A medical imaging system includes a stationary gantry and a rotating gantry that rotates around an examination region about a z-axis. An air bearing rotatably couples the rotating gantry to the stationary gantry. A radiation source is affixed to the rotating gantry and rotates with the rotating gantry and emits radiation that traverses the examination region. A detector array is affixed to the rotating gantry on an opposite side of the examination region with respect to the radiation source and detects radiation traversing the examination region. A dynamic z-axis imbalance determination system determines an imbalance of the rotating gantry in the z-axis direction directly from the air bearing, and the determined imbalance is used to position a balance mass affixed to the rotating gantry in the z-axis direction, thereby balancing the rotating gantry along the z-axis.
