MR imaging visualization of the cerebral microvasculature: a comparison of live and postmortem studies at 8 T.

SUMMARY: In this study, we compared 8-T gradient-echo MR images of the microvasculature in the live human brain with images of the unembalmed and embalmed postmortem brain. Small vessels were well visualized in the live brain and even better seen in the unembalmed postmortem brain, but they could not be visualized in the embalmed postmortem brain. These findings are important for direct comparisons of the microvasculature on 8-T MR images and on histologic sections.

Epoxy-resin injection of the cerebral arterial microvasculature: An evaluation of the limits of spatial resolution in 8 Tesla MRI.

The purpose of this study was to quantify the spatial resolution of microscopic arteries on magnetic resonance images acquired at 8 Tesla (T). Techniques similar to those used for standard MRI of the human brain in vivo at 8 T were utilized to generate high-resolution gradient echo (GE) images of a whole postmortem human brain whose common carotid arterial system had been injected with an epoxy-resin. Single slice images, along with summed images of up to 5 contiguous slices, were then compared to color digital photographs detailing the distribution of the arterial system on the surface of the same injected brain. There was excellent MR visualization of the microscopic cerebral arteries down to a spatial resolution of 200 microm. Through the use of an 8 T whole-body MRI scanner and standard GE imaging sequences, microscopic arterial structures can be clearly resolved down to a dimension of 200 microm.

High-resolution 8 Tesla imaging of the formalin-fixed normal human hippocampus.

The purpose of this study was to evaluate the capacity of high-resolution magnetic resonance imaging (MRI) to visualize the normal anatomic features of the human hippocampus in vitro, using high field imaging equipment, parameters, and acquisition times appropriate for imaging human subjects in vivo. This research compared high field, high-resolution MRI of formalin-fixed normal human hippocampus specimens to histologic sectioning of the same hippocampus samples. Four specimens were evaluated using an 8 Tesla (T), 80 cm bore whole-body MRI scanner equipped with a 12.7 cm single strut transverse electromagnetic resonator (TEM) coil. Hahn spin echo images were acquired with a repetition time (TR) of 800 msec, echo times (TE) of 20, 50, 90, and 134 msec, and an acquisition time (TA) of 3.25 min. The image quality was superb with demonstration of most of the features of the hippocampus. High field, high-resolution MRI can be used to depict multiple layers of the formalin-fixed human hippocampus in vitro using an 8 T whole-body scanner, a TEM coil, and short acquisition times compatible with human imaging in vivo.

Limits of 8-Tesla magnetic resonance imaging spatial resolution of the deoxygenated cerebral microvasculature.

PURPOSE: To quantify the minimum magnetic resonance imaging (MRI) spatial resolution of the visible deoxygenated microscopic vessels of the human brain at 8 T. MATERIALS AND METHODS: This study compared 8-T gradient echo (GE) images of a human cadaver brain having an in-plane resolution of 195 x 195 microm to corresponding digital photographs of 205 cryomicrotome sections of the same cadaver brain, along with summed images of 25 contiguous cryomicrotome sections. One-millimeter-thick GE images of a 1-cm-thick unfixed whole coronal brain section were acquired using techniques similar to those commonly utilized for 8-T human imaging in vivo. RESULTS: There was excellent MR visualization of the deoxygenated microscopic vessels within the brain down to a resolution of approximately 100 microm. CONCLUSION: By taking advantage of magnetic susceptibility-based blood oxygenation level-dependent (BOLD) contrast, deoxygenated microscopic blood vessels smaller than the pixel dimensions used for imaging can be visualized using a whole-body 8-T MRI system.