A method of using a medical instrument (300, 400) comprising a magnetic resonance imaging (MRI) system (302). The MRI system acquires (100, 202) first magnetic resonance data (342) and reconstructs (102, 204) a first magnetic resonance image (344, 502). A registration (352) of multiple graphical objects (346, 510, 512) to the first magnetic resonance image is received which defines spatial positions of the multiple graphical objects in the first magnetic resonance image. The method further comprises repeatedly: acquiring (106, 210) second magnetic resonance data (354)； reconstructing (108, 212) a second magnetic resonance image (356, 502')； receiving (110, 214) repositioning coordinates (358, 700) in the second magnetic resonance image for a first group (348, 510) selected from the multiple graphical objects； and determining (112, 216) a coordinate transformation (359, 702) of a second group (350, 512) selected from the multiple graphical objects by applying a coordinate transformation model (364) to the repositioning coordinates.
