Magnetization transfer imaging of the pituitary gland.

Magnetization transfer (MT) techniques provide tissue contrast which depends mainly on the concentration of macromolecules. The magnetization transfer phenomenon is determined by the restricted macromolecular protons and is quantified by the magnetization transfer ratio (MTR). Since many macromolecular structures are implicated in the secretory activity of the pituitary gland, this imaging technique has recently been used for the study of the normal adenohypophysis and the pre-operative and post-operative evaluation of pituitary adenomas. Significant changes of the MTR with age occur in normal subjects. In patients with hyperprolactinemia, the MTR of prolactin-secreting tumors is higher and that of the non secreting adenomas is lower compared to the MTR values of the normal pituitary gland of age and sex matched controls. In some patients operated on for growth hormone adenomas, although classic MR images were negative for residual tumor, increased MTR values were highly suggestive of persistence of adenoma tissue, in agreement with biochemical findings of persisting secretory activity. These data suggest that MT techniques might be an additional useful tool in the assessment of pituitary gland disorders.