enables an individual in a wheelchair wearing a head-mounted display and a DataGlove to travel through a space testing for access, maneuverability, counter heights, and reach distances for doors and cabinets.

Finally, the use of VE is being explored for behavioral therapy. Hodges et al. (1993) report on a project at the Graphics, Visualization, and Usability Center at the Georgia Institute of Technology that makes use of VE technology to provide acrophobic patients with fear-producing experiences of heights in a safe situation. Advantages of this approach are that VE provides the therapist with control over the height stimulus parameters and with the ability to isolate those parameters that generate a phobic response in the individual. In another project, Kijima et al. (1994) have been exploring the use of VE technology to create a virtual sand box to be used for virtual sand play. Sand play, a technique used in diagnosing an individual's mental state and providing psychotherapy, involves patients creating landscapes and populating them with bridges, buildings, people, animals, and vegetation. An important advantage of using VE for sand play is that the patient's actions are recorded and can be viewed several times by several trained observers.

Issues to be Addressed

Although the long-term potential of VR for medical applications is suggested by an extrapolation from current demonstrations, a number of research problems must be addressed to fulfill this potential.

  • Simulations of higher fidelity. The simulated organs and body structures seen by the simulator user are far from realistic, with graphics that are primitive and cartoon-like. Tactile and force feedback, an important consideration in simulating the actual "feel" of a surgical procedure, is mostly absent. Changes in visual perspective are not seen by the user in real time.

  • Realistic models of organs and other body structures. In current simulations, organs and body structures do not morph as real tissue does; for example, they do not deform with gravity or change shape with manipulation. Blood vessels should bleed; bile ducts should ooze; hearts should pump.

  • Better image registration techniques for augmented reality. In many cases, a VR surgical or diagnostic aid will require the superposition of images acquired from a number of different modalities (e.g., a CAT scan coupled with an ultrasound image). See-through displays must superpose artificially generated images on the real image through the user's eyes. Techniques for aligning these images so that the right parts correspond to each other remains a considerable intellectual problem.

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