Xenon Ventilation Imaging Using Dual-Energy Computed Tomography in Asthmatics: Initial Experience

PURPOSE:To assess the feasibility of xenon ventilation computed tomography (CT) for evaluating ventilation abnormality in asthmatics. MATERIALS AND METHODS:Twenty-two, stable asthmatics (M:F = 10:12; mean age, 57.6) were included. Single-phase, whole-thorax, dual-energy CT was performed using dual-source CT (Somatom Definition, Siemens) after subjects had inhaled 30% xenon for 90 seconds. Parameters include 512 × 512 matrix; 14 × 1.2 mm collimation; 40/140 eff. mAs at 140/80 kV; 0.45 pitch; and 0.33 seconds rotation time. On the color-coded xenon map, the extent of the ventilation defect was visually assessed using a 5-point scale in each lobe (0, absent defect; 1, 0%–25%; 2, 25%–50%; 3, 50%–75%; and 4, 75%–100%), which was defined as defect score. On the weighted average image, airway wall dimensions were measured at 4 segmental bronchi in both upper and lower lobes. Patients were classified into a defect group and a defect-free group based on the presence of defects shown on the xenon map. Pulmonary function test parameters and airway wall dimensions were compared in those 2 groups. Correlation analyses between the defect score, pulmonary function test, and airway wall dimensions were performed. RESULTS:Sixteen asthmatics showed peripheral ventilation defects on the xenon map (defect score, 6.6 ± 4.2). The defect group had a significantly lower forced expiratory volume in 1 second (FEV1) and thicker airway wall than that of the defect-free group (P = 0.04 and 0.02, respectively). The defect score correlated negatively with a ratio of FEV1 and forced vital capacity (FEV1/FVC) (r = −0.44, P = 0.04) and corrected diffusing capacity (r = −0.76, P = 0.04) and correlated positively with total lung capacity, functional residual volume, and residual volume (r = 0.90, P = 0.005; r= 0.99, P < 0.001; r = 0.88, P = 0.008, respectively). CONCLUSIONS:The ventilation defects appeared on xenon ventilation CT in asthmatics with more severe airflow limitation and airway wall thickening. The extent of the ventilation defects showed correlations with parameters of pulmonary function test.