A moving slanted-edge method to measure the temporal modulation transfer function of fluoroscopic systems

S. N. Friedman, I. A. Cunningham

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

Lag in fluoroscopic systems introduces a frame-averaging effect that reduces measurements of image noise and incorrectly inflates measurements of the detective quantum efficiency (DQE). A correction can be implemented based on measurements of the temporal modulation transfer function (MTF). We introduce a method of measuring the temporal MTF under fluoroscopic conditions using a moving slanted edge, a generalization of the slanted-edge method used to measure the (spatial) MTF, providing the temporal MTF of the entire imaging system. The method uses a single x-ray exposure, constant edge velocity, and assumes spatial and temporal blurring are separable. The method was validated on a laboratory x-ray image intensifier (XRII) system by comparison with direct measurements of the XRII optical response, showing excellent agreement over the entire frequency range tested (±100 Hz). With proper access to linearized data and continuous fluoroscopy, this method can be implemented in a clinical setting on both XRII and flat-panel detectors. It is shown that the temporal MTF of the CsI-based validation system is a function of exposure rate. The rising-edge response showed more lag than the falling edge, and the temporal MTF decreased with decreasing exposure rate. It is suggested that a small-signal approach, in which the range of exposure rates is restricted to a linear range by using a semitransparent moving edge, would be appropriate for measuring the DQE of these systems.

Original languageEnglish
Pages (from-to)2473-2484
Number of pages12
JournalMedical physics
Volume35
Issue number6
DOIs
StatePublished - 2008

Keywords

  • Detective quantum efficiency
  • Edge
  • Edge spread function
  • Fluoroscopy
  • Lag
  • Line spread function
  • Modulation transfer function
  • Temporal MTF
  • X-ray imaging

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