Lung cancer screening: minimum tube current required for helical CT.
OBJECTIVE
To investigate the minimum tube current required for helical computed tomography (CT) for lung cancer screening.


METHODS
Thirty helical scans of the lung were obtained at effective tube currents of 50, 30, 20, 18, 12, 10, and 6 mAs in seven healthy volunteers. Computer-generated nodules 6 mm in diameter that showed ground-glass opacity were superimposed on the images. The image quality and detectability of nodules were evaluated subjectively by six observers. The SDs of measured CT numbers were calculated. The results were analyzed according to location in the lung.


RESULTS
Compared with the subjective quality of images obtained at 50 mAs, the subjective quality of images obtained at 20 mAs was not significantly different. The detectability of nodules was not significantly degraded by reducing the tube current to 20 mAs in the upper zone of the lung, to 12 mAs in the middle zone, or to 18 mAs in the lower zone. The SDs at the apex and base of the lung were larger than those at other levels, and the difference became greater as the dose was reduced.


CONCLUSIONS
The minimum tube current required for screening helical CT differs for different locations in the lung. An ideal CT protocol for the lung should permit the tube current to be changed during helical scanning.
Itoh
S
S
Department of Radiology, Nagoya University School of Medicine, 65 Turumai-cho Showa-ku, 466-0065 Nagoya, Japan.
Ikeda
M
M
Arahata
S
S
Kodaira
T
T
Isomura
T
T
Kato
T
T
Yamakawa
K
K
Maruyama
K
K
Ishigaki
T
T
D000328:Adult; D000465:Algorithms; D000704:Analysis of Variance; D016477:Artifacts; D004560:Electricity; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D008168:Lung / Q000000981:diagnostic imaging; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D008297:Male; D008403:Mass Screening; D008875:Middle Aged; D015588:Observer Variation; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*