Imaging at high magnetic fields: initial experiences at 4 T

Magn Reson Q. 1993 Dec;9(4):259-77.

Abstract

This article reviews the preliminary experiences and the results obtained on the human brain at 4 T at the University of Minnesota. Anatomical and functional images are presented. Contrary to initial expectations and the early results, it is possible to obtain high-resolution images of the human brain with exquisite T1 contrast, delineating structures especially in the basal ganglia and thalamus, which were not observed clearly in 1.5-T images until now. These 4-T images are possible using a new approach that achieves maximal contrast for different T1 values at approximately the same repetition time and has built-in tolerance to variations in B1 magnitude. For functional images, the high field provides increased contribution from the venuoles and the capillary bed because the susceptibility-induced alterations in 1/T2* from these small-diameter vessels increase quadratically with the magnitude of the main field. Images obtained with short echo times at 4 T, and by implication at lower fields with correspondingly longer echo times, are expected to be dominated by contributions from large venous vessel or in-flow effects from the large arteries; such images are undesirable because of their poor spatial correspondence with actual sites of neuronal activity.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Brain / anatomy & histology
  • Brain / blood supply
  • Brain / physiology
  • Echo-Planar Imaging / methods
  • Fourier Analysis
  • Humans
  • Image Enhancement / methods*
  • Magnetic Resonance Imaging / methods*
  • Magnetic Resonance Spectroscopy / methods
  • Magnetics
  • Models, Biological
  • Models, Theoretical
  • Motor Cortex / anatomy & histology
  • Motor Cortex / physiology
  • Motor Skills / physiology
  • Photic Stimulation
  • Speech / physiology
  • Visual Cortex / anatomy & histology
  • Visual Cortex / physiology