Tele-virtual sonography

3D-Ultrasound reconstruction, routinely available since 1994, has brought new technical capabilities such as virtual sonography that can be tele-consulted. Our experience is summarized in the present paper.

During one year, 73 3D-US volumetric images coming from 34 patients were acquired and 68 were consulted at distance. Acquisitions were carried out through an existing 2D device adding a magnetic tracking system on the US-probe. Probe positioning and video output was introduced into a PC running software that allows the generation of 2D-orthogonal and 3D volume images, as well as tele-consultation. Several image analysis techniques for 3D-reconstruction were evaluated.

Final volumes were small (1.5 Mb) and required about 4+/-2 min to be transmitted over one ISDN channel (64 Kbs). Good correlation (k = 0.7) was found between local and distant diagnoses. In 30%, images were considered of low quality and in 29% of good quality; diagnosis could be done with confidence in all except 7 cases. Virtual sonography, by means of oblique cuts in all space directions, improved distant diagnostic confidence. Limitations were linked to incomplete sampling due to the short acquisition time periods (26 s) and difficulties on hand-free probe movement. 3D reconstructions were time consuming (20 min to 4 h) and of limited indication.

3D reconstruction could reduce multiple explorations due to image constrains such as suboptimal fetal positioning, among others. Virtual sonography was important to reach confidence on distant diagnosis; it was also considered a tool for off-line local review of non-trained sonographer acquisitions.