The aortic knob becomes visible with LUL collapse.
==> Superior segment of LLL (LB6) hyperinflation –produces a crescent of lucency along the mediastinum and aortic knuckle
PA view and Lateral view
1.Upper part of the major fissure: downward
2.Lower part of the major fissure: backward
3.The collapsed lobe: Downward, posteriorly, and medially. (向下、向後、向內)
4.Shadow of L’t diaphragm is lost along the airless lobe
5.Loss of D-aorta shadow at heart level
LLL collapse特別的表徵：
1.Flat waist sign(紅色箭頭)
正常左邊的心臟邊緣成凹陷狀，而當severe LLL collapse時，心臟還會作輕微的right anterior oblique rotation，以致於左側心臟的normal concavity消失，因而呈平坦狀。
2.Top-of-knob sign
當severe LLL collapse時，anterior junctional line會向左位移，在left upper mediastinum可見一條幾乎垂直的vertical interface，會跨過aortic knob
RUL Collapse
1.Elevation of minor fissure
2.Complete RUL collapse:看起來就像只有widening of the superior mediastinum
3.Indirect sign (hilum elevation) may be evident
Specific signs of RUL collapse
1.Reverse S sign(Golden S sign)紅色箭頭
2.J-P sign
