Magnetic resonance imaging of blood vessels at high fields: <i>In vivo</i> and <i>in vitro</i> measurements and image simulation

TLDR

High‑field MRI of the brain shows unusually high contrast when blood oxygenation is lowered, attributed to magnetic susceptibility from paramagnetic deoxyhemoglobin. When a vessel’s axis is not parallel to the main field, susceptibility differences create local field variations that cause intravoxel dephasing in gradient‑echo images but not in spin‑echo images. In vitro experiments, simulations, and mouse brain imaging confirm that contrast depends on vessel orientation and field strength, with simulations estimating the field‑strength dependence. © 1990 Academic Press, Inc.

Abstract

Abstract Unusually high image contrast in vivo magnetic resonance imaging of the brain becomes observable at high magnetic fields when the blood oxygenation level is lowered. The cause of the contrast has been attributed to a magnetic susceptibility effect induced by paramagnetic deoxyhemoglobin in red cells. When the cylinder axis of a blood vessel is not parallel to the main magnetic field, the susceptibility difference produces varying local fields around the blood vessel. In gradient‐echo images, not in spin‐echo images, these local fields cause intravoxel dephasing of the water signal of the surrounding tissue. This description of the contrast enhancement has been confirmed by a series of in vitro blood sample experiments and image simulations. A predicted contrast change has been demonstrated in brain images of a mouse placed at two different orientations in the magnet. From the simulated images, the dependence of the contrast on the field strength has been estimated. © 1990 Academic Press, Inc.