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Medical Physics / Volume 37 / Issue 7 / RADIATION IMAGING PHYSICS

Med. Phys. 37, 3527 (2010); http://dx.doi.org/10.1118/1.3447720 (11 pages)

Noise variance analysis using a flat panel x-ray detector: A method for additive noise assessment with application to breast CT applications

Kai Yang

Department of Radiology, University of California, Davis Medical Center, 4860 Y Street, Suite 3100 Ellison Building, Sacramento, California 95817

Shih-Ying Huang, Nathan J. Packard, and John M. Boone

Department of Radiology, University of California, Davis Medical Center, 4860 Y Street, Suite 3100 Ellison Building, Sacramento, California 95817 and Department of Biomedical Engineering, University of California, Davis, Davis, California, 95616

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(Received 16 December 2009; accepted 14 May 2010; revised 10 May 2010; published online 15 June 2010)

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Purpose: A simplified linear model approach was proposed to accurately model the response of a flat panel detector used for breast CT (bCT).
Methods: Individual detector pixel mean and variance were measured from bCT projection images acquired both in air and with a polyethylene cylinder, with the detector operating in both fixed low gain and dynamic gain mode. Once the coefficients of the linear model are determined, the fractional additive noise can be used as a quantitative metric to evaluate the system’s efficiency in utilizing x-ray photons, including the performance of different gain modes of the detector.
Results: Fractional additive noise increases as the object thickness increases or as the radiation dose to the detector decreases. For bCT scan techniques on the UC Davis prototype scanner (80 kVp, 500 views total, 30 frames/s), in the low gain mode, additive noise contributes 21% of the total pixel noise variance for a 10 cm object and 44% for a 17 cm object. With the dynamic gain mode, additive noise only represents approximately 2.6% of the total pixel noise variance for a 10 cm object and 7.3% for a 17 cm object.
Conclusions: The existence of the signal-independent additive noise is the primary cause for a quadratic relationship between bCT noise variance and the inverse of radiation dose at the detector. With the knowledge of the additive noise contribution to experimentally acquired images, system modifications can be made to reduce the impact of additive noise and improve the quantum noise efficiency of the bCT system.

© 2010 American Association of Physicists in Medicine

ACKNOWLEDGMENTS

The authors would like to thank Dr. Norbert J. Pelc at Stanford University, Dr. Jeffrey H. Siewerdson at Johns Hopkins University, Dr. Bruce R. Whiting at Washington University in St. Louis, and Dr. George Zentai and Dr. Gerhard Roos at Varian, for substantive and meaningful discussions related to additive noise. This work was supported by a grant from the National Institute for Biomedical Imaging and Bioengineering (Grant No. R01 EB002138).

Article Outline

  1. INTRODUCTION
  2. METHODS AND MATERIALS
    1. Experimental setup and data analysis
    2. Linear models for signal mean and variance
    3. Detector gain modes
    4. Fractional additive noise
    5. Quadratic relationship for CT noise variance
  3. RESULTS
    1. X-ray source fluctuation
    2. Linear model coefficients
    3. Different detector gain modes
    4. Fractional additive noise
    5. Quadratic relationship
  4. DISCUSSION
  5. CONCLUSIONS
Digital Object Identifier
http://dx.doi.org/10.1118/1.3447720

KEYWORDS and PACS

Keywords

AWGN, computerised tomography, mammography, physiological models, quantum noise, X-ray detection, noise variance, additive noise, flat panel detector, cone-beam, computerized tomography (CT)

PACS

PUBLICATION DATA

ISSN

0094-2405 (print)  

Publisher

$abstract.society.value is a Member of CrossRef American Association of Physicists in Medicine

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