3[3]Chang YS, Wang HP, Huang GT, Wu MS, Lin JT.Sonographic "gastric corona sign": diagnosis of gastric pneumatosis caused by a penetrating gastric ulcer. J Clin Ultrasound, 1999, 27: 409~412.
4[4]Chau WK, Chan SC. Sonographic diagnosis of a small fistulous communication between a subphrenic abscess and a perforated duodenal ulcer.J Clin Ultrasound, 2000, 28: 153~156.
5[5]Chang-Chien CS, Lin HH, Yen CL, Lee CM, Lin SM. Sonographic demonstration of free air in perforated peptic ulcers: comparison of sonography with radiography. J Clin Ultrasound, 1989, 17:95 ~ 100.