Abstract
Magnetic resonance imaging (MRI) and angiography are synergistic diagnostic methods that together can often provide clues to lesions that are beyond the abilities of each procedure alone. MRI is a tomographic method which produces a layered picture of the brain parenchyma in three image dimensions: the parenchyma of the brain is illustrated. Angiography involves projection through a contrast medium. The contours of the contrast medium-filled vessels are projected via the exposure of the plain X-ray film or the digital image intensifier: changes in the arteries and veins are visualized indirectly. Magnetic resonance angiography (MRA), which uses the flowing protons of the blood to produce a three-dimensional display of the vessel, has been discussed as an alternative to conventional angiography but its resolution is much lower than that of conventional angiography or even of the currently common digital substraction angiography (DSA): the conventional plain-film technique can discriminate 5 line pairs/mm, while DSA with a 512 ×512 matrix can resolve 2 line pairs/mm, and MRA is only capable of resolving approximately 0.5 line pairs/mm, assuming that a sequence is chosen which works with a normal duration of measurement and a 254 ×256 matrix.
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