Monochromatic images erase beam-hardening artifacts

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Synthesized monochromatic imaging with fast kV switching at 40 keV to 70 keV may boost the magnitude and uniformity of aortic enhancement for a wide range of body sizes, say researchers at Duke University.

A recent study in Radiology by Schindera and colleagues showed that beam-hardening artifacts may "substantially contribute to reduced arterial enhancement" in larger patients undergoing thoracoabdominal CT angiography, particularly at higher tube voltages, co-investigator Dr. Daniele Marin told AuntMinnie.com.

But synthesized monochromatic imaging could be the cure. To test the hypothesis that monochromatic images generated from a fast kV-switching, single-source, dual-energy CT acquisition may correct for beam-hardening artifacts, Marin and her colleagues performed a phantom study simulating typical contrast enhancement in the abdominal aorta. The phantoms were filled with a mixture of iodine and water.

In addition to the polychromatic 140-kVp source images, synthesized monochromatic datasets were reconstructed at x-ray energies ranging from 40 keV to 140 keV at 10-keV increments. The investigators drew regions of interest in the aortic lumen and background water at eight different locations along the z-axis of the phantom, and they measured aortic attenuation and signal-to-noise (S/N) ratio in various cross sections of the phantom and different datasets.

In every dataset, there was a negative correlation between the phantom's cross-section area and aortic attenuation measured as S/N ratio, they reported. The difference in aortic attenuation between the smallest and largest cross-section area of the phantom was significantly smaller for the 40-, 50-, 60-, 70-, and 80-keV datasets compared with the other monochromatic datasets.

Mean S/N ratio was also significantly higher for the 40-, 50-, 60-, and 70-keV datasets compared with the other monochromatic datasets and the 140-kVp polychromatic dataset (p < 0.05 for all comparisons), Marin and colleagues Dr. Rendon Nelson; Jim Colsher, PhD; and Joshua Wilson, PhD, reported.

Synthesized monochromatic imaging at x-ray energies ranging from 40 keV to 70 keV may improve the magnitude and uniformity of aortic enhancement for different body sizes.

"Within a certain range of x-ray energies, synthesized monochromatic imaging has the potential to minimize beam-hardening artifacts, yielding uniform aortic enhancement across different body sizes," according to Marin. "This may increase the reproducibility of vascular and parenchymal contrast enhancement among different patients, using body weight-adjusted contrast medium injection protocols."

Synthesized monochromatic imaging can be easily and rapidly generated at 101 different energies (from 40 keV to 140 keV with 1-keV increments), using the Gemstone Spectral Imaging (GE Healthcare) viewer, she said.