RC 113 - Single-dual-multi-energy CT
1. To learn about the basics of dual-energy CT (DECT).
2. To understand today's photon counting detector technology.
3. To learn how DECT is applied in clinical practice.
Dual-energy CT acquisition is possible using either single-source CT or dual-source CT. In single-source CT units, a generator switches x-ray tube potential from 80 kVp to 140 kVp corresponding to photon energies from about 40 keV to 140 keV. For each exposure, the exposure time is only 0.5 msec, allowing simultaneous acquisition of low-kVp and high-kVp images. Dual-source CT scanners are composed of 2 tubes and 2 detector arrays. The 2 tubes are positioned at 90 degrees from each other. For dual-energy CT the potential applied across the 2 tubes is 80 kVp to 140 kVp. The tube load (mAs) is adjusted accordingly to 50 mAs for the high-kVp tube and 200 mAs for the low-kVp tube. Other approaches have been introduced through energy-sensitive detectors and photon counting detectors. All CT examinations should be optimised to achieve diagnostic image quality with the lowest radiation dose possible. Dose optimisation of dual-energy examinations is an area of great interest for both medical physicists and radiologists. The replacement of pre-contrast imaging by virtual non-contrast-enhanced imaging provides a great opportunity of radiation dose reduction. Moreover, several techniques and tools have been developed for CT dose optimisation and these methods are also applicable for dual-energy CT studies. For example, application of new iterative reconstruction algorithms, use of automatic exposure control and other dose saving tools may help to reduce patient doses considerably.
1. To learn about the underlying physics and today’s technology.
2. To see potential advantages compared to single-energy CT.
3. To appreciate the rationale behind clinical applications.
Although the first applications of dual-energy CT (DECT) were already introduced in the 1980s, they were not adopted in clinical practice. However, with advancements in the CT systems, DECT experienced its comeback and is now clinically emerging. In this talk, we will explain the technological basics of diagnostic DECT and show its clinical potential. First, the general idea of CT acquisition is reviewed to acknowledge the spectral information that DECT provides. The fundamental underlying physics of DECT is explained. In particular, it is derived how spectral acquisition allows to parameterise the energy-dependent attenuation coefficient inaccessible to single-energy CT. The different techniques for acquisition of DECT will be shortly compared. Dual-energy data can be post-processed and presented in various ways (e.g. monochromatic images, iodine maps or virtual non-contrast images). The individual possibilities are thereby described on the basis of the introduced physical principles. Finally, an overview of main clinical applications of DECT is given including the detailed review of different clinical example cases. Where appropriate, a comparison to single-energy CT is given to fully appreciate the additional value of DECT.
1. To learn about the underlying physics and technological solutions.
2. To understand the potential advantages compared to dual-energy CT.
3. To appreciate how mature today’s photon counting technology is.
Medical CT imaging has recently advanced due to the introduction of dual-energy techniques. Material composition and density in the body are disentangled using the energy information in the x-rays traversing the body. The added information can be combined with the conventional image using colours or other techniques. Realizing the full potential of the newly tapped energy information will require a major technological change from the scintillating crystals and light sensing electronics in current use to semiconductor detectors and electronics sensitive to each photon and its energy, individually. The current technology is called indirect and integrating detection, and the new and emergent technology is called direct conversion photon counting. Photons are absorbed in high Z, high band gap, high crystallinity, thick semiconductors, notably Cd(Zn)Te, producing a very compact ball of electric charge that is transferred to external electronics by a fine grid of contact electrodes on the semiconductor surface. The small size of the charge ball also permits a high resolution and contrast improvement in CT, potentially without an increase of patient dose. The new technology has been introduced commercially in the past decade in less demanding SPECT imaging at 10-1photons/s/mm2 and now in our CT research prototypes the detector development has permitted close to the 109photons/s/mm2 needed for CT. Verification images from phantoms and preclinical trials, including resolution tests, and high Z contrast agents will be shown.
1. To learn about medical applications and potential benefits.
2. To see which single energy applications should be replaced by dual-energy applications, and why.
3. To find out what additional multi-energy CT applications would be nice to have.
Dual-energy CT has been introduced more than ten years ago and since then various clinical applications from head to toe have been described in the scientific literature. A clear added value of each clinical application needs to be proven to transfer them into clinical routine. Besides optimization of the clinical workflow of dual-energy CT, including post-processing of the additional datasets, the radiation exposure to the patient is an important aspect which decides if dual energy maintains a success story. To promote the wide-spread use of dual-energy CT, there is a definite need for future investigations on the outcome of dual-energy CT, such as patient care, costs and workflow.