Diagnostic imaging items are subject to a multiple services rule. There are 3 rules, A, B and C, which may apply together.
Rule A. If 2 or more diagnostic imaging services are provided to a patient on the same day, the fee for the second and subsequent items is reduced by $5.
Rule B. When at least one consultation is provided to a patient on the same day, there is a reduction in the fee for the diagnostic imaging service of $35. Consultations are defined as items 1 to 10816.
Rule C. When a diagnostic imaging service and at least one non-consultation service is provided to the same patient on the same day, the fee for the diagnostic imaging service with the highest Schedule fee is reduced by $5.
Full details of the multiple diagnostic imaging rule is give at this link on the Medicare website.