The design of the phantom Pro-Dent CT 161 conforming to the German standard DIN 6868-161 is depicted in Figure 2. It consists of four sections and all image quality parameters according to are determinable:
-  Approximated MTF Assessment of in-plane spatial resolution by using an approximation procedure.
-  Contrast-to-noise indicator (CNI) PVC-PMMA contrast in relation to the noise of the PVC-PMMA test insert.
-  Uniformity indicator (UI*) PVC-PMMA contrast in relation to the maximum difference between the mean CT value of four peripheral ROIs and the mean CT value measured for a central ROI.
- Acceptance indicator (AI) CNI weighted by the dose at the axis of rotation and by the 50% value of the approximated MTF.
The specification and the placement of the ROIs used for determining all these image quality parameters are given in Table 1 and Figure 3.
It should be noted that the dose at the axis of rotation has to be entered as an additional evaluation parameter when prompted by the application.



Figure 1.Transverse and coronal views of an exemplary volume data set.



Figure 2: Design of the phantom Pro-Dent CT 161 (a)–(d) Ideal transverse views of section 1–4 (C=0 HU, W=1000 HU).



Table 1: Specification of the evaluation ROIs for the phantom



Figure 3: Schematic placement of the evaluation ROIs for the Phantom Pro-Dent CT 161 shown for the ideal transverse views of section 1 (a), 2 (b), 3 (c), and 4 (d). Each ROI is labeled by its individual ID.

Technical data
(can be modified to customer specifications):
• diameter: 160 mm
• 20 mm thick main module containing:
   – test object containing equivalents of air, soft tissue and bone
   – positioning markers
   – bubble level
• 20 mm, 50 mm and 60 mm thick PMMA modules with positioning aids
• test stand with a table for placing the phantom in the test position
• folding base for test stand positioning on the X-ray unit’s chair
• convenient, portable case for storing and transporting the phantom

Product features:
• Complies with:
   – DIN 6868-161
   – QS-RL
• CE certified
• the Manual provides detailed guidelines for carrying out each test, results assessment and registration