How can we get the images twice faster altough the two tubes have different keVs?

The following question has been sent by KoYH:

How can we get the images twice faster altough the two tubes have different keVs?

Hello. I’m a radiology resident doctor in South Korea. First of all, sorry for my poor English.

I haven’t understood the basic principle of DSCT. My question is how can we get the images twice faster altough the two tubes have different keVs?

I read some articles that says attenuation, noise and contrast characteristics differ according to different keVs, therefore we can differentiate the contrast materials from bone using DSCT.

But how can we get the images faster, although the two tubes have different keVs (which makes the different HU results, noises and contrasts)? I mean, how is it possible to combine the images from each tubes into ONE set of images of ONE charateristics?

Thank you.

Hyun Woo Goo, M.D., Asan Medical Center, Seoul:

For dual energy CT, gantry rotation speed of 330 ms is used, which is different from cardiac application of dual-source CT. So it is not faster than usual scan mode. However, it is faster than any other CT systems with dual-energy scan mode.

Two x-ray tubes produce two different levels of tube potentials (kV or kVp). KeVs are not appropriate for polychromatic x-ray used in clinical CT systems. Monochromatic x-ray is used in synchrotron CT. To obtain comparable image noises of the two datasets, higher mA is used for a low kV (80 or 100). To produce dual-energy CT images, material decomposition algorithm is used and image-based method is used for combining the two image datasets.

For more information, I recommend a nice review article as follows: Johnson TR, Krauss B, Sedlmair M et al (2007) Material differentiation by dual energy CT: initial experience. Eur Radiol 17:1510-1517

Sincerely yours,

Hyun Woo Goo, M.D.

This question has also been answered by Anja Reimann, M.D. Read the article.