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A novel integrated circular radiography (ICRAD) phantom for evaluating non-uniform image quality metrics in
Che-Lun Hsu1,2, Ming-Chung Chou1,3,4,5
1Department of Medical Imaging and Radiological Sciences, Kaohsiung Medical University, Kaohsiung, Taiwan.
Background:
Anode heel effects have been shown to cause a non-uniform distribution of X-ray photon fluence, and anode angle could cause focal spot size variations across field. However, no previous study has investigated their effects on image quality metrics in radiography.
Purpose:
The present study aimed to propose an integrated circular radiography (ICRAD) phantom for assessing non-uniform image quality metrics in digital radiography.
Methods:
The phantom was fabricated using multi-layer circular acrylic plates with various sized details and an outer ring of tungsten. It was exposed ten times at different tube voltage and current-time product settings using a digital radiographic system. The visible ratio (VR), normalized mutual information (nMI), and modulation transfer function at 10% (MTF10%) and 50% contrast (MTF50%) were calculated from different orientations to evaluate the non-uniform image quality in radiography. For comparison, a conventional contrast-detail radiography (CDRAD) phantom was also exposed ten times at the same tube voltage and tube current-time product, and rotated at angles of 0, 90, 180, and 270 degrees to understand the effect of anode angle on image quality evaluation using the inverse image quality figure (IQFinv). Statistical comparisons and correlation analysis were performed and the results were considered significant if P < 0.05.
Results:
The results demonstrated that the VR, nMI, MTF50%, and IQFinv increased with tube voltage and tube current-time product, and all metrics were significantly correlated with each other. The VR, nMI, and MTF50% metrics were significantly higher in the cathode direction than in the anode direction, while the IQFinv metric was significantly greater when small details were placed toward the cathode direction compared to the anode direction. Moreover, the MTF10% metric was significantly lower in the cathode direction than in the anode direction.
Conclusion:
The proposed ICRAD phantom is a suitable tool for assessing non-uniform image quality and spatial resolution caused by the anode heel effect in digital radiography.
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