A medical apparatus (300, 400, 500, 600) comprising a magnetic resonance imaging system (302). The medical apparatus further comprises a memory (332) storing machine readable instructions (352, 354, 356, 358, 470, 472, 474) for execution by a processor (326). Execution of the instructions causes the processor to acquire (100, 202) spectroscopic magnetic resonance data (334). Execution of the instructions further cause the processor to calculate (102, 204) a calibration thermal map (336) using the spectroscopic magnetic resonance data. Execution of the instructions further causes the processor to acquire (104, 206) baseline magnetic resonance thermometry data (338). Execution of the instructions further causes the processor to repeatedly acquire (106, 212) magnetic resonance thermometry data (340). Execution of the instructions further cause the processor to calculate (108, 214) a temperature map (351) using the magnetic resonance thermometry data, the calibration thermal map, and the baseline magnetic resonance thermometry data.
