The system under consideration may be represented by a single node GI/Gl1 queue with multiple classes of scheduled patients and a stream of unscheduled low priority arrivals with no return or repeat patient visits. To parameterize the simulation models. data on arrival patterns, unpunctuality and service times were collected with direct observations and from the log books of the MRI section. The service time was defined as the difference in time when a patient enters the MRI room and when the patient exits