Ans. is 'd' i.e., USG Investigations of choice in GITo Investigation of choice for esophageal motility disorders (Achalasia, , Diffuse esophageal spasm Esophageal atresia, nutcracker esophagus) - Manometryo Best diagnosis of Barret's esophagus - Endoscopy and biopsy,o Investigation of choice for gastroesophageal reflux disease - Endoscopyo Best investigation for documenting episode of GERD - pH and radionuclide study,o Investigation of choice for esophageal carcinoma - Esophageoscopy (endoscopy)o Investigation of choice for small bowrel tumor - Small bowel enema (Barium follow through)o Gastrointestinal contrast medium of choice (including small bowel enema) - Barium sulfateo Substance used for OCG - lopanoic acido Investigation of choice for gall stone and obstructive jaundice - USGo Investigation of choice for acute cholecystitis - Transabdominal USGo Best (most accurate) investigation for acute cholecvstis - Radionuclide scano Investigation of choice for acute cholangititis - Transabdominal USGo Investigation of choice for acute pancreatitis - CECTo Investigation of choice for chronic pancreatitis - ERCPo Investigation of choice for pancreatic carcinoma - CECTo Investigation of choice to detect minimal ascites - USGo Most sensitive investigation for Caroli's disease - Cholangiography.o Investigation of choice for upper abdominal trauma - CT scano Investigation of choice for diagnosis and staging of GIST - CT scan.o Investigation of choice for assessment of treatment response and recurrence of GIST - PET preferably in combination with CTo Intitial & most important imaging modality in cases of acute abdomen due to intestinal obstruction and perforation - Plain x-ray.o Screening modality of choice when acute abdomen is suspected to be of biliary' origin - USG.o Investigation of choice for acute abdomen especially those suffering from pancreatitis and intrabdominal abscess - CT scan..