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Introduction
Three-dimensional imaging offers a new approach to the analysis of complex anatomic relationships.1"4 Although three-dimensional reconstruction of CT data has been available since the late 1970s5, its acceptance has been hampered by a number of factors, including suboptimal image quality, limited display formats, lack of a user-friendly interface, and high cost. This article will present an overview of the state of the art in 3D imaging in 1988 as well as present a brief look at the future of 3D imaging.
Available Imaging Systems
The available 3D imaging systems can be divided into two broad categories: freestanding 3D imaging systems and add-on 3D software packages to the CT scanner. The freestanding systems include the Cemax 1500, (Cemax, Santa Clara, CA), DMI (Dimensional Medicine Ine, Minnetonka, MN), Camra SlOO (ISG Technologies, Ine, Mississauga, Ontario) and the PIC 2000 (Philips Medical Systems, Shelton, CT). The add-on systems include the 3D98 program by General Electric (for GE-9800 scanners) and the 3DCT program by Siemens (for the Siemens Somatom scanners).
The price for freestanding systems in early 1987 was in the range of $200,000 to $250,000; by early 1988, many system prices listed between $90,000 and $150,000, depending on the system and options chosen. The add-on programs cost in the range of $10,000 to $15,000.
Although a comparison of imaging systems always has the potential for observer bias, a review of the literature suggests that a comparison based on specific parameters may be possible. Therefore, systems were compared based on 1) image quality, 2) user interface, 3) system flexibility and capabilities, 4) clinical performance, and 5) image display formats.
Image Quality
One of the major limitations to the acceptance of 3D imaging has been image quality. The few articles and exhibits published and presented have had images that were not impressive. Product advertisements (presumably representing the "best" images an imaging system can provide) were of poor quality. The introduction of noise and artifact into such images was unacceptable and limited the growth of 3D imaging. A major part of the poor image quality can be ascribed to the reconstruction algorithm used.6 All freestanding and add-on 3D systems use a thresholding technique as a required preprocessing step prior to 3D reconstruction. By redistributing a continuous CT data spectrum...