New Insights into the Hemodynamic Blood Oxygenation Level-Dependent Response through Combination of Functional Magnetic Resonance Imaging and Optical Recording in Gerbil Barrel Cortex

Abstract

Fast, low-angle shoot functional magnetic resonance imaging (fMRI), based on the blood oxygenation level-dependent (BOLD) effect, was combined with optical recording of intrinsic signals (ORIS) and 2-deoxyglucose labeling in gerbil barrel cortex. We observed over the activated barrel a positive BOLD signal and increased levels of deoxyhemoglobin and total hemoglobin during each period of prolonged (30 sec) D2 vibrissal stimulation. These data show that the hemodynamic basis of this fMRI signal is not necessarily a washout of deoxyhemoglobin, as generally assumed. Instead, they suggest that a positive BOLD signal can also be caused by a local increase of blood volume, even if deoxyhemoglobin levels are persistently elevated. We also show that this alternative interpretation is consistent with theoretical models of the BOLD signal. The changes in BOLD signal and blood volume, which are most tightly correlated with the periodic stimulation, peak at the site of neuronal activation. These results contribute to the understanding of the hemodynamic mechanisms underlying the BOLD signal and also suggest analysis methods, which improve the spatial localization of neuronal activation with both fMRI and ORIS.

The roles of changes in deoxyhemoglobin concentration and regional cerebral blood volume in the fMRI BOLD signal

“…Indeed, the positive values of A P /A R obtained in this study indicate that an increase in the blood volume correlates with an increase in the BOLD signal, as does the decrease in [HHb]. At a magnetic field strength of 1.5 T, and using a TE of 40 ms, the values of the parameters k 1 , k 2 , and k 3 are approximately 2.8, 0.57, and 0.43, respectively (Hess at al., 2000). Therefore the values of A P /A R obtained here are in a relatively good quantitative agreement with the ratio (k 1 ϩ k 2 )/(k 2 ϩ k 3 ) ϭ 3.37.…”

“…For this reason, the behavior of such important cerebral parameters as regional cerebral blood flow (rCBF), volume (rCBV), oxygenation (rCBO), and cerebral oxygen metabolic rate (CMRO 2 ) during cerebral activation remains controversial. In one study (Bandettini et al, 1997) the authors concluded that both rCBF and CMRO 2 remain constant during cortical activation, while other groups have reported significant changes in these parameters (Buxton et al, 1998;Feng et al, 2001;Hess et al, 2000). The basic idea of our work is to approach the problem by using two different measurement techniques, functional magnetic resonance imaging (fMRI) and nearinfrared spectroscopy (NIRS).…”

“…Many studies have focused on assessment of the roles of various parameters characterizing this mechanism (Vanzetta and Grinvald, 1999;Ugurbil et al, 2000;Fox et al, 1986;Belliveau et al, 1991;Buxton et al, 1998;Feng et al, 2001;Hess et al, 2000). The problem, however, is that the output signals of most measurement techniques depend upon many different interrelated parameters.…”

Modeling the hemodynamic response to brain activation

“…The result is a BOLD signal increase with no change in deoxyhemoglobin. This subtlety of the BOLD signal may become important in comparing fMRI data with optical or near-infrared results that are sensitive to deoxyhemoglobin and oxyhemoglobin: there is no one-to-one correspondence between the BOLD signal and the total deoxyhemoglobin (Hess et al, 2000).…”

Measuring the Reliability of Geometries in Magnet Resonance Angiography A Reference for Multimodal Image Registration?

“…Several applications of MR small animal brain image analysis like the generation of generic functional atlases or the combination of functional data from different modalities [1] rely on the comparison and combination of numerous images of the same or distinct specimens. In this context cerebral vascular MR angiograms play an important role as blood vessels can be used as excellent landmarks for image registration.…”