title: Bridging macroscopic and microscopic methods for the measurements of cerebral blood flow: Toward finding the determinants in maintaining the CBF homeostasis.
abstract: Methods exist to evaluate the cerebral blood flow (CBF) at both the macroscopic and microscopic spatial scales. These methods provide complementary information for understanding the mechanism in maintaining an adequate blood supply in response to neural demand. The macroscopic CBF assesses perfusion flow, which is usually measured using radioactive tracers, such as diffusible, nondiffusible, or microsphere. Each of them determines CBF based on indicator dilution principle or particle fraction principle under the assumption that CBF is steady state during the measurement. Macroscopic CBF therefore represents averaged CBF over a certain space and time domains. On the other hand, the microscopic CBF assesses bulk flow, usually measures using real-time microscopy. The method assesses hemodynamics of microvessels, ie, vascular dimensions and flow velocities of fluorescently labeled or nonlabeled RBC and plasma markers. The microscopic CBF continuously fluctuates in time and space. Smoothing out this heterogeneity may lead to underestimation in the macroscopic CBF. To link the two measurements, it is needed to introduce a common parameter which is measurable for the both methods, such as mean transit time. Additionally, applying the defined physiological and/or pharmacological perturbation may provide a good exercise to determine how the specific perturbations interfere the quantitative relationships between the macroscopic and microscopic CBF. Finally, bridging these two-scale methods potentially gives a further indication how the absolute CBF is regulated with respect to a specific type of the cerebrovascular tones or capillary flow velocities in the brain.
authors.affiliation: Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan. Electronic address: kanno1009@gmail.com.
authors.forename: I
authors.initials: I
authors.lastname: Kanno
authors.affiliation: Brain Science Inspired Life Support Research Center, University of Electro-Communications, Tokyo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Masamoto
mesh_terms: D000818:Animals; D001921:Brain / Q000098:blood supply*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006439:Hemodynamics; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D000069336:Neurovascular Coupling / Q000502:physiology*
keywords: Bulk flow; Diffusible tracer; Fluorescent tracer; Heterogeneity; Microsphere tracer; Neurovascular unit; Nondiffusible tracer; Perfusion flow; Quantitative measurement; Radioisotope tracer