This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Surgery
Investigation of choice to diagnose hyperophic pyloric Stenosis in infants is 
Select and explain. 
A. Contrast radiology, B. Gastroscopy, C. Ultrasound abdomen, D. CT scan abdomen
C: Ultrasound abdomen
Answer: C: Ultrasound abdomen 
Explanation: Ultrasonography is recommended because its sensitivity and specificity are close to 100% for this disease. Ultrasound is reliable and easily performed and has replaced barium studies as the main investigation.There is a normal variation of pylorus muscle measurements with age and gestation but ultrasound has a very high sensitivity and specificity.