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Detection of Nodules Showing Ground-Glass Opacity in the Lungs at Low-Dose Multidetector Computed Tomography: Phantom and Clinical Study

Funama, Yoshinori PhD*; Awai, Kazuo MD; Liu, Duo MD; Oda, Seitaro MD; Yanaga, Yumi MD; Nakaura, Takeshi MD; Kawanaka, Koichi MD; Shimamura, Masamichi PhD*; Yamashita, Yasuyuki MD

Journal of Computer Assisted Tomography: January-February 2009 - Volume 33 - Issue 1 - p 49-53
doi: 10.1097/RCT.0b013e31815e6291
Thoracic Imaging: Original Article
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To investigate the effect of the radiation dose (tube current second product) and the attenuation value of nodules with ground-glass opacity (GGO) on their detectability at multidetector computed tomography (MDCT).

Methods: We scanned a chest CT phantom that included simulated GGO nodules with an MDCT scanner. The attenuation value of the simulated lung parenchyma was −900 Hounsfield units (HU); it was −800 and −650 HU for the simulated GGO nodules. We used a tube current second product of 180 mA as the standard and 21, 45, 60, and 90 mAs as the low-dose and performed receiver operating characteristic analysis to compare the performance of 5 radiologists in detecting GGO nodules at each milliampere. To assess the detectability of GGO nodules on human lung images, the observers were presented with 38 GGO nodules from 15 patients. The 5 radiologists independently reviewed chest CT images at 21 and 45 mAs.

Results: In the phantom study, the Az value for GGO nodules with a CT number of −800 HU was significantly lower at 21 than 180 effective mA (0.86 vs. 0.96; P < 0.01). There was no statistically significant difference in the Az value of GGO nodules with a CT number of −650 HU, irrespective of milliamperes used (P = 0.165). In the clinical study, 39.5% and 25.8% of GGO were missed at 21 and 45 mAs, respectively.

Conclusions: At MDCT, GGO nodules with a CT number of −650 HU or less were difficult to detect at the lower milliampere settings (21 and 45 mAs).

From the * Department of Radiological Sciences, School of Health Sciences; and †Department of Diagnostic Radiology, Graduate School of Medical Sciences, Kumamoto University, Kumamoto, Japan.

Received for publication September 2, 2007; accepted October 12, 2007.

Reprints: Yoshinori Funama, PhD, Department of Radiological Sciences, School of Health Sciences, Kumamoto University, 4-24-1 Kuhonji, Kumamoto 862-0976, Japan (e-mail: funama@kumamoto-u.ac.jp).

© 2009 Lippincott Williams & Wilkins, Inc.