Scanning Laser-Doppler Flowmetry of Rat Cerebral Circulation during Cortical Spreading Depression

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Abstract

Scanning laser-Doppler flowmetry (SLDF) generates two-dimensional images of blood flow. This study compared SLDF to conventional laser-Doppler flowmetry (LDF) in the cerebral circulation. Test stimuli were episodes of cortical spreading depression (CSD) elicited in brains of halothane anaesthetised rats (n = 9). The LDF instrument used two wavelengths of laser light to record relative changes of cerebral blood flow (CBF) up to an approximate depth of 250 µm (543 nm) and 500 µm (780 nm). Under resting conditions, SLDF images showed a heterogeneous pattern of flow in pial vessels with high flow rates in arterioles, and lower rates in venules and small vessels (<30 µm). Arterioles constituted about 6%, venules 12% and small vessels 2% of the image area, while approximately 80% were background with a laser-Doppler signal corresponding to zero calibration. During CSD, the relative increase of area was largest for small vessels and less for venules and arterioles. Similar changes were observed for blood flow in the three vessel structures. For both wavelengths of LDF, flow changes correlated with SLDF (r ≈ 0.7). In conclusion, SLDF provides images of flow in pial vessels and capillaries at, or just beneath the cortical surface. SLDF and LDF are complementary, but cannot substitute for one another as they measure flow in different layers of the cortex.

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Laser Doppler perfusion imaging by dynamic light scattering.

K Wårdell, A Jakobsson, G.E. Nilsson (1993)

Imaging of tissue perfusion is important in assessing the influence of peripheral vascular disease on microcirculation. This paper reports on a laser Doppler perfusion imaging technique based on dynamic light scattering in tissue. When a laser beam sequentially scans the tissue (maximal area approximately 12 cm *12 cm), moving blood cells generate Doppler components in the back-scattered light. A fraction of this light is detected by a remote photodiode and converted into an electrical signal. In the signal processor, a signal proportional to the tissue perfusion at each measurement point is calculated and stored. When the scanning procedure is completed, the system generates a color-coded perfusion image on a monitor. A perfusion image is typically built up of data from 4,096 measurement sites, recorded during a time period of 4 min. This image has a spatial resolution of about 2 mm * 2 mm. A theory for the system inherent amplification factor dependence on the distance between individual measurement points and detector is proposed and correction measures are presented. The performance of the laser Doppler perfusion imager was evaluated using a flow simulator. The correlation coefficient between the estimated flow parameter and the perfusion through a mechanical flow simulator was calculated to r = 0.996. To assess the sampling depth of the laser beam, light scattering in tissue was simulated by a Monte Carlo technique. The average sampling depth for skin tissue was calculated to 200-240 microns, depending on the blood content.(ABSTRACT TRUNCATED AT 250 WORDS)

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Vascular imprints of neuronal activity: Relationships between the dynamics of cortical blood flow, oxygenation, and volume changes following sensory stimulation

K. Yamada, I Kanno, A Grinvald … (1997)

Modern functional neuroimaging methods, such as positron-emission tomography (PET), optical imaging of intrinsic signals, and functional MRI (fMRI) utilize activity-dependent hemodynamic changes to obtain indirect maps of the evoked electrical activity in the brain. Whereas PET and flow-sensitive MRI map cerebral blood flow (CBF) changes, optical imaging and blood oxygenation level-dependent MRI map areas with changes in the concentration of deoxygenated hemoglobin (HbR). However, the relationship between CBF and HbR during functional activation has never been tested experimentally. Therefore, we investigated this relationship by using imaging spectroscopy and laser-Doppler flowmetry techniques, simultaneously, in the visual cortex of anesthetized cats during sensory stimulation. We found that the earliest microcirculatory change was indeed an increase in HbR, whereas the CBF increase lagged by more than a second after the increase in HbR. The increased HbR was accompanied by a simultaneous increase in total hemoglobin concentration (Hbt), presumably reflecting an early blood volume increase. We found that the CBF changes lagged after Hbt changes by 1 to 2 sec throughout the response. These results support the notion of active neurovascular regulation of blood volume in the capillary bed and the existence of a delayed, passive process of capillary filling.

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Laminar analysis of cerebral blood flow in cortex of rats by laser-Doppler flowmetry: a pilot study.

M Fabricius, N Akgören, Ulrich Dirnagl … (1997)

Laser-Doppler flowmetry (LDF) is a reliable method for estimation of relative changes of CBF. The measurement depth depends on wavelength of the laser light and the separation distance of transmitting and recording optical fibers. We designed an LDF probe using two wavelengths of laser light (543 nm and 780 nm), and three separation distances of optical fibers to measure CBF in four layers of the cerebral cortex at the same time. In vitro comparison with electromagnetic flow measurements showed linear relationship between LDF and blood flow velocity at four depths within the range relevant to physiologic measurements. Using artificial brain tissue slices we showed that the signal for each channel decreased in a theoretically predictable fashion as a function of slice thickness. Application of adenosine at various depths in neocortex of halothane-anesthetized rats showed a predominant CBF increase at the level of application. Electrical stimulation at the surface of the cerebellar cortex demonstrated superficial predominance of increased CBF as predicted from the distribution of neuronal activity. In the cerebellum, hypercapnia increased CBF in a heterogeneous fashion, the major increase being at apparent depths of approximately 300 and 600 microns, whereas in the cerebral cortex, hypercapnia induced a uniform increase. In contrast, the CBF response to cortical spreading depression in the cerebral cortex was markedly heterogeneous. Thus, real-time laminar analysis of CBF with spatial resolution of 200 to 300 microns may be achieved by LDF. The real-time in depth resolution may give insight into the functional organization of the cortical microcirculation and adaptive features of CBF regulation in response to physiologic and pathophysiologic stimuli.

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Author and article information

Journal

Journal ID (publisher-id): JVR

Journal ID (nlm-ta): J Vasc Res

Journal ID (doi): 10.1159/issn.1018-1172

Title: Journal of Vascular Research

Publisher: S. Karger AG

ISSN (Print): 1018-1172

ISSN (Electronic): 1423-0135

Publication date Subscription-year: 2000

Publication date (Print): December 2000

Publication date (Electronic): 10 January 2001

Volume: 37

Issue: 6

Pages: 513-522

Affiliations

^aDepartment of Medical Physiology, University of Copenhagen, and ^bDepartment of Clinical Neurophysiology, Glostrup Hospital, Copenhagen, Denmark

Article

Publisher ID: 54084 Other ID: J Vasc Res 2000;37:513–522

DOI: 10.1159/000054084

PubMed ID: 11146405

SO-VID: a42c5b30-1d26-4f88-a3fa-a0d619abfd44

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Scanning Laser-Doppler Flowmetry of Rat Cerebral Circulation during Cortical Spreading Depression

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Karger: Cardiovascular System

Most cited references 3

Laser Doppler perfusion imaging by dynamic light scattering.

Vascular imprints of neuronal activity: Relationships between the dynamics of cortical blood flow, oxygenation, and volume changes following sensory stimulation

Laminar analysis of cerebral blood flow in cortex of rats by laser-Doppler flowmetry: a pilot study.

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