A majority of volume data is currently viewed as a series of static cross- sections which have been output to film. While this provides a direct representation of the data, the slices are fixed in their orientation, significantly restricting the doctor's view of the complete volume.
An improved environment for visualizing three-dimensional medical image data must include preserving the accuracy of the original data, while providing information to the user in a more efficient manner, and insuring that the new environment would be easily accessible by doctors and radiologists. Interactive slicing, for example, would be a significant improvement over a series of static slices, as it establishes a feedback loop between the user and the data.
The usefulness of any new modality for viewing volume data may be limited by the accessibility of the new technology. If there is only one machine in a hospital which can generate the new images, while static films remain significantly more accessible, then a majority of users will tend to make active use only of representations to which they feel they have the best access.
In defining an improved system for visualizing volume data, Vox-L sought to develop a solution which would not only provide a new angle on the data, but one which would be easily accessible to the user. The Vox-L system has been developed to address these considerations. It provides a highly graphical user interface which can be used directly by a physician without the assistance of a computer technician. Because the software components were developed to work with open systems, Vox-L was able to realize a reduction in the overall cost of its solution compared with related, dedicated technologies. This makes it possible for a hospital to provide a greater number of stations where the information can be reviewed using the new environment.
A ray-traced volume rendering creates images which accurately reflect the value of the model at each voxel (VOlume piXEL). Despite the obvious advantages of working directly with the voxel data, this approach has often been overlooked due to the computational expense of generating an image from a voxel dataset, which may range from sixteen to sixty-four megabytes in size, as as compared with the expense of working with polygonal datasets, which are often no more than a megabyte or two in size. Recent advances in the speed of general purpose computers combined with developments in the field of discrete ray-tracing algorithms have enabled Vox-L to maintain interactive ray-tracing rates even when working with full voxel datasets on desktop workstations.
By providing a stereoscopic view of the data, ambiguities are reduced and the amount of information conveyed simultaneously to the user is increased. This effect is most prominent when the three-dimensional reconstruction is translucent in nature, making visible structures within structures. The spatial relationships of these structures is then emphasized through stereopsis. The finer the detail of the model, the greater the gain realized when going to a full stereoscopic representation. While a polygonal model can be made translucent, there are often no more than a handful of surfaces within the model. In tracing a single ray through a voxel model, several hundred surfaces may be traversed, one for each voxel along the ray. All of the fine detail encountered during the ray-tracing process is then rapidly conveyed to the user by making full use of the human visual system.
The environment integrates a complete range of volume viewing capabilities, including interactive orthogonal and oblique slicing, surface rendering with variable thresholding, and true, stereoscopic ray traced volume rendering. When used in conjunction with traditional methods of viewing volume data, these new tools allow a user to comprehend and explore a volume data set in new ways, adding valuable insight to clinical diagnosis and medical research.
Stuart Bar-On or Tom Beshaw of Parallel Performance Group, at (602) 282-6300, or E-mail at ppg@ppgsoft.com, will be glad to answer any questions and provide information about Medical Imaging and Vox-L hardware and software. To get a free e-mail Newsletter subscription, send "Subscribe Imaging Newsletter" message to subscribe@ppgsoft.com.