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Proceedings Paper

Efficiency of the human observer compared to an ideal observer based on a generalized NEQ which incorporates scatter and geometric unsharpness: evaluation with a 2AFC experiment
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Paper Abstract

Under certain assumptions the detectability of the ideal observer can be defined as the integral of the system Noise Equivalent Quanta multiplied by the squared object spatial frequency distribution. Using the detector Noise-Equivalent-Quanta (NEQD) for the calculation of detectability inadequately describes the performance of an x-ray imaging system because it does not take into account the effects of patient scatter and geometric unsharpness. As a result, the ideal detectability index is overestimated, and hence the efficiency of the human observer in detecting objects is underestimated. We define a Generalized-NEQ (GNEQ) for an x-ray system referenced at the object plane that incorporates the scatter fraction, the spatial distributions of scatter and focal spot, the detector MTFD, and the detector Normalized-Noise-Power-Spectrum (NNPSD). This GNEQ was used in the definition of the ideal detectability for the evaluation of the human observer efficiency during a two Alternative Forced Choice (2-AFC) experiment, and was compared with the case where only the NEQD was used in the detectability calculations. The 2-AFC experiment involved the detection of images of polyethylene tubes (diameters between 100-300 um) filled with iodine contrast (concentrations between 0-120 mg/cm3) placed onto a uniform head equivalent phantom placed near the surface of a microangiographic detector (43 um pixel size). The resulting efficiency of the human observer without regarding the effects of scatter and geometric unsharpness was 30%. When these effects were considered the efficiency was increased to 70%. The ideal observer with the GNEQ can be a simple optimization method of a complete imaging system.

Paper Details

Date Published: 6 April 2005
PDF: 12 pages
Proc. SPIE 5749, Medical Imaging 2005: Image Perception, Observer Performance, and Technology Assessment, (6 April 2005); doi: 10.1117/12.595870
Show Author Affiliations
Iacovos S. Kyprianou, Lab. for the Assessment of Medical Imaging Systems, NIBIB/CDRH, US FDA (United States)
Arundhuti Ganguly, Stanford Univ. (United States)
Stephen Rudin, Univ. at Buffalo (United States)
Daniel R. Bednarek, Univ. at Buffalo (United States)
Brandon D. Gallas, Lab. for the Assessment of Medical Imaging Systems, NIBIB/CDRH, US FDA (United States)
Kyle J. Myers, Lab. for the Assessment of Medical Imaging Systems, NIBIB/CDRH, US FDA (United States)


Published in SPIE Proceedings Vol. 5749:
Medical Imaging 2005: Image Perception, Observer Performance, and Technology Assessment
Miguel P. Eckstein; Yulei Jiang, Editor(s)

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