title: How spectroscopic x-ray imaging benefits from inter-pixel communication.
abstract: Spectroscopic x-ray imaging based on pixellated semiconductor detectors can be sensitive to charge sharing and K-fluorescence, depending on the sensor material used, its thickness and the pixel pitch employed. As a consequence, spectroscopic resolution is partially lost. In this paper, we study a new detector ASIC, the Medipix3RX, that offers a novel feature called charge summing, which is established by making adjacent pixels communicate with each other. Consequently, single photon interactions resulting in multiple hits are almost completely avoided. We investigate this charge summing mode with respect to those of its imaging properties that are of interest in medical physics and benchmark them against the case without charge summing. In particular, we review its influence on spectroscopic resolution and find that the low energy bias normally present when recording energy spectra is dramatically reduced. Furthermore, we show that charge summing provides a modulation transfer function which is almost independent of the energy threshold setting, which is in contrast to approaches common so far. We demonstrate that this property is directly linked to the detective quantum efficiency, which is found to increase by a factor of three or more when the energy threshold approaches the photon energy and when using charge summing. As a consequence, the contrast-to-noise ratio is found to double at elevated threshold levels and the dynamic range increases for a given counter depth. All these effects are shown to lead to an improved ability to perform material discrimination in spectroscopic CT, using iodine and gadolinium contrast agents. Hence, when compared to conventional photon counting detectors, these benefits carry the potential of substantially reducing the imaging dose a patient is exposed to during diagnostic CT examinations.
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute for Photon Science and Synchrotron Radiation (IPS) and ANKA Synchrotron Radiation Facility, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Koenig
authors.forename: Marcus
authors.initials: M
authors.lastname: Zuber
authors.forename: Elias
authors.initials: E
authors.lastname: Hamann
authors.forename: Angelica
authors.initials: A
authors.lastname: Cecilia
authors.forename: Rafael
authors.initials: R
authors.lastname: Ballabriga
authors.forename: Michael
authors.initials: M
authors.lastname: Campbell
authors.forename: Marie
authors.initials: M
authors.lastname: Ruat
authors.forename: Lukas
authors.initials: L
authors.lastname: Tlustos
authors.forename: Alex
authors.initials: A
authors.lastname: Fauler
authors.forename: Michael
authors.initials: M
authors.lastname: Fiederle
authors.forename: Tilo
authors.initials: T
authors.lastname: Baumbach
mesh_terms: D056951:Photoelectron Spectroscopy / Q000295:instrumentation / Q000379:methods*; D017785:Photons; D011859:Radiography / Q000295:instrumentation / Q000379:methods*; D012666:Semiconductors; D014965:X-Rays