A 52 year old obese female with a history of recurrent biliary colic comes to the Emergency Room at Santa Rosa Medical Center with right upper quadrant pain which developed 30 minutes after she ate a fat laden meal. Her vital signs are temp 98, P 98, RR 18 and BP 150/88. Her abdomen shows mild right upper quadrant pain but no frank peritoneal signs. Her chemistry panel demonstrates elevated total bilirubin, alkaline phosphatase and gamma gluamyl-transferase. What is the most appropriate next step in the diagnostic evaluation?