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Regional Heterogeneity of Air Trapping at Expiratory Thin-Section CT of Patients with Bronchiolitis: Potential Implications for Dose Reduction and CT Protocol Planning¹

¹ From the Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave, Boston, MA 02215 (A.A.B.); Department of Radiology, Medical University of Vienna, Austria (S.M., D.K., M.W.); and Lung Transplantation Unit (M.E.) and Department of Radiology (P.A.G.), Erasme University Hospital, Université Libre de Bruxelles, Brussels, Belgium. Received July 23, 2007; revision requested September 20; revision received October 10; accepted December 17; final version accepted January 7, 2008. Address correspondence to A.A.B. (e-mail: abankier{at}bidmc.harvard.edu).

Purpose: To prospectively determine whether the regional distribution of air trapping in patients with suspected or overt bronchiolitis is heterogeneous, and to determine the effect that a simulated reduction of computed tomographic (CT) sections and of scanned anatomic regions would have on the assessment of the extent of air trapping.

Materials and Methods: For this Ethical Committee–approved study, multi–detector row CT (collimation, 4 x 1 mm; rotation time, 0.5 second; 140 kVp; and 80 effective mAs) was performed in 47 lung transplant recipients (23 women, 24 men; mean age, 41 years ± 12 [standard deviation]; 18 without bronchiolitis, 18 with potential bronchiolitis, and 11 with bronchiolitis, as determined by lung function measurements). Images were reconstructed with a thickness of 1 mm at an increment of 10 mm. The extent of air trapping in the upper, middle, and lower lung regions was correlated. Differences between regions and the interaction between patients and regions were tested with an analysis of variance. The extent of air trapping was calculated for six simulated examination protocols.

Results: Correlations between the upper and middle (r = 0.930), the upper and lower (r = 0.756), and the middle and lower lung regions (r = 0.863) were significant (P < .001). The extent of air trapping increased from the upper to the lower lung region, with significant differences between regions (P < .001). There was a significant interaction between patients and lung regions (P < .001). Simulated examination protocols resulted in significantly different extents of air trapping (P < .001).

Conclusion: The regional distribution of the extent of air trapping in suspected or overt bronchiolitis is heterogeneous. Because the extent of air trapping can depend on the examination protocol, identical protocols are needed when air trapping is being compared within and between patients.

© RSNA, 2008