Radiation dose reduction with the wide-volume scan mode for interstitial lung diseases

The wide-volume mode, available on wide-area detector row CTs, has the advantage of reducing exposure time and radiation dose. It is infrequently used for lung diseases. The purpose of this study is to compare image quality and radiation dose of wide-volume chest CT to those of standard helical CT in the setting of interstitial lung diseases. Retrospective monocentric study including 50 consecutive patients referred for follow-up or screening of interstitial lung diseases, requiring prone scan, acquired with the wide-volume mode, in addition to the routine supine scan, acquired with the helical mode. The optimal collimation in wide-volume mode (320 $\times$ 0.5 mm or 240 $\times$ 0.5 mm) was chosen according to the length of the thorax. Wide-volume acquisitions were compared to helical acquisitions for radiation dose (CTDI${}_{vol}$, DLP) and image quality, including analysis of normal structures, lesions, overall image quality, and artifacts (Wilcoxon signed-rank test). Median CTDI${}_{vol}$ and DLP with wide volumes (3.1 mGy and 94.6 mGy $\cdot$ cm) were significantly reduced (p < 0.0001) as compared to helical mode (3.7mGy and 122.1 mGy $\cdot$ cm), leading to a median 21% and 32% relative reduction of CTDI${}_{vol}$ and DLP, respectively. Image noise and quality were not significantly different between the two modes. Misalignment artifact at the junction of two volumes was occasionally seen in the wide-volume scans and, when present, did not impair the diagnostic quality in the majority of cases. Wide-volume mode allows 32% radiation dose reduction compared to the standard helical mode and could be used routinely for diagnosis and follow-up of interstitial lung diseases.