At RSNA, Philips is introducing its IQon Spectral CT system, the world’s first spectral-detector CT scanner. Spectral CT provides information about tissue composition by determining energy levels of detected X-ray photons. The information provided is similar to that obtained by dual-energy CT, but without some of the typical trade-offs associated with that technique.
At the core of the IQon Spectral CT lies a fundamentally new spectral detector, that can discriminate between X-ray photons of multiple high and low energies simultaneously. Philips likens this to using a prism to split a beam of white light into its components, the colors of the rainbow. This way not only anatomical information is obtained, but also information about the composition of the scanned tissue. This data is visualized by a color image or can be integrated for further image processing.
Some of the substances typically visualized with spectral CT data are calcium, iodine, and uric acid crystals. This has been used, for example, to quantify calcium content, determine kidney stone composition, and to characterize plaques. One of the most useful applications, perhaps, is the ability to reconstruct virtual non-contrast exams, by subtracting the iodine signal from post-contrast images. This way only a post-contrast scan needs to be obtained instead of both a pre- and post-contrast scan, so the radiation dose is halved. Many more potential applications exist and in theory it should also allow for scans with much lower doses of contrast medium.
In comparison to dual-energy CT, spectral CT is always on, with all information obtained during the single scan. Thus, there is no need to determine beforehand whether this information is actually needed, as it can be accessed at any time. Furthermore, the radiation dose is not increased, whereas for dual-energy CT the radiation dose tends to be higher than for conventional scans. Also, because data is obtained in a single scan, it is not affected by movement artifacts which may occur when two separate acquisitions are needed, as with some dual-energy CT’s. Altogether, spectral CT seems to be a major step forward in CT technology, but we will have to wait a little longer to see it in practice, as the IQon Spectral CT is still awaiting FDA clearance.
White paper describing spectral CT: Exploring the spectrum – Advances and potential of spectral CT…