Resolution and signal-to-noise relationships in NMR imaging in the human body

When nuclear magnetic resonance techniques are applied to the imaging of structures deep inside the human body, it becomes important to consider the degrading effects of the surrounding body tissues on the signal-to-noise ratio of the received resonance signal. The passage of the NMR signal through the surrounding conductive tissue casues an appreciable loss of signal strength at high frequencies. Also, the presence of a large resistive medium, such as a portion of the body, inside the receiving coil causes a significant amount of thermal noise to be detected. The levels of the signal-to-noise ratio and the corresponding spatial resolution are quantitatively discussed in this paper. Expressions are obtained which enable the resolution to be estimated for a variety of medical imaging systems.