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Effective DQE (eDQE) and speed of digital radiographic systems: An experimental methodology
Author(s) -
Samei Ehsan,
Ranger Nicole T.,
MacKenzie Alistair,
Honey Ian D.,
Dobbins James T.,
Ravin Carl E.
Publication year - 2009
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 - 10.1118/1.3171690
Subject(s) - detective quantum efficiency , imaging phantom , optical transfer function , optics , digital radiography , magnification , computed radiography , radiography , attenuation , flat panel detector , detector , image quality , noise (video) , medical imaging , image guided radiation therapy , physics , nuclear medicine , computer science , artificial intelligence , medicine , nuclear physics , image (mathematics)
Prior studies on performance evaluation of digital radiographic systems have primarily focused on the assessment of the detector performance alone. However, the clinical performance of such systems is also substantially impacted by magnification, focal spot blur, the presence of scattered radiation, and the presence of an antiscatter grid. The purpose of this study is to evaluate an experimental methodology to assess the performance of a digital radiographic system, including those attributes, and to propose a new metric, effective detective quantum efficiency (eDQE), a candidate for defining the efficiency or speed of digital radiographic imaging systems. The study employed a geometric phantom simulating the attenuation and scatter properties of the adult human thorax and a representative indirect flat‐panel‐based clinical digital radiographic imaging system. The noise power spectrum (NPS) was derived from images of the phantom acquired at three exposure levels spanning the operating range of the clinical system. The modulation transfer function (MTF) was measured using an edge device positioned at the surface of the phantom, facing the x‐ray source. Scatter measurements were made using a beam stop technique. The eDQE was then computed from these measurements, along with measures of phantom attenuation and x‐ray flux. The MTF results showed notable impact from the focal spot blur, while the NPS depicted a large component of structured noise resulting from use of an antiscatter grid. The eDQE was found to be an order of magnitude lower than the conventional DQE. At 120 kVp , eDQE(0) was in the 8%–9% range, fivefold lower than DQE(0) at the same technique. The eDQE method yielded reproducible estimates of the system performance in a clinically relevant context by quantifying the inherent speed of the system, that is, the actual signal to noise ratio that would be measured under clinical operating conditions.