High signal on T1-weighted MR images of the head: a pictorial essay.

T1-weighted magnetic resonance images (T1WI) of the head may manifest high signal in many normal and pathologic situations. Normally, it may be seen in fatty tissues, certain artifacts, and in areas without a blood-brain barrier after gadolinium administration. It is also seen in the posterior pituitary gland and in certain instances in the anterior pituitary gland. Pathologically, it may occur in many lesions after gadolinium enhancement, in fatty and cystic lesions, and in lesions with paramagnetic content. Occasionally, it may be seen in calcium deposition. Many of these are described and illustrated.