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Title: Fundamental x-ray interaction limits in diagnostic imaging detectors: Frequency-dependent Swank noise

A frequency-dependent x-ray Swank factor based on the ''x-ray interaction'' modulation transfer function and normalized noise power spectrum is determined from a Monte Carlo analysis. This factor was calculated in four converter materials: amorphous silicon (a-Si), amorphous selenium (a-Se), cesium iodide (CsI), and lead iodide (PbI{sub 2}) for incident photon energies between 10 and 150 keV and various converter thicknesses. When scaled by the quantum efficiency, the x-ray Swank factor describes the best possible detective quantum efficiency (DQE) a detector can have. As such, this x-ray interaction DQE provides a target performance benchmark. It is expressed as a function of (Fourier-based) spatial frequency and takes into consideration signal and noise correlations introduced by reabsorption of Compton scatter and photoelectric characteristic emissions. It is shown that the x-ray Swank factor is largely insensitive to converter thickness for quantum efficiency values greater than 0.5. Thus, while most of the tabulated values correspond to thick converters with a quantum efficiency of 0.99, they are appropriate to use for many detectors in current use. A simple expression for the x-ray interaction DQE of digital detectors (including noise aliasing) is derived in terms of the quantum efficiency, x-ray Swank factor, detector element size, and fillmore » factor. Good agreement is shown with DQE curves published by other investigators for each converter material, and the conditions required to achieve this ideal performance are discussed. For high-resolution imaging applications, the x-ray Swank factor indicates: (i) a-Si should only be used at low-energy (e.g., mammography); (ii) a-Se has the most promise for any application below 100 keV; and (iii) while quantum efficiency may be increased at energies just above the K edge in CsI and PbI{sub 2}, this benefit is offset by a substantial drop in the x-ray Swank factor, particularly at high spatial frequencies.« less
Authors:
; ;  [1] ;  [2] ;  [3] ;  [4]
  1. Imaging Research Laboratories, Robarts Research Institute, P.O. Box 5015, London, Ontario N6A 5K8 (Canada)
  2. (Canada) and Department of Medical Biophysics, University of Western Ontario, London, Ontario, N6A 3K7 (Canada)
  3. (Canada) and London Regional Cancer Program, London Health Sciences Centre, London, Ontario, N6A 4L6 (Canada)
  4. (Canada) Departments of Diagnostic Radiology and Nuclear Medicine, London Health Sciences Centre, London, Ontario, N6A 5W9 (Canada) and Department of Medical Biophysics, University of Western Ontario, London, Ontario, N6A 3K7 (Canada)
Publication Date:
OSTI Identifier:
21120851
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 35; Journal Issue: 7; Other Information: DOI: 10.1118/1.2936412; (c) 2008 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; BIOMEDICAL RADIOGRAPHY; CESIUM IODIDES; COMPTON EFFECT; IMAGE PROCESSING; LEAD IODIDES; MAMMARY GLANDS; MONTE CARLO METHOD; PHOTOEMISSION; QUANTUM EFFICIENCY; SEMICONDUCTOR MATERIALS; TRANSFER FUNCTIONS; X RADIATION