What is the role of a saturation pulse in magnetisation transfer?

The role of a saturation pulse in magnetisation transfer is primarily to inhibit bound protons from aiding in the relaxation of free protons. When a saturation pulse is applied, it selectively saturates the magnetization of the bound protons in the tissue, which diminishes their contribution to the overall signal. This process helps to highlight the distinction between free protons, typically found in the mobile water environment, and bound protons associated with macromolecules.

In this context, the saturation pulse reduces the likelihood that the energy transfer from bound protons will influence the relaxation times of free protons. As a consequence, the resulting MRI signal reflects more clearly the dynamics of the free protons, making it possible to analyze the interstitial environment in greater detail. Ultimately, the application of the saturation pulse aids in enhancing the contrast and the diagnostic capability of the MRI images, particularly in tissues where magnetisation transfer effects are significant.