Need to understand the MRI signal well enough to understand how we get an image, what it relates to, what properties will the signal have. Faraday's Law tells us that if you know that something is producing a magnetic field you can calculate how much flux it will generate through a coil, and measure a voltage. In MRI we measure the signal from the coil, and need to determine the magnetic fields (in our case spin distribution) that produces such a signal. How do we do that ???
often refer to the ability to invert such electromagnetic problems as ``principle of reciprocity''