This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oesophagus, Subject name: Surgery
Safest contrast in esophageal perforation 
Select and explain. 
A. Iohexol, B. Barium sulphate, C. Gadolinium, D. Methylene blue
A: Iohexol
Answer: A: Iohexol 
Explanation: Ans. (a) IohexolRef: Shackelford, 7th Edition, Page 86Contrasts to detect leak and perforation:Two contrasts are commonly used to detect perforation* Barium* Water soluble contrasts:# Low osmolar: Iohexol, Metrizamide# High Osmolar: Diatrazoate (Gastrograffin)* High osmolar Gastrograffin (Diatrozoate meglumine): has more chances of pulmonary edema than low osmolar contrasts like Iohexol (Omnipaque) and metrizamide (Amnipaque).In conclusion:* Best to diagnose perforations - High density Barium* Safest in usage: Low osmolar Water soluble contrasts like Iohexol and Metrizamide