The invention provides for a medical apparatus (300) comprising: a magnetic resonance imaging system (302); an ultrasonic system (322) for connecting to a catheter (324, 504, 600) with an ultrasound array (400, 402, 404, 508, 602, 604). The ultrasonic system is operable for driving the ultrasound array. Machine executable instructions (354, 356, 358) cause a processor (334) for controlling the medical apparatus to: generate (100, 202) at least one acoustic radiation impulse with the ultrasonic system, wherein the generated ultrasound energy is below a predetermined level; acquire (102, 204) the magnetic resonance data using an acoustic radiation force imaging pulse sequence; reconstruct (104, 206) at least one acoustic radiation force pulse image using the magnetic resonance data; and determine (106, 208) an energy deposition zone for the catheter using at least partially the at least one acoustic radiation force pulse image.