Tracking the effects of crusher gradients on gradient-echo BOLD signal in space and time during rat sensory stimulation
✍ Scribed by Gadi Goelman; Galit Pelled; Steve Dodd; Alan Koretsky
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 741 KB
- Volume
- 60
- Category
- Article
- ISSN
- 0740-3194
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
A unique method to map the effect of crusher gradients in space and time on the gradient echo blood oxygen level dependent (BOLD) signal is introduced. Using the __Radial C__orrelation __C__ontrast (RCC) analysis method, amplitude‐RCC maps at different time segments and different gradient strengths were obtained. The ratio of amplitude‐RCC cluster volumes, with and without crusher gradients, showed a temporal dependency with stronger volume reduction for stimulation‐onset versus stimulation‐decline. Aside from signal‐to‐noise ratio reduction in diffusion weighted images, the average temporal patterns were equal. Comparison of the data with and without crushers showed a stronger reduction in local coherence for stimulation‐onset times. We hypothesize that the stimulation decline was weighted by extravascular effects originating in expanded veins due to their larger volume and long range susceptibility which couples neighboring voxels. The ratio of amplitude‐RCC with and without crushers calculated for each voxel at each time segment yielded a spatial–temporal mapping of the crusher effect. These maps suggest that early stimulation‐onset (∼9 s) is weighted by flow; later a dynamic steady‐state between intra‐ and extravascular effects is obtained. Stimulation‐decline was dominated by extravascular effects, and at late stimulation decline as well as at early stimulation onset, clusters were small and localized to expected site of neuronal activity. Magn Reson Med 60:548–554, 2008. © 2008 Wiley‐Liss, Inc.