"PVB is a highly interactive viewing system", stated PSC computer scientist Arthur Wetzel, who leads the PVB team. "It allows users to navigate easily through the Visible Human or other volumetric data and to select 2D slices for viewing with complete freedom, as suggested by the orientation of an object, not limited to top, front, and side views. The design of PVB allows this to happen quickly enough to serve a large number of simultaneously navigating users."
A 3D digital reconstruction of human male and female anatomy created in the mid-1990s, the NLM Visible Human is widely used as a resource in books, CD-ROMS and software. Its usefulness has been limited, nevertheless, by most viewing technologies, which only allow access from the customary right-angle planes, and by the need to display and manipulate large-volume graphical data at reasonable speed.
With primary support from the NLM grant and additional support from the National Institute of Health's (NIH) National Center for Research Resources, the PSC and UM researchers have developed a system that overcomes these limitations. PVB employs a unique axis-neutral system of data-structuring that facilitates viewing arbitrary slice-angles, which can make a pivotal difference in appreciating anatomical relationships. "Looking at the heart from only a front or side view", explained Dr. Wetzel, "does not allow you to see how close it is to the spine."
To gain speed, PVB employs innovative data-compression to represent large-volume graphical data. For highly compressible data, PVB achieves a compression-ratio greater than 30:1. Display response is further enhanced with a specially designed network-delivery system that allows up to 40 people simultaneously to navigate independently through the data in near real time. The compressed and restructured dataset is served from a high-speed network server at PSC.
Initial release is for the Visible Human Female and a subset of the Visible Mouse, a magnetic resonance microscopy dataset from Duke's Center for In Vivo Microscopy. PVB employs high-performance networking and performance monitoring to adapt to changing network conditions and load levels. This is facilitated through Web100 network performance tools developed at PSC and running on the PSC Visible Human server.
PVB also provides tools for users to segment and label anatomical structures. Work now in progress with UM anatomists involves tracing and capturing defined structures in three dimensions for incorporation into a comprehensive anatomical directory. Though not part of the initial release, PVB also supports a collaborative mode that lets a number of widely separated users share the same view and exchange control, helpful with teaching and research. EdgeWARP, a tool for morphometric analysis developed at UM, can also access the PSC Visible Human server. Another UM browser, iVoxel, is in development.
The NLM Visible Human was created by a team at the University of Colorado at Denver led by Victor M. Spitzer. Each dataset, male and female, is a digital reconstruction from thousands of ultra-thin, head-to-toe, vertical cross-sections, including 5189 slices at 0.33 mm intervals for the Visible Human Female. The original Visible Human Female comprises about 40 gigabtyes. Removal of the data that represents ice, from freezing the cadaver in blue gel, reduces this to about seven gigabytes. PVB data-compression allows it to be represented without loss of realism in about 3.5 gigabytes on the PSC Visible Human server.
PVB is supported by contract # N01-LM-0-3511 from the National Library of Medicine, titled "NGI Implementation to Serve Visible Human Datasets Phase II: Development of Test Beds". The Pittsburgh Supercomputing Center is a joint effort of Carnegie Mellon University and the University of Pittsburgh together with the Westinghouse Electric Company. It was established in 1986 and is supported by several federal agencies, the Commonwealth of Pennsylvania, and private industry.
More information, including image library, and download of PVB is available at the Pittsburgh Supercomputing Center Web site. Further details on the NLM Visible Human can be checked out at the National Library of Medicine Web site.