Spectral/photon-counting computed tomography

For over 100 years, x-rays have played a crucial role in imaging the internal structure of objects nondestructively. e usefulness of x-rays for medical purposes was recognized as soon as Wilhelm C. Röntgen took the famous transmission image of his wife’s hand in 1895 (Kevles 1996). For the next 7 decades, the same simple two-dimensional projection method, still known from dental x-rays, for example, remained the state of the art for medical imaging. It was not until the 1970s that x-ray imaging fundamentally changed with the invention of computed tomography (CT) (Ambrose 1973; Hounseld 1973) and the necessary reconstruction algorithms (Cormack 1963, 1964). Hounseld’s CT scanner allowed visualization of two-dimensional slices of the human body rather than projection images where all the organs are superimposed and overlapped. e technology was rened quickly over the next 20 years, decreasing scan times and radiation dose and increasing the spatial resolution and the eldof-view size. Medical imaging experienced another boost in the 1990s with the advent of multislice CT scanners. ey allowed acquisition of true three-dimensional data sets and reconstruction of volumetric images in a single scan. Even whole-body scans became possible with clinically acceptable scan times and radiation dose levels. Multislice CT (or MDCT for multidetector CT) is now the state-of-the-art technology for fast, high-resolution, and cost-eective imaging of the human body with a wide range of clinical applications. With gantry rotation times of <0.3 s and detectors with up to 320 rows, it is possible to scan entire organs like the heart in <1 s.