Multimodal measurements of blood plasma and red blood cell volumes during functional brain activation

• Published in: Journal of cerebral blood flow and metabolism Vol. 29; no. 1; pp. 19 - 24
• Main Authors: Herman, Peter, Sanganahalli, Basavaraju G, Hyder, Fahmeed
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 01-01-2009; Nature Publishing Group; Sage Publications Ltd
• Subjects: Animals; Biological and medical sciences; Blood Volume; Brain - blood supply; Brain - physiology; Erythrocytes; Investigative techniques, diagnostic techniques (general aspects); Magnetic Resonance Imaging; Medical sciences; Nervous system; Neurology; Radionuclide investigations; Rats; Rats, Sprague-Dawley; Regional Blood Flow; Vascular diseases and vascular malformations of the nervous system; hematocrit; nitric oxide; metabolism; blood flow; Biosensor; energetics; Nervous system diseases; biosensor; Activation volume; Hematocrit; Red blood cell; Metabolism; Cerebral disorder; Blood flow; Encephalon; Blood volume; Nitric oxide; Central nervous system disease; Cerebrovascular disease
• ISSN: 0271-678X; 1559-7016
• DOI: 10.1038/jcbfm.2008.100

As an alternative to functional magnetic resonance imaging (fMRI) with blood oxygenation level dependent (BOLD) contrast, cerebral blood volume (CBV)-weighted fMRI with intravascular contrast agents in animal models have become popular. In this study, dynamic measurements of CBV were performed by magnetic resonance imaging (MRI) and laser-Doppler flowmetry (LDF) in α-chloralose anesthetized rats during forepaw stimulation. All recordings were localized to the contralateral primary somatosensory cortex as revealed by BOLD at 11.7 T. Ultra-small superparamagnetic iron oxide (15mg/kg)—a plasma-borne MRI contrast agent with a half-life of several hours in blood circulation—was used to quantify changes in magnetic field inhomogeneity in blood plasma. The LDF backscattered laser light (805 nm), which reflects the amount of red blood cells, was used to measure alterations in the non-plasma compartment. Dynamic and layer-specific comparisons of the two CBV signals during functional hyperemia revealed excellent correlations (> 0.86). These results suggest that CBV measurements from either compartment may be used to reflect dynamic changes in total CBV. Furthermore, by assuming steady-state mass balance and negligible counter flow, these results indicate that volume hematocrit is not appreciably affected during functional activation.