What is the process by which substance move randomly from an area of higher concentration to an area of low concentration

This patient undergoes a gallbladder sonogram due to epigastric pain. the report indicates that the visualized portions of the liver are normal. no free fluid noted within morisons pouch. the gallbladder is identified and is empty no evidence of wall thickening or surrounding fluid is seen there is no ductal dilation. the common hepatic duct and common bile duct measure 0.4 and 0.8 cm respectively. the common bile ductmeasurement is at the upper limits of normal what cpt code in icd-10 cm code was used