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The Migraine And Headache Program

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Most pathology

Gray/black

White

Signal intensity (SI) dictates appearance on a gray scale. High signal is white; low signal is black. Substance is often compared to the SI of gray matter.

Signal intensity (SI) dictates appearance on a gray scale. High signal is white; low signal is black. Substance is often compared to the SI of gray matter.

ning include: functional (f)MRI [9], MR spectroscopy (MRS) [10], MR-guided therapy (MRT) [11], and perfusion and diffusion MRI [12].

Use of Contrast Media

Gadolinium, a rare earth metal, is used frequently in MRI. The paramagnetic properties of gadolinium affect free protons and hence shorten T1-weighted signal. It is not the gadolinium that is being visualized but its effect on free protons. Where there are increased concentrations of gadolinium, this will result in high signal, i.e. enhancement, on T1 weighting. It highlights areas of blood-brain barrier breakdown, areas of inflammation and increased vascularity. Marked enhancement is visible normally in the pituitary, the choroid plexus, the nasal mucosa and turbinates, and in slow-flowing blood in vessels. Contrast enhancement is used frequently to improve detection and definition of tumors, infection, meningeal disease, vascular disease and the "post-operative spine". Gadolinium is an extremely safe substance and has been used in millions of cases worldwide with side-effects that are less common and less severe than with the iodinated contrast media used in CT.

MRI of Intracranial Hemorrhage

The appearances of hemorrhage on MRI demonstrate the possible permutations of signal

Fig. 2.4 a-b MRI scan for severe intermittent headaches. a Sagittal T1 with a high-signal mass in the region of the foramen of Monro. b Coronal FSE T2, with a low-signal mass. The position and signal changes are characteristic of a colloid cyst.

Fig. 2.4 a-b MRI scan for severe intermittent headaches. a Sagittal T1 with a high-signal mass in the region of the foramen of Monro. b Coronal FSE T2, with a low-signal mass. The position and signal changes are characteristic of a colloid cyst.

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