...Quality control for radiological system and observer ...

Introduction The Artinis CDDISC 2.0 phantom, was introduced at the RSNA 2000. It is based on the principle of the CDRAD phantom. The phantom is especially designed for the evaluation of fluoroscopes.  With the CDDISC phantom it is possible to quantify both, detail and contrast, as observed by the radiologist. 

Construction The Artinis CDDISC phantom consists of a Plexiglass tablet with cylindrical holes of exact diameter and depth (tolerances: 0.02 mm.). Together with additional Plexiglass tablets, to simulate the dimensions of the patient, the radiographic image of the phantom gives information about the imaging performance of the whole system (refs. 1 and 2). The image shows 240 curved segments. These segments are formed by 16 concentric rings divided by 15 rays from the center of the rings. In each segment one spot is present, in a randomly chosen corner, being the images of the hole (figure).The optical densities of the spots are higher as compared to the uniform background. Due to the (exponentially) increasing depth of the holes in clockwise direction, (from 0.3 to 8.0 mm) the image shows 15 disc-segments of spots with increasing contrast. From the center towards the edge the diameter of the holes increases stepwise and exponentially from 0.3 tot 8.0 mm. For the image this means 16 rings of spots with increasing spatial resolution.

Evaluation For evaluation of the phantom image the observer indicates the location of the second spot in each square. Correct indication proves that a contrast is really seen. At the transition from visible to invisible it is difficult to decide in which corner the second spot is located and the response equals pure chance. The line connecting the central spots with smallest visible diameter and contrast is called the Contrast-Detail (CD) curve. For comparison of the imaging performance of different systems, phantom images are made under identical conditions and evaluated by the same observer and at the same time. The better system will produce an image in which smaller contrasts and details are visible. This results in a shift of the CD-curve to the lower left part it.
Comparison of the performance of several observers is also possible. The better performing observer produces a CD-curve more to the lower left part of the image. 

References
1. Thijssen MAO, et al: Quality Analysis of DSA equipment, Neuroradiology (1988)30: 561-568.
2. Thijssen MAO, Rosenbush G, Gerlach H.J.: Reduction of exposure in fluoroscopy, Electromedica (198804) 56: 126.133.
3. Rose A: Vision, human and electronic, Plenum, New York, 1974.

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