Measurement of AP and TS diameter of the chest wall on the reformatted axial image. (a) Upper level at the carina (C), maximal inspiratory image. (b) Lower level at the apical vertebra (A), maximal inspiratory image. Tangential lines are drawn to the anterior, posterior and lateral lung surfaces. The chest wall dimensions are then measured as the largest anteroposterior (AP, thick solid lines) and transverse (TS, dotted lines) dimensions on either side of the scoliosis separately. The chest wall motion is calculated as the difference between inspiration and expiration.