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Photon-counting mammography was introduced commercially in 2003 and was the first widely available application of photon-counting detector technology in medical x-ray imaging. [1] Photon-counting mammography improves dose efficiency compared to conventional technologies, [ 2 ] and enables spectral imaging .
Dual-energy imaging, i.e. imaging at two energy levels, is a special case of spectral imaging and is still the most widely used terminology, but the terms "spectral imaging" and "spectral CT" have been coined to acknowledge the fact that photon-counting detectors have the potential for measurements at a larger number of energy levels. [2] [3]
[2] [3] Due to the large volumes and rates of data required (up to several hundred million photon interactions per mm 2 and second [4]) the use of PCDs in CT scanners has become feasible only with recent improvements in detector technology. As of January 2021 photon-counting CT is in use at five clinical sites.
Medipix-3 is the latest generation of photon counting devices for X-ray imaging. The pixel pitch remains the same (55 μm) as well as the pixel array size (256x256). It has better energy resolution through real time correction of charge sharing.
Photon counting eliminates gain noise, where the proportionality constant between analog signal out and number of photons varies randomly. Thus, the excess noise factor of a photon-counting detector is unity, and the achievable signal-to-noise ratio for a fixed number of photons is generally higher than the same detector without photon counting.
Metal K-edge spectroscopy is a spectroscopic technique used to study the electronic structures of transition metal atoms and complexes. This method measures X-ray absorption caused by the excitation of a 1s electron to valence bound states localized on the metal, which creates a characteristic absorption peak called the K-edge. The K-edge can ...
Iodine-123 (123 I) is a radioactive isotope of iodine used in nuclear medicine imaging, including single-photon emission computed tomography (SPECT) or SPECT/CT exams. The isotope's half-life is 13.2232 hours; [1] the decay by electron capture to tellurium-123 emits gamma radiation with a predominant energy of 159 keV (this is the gamma primarily used for imaging).
Especially in photon counting detectors, the energy of an incident photon is correlated with the net sum of the charge in the primary charge cloud. This kind of detectors often use thresholds to be able to act over a certain noise level but also to discriminate incident photons of different energies.