Lack of magnetization transfer from the ferritin molecule

Magnetization transfer ( MT ) has recently become popular as a means to improve contrast in in vivo MRI by demonstra- ting transfer of magnetization between the macromolecular compound and the surrounding free water in a tissue ( 1 ) . Use of this technique has been reported in imaging of several parts of the human body, including knee (2, 3), liver (4), leg (5), breast (3), heart (6), and brain (7-10). In particular, published T1-weighted images based on magnetization trans- fer contrast ( MTC ) at 1.5 T ( 9 ) have shown hyperintensity in areas such as the substantia nigra, putamen, and globus pallidus known to be rich in iron, and the question has been posed whether MTC can be used to improve MRI localiza- tion and quantitation of brain iron. The present note tries to answer this question. The answer depends on whether iron in the areas mentioned behaves fully as a T1-lowering para- magnetic agent, or is effectively screened by the protein layers.