  In recent decades, developments in detectors for X-ray imaging have improved
dose efficiency. This has been accomplished with for example, structured
scintillators such as columnar CsI, or with direct detectors where the X rays
are converted to electric charge carriers in a semiconductor. Scattered
radiation remains a major noise source, and fairly inefficient anti-scatter
grids are still a gold standard. Hence, any future development should include
improved scatter rejection. In recent years, photon-counting detectors have
generated significant interest by several companies as well as academic
research groups. This method eliminates electronic noise, which is an advantage
in low-dose applications. Moreover, energy-sensitive photon-counting detectors
allow for further improvements by optimising the signal-to-quantum-noise ratio,
anatomical background subtraction or quantitative analysis of object
constituents. This paper reviews state-of-the-art photon-counting detectors,
scatter control and their application in diagnostic X-ray medical imaging. In
particular, spectral imaging with photon-counting detectors, pitfalls such as
charge sharing and high rates and various proposals for mitigation are
discussed.
