Dimensional Media develops methodfor displaying volumetric 3-D images

Technology may lead to surgical simulators

Visualize a lifelike image of internal organs suspended abovean operating table. You reach out and touch the organ and "feel"it move in response to your probes. A scalpel incision dissectsthe tissue, which starts to bleed. You are learning a new procedureon a virtual cadaver. Is this a scene from Star Trek? It couldbe, but if all goes as planned, Dimensional Media Associates (DMA)of New York City could have a system to do this within a few years.

Dimensional Media's images are volumetric 3-D presentations thatdo not require special glasses or head-mounted displays for viewing,according to president Dr. Jonathan Prince.

"You can actually reach out and start to interact with thisimage," Prince said. "You can walk around it and seethe object from different angles, just as in real life."

Volumetric displays create images that physically fill a volumein space. The goal of such systems is to permit group viewingof 3-D objects with the naked eye, with no angular dependence,and in real time. Medical applications include high-resolutiondisplay of inherently 3-D diagnostic modalities such as MR andCT, as well as constructed 3-D data sets from PET or digital subtractionangiography. Eventually, even 3-D video endoscopy may be visualizedin this manner.

Under a contract from the Department of Defense's Advanced ResearchProject Agency (ARPA), Dimensional Media will develop a systemdesigned for use as a virtual surgical simulator. Surgical simulatorsuse a variety of virtual reality technologies and are being developedby a number of companies.

Some think the use of simulation in medical training will soonbecome widespread in much the same way that pilots are trainedon flight simulators. The first medical simulators are being evaluatedin education programs.

Dimensional Media will act as the program coordinator for thesimulator, which is targeted primarily for open-surgery applications.It will also supply its unique 3-D imaging technology.

Boston Dynamic of Boston will develop force feedback haptic devices,which allow users to interact with images floating in space. TheHuman Interface Lab of the University of Washington in Seattlewill help with other issues related to helping users effectivelyinteract with the 3-D image and manipulate objects. In addition,DMA recently announced that it will also work with the CentralResearch Labs, a London-based subsidiary of Thorn EMI, to developliquid crystal display (LCD) technology for use in 3-D image generation.

Full-motion images. Exactly how the 3-D suspended image is createdis still a closely guarded secret. But according to Prince, thekey is to construct a 3-D image from a series of planar imageslices, such as from a CT or MR scanner. Almost any image source,such as a CRT, LCD, or even a laser image, can be used as theinput to the projection system. Using a technique called multiplanaroptical elements, Dimensional Media projects the image, one planeat a time, into free space. By creating enough image planes anddoing it quickly enough, it creates the effect of a continuous,high-resolution 3-D image that floats in free space.

The approach uses some elements of holography but DMA does notconsider it purely holographic, according to Prince. Voxel ofLaguna Hills, CA, is one company developing a holographic-baseddisplay system for medical images (SCAN 9/23/92).

DMA creates a 3-D image by bouncing each planar image slice offmicro-moving optical surfaces, which are similar to devices usedto create laser light shows. The result is a virtual image thatcan be displayed inches or tens of feet from the projection point.The image can be made to focus in free space without the aid ofa surface to image upon. The technology also supports full-motionimages, Prince said.

Dimensional Media views development of medical products as theleading edge of technology commercialization. The company hasseveral commercial products for entertainment, point-of-purchaseretailing, and interactive kiosks. DMA anticipates having a productavailable for the medical market in the next two years.

Improving the image quality and viewing angles of the displayis where most of DMA's development efforts are focused. One wayto improve the image quality is to increase the number of planarimage layers that contribute to the full 3-D image. Another wayis to increase the resolution in the image plane.

Improving the technology requires very powerful graphics computers,such as Silicon Graphics Reality Engines, to display more pixelsin a shorter amount of time.

"Our current commercial products have about nine to 10 layersin the Z plane," Prince said. "With this ARPA contract,we plan to increase the number of layers to perhaps 50 to 60,at which point the transition between layers will not be visiblydiscernible."

Such a system will offer new capabilities, according to Prince.

"Not only will it improve the image quality by getting ridof any jaggies (step-like discontinuities in lines), but you willactually be able to put a ruler inside the image and measure afeature," he said.

This might be particularly useful for determination of tumorsizes, he said.

Dimensional Media Associates is a privately held company thatwas founded in 1993. It has several patents on its core technologywith more pending. It has aggressively sought out other volumetricdisplay developers, according to Prince.

"We have either bought or licensed their patents, or areworking on joint ventures with them," Prince said.