This feasibility study in healthy animals should prove the concept that it is possible to quantitatively assess the effects of different ventilatory settings on the lung parenchyma during ongoing ventilation in respiratory gated 4-dimensional (D)-computed tomography (CT). For this purpose, the influence of different tidal volumes and positive end-expiratory pressure (PEEP) on quantitative assessment of lung volumes (LVs) and lung compartments was analyzed.Methods:
Five anesthetized and ventilated (20 breaths/min, inspiratory/expiratory ratio of 1:2) healthy pigs underwent 16-row multidetector CT with retrospective respiratory gating using a noncontact charge-coupled device camera as a gating device. The device was connected to the scanner instead of the electrocardiogram gating unit. Parameters for retrospective scans were collimation 1 mm, 120 kV, 300 mA, gantry rotation time 0.5 seconds, helical pitch 2.4. Two tidal volumes (300 mL and 450 mL) and 3 PEEP levels (0, 5, and 10 cm H2O) were applied resulting in 6 scans per animal. Images were reconstructed throughout the respiratory cycle in increments of 10%. Semiautomatic segmentation provided LV, mean lung density (MLD), and different lung compartments (atelectasis, hypoventilated, normal ventilated, hyperventilated).Results:
At tidal volume 300 mL the inspiratory LV were 1.05, 1.26, and 1.5 L and expiratory LV 0.75, 0.99, and 1.24 L (PEEP 0, 5, 10 cm H2O, respectively). Differences of MLD between inspiration and expiration were 86, 65, and 46 HU. At tidal volume 450 mL, the inspiratory LV were 1.21, 1.43, and 1.72 L, and expiratory LV were 0.78, 1.01, and 1.34 L (for PEEP 0, 5, 10 cm H2O). Differences of MLD between inspiration and expiration were 109, 86, and 59 HU. A clear oscillatory wave of the normal and hypoventilated volumes was found at PEEP 0, with increase in PEEP the hypoventilated areas became increasingly normal ventilated, the amplitude of the curves decreased, and hyperventilated areas increased.Conclusion:
Using a new 4D-CT technique we were able to demonstrate the effect of different ventilation settings on the whole lung during the whole respiratory cycle. The disadvantages of static lung imaging or dynamic 2D-CT can be overcome. The possibility of quantitative evaluation of the whole lung and direct visualization and measurement of recruitment during different ventilation settings might be a great benefit for patients suffering from inhomogeneous lung injury and failure.