Signal and Noise

Azim Celik1, Weili Lin1

1 The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
Publication Name:  Current Protocols in Magnetic Resonance Imaging
Unit Number:  Unit B6.1
DOI:  10.1002/0471142719.mib0601s00
Online Posting Date:  May, 2001
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Abstract

Signal and Noise (Azim Celik and Weili Lin, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina). This unit discusses the basic signal detection technique in magnetic resonance imaging based on quadrature (i.e., measured in two orthogonal channels) technique. The detected signal is demodulated with respect to the Larmor frequency and digitized. The measured MR signal also includes noise. The noise in MR generally derives from the random fluctuations in the receive coil electronics and from the sample. Even though there are other sources of signal fluctuations such as digitization noise and pseudo‚Äźrandom ghosting due to moving spins, these sources are minimized in an ideal experiment. The effect of these noises in MRI image reconstruction is explained in this unit.

     
 
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Table of Contents

  • Overview
  • Technical Discussion
  • Figures
     
 
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Materials

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Figures

Videos

Literature Cited

Literature Cited
   Gudbjartson, H. and Patz, S. 1995. The Rician distribution of noisy MRI data. Magn. Reson. Med. 34:910‐914.
   Henkelman, R.M. 1985. Measurement of signal intensities in the presence of noise in MR images. Med. Phys. 12:232‐233.
   Kittel, C. 1969. Thermal Physics. John Wiley & Sons, New York.
   Papoulis, A. 1991. Probability, Random Variables, and Stochastic Processes. McGraw‐Hill, New York.
Key References
   Gudbjartson and Patz, 1995. See above.
  This article provides a detailed discussion of noise in magnitude and phase images in MR.
   Haacke, E.M., Brown, R.W., Thompson, M.R., and Venkatesan, R. 1999. Magnetic Resonance Imaging: Physical Principles and Sequence Design. John Wiley & Sons, New York.
  This text is an excellent reference on MR physics and covers most of the technical discussion presented in this unit.
   Henkelman, 1985. See above.
  Basic concepts of signal and noise in MR are well described in this paper.
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