Magnetization transfer in magnetic resonance imaging.

Two populations of hydrogen protons exist in magnetic resonance imaging: free protons and bound protons. Bound protons do not contribute to normal MR signal because they resonate somewhat off the center frequency of water. A special pulse sequence called magnetization transfer contrast (MTC) was developed to compensate for this off-resonance limitation. A saturation transfer of bound protons occurs during MTC, enabling a transfer of energy to the free proton pool and thereby contributing to the overall MR signal. This article describes MTC, reviews its applications and explains how it improves lesion conspicuity, small vessel detail and background suppression.