title: Imaging properties of small-pixel spectroscopic x-ray detectors based on cadmium telluride sensors.
abstract: Spectroscopic x-ray imaging by means of photon counting detectors has received growing interest during the past years. Critical to the image quality of such devices is their pixel pitch and the sensor material employed. This paper describes the imaging properties of Medipix2 MXR multi-chip assemblies bump bonded to 1 mm thick CdTe sensors. Two systems were investigated with pixel pitches of 110 and 165 μm, which are in the order of the mean free path lengths of the characteristic x-rays produced in their sensors. Peak widths were found to be almost constant across the energy range of 10 to 60 keV, with values of 2.3 and 2.2 keV (FWHM) for the two pixel pitches. The average number of pixels responding to a single incoming photon are about 1.85 and 1.45 at 60 keV, amounting to detective quantum efficiencies of 0.77 and 0.84 at a spatial frequency of zero. Energy selective CT acquisitions are presented, and the two pixel pitches' abilities to discriminate between iodine and gadolinium contrast agents are examined. It is shown that the choice of the pixel pitch translates into a minimum contrast agent concentration for which material discrimination is still possible. We finally investigate saturation effects at high x-ray fluxes and conclude with the finding that higher maximum count rates come at the cost of a reduced energy resolution.
authors.affiliation: German Cancer Research Center-DKFZ, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany. thomas.koenig@kit.edu
authors.forename: Thomas
authors.initials: T
authors.lastname: Koenig
authors.forename: Julia
authors.initials: J
authors.lastname: Schulze
authors.forename: Marcus
authors.initials: M
authors.lastname: Zuber
authors.forename: Kristian
authors.initials: K
authors.lastname: Rink
authors.forename: Jochen
authors.initials: J
authors.lastname: Butzer
authors.forename: Elias
authors.initials: E
authors.lastname: Hamann
authors.forename: Angelica
authors.initials: A
authors.lastname: Cecilia
authors.forename: Andreas
authors.initials: A
authors.lastname: Zwerger
authors.forename: Alex
authors.initials: A
authors.lastname: Fauler
authors.forename: Michael
authors.initials: M
authors.lastname: Fiederle
authors.forename: Uwe
authors.initials: U
authors.lastname: Oelfke
mesh_terms: D019187:Cadmium Compounds; D003287:Contrast Media; D007091:Image Processing, Computer-Assisted; D019047:Phantoms, Imaging; D011874:Radiometry; D013691:Tellurium; D013696:Temperature; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014867:Water
chemical_list: D019187:Cadmium Compounds; D003287:Contrast Media; D014867:Water; D013691:Tellurium; C028337:cadmium telluride