1. 1. JP Morgan, and S. Silverman, Techniques of Veterinary Radiography . Ames: Iowa State University Press, 1989 ;284 -287 .
2. 2. TR O'Brien, DN Biery, RD Park, and JE Bartels , Radiographic Diagnosis of Abdominal Disorders in the Dog and Cat: Radiographic Interpretation-Clinical Signs-Pathophysiology . Philadelphia: WB Saunders Co., 1978 ;204 -351 .
3. Contrast Radiography of the Upper Gastrointestinal Tract in the Dog: A Comparison of Micropulverized Barium Sulfate and U.S.P. Barium Sulfate Suspensions in Clinically Normal Dogs
4. 5. DE. Thrall, Textbook of Veterinary Diagnostic Radiology . Philadelphia: WB Saunders Co., 1986 ;473 -510 .