Small intestine. Coloured 3-D ultrasound scan of the ileum region of the small intestine of an adult woman. Digested food passes into the small intestine from the stomach. Nutrients are absorbed from the food into the blood across the intestinal wall. The small intestine is around 6.5 metres long. This provides a large surface area for nutrient absorption. Ultrasound is a diagnostic technique that sends high-frequency sound waves into the body via a transducer. The returning echoes are recorded and used to build an image of an internal structure. 3-D scanning uses computer technology to return more detailed images than conventional 2-D scans.