Korean J Radiol.  2008 Apr;9(2):95-101. 10.3348/kjr.2008.9.2.95.

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

• Lee JY
• Chung MJ
• Yi CA
• Lee KS

• KMID: 1098187
• DOI: http://doi.org/10.3348/kjr.2008.9.2.95

Abstract

OBJECTIVE
To 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 METHODS: Twenty-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. RESULTS: A 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). CONCLUSION: Reducing 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.

Keyword

Lung neoplasm, CT; Computed tomography (CT), radiation exposure; Computer, diagnostic aid

MeSH Terms

Adult
Aged
Body Mass Index
Computer-Aided Design
Female
Humans
Lung/radiography
Lung Neoplasms/*radiography
Male
Middle Aged
Prospective Studies
*Radiation Dosage
*Tomography, X-Ray Computed

Figure

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  Fig. 1 Transverse CT scans were acquired at tube currents of 32 (A), 16 (B), 8 (C), and 4 (D) mAs. Note that image quality was reduced and noise was increased as tube currents were decreased.

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  Fig. 2 Five-mm nodule in right lower lobe superior segment, which was detected at 32 (A), 16 and 8 mAs/slice (not shown in this figure), but not at 4 mAs/slice (C) on the CAD system. Note that volume-rendering image obtained at 32 mAs (B) is sharper than that obtained at 4 mAs (D).

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