3D outperforms 2D in compressing thinner CT slices

Contrary to studies in the current literature and accepted practice, the 2D JPEG2000 compression standard may not provide acceptable compression for the thinnest CT slices that are being produced today. The proposed 3D JPEG2000 compression standard provides significant advantages over its 2D counterpart for these thinner slices, according to a study from the Geisinger Medical Center in Danville, PA.

Information and data overload introduced by multidetector CT scanners provided the incentive for the researchers to discover acceptable levels of image compression. Citing a dearth of academic literature addressing the compression of the thinner CT slices, they set out to compare the current 2D compression standard with the developmental 3D JPEG2000 standard, said Dr. Eliot Siegel, chief of radiology and nuclear medicine at the VA Maryland Health Care System, during a Saturday SCAR scientific session.

Researchers led by Dr. Khan M. Siddiqui from Geisinger Medical Center examined five thoracic CT data sets gathered from a 16-detector scanner. They used 0.75-mm collimation and reconstructed the slices into thicknesses of 0.75 mm, 1.5 mm, 3 mm, 6 mm, and 10 mm. They used compression levels ranging from 4:1 to 64:1 for both the 2D and 3D compression modes.

The team measured the outcomes using peak signal-to-noise ratio and the Sarnoff's JNDmetrix visual discrimination model.

"We were trying to figure out what level of compression one could apply and still have the images remain visually lossless," Siegel said.

The thinnest slices proved to be the least compressible using the 2D compression standard. The effect was especially marked at higher compression levels. The 3D compression method, however, resulted in much higher quality compressed images. And with the 0.75-mm slices, the 3D technique did not show image degradation like the 2D standard, but was comparable to the image quality of the 10-mm slices at all levels of compression.

The research suggests that 2D compression of 0.75-mm slices could result in clinically significant degradation of the images, Siegel said.

The adoption of a 3D JPEG2000 compression standard by vendors and the medical community would likely result in improved ratios of compression for large CT data sets, according to Siegel. He cautioned, however, that future studies would have to examine how CAD systems, which do not use the same visual systems that humans do for detection, would respond to the compression.