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Advancement of the tube tip generally refers to barium studies for small bowel ( Enteroclysis) , in which the naso/oro gastric feeding tube is passed down the pharynx esophagus stomach duodenum beyond the 4th part of the duodenum across the duodeno- jejunal junction into the first part of the jejunum & then oral gastric contrast like barium is pushed in from proximal end of tube , this helps to delineate the mucosa of the small bowel & to pick up any abnormalities .
Hope this answers your query. Feel free to contact me if you have any other doubts.
Dr. Rohit Malik