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A moving slanted‐edge method to measure the temporal modulation transfer function of fluoroscopic systems
Author(s) -
Friedman S. N.,
Cunningham I. A.
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2919724
Subject(s) - measure (data warehouse) , optical transfer function , transfer function , enhanced data rates for gsm evolution , function (biology) , optics , physics , medical imaging , modulation (music) , fluoroscopy , computer science , computer vision , artificial intelligence , acoustics , engineering , electrical engineering , nuclear physics , database , evolutionary biology , biology
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.