Dual Energy CT – an Introduction (T. Johnson)

Dual Source CT (DSCT) was initially developed by Siemens to increase the temporal resolution of computed tomography for cardiac imaging.
The gantry rotation time of 0.33 seconds presented a physical boundary for scan speed that could only be overcome with an entirely new scanner design (1). As projection data from all aspects of an object are required to reconstruct an axial image, the new design with two orthogonal x-ray tubes and detectors could help to cut the time of data acquisition into half, thus doubling the temporal resolution to 75–83 ms. Several studies have meanwhile confirmed the clinical benefits of DSCT. In particular, cardiac imaging at high heart rates has become more robust, and dynamic evaluation of valves or myocardial motion is now feasible in CT(2-4).

Furthermore, it was evident that it would be possible to run both x-ray tubes at different potentials to obtain different x-ray spectra. It was conceivable that this would make further material differentiation possible versus that achieved with x-ray attenuation in Hounsfield units.

The idea of Dual Energy CT was not entirely new when DSCT became available. Already in the late 1970s there had been attempts to exploit the spectral information of CT scans acquired at different tube potentials(5-7). However, because it was necessary to scan the object twice, the distribution of iodine would change between both acquisitions, making detection of iodine in the dataset impossible. With DSCT, simultaneous acquisition has become feasible, opening the door to a multitude of new applications.

By now, Dual Energy CT is ready for routine clinical use. Several scan protocols offer additional clinically relevant information without additional contrast material or dose. Clinical applications include, for example, the assessment of contrast enhancement in focal organ lesions, pulmonary perfusion and ventilation imaging, angiography with bone removal and display of plaque distribution, kidney stone differentiation, and visualization of tendons and ligaments.

If this article was interesting for you, read other articles from our Dual Energy series by Thorsten Johnson:

• Technical Implementation of Dual Energy CT
• Physics of Dual Energy CT
• Clinical Applications of Dual Energy CT

References:

1. Flohr TG, McCollough CH, Bruder H, et al. First performance evaluation of a dual-source CT (DSCT) system. Eur Radiol 2006; 16:256-268.
2. Johnson TR, Nikolaou K, Wintersperger BJ, et al. Dual-source CT cardiac imaging: initial experience.Eur Radiol 2006; 16:1409-1415.
3. Johnson TR, Nikolaou K, Busch S, et al. Diagnostic accuracy of dual-source computed tomography in the diagnosis of coronary artery disease. Invest Radiol 2007; 42:684-691.
4. Leber AW, Johnson T, Becker A, et al. Diagnostic accuracy of dual-source multi-slice CT-coronary angiography in patients with an intermediate pretest likelihood for coronary artery disease. Eur Heart J 2007.
5. Avrin DE, Macovski A, Zatz LE. Clinical application of Compton and photo-electric reconstruction in computed tomography: preliminary results. Invest Radiol 1978; 13:217-222.
6. Chiro GD, Brooks RA, Kessler RM, et al. Tissue signatures with dual-energy computed tomography. Radiology 1979; 131:521-523.
7. Millner MR, McDavid WD, Waggener RG, Dennis MJ, Payne WH, Sank VJ. Extraction of information from CT scans at different energies. Med Phys 1979; 6:70-71.