Ultra-Low-Dose MDCT of the Chest: Influence on Automated Lung Nodule Detection

Abstract

ObjectiveTo evaluate the relationship between CT dose and the performance of a computer-aided diagnosis (CAD) system, and to determine how best to minimize patient exposure to ionizing radiation while maintaining sufficient image quality for automated lung nodule detection, by the use of lung cancer screening CT.Materials and MethodsTwenty-five asymptomatic volunteers participated in the study. Each volunteer underwent a low-dose CT scan without contrast enhancement (multidetector CT with 16 detector rows, 1.25 mm section thickness, 120 kVp, beam pitch 1.35, 0.6 second rotation time, with 1.25 mm thickness reconstruction at 1.25 mm intervals) using four different amperages 32, 16, 8, and 4 mAs. All series were analyzed using a commercially available CAD system for automatic lung nodule detection and the results were reviewed by a consensus reading by two radiologists. The McNemar test and Kappa analysis were used to compare differences in terms of the abilities to detect pulmonary nodules.ResultsA total of 78 non-calcified true nodules were visualized in the 25 study subjects. The sensitivities for nodule detection were as follows: 72% at 32 mAs, 64% at 16 mAs, 59% at 8 mAs, and 40% at 4 mAs. Although the overall nodule-detecting performance was best at 32 mAs, no significant difference in nodule detectability was observed between scans at 16 mAs or 8 mAs versus 32 mAs. However, scans performed at 4 mAs were significantly inferior to those performed at 32 mAs (p < 0.001).ConclusionReducing the radiation dose (i.e. reducing the amperage) lowers lung nodule detectability by CAD. However, relatively low dose scans were found to be acceptable and to cause no significant reduction in nodule detectability versus usual low-dose CT.

Ultra-Low-Dose CT of the Thorax Using Iterative Reconstruction: Evaluation of Image Quality and Radiation Dose Reduction

“…In terms of chest CT protocols, the use of unenhanced chest CT including high-resolution CT or low-dose CT has been increasing, and most patients undergo such tests to evaluate benign disease or to screen for lung cancer. Therefore, radiation dose limitation is a constant safety issue, particularly in young patients or those undergoing screening CT [12][13][14][15].…”

Low-dose CT: technique, reading methods and image interpretation

“…The use of CAD system seems to be poorly affected by dose level. Lee et al [ 25 ] used 4 different tube currents (32, 16, 8 and 4 mAs) in 25 volunteers and found no significant differences in nodule detection between the scans with 8 mAs and those with 32 mAs. The reader’s experience using CAD systems is also significant.…”

Lung Cancer Screening, Version 1.2015

“…LDCT has been shown to be as accurate as standarddose CT for detecting solid pulmonary nodules, although nodule detection with LDCT may be limited in larger individuals. 105,106 LDCT may be less sensitive for detecting very low-density nonsolid nodules. 107 Decreasing the radiation dose does not significantly affect the measurement of nodule size when using 1mm-thick slices.…”