An MRI system is employed to aim an ultrasonic transducer at tissues to be treated and to produce images which enable the treatment of the tissues to be monitored. A pulse sequence is used which produces both a spin-echo NMR signal and a gradient-echo NMR signal and changes in phase between these two signals is measured and used to produce a temperature map. Changes in amplitude of the spin-echo NMR signal from a reference spin-echo NMR signal is used to produce images which indicate temperature changes in both fat and water. These temperature maps may be used to aim the heat treatment device.