Networking of three dimensional sonography volume data.
Three-dimensioned (3D) sonography enables the examiner to store, instead of copies from single B-scan planes, a volume consisting of 300 scan planes. The volume is displayed on a monitor in form of three orthogonal planes--longitudinal, axial and coronal. Translation and rotation facilitates anatomical orientation and provides any arbitrary plane within the volume to generate organ optimized scan planes. Different algorithms allow the extraction of different information such as surface, or bone structures by maximum mode, or fluid filled structures, such as vessels by the minimum mode. The volume may contain as well color information of vessels. The digitized information is stored on a magnetic optical disc. This allows virtual scanning in absence of the patient under the same conditions as the volume was primarily stored. The volume size is dependent on different, examiner-controlled settings. A volume may need a storage capacity between 2 and 16 MB of 8-bit gray level information. As such huge data sets are unsuitable for network transfer, data compression is of paramount interest. 100 stored volumes were submitted to JPEG, MPEG, and biorthogonal wavelet compression. The original and compressed volumes were randomly shown on two monitors. In case of noticeable image degradation, information on the location of the original and compressed volume and the ratio of compression was read. Numerical values for proving compression fidelity as pixel error calculation and computation of square root error have been unsuitable for evaluating image degradation. The best results in recognizing image degradation were achieved by image experts. The experts disagreed on the ratio where image degradation became visible in only 4% of the volumes. Wavelet compression ratios of 20:1 or 30:1 could be performed without discernible information reduction. The effect of volume compression is reflected both in the reduction of transfer time and in storage capacity. Transmission time for a volume of 6 MB using a normal telephone with a data flow of 56 kB/s was reduced from 14 min to 28 s at a compression rate of 30:1. Compression reduced storage requirements from 6 MB uncompressed to 200 kB at a compression rate of 30:1. This successful compression opens new possibilities of intra- and extra-hospital and global information for 3D sonography. The key to this communication is not only volume compression, but also the fact that the 3D examination can be simulated on any PC by the developed 3D software. PACS teleradiology using digitized radiographs transmitted over standard telephone lines. Systems in combination with the management systems of HIS and RIS are available for archiving, retrieval of images and reports and for local and global communication. This form of tele-medicine will have an impact on cost reduction in hospitals, reduction of transport costs. On this fundament worldwide education and multi-center studies becomes possible.
Kratochwil
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Department of Radiotherapy, University of Vienna, Währinger Gürtel 18-20, A 1090 Vienna, Austria.
Lee
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Schoisswohl
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D000465:Algorithms; D016477:Artifacts; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016247:Information Storage and Retrieval; D011873:Radiology Information Systems; D019112:Teleradiology / Q000379:methods*; D016216:Ultrasonography, Prenatal / Q000379:methods*