I am not aware of such a concept that creates a certain magnetic field and then excites the spins there with the right frequency. That also seems to be quite challenging, since it is not so easy to form spaitally fitting magnetic fields.
However, there is a concept that uses a technique called parallel transmission (pTX), but in an alternative (therapeutic) fashion. However, this is still a pure research topic and not in wide use up to my knowledge. You could search for Thoralf Niendorf and his research on this subject.
In a nutshell:
Original intention of pTX
At ultra-high magnetic fields, such as 7T, MRI becomes very challenging, since the excitation wave lengths of the radio-frequency (RF) wave becomes so short that it is in the order of the spatial dimensions of the human body that you would like to measure. Hence, you are facing interference effects resulting in non-uniform excitation of the tissue and therefore varying image intensity, which is undesired. A solution to this problem is to use multiple RF transmitters that can transmit RF pulses independently (meaning different amplitude an phase). With an array of e.g. 8 transmit channels, the area can be excited much more homogeniously.
You can acquire an image of the tissue that contains a tumor or something alike. Then you can base treatment planning on this image, i.e. defining organs at risk and the target area. You then use the pTX technique but not to excite the magnetization homogeniously, but inhomogeniously. This means: Making sure that the RF waves interfere constructively in the treatment area, and destructively in the other areas, especially the organs at risk. By this technique you apply the maximum RF energy to the tumor and hence having the most destructive effect there.