<prompt> Double track sign is seen in -Duodenal atresiaCHPSGastric ulcerAchalasia  <response>: On upper gastrointestinal fluoroscopy: delayed gastric emptying peristaltic waves caterpillar sign elongated pylorus with a narrow lumen string sign which may appear duplicated due to puckering of the mucosa double-track sign the pylorus indents the contrast-filled antrum shoulder sign or base of the duodenal bulb mushroom sign the entrance to the pylorus may be beak-shaped beak sign 