I have described a little about gastric banding at : http://www.ultrasound-images.com/git.htm#Gastric_band_%28gastric_banding_in_obesity%29
Gastric band is a simple "tourniquet" around the upper part of the stomach, just below the fundus, aimed at reducing the functional volume of the stomach. This is useful in controlling the food intake in obese patients. What has ultrasound got to do with gastric band? Plenty- ultrasound imaging of the gastric band post-surgical case helps determine the position and effectiveness of the gastric band. How good is ultrasound at imaging it? Have a look at the link above.