Optimal beam quality for chest computed radiography.

Abstract

RATIONALE AND OBJECTIVES: Optimal x-ray beam quality for chest computed radiography (CR) has not been determined. To investigate the optimal beam quality for chest CR, the authors measured the radiographic contrasts and compared the image quality of chest CR and screen-film (SF) radiographs using various x-ray tube voltages. METHODS: Chest CR and SF radiographs were obtained on a phantom lung and human volunteers with or without a variety of simulated lung opacities using various x-ray tube voltage levels. Exposures were set to maintain identical patient exposure doses for all images. The contrast between peripheral lung and rib or heart was measured on these images and the differences were compared. The quality of the images of each simulated opacity was evaluated by five radiologists using a five-point grading scale. RESULTS: Contrast between peripheral lung and rib or heart increased on CR images obtained by lowering the tube voltage from 140 to 80 kV, but the degree of increase was less than half the increase on SF images. The CR images of the simulated opacities obtained using a lower tube voltage were judged to be superior to those obtained with a higher tube voltage. Scattered radiation was reduced on CR images with a lower tube voltage. CONCLUSION: The image quality of chest CR was improved by using a lower tube voltage than that used for conventional SF chest radiography. Considering the problem of tube loading in clinical applications, a tube voltage of 100 kV is recommended for chest CR.