Related Experiment Video
Updated: Aug 9, 2026
Cardiac Magnetic Resonance Imaging at 7 Tesla
Published on: January 6, 2019
Investigation of the initial dip in fMRI at 7 Tesla
E Yacoub1, A Shmuel, J Pfeuffer
1Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN 55455, USA.
Abstract:
In agreement with optical imaging studies, previous fMRI studies have reported an initial decrease (i.e. the initial dip) in the BOLD response, which is believed to arise from an increase in oxygen consumption and to be mostly microvascular. To date, experimental studies of the initial dip in humans have been performed at fields up to 4 T, with relatively low spatial resolution. Because the sensitivity to microvascular contribution is increased at high magnetic fields, the present study investigated the initial dip at 7 T. In addition, to reduce the partial volume effect, the study is conducted at a high spatial resolution. The initial dip was detected in all subjects studied and was found to reside mostly in the gray matter. The relative amplitude of the early response was found to be 0.6, higher than that at 4 T (0.3) and 1.5 T (0.11). In addition, based on the assumption that the initial dip is a result of increased oxygen utilization, the fractional change in oxygen utilization was estimated to be 40% of that of the fractional change in cerebral blood flow. These results are in agreement with the notion that the initial dip arises from an increase in oxygen consumption.
Insights
This study investigated the brain's initial dip in blood-oxygen-level-dependent (BOLD) response using high-field 7 Tesla fMRI. Results confirm the initial dip reflects increased oxygen consumption, primarily in gray matter.
Area of Science:
- Neuroimaging
- Physiology
- Biophysics
Background:
- Previous functional magnetic resonance imaging (fMRI) studies report an initial dip in the blood-oxygen-level-dependent (BOLD) response, attributed to increased oxygen consumption and microvascular changes.
- Human studies of the initial dip have been limited to magnetic fields up to 4 Tesla (T) and relatively low spatial resolution.
Purpose of the Study:
- To investigate the initial dip at a higher magnetic field (7 T) to enhance sensitivity to microvascular contributions.
- To improve spatial resolution to mitigate partial volume effects.
Main Methods:
- Utilized 7 Tesla functional magnetic resonance imaging (fMRI) with high spatial resolution.
- Analyzed the blood-oxygen-level-dependent (BOLD) response to detect the initial dip.
Main Results:
- The initial dip was consistently detected in all subjects, predominantly within gray matter.
- The relative amplitude of the initial dip was 0.6 at 7 T, significantly higher than previously reported values at 4 T (0.3) and 1.5 T (0.11).
- Estimated fractional change in oxygen utilization was 40% of the fractional change in cerebral blood flow.
Conclusions:
- The findings support the hypothesis that the initial dip in the BOLD response is a marker of increased oxygen consumption.
- High-field (7 T) fMRI at high spatial resolution enhances the detection and characterization of the microvascular component of the BOLD response.
