title: Evaluation of imaging performance of a taper optics CCD; FReLoN' camera designed for medical imaging.
abstract: The purpose of this work was to assess the imaging performance of an indirect conversion detector (taper optics CCD; FReLoN' camera) in terms of the modulation transfer function (MTF), normalized noise power spectrum (NNPS) and detective quantum efficiency (DQE). Measurements were made with a synchrotron radiation laminar beam at various monochromatic energies in the 20-51.5 keV range for a gadolinium-based fluorescent screen varying in thickness; data acquisition and analysis were made by adapting to this beam geometry protocols used for conventional cone beams. The pre-sampled MTFs of the systems were measured using an edge method. The NNPS of the systems were determined for a range of exposure levels by two-dimensional Fourier analysis of uniformly exposed radiographs. The DQEs were assessed from the measured MTF, NNPS, exposure and incoming number of photons. The MTF, for a given screen, was found to be almost energy independent and, for a given energy, higher for the thinnest screen. At 33 keV and for the 40 (100) microm screen, at 10% the MTF is 9.2 (8.6) line-pairs mm(-1). The NNPS was found to be different in the two analyzed directions in relation to frequency. Highest DQE values were found for the combination 100 microm and 25 keV (0.5); it was still equal to 0.4 at 51.5 keV (above the gadolinium K-edge). The DQE is limited by the phosphor screen conversion yield and by the CCD efficiency. At the end of the manuscript the results of the FReLoN characterization and those from a selected number of detectors presented in the literature are compared.
authors.affiliation: European Synchrotron Radiation Facility, BP 220, 6 rue Horowitz, 38043 Grenoble CEDEX 9, France.
authors.forename: Paola
authors.initials: P
authors.lastname: Coan
authors.forename: Angela
authors.initials: A
authors.lastname: Peterzol
authors.forename: Stefan
authors.initials: S
authors.lastname: Fiedler
authors.forename: Cyril
authors.initials: C
authors.lastname: Ponchut
authors.forename: Jean Claude
authors.initials: JC
authors.lastname: Labiche
authors.forename: Alberto
authors.initials: A
authors.lastname: Bravin
mesh_terms: D003952:Diagnostic Imaging / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D055095:Optics and Photonics / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D014159:Transducers