what is Dual energy CT?

​Dual Energy CT (DECT) is a useful modern technology that expands the clinical utility of CT exams. By transmitting two different x-ray energy spectras through the patient's body, due to differential x-ray photon attenuation by your body's tissues as a function of energy, we can separate materials that previously looked identical in traditional CT scanning due to having similar attenuation at one energy.

For example, bone, hemorrhagic blood, iodine, crystals in kidney stones and gout, metallic stents, all appeared "white" (high attenuation) on traditional CT. Now we can tease all of these materials apart to provide better material characterization to radiologists. We are using this in hemorrhagic stroke patients as well as oncology diagnosis and treatment planning.
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Although installed at the hospital by service engineers, DECT comes with a complex background of physics, requiring a medical physicist to learn the concepts of x-ray production and interactions in the body, as well as vendor-specific acquisition methods & limitations in order to teach imaging technologists, radiologists, and other physicians to identify possible clinical applications of interest, facilitate clinical scan acquisition, image reconstruction, and the radiologic evaluation processes to get accurate and efficient utility out of the technology.

The AAPM's Task Group 291 recently published a helpful educational document called Principles and Applications of Multi-energy CT. You can read more about it here.