Further reduction of radiation dose in helical CT for lung cancer screening using small tube current and a newly designed filter

A new aluminum filter, 5.8 mm thick at the center, was designed. The effect ive energy, exposure dose, absorbed dose, and noise were measured by using low-dose technique, very low-dose technique with a conventional filter, and very low-dose technique with a new filter on a chest phantom. Accuracy of very low-dose computed tomography (CT) with a new filter was compared again st standard helical CT in 40 patients and against chest radiography in 35 p atients. Effective energies were 42.6 keV and 51.6 keV at a conventional fi lter and the new filter, respectively. Compared against 20mA with a convent ional filter, exposure dose was reduced by 17%, and absorbed dose was equiv alent, at 30 mA with the new filter. Noise was improved by 9%. Compared wit h standard helical CT, the sensitivity, specificity, and accuracy of very-l ow-dose helical CT were 100%, 88%, and 95%, respectively. Very-low-dose hel ical CT was found to be significantly superior to chest radiography in the detection of lung cancers. Using a smaller tube current and an appropriate filter allows a further reduction in radiation dose in helical CT for lung cancer screening.