4.1　Transabdominal Ultrasound（TUS）

Transabdominal ultrasound（TUS）is generally used as the first imaging method for patients with suspected CP.The primary diagnostic findings of CP on abdominal US include pancreatic calcifications，a dilated pancreatic duct，gland atrophy or enlargement，irregular gland margins，pseudocysts，and changes in gland echotexture.The sensitivity reported for US in CP ranges from 49 to 96%（Rosch et al.2000）.The low sensitivity is partly a result of the difficulty of visualizing the pancreas from overlying bowel gas.One additional problem that can make the interpretation of abdominal ultrasonograpy challenging is the tremendous spectrum of changes that can occur in the pancreas as a consequence of aging.Changes in echotexture，pancreatic duct dilation，cystic cavities，and even ductal calcifications may develop with aging（Keller et al.2014a）.These findings mimic those in CP.It can be difficult or impossible in some patients to differentiate age-related changes from pathological CP.Nonetheless，TUS remains a very useful diagnostic test for CP and is often able to identify pancreatic cancer and biliary disease，as well as pseudocyst or biliary obstruction（Forsmark 2005）.Abdominal ultrasonography is widely available，inexpensive，and risk-free.(https://www.daowen.com)