An apparatus for performing error tracking and calibration of a mechanical image acquisition system comprising: - an input unit ; and - a processing unit , wherein the input unit is configured to acquire at least first and second 2D projection frame sequences of an examination area of the mechanical image acquisition system at different times using the same mechanical image acquisition system in first and second acquisitions, and to acquire expected calibration data defining an expected calibrated geometry of the mechanical image acquisition system; and wherein the processing unit is configured to apply rigid motion compensation separately to at least the first and second 2D projection sequences and to compare the compensated first and second 2D projection sequences separately to the expected calibrated geometry, to thus generate a first sequence and a second sequence of frame deviation measures representing a geometric deviation of the mechanical image acquisition system from the expected calibrated geometry occurring during the first and second acquisitions, to determine a resemblance between the first sequence of frame deviation measures and the second sequence of frame deviation measures, and, if a resemblance between at least a portion of the first and second sequences of the frame deviation measures is determined, to perform one or more calibration actions. - an input unit ; and - a processing unit , wherein the input unit is configured to acquire at least first and second 2D projection frame sequences of an examination area of the mechanical image acquisition system at different times using the same mechanical image acquisition system in first and second acquisitions, and to acquire expected calibration data defining an expected calibrated geometry of the mechanical image acquisition system; and wherein the processing unit is configured to apply rigid motion compensation separately to at least the first and second 2D projection sequences and to compare the compensated first and second 2D projection sequences separately to the expected calibrated geometry, to thus generate a first sequence and a second sequence of frame deviation measures representing a geometric deviation of the mechanical image acquisition system from the expected calibrated geometry occurring during the first and second acquisitions, to determine a resemblance between the first sequence of frame deviation measures and the second sequence of frame deviation measures, and, if a resemblance between at least a portion of the first and second sequences of the frame deviation measures is determined, to perform one or more calibration actions. wherein the input unit is configured to acquire at least first and second 2D projection frame sequences of an examination area of the mechanical image acquisition system at different times using the same mechanical image acquisition system in first and second acquisitions, and to acquire expected calibration data defining an expected calibrated geometry of the mechanical image acquisition system; and wherein the processing unit is configured to apply rigid motion compensation separately to at least the first and second 2D projection sequences and to compare the compensated first and second 2D projection sequences separately to the expected calibrated geometry, to thus generate a first sequence and a second sequence of frame deviation measures representing a geometric deviation of the mechanical image acquisition system from the expected calibrated geometry occurring during the first and second acquisitions, to determine a resemblance between the first sequence of frame deviation measures and the second sequence of frame deviation measures, and, if a resemblance between at least a portion of the first and second sequences of the frame deviation measures is determined, to perform one or more calibration actions. <EOS>