value t 5 to t 6 would not be accurate since the magnetic field is altered to the point that the phase changes of the mr signals are not representative of the temperature change the inability to measure the temperature value t 6 is problematic since that implies that all temperature values after t 5 cannot be measured the different orientations of the transducer as determined by the motor control of the ultrasound control unit 20 are communicated to the host computer 15 of the system 1 see fig1 the host computer 15 refers to the acoustic intensity profile in the plane at the new orientation of the transducer based on the acoustic intensity distribution at the new orientation and the temperature distribution at the time before the rotation of the transducer a bioheat modeling using the finite difference method can be applied to compute the temperature distribution immediately after the rotation of the transducer a simpler alternative is to employ a look up table for temperature changes at point 23 obtained through prior bioheat modeling or through phantom experiments these techniques enable the mr based temperature monitoring process to continue immediately after rotation of the transducer in accordance with the invention it is not necessary to allow the tissue to cool to the baseline temperature value before further sonications the thermal dose depends on the entire temperature history and hence the invention enables the accurate computation of the thermal dose beyond the instant at.