Abstract
BackgroundOur previous study has shown that prenatal exposure to X-ray irradiation causes cerebral hypo-perfusion during the postnatal development of central nervous system (CNS). However, the source of the hypo-perfusion and its impact on the CNS development remains unclear. The present study developed an automatic analysis method to determine the mean red blood cell (RBC) speed through single microvessels imaged with two-photon microscopy in the cerebral cortex of rats prenatally exposed to X-ray irradiation (1.5 Gy).Methodology/Principal FindingsWe obtained a mean RBC speed (0.9±0.6 mm/sec) that ranged from 0.2 to 4.4 mm/sec from 121 vessels in the radiation-exposed rats, which was about 40% lower than that of normal rats that were not exposed. These results were then compared with the conventional method for monitoring microvascular perfusion using the arteriovenous transit time (AVTT) determined by tracking fluorescent markers. A significant increase in the AVTT was observed in the exposed rats (1.9±0.6 sec) as compared to the age-matched non-exposed rats (1.2±0.3 sec). The results indicate that parenchyma capillary blood velocity in the exposed rats was approximately 37% lower than in non-exposed rats.Conclusions/SignificanceThe algorithm presented is simple and robust relative to monitoring individual RBC speeds, which is superior in terms of noise tolerance and computation time. The demonstrative results show that the method developed in this study for determining the mean RBC speed in the spatial frequency domain was consistent with the conventional transit time method.
Highlights
Prenatal exposure to X-ray irradiation is a leading cause of postnatal development deficits such as a decrease in brain size and retardation of behavioral and mental activity [1]
Because the cerebral blood flow (CBF) reflects a product of cortical blood volume per unit tissue volume and cross-sectional blood velocity in the vessels, the cerebral hypo-perfusion observed in the exposed subjects could be due to low blood volume in the parenchyma tissue relative to non-exposed subjects, or it could be due to a decrease in blood velocity through the parenchyma capillaries
The time required to compute the mean red blood cell (RBC) speed was 0.60 sec per image with the proposed method, which was faster than a method employing singular value decomposition (SVD) (4.74 sec per image), and almost equivalent to a method using the Radon transform (0.75 sec per image)
Summary
Prenatal exposure to X-ray irradiation is a leading cause of postnatal development deficits such as a decrease in brain size and retardation of behavioral and mental activity [1]. Following prenatal exposure to irradiation, newborn rats showed reduced cerebral blood flow (CBF), which was only half of that observed in age-matched non-exposed rats [2] These findings suggest that immature development of the brain vasculature, including cerebral hypo-perfusion, is of etiological importance in the delayed development of the central nervous system (CNS) observed in subjects following prenatal exposure to X-ray irradiation. Because the CBF reflects a product of cortical blood volume per unit tissue volume and cross-sectional blood velocity in the vessels, the cerebral hypo-perfusion observed in the exposed subjects could be due to low blood volume (i.e., decrease in capillary density) in the parenchyma tissue relative to non-exposed subjects, or it could be due to a decrease in blood velocity through the parenchyma capillaries In the former case, low blood volume may result from an immature development of the microvasculature. The present study developed an automatic analysis method to determine the mean red blood cell (RBC) speed through single microvessels imaged with two-photon microscopy in the cerebral cortex of rats prenatally exposed to X-ray irradiation (1.5 Gy)
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