2Chang CS,Lin HH,Yen CL,et al.Sonographic demonstration of free air in perforated peptic ulcers:Comparison of sonography with radiography.J Clin Ultrasound,1989,17:95-100.
3Chen CH,Yang CC,Yeh YH.Role of upright chest radiography and ultrasonography in demonstrating free air of perforated peptic ulcers.Hepatogastroenterology,2001,48:1082-1084.
