Coronal reformations of volumetric expiratory high-resolution CT of the lung

Objective. The purposes of this study were to evaluate the quality of coronal reformatted images obtained from volumetric expiratory high-resolution CT imaging and to compare coronal and axial images with regard to their usefulness in detecting and characterizing air trapping. Subjects and Methods. We studied 40 consecutive patients with known or suspected diffuse lung diseases with airway abnormalities who underwent volumetric expiratory high-resolution CT between May and July 2003. Respiratory motion artifacts were evaluated at upper, middle, and lower lung areas. Cardiac motion, beam-hardening, and other artifacts were evaluated throughout the lung fields. Detectability, clarity of borders, size, distribution, and extent of air trapping were compared on axial versus coronal end-expiratory high-resolution CT images. Results. Respiratory motion artifacts were either imperceptible or not diagnostically limiting in all patients except three (7%) with diagnostically limiting image degradation at lower lung areas. Other diagnostically limiting image degradation was caused by beam-hardening artifacts in two patients (5%) and by quantum noise in two other patients (5%). The borders of air trapping were more clearly identified on coronal images than on axial images (grade 1 [vague], nine vs three; grade 2 [partially clear], 23 vs 21; grade 3 [completely clear], eight vs 16; median, two vs two; p=0.001). The coronal reformatted images were as informative as axial images for detecting and assessing the classification and extent of air trapping. Conclusion. Coronal reformations of volumetric expiratory high-resolution CT scans were acceptable in image quality and provided additional value by affording clearer visualization of the borders of air trapping than was found in contiguous axial images.