The most commonly used technique to assess air entrapment is post-expiratory thin-section CT. Each post-expiratory image should be compared to the inspiratory image closest to that level to detect air entrapment. A dynamic expiratory maneuver performed during a helical CT acquisition is described. This slightly increases the degree of exhalation and improves the detection of air trapping. This technique is recommended when patients have difficulty performing adequate expiratory maneuvers. The use of low- or ultra-low-dose MDCT with thin collimation and iterative reconstruction over the lungs, or the use of soft-tissue cores with filtered backprojection, reduces the prominence of associated air entrapment using minimal techniques. It is routinely performed in many facilities to improve apparent coverage. IP increases the contrast between normal and hypopulmonary regions. This helps to demonstrate the mosaic perfusion pattern. Its application in expiratory CT may also facilitate assessment of the presence and extent of air entrapment. The degree of air entrapment present in expiratory images can be measured using a semi-quantitative grading system that estimates the percentage of lung that appears abnormal in each section. The air entrapment value is the sum of these numbers for the various levels investigated. This scoring system provides good inter- and intra-observer agreement. In patients with bronchiolitis obliterans, the degree of expiratory confinement on CT has been shown to correlate with the degree of airway obstruction on pulmonary function testing. Air entrainment can be measured objectively using CT densitometry. Using the density mask technique, all pixels contained in regions with air voids are segmented, highlighted by a threshold of -910 HU, and counted automatically. You can compare the density change between full inspiration and full expiration to calculate the exhaled/inhaled ratio. Density masks have the advantage of combining density measurements with visual assessment of pathology. Multislice CT with thin collimation applied across the lung and performed on full exhalation can provide a comprehensive assessment of air entrapment volume and 3D visualization of air entrapment distribution. Air pockets are an important cause of hyperpermeable lungs. Air trapping has the effect of dilating alveoli, compressing capillaries and arterioles, and reducing pulmonary blood flow. However, this is arguably an oversimplification of the pathological mechanism by which air pockets lead to reduced pulmonary vessel size. Acute asthma attacks are one of the most striking examples of transient air trapping. It is well known that bronchial asthma usually causes few radiographic abnormalities, except during acute attacks. Acute bronchiolitis is another important cause of diffuse air entrapment, but primarily a disease of the pediatric age group. In either situation, the airlock is temporary. Air entrapment is confirmed by tests performed during the expiratory phase of respiration. A few degrees of patient rotation can lead to differences in the relative densities of the two hemithoraxes. The most common chest wall abnormality associated with unilateral hyperpermeability is mastectomy. However, it may be due to rare congenital anomalies such as the absence of pectoral muscles or a stroke that leads to unilateral atrophy of the chest wall muscles. Some major endovascular diseases, pulmonary embolism, can cause hyperpermeability of the lungs or parts of the lungs. However, these disturbances do not cause air pockets. Hyperpermeable vascular causes can be distinguished from air pockets by expiratory X-rays. A chest breath X-ray is the simplest and easiest way to demonstrate air trapping.