Gigapixel software: 'zoom and enhance' for MRI

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  • Published: Nov 1, 2010
  • Author: David Bradley
  • Channels: MRI Spectroscopy
thumbnail image: Gigapixel software: 'zoom and enhance' for MRI

Gigapixel imagery

Computer scientists at the University of Utah have developed software that can generate rapid previews of super-high resolution images for medical, astronomical, and other applications. Images containing billions to hundreds of billions of pixels drain computer resources rapidly but a new technique for analysing the data could allow gigapixel MRI scans and other images to be previewed and manipulated much more easily and quickly than is currently possible.

Valerio Pascucci of the University of Utah and its Scientific Computing and Imaging (SCI) Institute explains how sampling only a fraction of the pixels in an enormous image, whether satellite photo or composite of hundreds of high-resolution images it is possible to generate a good approximation or preview so that the viewer can interact or quickly zoom in on areas of interest. The classic "zoom and enhance" of TV and movie fiction.

Atlanta and Salt Lake

"You can go anywhere you want in the image," explains Pascucci. "You can zoom in, go left, right. From your perspective, it is as if the full 'solved' image has been computed." The new software - Visualization Streams for Ultimate Scalability, or ViSUS - runs just as well on a large computer as on a smart phone, he adds.

The software has two key characteristics that work together: "One is the way we store the images - the order in which we store the pixels on the disk. That is part of the technology being patented" because the storage format "allows you to retrieve the sample of pixels you want really fast," says Pascucci. The second characteristic is how the data is processed. The software handles image data as a subset of the total pixels. The image processing method can produce previews at various resolutions by taking progressively more and more pixels from the data that make up the entire full-resolution image. "The preview has constant size, so it can always fit in memory, even if the fine-resolution data keep growing," Pascucci adds. "We don't need to read all the data to give you an approximation of the full image."

If an image contained a terabyte of data - a trillion bytes - the software could produce a good approximation of the image using only one-millionth of the total image data, or about a megabyte, Pascucci says. In a trial run, the researchers used the software to seamlessly merge images. They combined a 3.7-gigapixel image of the entire Earth with a 116-gigapixel satellite photo of the city of Atlanta, zooming in on the Gulf of Mexico and putting Atlanta underwater there to demonstrate how overlays might be done as well as offering a nod to artistic potential.

The team also used a camera mounted on a robotic panning device and placed atop a University of Utah building to take 611 photographs during a six-hour period. Together, the photos recorded images of the entire Salt Lake Valley. At full resolution, it took them four hours to do "panorama stitching," which is stitching the mosaic of photos together into a 3.27-gigapixel panorama of the valley that eliminated the seams between the images and differences in their exposures. Using ViSUS, it took only two seconds to create a "global preview" of the entire Salt Lake panorama that looked almost as good - and had a relatively low resolution of only 0.9-megapixels, or only one-3,600th as much data as full-resolution panorama. And that preview image is interactive, so a photo editor can make different adjustments - such as tint, colour intensity and contrast - and see the effects in seconds.

3D MRI on an iPad

The team has now gone beyond the 116-gigapixel Atlanta image and, in unpublished work, have edited satellite images of multiple cities exceeding 500 gigapixels. The next target: a terapixel image - 1,000 gigapixels or 1 trillion pixels. The researchers suggest that the method might be used to edit medical images such as MRI and CT scans. He adds that the software could handle 3D just as effectively as it can handle two-dimensional images. The software will also be useful in examining high-resolution micrographs.

Pascucci worked with colleagues Brian Summa, a doctoral student in computing, Giorgio Scorzelli, a senior software developer; and Peer-Timo Bremer, a computer scientist at Lawrence Livermore National Laboratory in California, where co-author Ming Jiang also works.

Pascucci told SpectroscopyNOW that, "We already have a working prototype for 3D imaging where one can visualize large data sets like the anatomical images of the Visible Human Female (VHF)." He points out that this works locally and remotely on a device like an iPhone or iPad.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

This panoramic mosaic of the Salt Lake Valley was taken by a camera mounted on a robotic panning device atop a University of Utah building. It consists of more than 600 separate photographs that contain a total of 3.27 gigapixels (3.27 billion pixels) of image data. The seams between individual photos are readily apparent, as are differences in light exposure. To edit the photos into a single, seamless, evenly exposed panorama would take hours using normal methods to edit such huge images. The mosaic has been reduced to about 1 megabyte in this image.
Coping with gigapixels
MRI on an iPad (Credit: Pascucci)
MRI on an Apple iPad

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