequence of three-dimensional projections, the impression of a threedimensional object rotating in space is attained. Thus, orientation and spacial distribution of threedimensional objects can be easily recognized and analysed. By means of this reconstruction technique, transparency and three-dimensional character are emphasized during the perception. Diagnostic interpretation far beyond the possibilities of a simple static projection is achieved. Using this technique in oral-maxillo-facial surgery we found improvement in diagnostic possibilities and diagnostic safety in the following applications: tumor diagnostics in oncology, improved localisation in surgery, scanning of the temporomandibular joint, volume calculation of organs, volume calculation of arteriosclerotic plaques, localisation and treatment diagnostics in lithotripsy. The possibilities in the different applications are presented in selected cases. Our experiences show that 3-D sonography is now at the point where clinical use in different applications is possible. Further clinical trials will determine their benefits in daily clinical practice.