The technical background of Dual Energy Imaging

A dual-source CT system* simultaneously uses two x-ray sources at different energy levels. This makes it possible to differentiate between fat, soft tissue and contrast material (iodine) on the basis of their unique energy-dependent attenuation profiles.

The Principle of Two X-ray Sources

With two x-ray sources, a DSCT system allows two different kV levels and mAs settings to be used simultaneously. The x-ray tube’s kilovoltage (kV) determines the average energy of the photons in the x-ray beam. Changing the tube potential alters the photon energy, resulting in a corresponding modification of the attenuation of the x-ray beam in the scanned materials. Thus, the x-ray absorption is energy dependent: scanning an object with 80 kV (attenuation A) results in a different attenuation than with 140 kV (attenuation B).

Figure 1: Schematic illustration of the principle of Dual Energy imaging with a DSCT system. Both tube/detector systems are mounted with an angle of 90°; images at low and high voltage are acquired simultaneously. Because x-ray absorption is energy dependent, changing the tube’s kilovoltage results in a material-specific change of attenuation.

Differentiation of Materials and Tissues

With DSCT, different tissues and materials appear in different colors, allowing them to be more easily identified, differentiated, characterized, and isolated. Improved differentiation of difficult-to-analyze anatomical areas may be especially important prior to surgery or for a special diagnosis.

Gathering Additional Information

Depending on the clinical question, images may be further processed with specific software algorithms implemented in the syngo Dual Energy software. Dual Energy techniques can be used to remove the contrast material from the image, as well as to characterize the composition of an article of interest in the image – for example, a stone. In addition, fused images are provided for initial diagnosis. These are created as a weighted average that has a low image noise and a normal attenuation, like images scanned at 120 kV tube potential.

Dual Energy CT adds functional information to morphological information based on x-ray attenuation coefficients.

*all parameters are given for the Somatom Definition®