X-ray computed tomography (CT) was invented in the late 1960s and early 1970s by Godfrey Hounsfield and Allan McLeod Cormack [1]. It has now become a very valuable medical imaging technology with applications in the diagnosis of many different conditions and injuries. The number of CT scans performed worldwide per year is now numbered in the hundreds of millions. Every material or substance has a characteristic, energy dependent X-ray attenuation profile, which influences the attenuation or image contrast observed in CT images acquired at different X-ray tube voltages. For example, see Figure 1, where the energy attenuation profiles of gold and iodine are presented. In Hounsfield's original paper on CT, he raised the possibility that materials could be identified via two CT scans performed at different X-ray tube voltages and the comparison of the data thus acquired [2], a technique sometimes referred to as "dual energy" CT. This is normally carried out with X-ray tube voltages of 80 and 140 kV. There are many applications of dual energy CT, for example in atherosclerosis [3], the diagnosis of gout [4], bone density determinations [5], iron quantification [6] and detection of urinary calculi [7]. This technique was first explored in the late 1970s and 1980s [8, 9], but the scans had to be performed at the two energies one after the other, which led to problems in image registration and other difficulties that discouraged development in this area [10].

Original languageEnglish
Issue number1
StatePublished - 2011


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