Best Gastroenterologist in Southern California, Endoscopy. Dr. Gilbert Simoni and the Advanced GI team have been serving Southern California for more than a decade with a remarkable record of early detection and latest gastrointestinal treatments. He is the founder of Advanced Gastroenterology, Inc. (AGI) and Advanced Digestive Center of ...About Dr. Simoni‧What We Treat‧Videos‧Patients‧Blog‧Testimonials.