Similarities and Differences in Arterial Responses to Hypercapnia and Visual Stimulation

Abstract

Despite the different origins of cerebrovascular activity induced by neurogenic and nonneurogenic conditions, a standard assumption in functional studies is that the consequence on the vascular system will be mechanically similar. Using a recently developed arterial spin labeling method, we examined arterial blood volume, arterial-microvascular transit time, and cerebral blood flow (CBF) in the gray matter and in areas with large arterial vessels under hypercapnia, visual stimulation, and a combination of the two. Spatial heterogeneity in arterial reactivity was observed between conditions. During hypercapnia, large arterial volume changes contributed to CBF increase and further downstream, there were reductions in the gray matter transit time. These changes were not significant during visual stimulation, and during the combined condition they were moderated. These findings suggest distinct vascular mechanisms for large and small arterial segments that may be condition specific. However, the power relationships between gray matter arterial blood volume and CBF in hypercapnia (a = 0.69 ± 0.24) and visual stimulation (a = 0.68 ± 0.20) were similar. Assuming consistent capillary and venous volume responses across these conditions, these results offer support for a consistent total CBV-flow relationship typically assumed in blood oxygen-level dependent calibration techniques.

Multiparametric estimation of brain hemodynamics with MR fingerprinting ASL

“…The hemodynamic parameters measured with MRF‐ASL were in general agreement with previous literature and are within the expected range. Similarly, our observations of an increased CBF (by approximately 58%) and a decreased BAT (by approximately 14%) during CO 2 inhalation are in good agreement with reports of Ho et al and Donahue et al . Overall, we found that the hemodynamic parameters estimated are reproducible across runs, with a COV of CBF and BAT being 9.6 and 3.6%, respectively.…”

Assessment of hypertensive cerebrovascular alterations with multiband Look–Locker arterial spin labeling

“…Although the sequence parameters were different from the one used in the hypertension study, the resultant optimal strength is expected to be independent of the sequence parameters because all the dataset was eventually compared against the highest b value dataset acquired with the same sequence. The optimized b value of 3 s/mm 2 in our study is similar to the b values used in previous human studies ( b = 1.8–4.5 s/mm 2 ) . Even though different crushing gradient strengths have different cutoff velocities, the separation of different arterial segments by the crushing gradients was not feasible.…”

Comparison of pulsed and pseudocontinuous arterial spin‐labeling for measuring CO2‐induced cerebrovascular reactivity

“…Further study using methods such as phase-contrast flow quantification is clearly warranted. Another promising avenue of investigation is the use of pulsed or continuous ASL methods with variable delay times (31), which allow measurement of the tag inflow curve and, by fitting with kinetic models, quantitative estimation of CBF. These may help refining and validating single-subtraction versions of ASL techniques.…”