Modulation Transfer Function on Type 38

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IQI MTF 38 ROIs.png
IQI MTF ROIs legend.png

Modulation Transfer Function (MTF) values are calculated according to Droege RT, Morin RL. "A practical method to measure the MTF of CT scanners" (Med Phys. 1982 Sep-Oct;9(5):758-60). Authors demonstrate how MTF is related to the standard distribution of pixel values inside a region taken from a bar pattern, with the following relations:

MTF(f)=π24M(f)M0,π24M0M2(f)M2(3f)9M2(5f)25M2(7f)49,if ffc/3if ffc/11

where:

M(f)=σ2DN2
M0=|μbarμbkg|nbarnbkg(nbar+nbkg)
N=(σ2bar+σ2bkg)2

and:

  • σD: standard deviation of pixel values inside the bar pattern (detail) region
  • μbar: mean pixel value of the bars reference region
  • μbkg: mean pixel value of the background reference region
  • nbar: number of pixels of the bars reference region
  • nbkg: number of pixels of the background reference region
  • σbar: standard deviation of pixel values inside the bars reference region
  • σbkg: standard deviation of pixel values inside the background reference region

For frequencies outside the range given by the formulas, a linear interpolation is performed.