Dual Source CT Scanners

Dual Xray Tube and Dual Detectors CT Scan

Dual Source CT scanner is a new CT technology and it was introduced to U.S hospital in 2006. Known as dual source CT, the new design uses two sets of xray tube and two corresponding detector arrays in a single CT scan gantry.

The dual-source CT design uses two x-ray tubes and two corresponding detectors positioned at 90°
from each other. (Reprinted with permission from Flohr TG, Schoept UJ, Ohnesorge BM. Chasing the heart: new developments for cardiac CT.

In practical application, the second detector array is restricted by the space available in the gantry. Therefore, one detector array covers the entire scan field of view (FOV) in approximately 50cm, whereas the 2nd detector is limited to a smaller central field of view.

In practical application, the second detector
array is restricted by the size available in the gantry. Therefore,
one detector array covers the entire scan field of view
(approximately 50 cm), whereas the second detector is limited
to a smaller, central field of view. (Reprinted with permission
from Flohr TG, Schoept UJ, Ohnesorge BM. Chasing the
heart: new developments for cardiac CT. J Thorac Imag
2007;22:4–16.)

With the 2 tubes and detector mounted at right angles, both helical acquisitions run simultaneously. The ideal of the dual source CT is not new. The concept was attempted years ago on single slice scanner, but the early helical scan technology limited its application. Siemens Medical Solutions (Forchheim, Germany) resurrected the idea to produce the Somatom Definition CT Scanner.

Dual Source CT Advantage

The primary goal and function of the dual source CT scanner design is to increase the scan speed. This is particularly valuable in cardiac scanning in which it is hoped that the increased speed will allow clinicians to dispense with the use of B-blockers for slowing heart rates during Cardiac Scan studies. The radiation dose to the patient is not higher when the dual source CT scanner is used in cardiac scanning.

A second potential advantage of the dual source CT system arises from the fact that the two xray tubes, although working simultaneously, have the ability to produce xray photons possessing different energies. That is for a given scan each xray tube can use a different kVp setting. Recall that beam attenuation is caused by absorption and scattering of radiation by the object scanned. The attenuation is dependent not just on the density of the object scanned but also on the energy of the xray photons. Thus, additional information can be learned about the object scanned when two xray energies are used and the different in attenuation is analyzed. This works particularly well in materials with high atomic numbers, such as iodine. Theoretically, this strategy can be used to differentiate iodine from other dense materials. Another idea is to use the dual energy concept to differentiate body tissues without the application of contrast media. However, because soft tissue do not possess high atomic numbers this is likely to be more difficult to achieve.