Optimal beam quality for chest flat panel detector system: realistic phantom study

Abstract

Objective: To investigate optimal beam quality for chest flat panel detector (FPD) system by semi-quantitatively assessment using a realistic lung phantom.

Materials and methods: Chest FPD radiographs were obtained on a realistic lung phantom with simulated lung opacities using various X-ray tube voltage levels (90-140 kV) with/without copper filter. Entrance skin dose was set to maintain identical for all images (0.1 mGy). Three chest radiologists unaware of the exposure settings independently evaluated the image quality of each simulated opacity and normal structure using a 5-point scale (+ 2: clearly superior to the standard; + 1: slightly superior to the standard; 0: equal to the standard; - 1: slightly inferior to the standard; - 2: clearly inferior to the standard). The traditional FPD image obtained at a tube voltage of 120 kV was used as the standard. The scores of image quality were statistically compared using the Wilcoxon rank test with Bonferroni correction.

Results: FPD images using 90-kV shot with copper filter were superior to the traditional 120-kV shot without filter with respect to the visibility of vertebra, pulmonary vessels, and nodules overlapping diaphragm and heart (p < 0.05). There was no significant difference with respect to the visibility of all other simulated lung opacities (lung nodules except for overlying diaphragm/heart and honeycomb opacity) between each tube voltage level with/without copper filter and the traditional 120-kV shot without filter.

Conclusion: Image quality of FPD images using 90 kV with copper filtration is superior to that using standard tube voltage when dose is identical.

Key points: • FPD image quality using 90 kV with filter is superior to that using traditional beam. • Ninety-kilovolt shot with copper filter may be suitable for chest FPD image. • Clinical study dealing with chest FPD beam optimization would be warranted.

Keywords: Chest radiography; Digital radiography; Dose; Image quality; Physics.