Normalization of the modulation transfer function: The open-field approach

S. N. Friedman, I. A. Cunningham

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


The modulation transfer function (MTF) is widely used to describe the spatial resolution of x-ray imaging systems. The MTF is defined to have a zero-frequency value of unity, and it is common practice to ensure this by normalizing a measured MTF curve by the zero-frequency value. However, truncation of the line spread function (LSF) within a finite region of interest (ROI) results in spectral leakage and causes a reduction in the measured MTF zero-frequency value equal to the area of truncated LSF tails. Subsequent normalization by this value may result in inflated MTF values. We show that open-field normalization with the edge method produces accurate MTF values at all nonzero frequencies without need for further normalization by the zero-frequency value, regardless of ROI size. While both normalization techniques are equivalent for a sufficiently large ROI, a 5% inflation in MTF values was observed for a CsI-based flat-panel system when using a 10 cm ROI. Use of open-field normalization avoids potential inflation caused by zero-frequency normalization.

Original languageEnglish
Pages (from-to)4443-4449
Number of pages7
JournalMedical physics
Issue number10
StatePublished - 2008


  • Detective quantum efficiency (DQE)
  • Edge
  • Edge spread function (ESF)
  • Line spread function (LSF)
  • Modulation transfer function (MTF)
  • Point spread function (PSF)
  • Slit
  • X-ray imaging


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