Mapping hypercapnia-induced cerebrovascular reactivity using BOLD MRI

Abstract

Severe carotid artery stenosis or occlusion may put patients at risk for ischaemic stroke. Reduced cerebrovascular reserve capacity is a possible indicator of an imminent ischaemic event and can be determined by assessment of cerebrovascular reactivity to a vasodilative stimulus. However, little is known about the distribution of cerebrovascular reactivity in healthy individuals. In 13 healthy volunteers, dynamic T2* MR images, acquired at alternating inspiratory pCO2 levels, showed a high percentage of signal change in grey matter, with a strong linear correlation with end-tidal pCO2. The mean percentages of signal change for grey and white matter were 5.9 +/- 1.2% and 1.9 +/- 0.5%, respectively. The mean time lag between CO2 stimulus and haemodynamic response was 15 +/- 4 s for grey matter and 180 +/- 12 s for white matter. Parameter mapping revealed a hemispherically symmetrical and homogeneous distribution of cerebrovascular reactivity over the entire grey matter. These findings indicate that it may be feasible to detect exhausted cerebrovascular autoregulation in patients with a compromised cerebral vasculature.

Functional mapping in the corpus callosum: A 4T fMRI study of white matter

“…There are two main reasons for the controversy: 1) BOLD signals rely in part on relatively small fluctuations in cerebral blood volume and flow, which are then 3-6 times lower in white matter ( [Preibisch & Haase, 2001], [Rostrup et al, 2000], [Helenius et al, 2003], [van der Zande et al, 2005] and [Wise et al, 2004]); and 2) the primary source of fMRI signal is thought to arise from post-synaptic potentials (which occur mainly in gray matter) as opposed to action potentials (Logothetis et al, 2001). To put the situation in context, of the 254 287 fMRI studies that have been published to date (according to PubMed at the time this paper was written), there are only nine reporting activation in white matter to our knowledge ( [Tettamanti et al, 2002], [Omura et al, 2004], [Weber et al, 2005], [ and [Mazerolle et al, 2010]).…”

Confirming white matter fMRI activation in the corpus callosum: Co-localization with DTI tractography

“…Traditionally, it has been thought that fMRI is restricted to gray matter due to the relatively greater blood flow and volume in gray matter ( [Helenius et al, 2003], [Preibisch and Haase, 2001], [Rostrup et al, 2000], [Van der Zande et al, 2005] and [Wise et al, 2004]). In addition, it is thought that the primary source of fMRI signals are hemodynamic responses to post-synaptic potentials, which mainly occur in gray matter (e.g., Logothetis et al, 2001 I pr Logothetis and Wandell, 2004, p. 755).…”

The change in cerebrovascular reactivity between 3 T and 7 T measured using graded hypercapnia

“…This technique has been applied to map the regional distribution of CVR in cerebrovascular disease such as stroke and carotid artery stenosis and occlusion (van der Zande et al 2005;Mandell et al 2008). The BOLD CVR is also of particular interest since it is used in calibrated BOLD: either the functional BOLD response to a task is divided by the BOLD response to mild hypercapnia on a voxel-byvoxel basis, or alternatively the functional BOLD response to a task is used to estimate δCMRO 2 based on the model of Davis et al(Davis et al 1998).…”

“…Many studies (Kastrup et al 2001;Vesely et al 2001;van der Zande et al 2005;Wise et al 2007;Prisman et al 2008) have measured BOLD CVR by inducing a step change in P a CO 2 . Since direct measurement of P a CO 2 is invasive, the exhaled 'end-tidal' PCO 2 (P ET CO 2 ) of expired gases is sampled instead.…”