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Introduction

Fast access to large data sets for study is still often limited by inefficiencies in image display imposed by current technology and implementation. Typically, a relatively small subset of an image database is loaded into the Random Access Memory (RAM) of a computer workstation. A user can then scan through these images efficiently because of the fast access to RAM memory. Delays in this process occur when the amount of data overwhelms the available RAM and the user must pause to load new images into RAM. The image review and analysis process becomes tedious. A partial solution to this is to add more RAM but this is expensive and inflexible.

Most image display systems rely on the common Graphical User Interface (GUI) consists of a menu sub system and various functions activated by travelling through layers of menus. While easy to implement, this approach does not provide the user with enough immediate feedback and interaction when dealing with large amount of images. Many powerful image-processing functions can be applied to the currently displayed image but switching from one image to another requires some effort. Since this imaging model normally requires an entire image to be in memory, animating hundreds or thousands of large images is also not practical.

Flashback Imaging has developed a radically different technique that bypasses RAM. The unique achievement of this approach is that the size of the database of images to be viewed is not limited by the amount of available RAM. It is only limited by the size of the hard disk upon which the data is stored. Image display and animation (or looping) takes place directly from disk. The computer monitor becomes a window onto the hard drive with the ability to view file sequences of unlimited length. The size of individual images does not affect the animation speed. The animation can be done with the full quantitative data set. Creation of MPEG, QuickTime or other special animation file formats (and the associated time-loss and data degradation) is not required.

Another very important feature is that the implementation is successful on conventional desktop PCs. Expensive workstations are not necessary for the display tasks. The application of this image browser software engine to the Visible Human Project data sets led to the software suite called The Visible Human Explorer. Even on a standard 486 or Pentium computer system with as little as 4 Megabytes of RAM, the software allows the user to freely scan along the axial, coronal, or sagittal images of the Visible Man or Visible Woman at full spatial resolution. Through mouse control, the user can loop, roam, and pan around in a sequence of images while animation continues. Furthermore, a 3D volumetric perspective mode is supported where the user can interactively navigate the entire Visible Man or Visible Woman bodies.

Successful implementation of this access capability has led to the evaluation of tasks in medical research and practice as well as education. Some of these are discussed here.

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