Detector or system? Extending the concept of detective quantum efficiency to characterize the performance of digital radiographic imaging systems.
OBJECTIVE
To develop an experimental method for measuring the effective detective quantum efficiency (eDQE) of digital radiographic imaging systems and evaluate its use in select imaging systems.


METHODS
A geometric phantom emulating the attenuation and scatter properties of the adult human thorax was employed to assess eight imaging systems in a total of nine configurations. The noise power spectrum (NPS) was derived from images of the phantom acquired at three exposure levels spanning the operating range of the system. The modulation transfer function (MTF) was measured by using an edge device positioned at the anterior surface of the phantom. Scatter measurements were made by using a beam-stop technique. All measurements, including those of phantom attenuation and estimates of x-ray flux, were used to compute the eDQE.


RESULTS
The MTF results showed notable degradation owing to focal spot blur. Scatter fractions ranged between 11% and 56%, depending on the system. The eDQE(0) results ranged from 1%-17%, indicating a reduction of up to one order of magnitude and different rank ordering and performance among systems, compared with that implied in reported conventional detective quantum efficiency results from the same systems.


CONCLUSIONS
The eDQE method was easy to implement, yielded reproducible results, and provided a meaningful reflection of system performance by quantifying image quality in a clinically relevant context. The difference in the magnitude of the measured eDQE and the ideal eDQE of 100% provides a great opportunity for improving the image quality of radiographic and mammographic systems while reducing patient dose.
Samei
Ehsan
E
Duke Advanced Imaging Laboratories, Department of Radiology, Duke University and Medical Center, 2424 Erwin Rd, Suite 302, Durham, NC 27705, USA.
Ranger
Nicole T
NT
MacKenzie
Alistair
A
Honey
Ian D
ID
Dobbins
James T
JT
Ravin
Carl E
CE
D004526:Efficiency; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement / Q000295:instrumentation* / Q000592:standards*; D013902:Radiography, Thoracic / Q000592:standards; D012542:Scattering, Radiation