Effects of acute normovolemic hemodilution on T2* ‐ weighted images of rat brain

Acute normovolemic hernodilution (HD) was induced in anesthetized rats to assess the effect of changes in hematocrit (Hct) on signal intensity in T2*‐weighted magnetic resonance (MR) images. Other relevant physiological parameters were maintained invariant. Two degrees of HD were induced: mild (Hct reduced from 42.6 ± 2.2% to 33.4 ± 2.1%) and moderate (Hct reduced from 44.6 ± 2.7% to 26.2 ± 1.7%). A two‐dimensional gradient‐echo sequence was used to monitor signal changes with high temporal resolution before, during, and after HD protocols. The time course of signal intensity change was closely related to that of changes in Hct. Corresponding changes in R2* (ΔR2*) with respect to the pre‐HD state were calculated for the brain parenchyma. Average ΔR2* values of −0.24 ± 0.06 s−1 and −0.40 ± 0.07 s−1 were obtained for the mild and moderate HD groups, respectively, during the final 2 min of MR imaging (proximal to correlative measurements of Hct). MR measured ΔR2* values were in close agreement with the expected changes in R2* predicted from theory when the measured changes in Hct were used as independent variables. These data are in good agreement with the current understanding of the effects of changes in the intravascular concentration of deoxyhemoglobin on induced magnetic susceptibility and hold promise for quantitative measurement of brain oxygenation in vivo.

[1]  M. Moseley,et al.  Real‐time observation of transient focal ischemia and hyperemia in cat brain , 1992, Magnetic resonance in medicine.

[2]  J. E. Cremer,et al.  Regional Brain Blood Flow, Blood Volume, and Haematocrit Values in the Adult Rat , 1983, Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism.

[3]  W. Rosenblum.  Effects of Reduced Hematocrit on Erythrocyte Velocity and Fluorescein Transit Time in the Cerebral Microcirculation of the Mouse , 1971, Circulation research.

[4]  R. Turner,et al.  Dynamic magnetic resonance imaging of human brain activity during primary sensory stimulation. , 1992, Proceedings of the National Academy of Sciences of the United States of America.

[5]  T. Yoshimoto,et al.  T2*-weighted magnetic resonance imaging of cerebrovascular reactivity in rat reversible focal cerebral ischemia , 1997, Brain Research.

[6]  F. Sakai,et al.  Journal of Cerebral Blood Flow and Metabolism Regional Cerebral Blood Volume and Hematocrit Measured in Normal Human Volunteers by Single-photon Emission Computed Tomography , 2022 .

[7]  N. Lassen,et al.  Blood flow and metabolic rate for oxygen in the cerebral cortex of the rat. , 1973, Acta physiologica Scandinavica.

[8]  F. Hall.  Minimal utilizable oxygen and the oxygen dissociation curve of blood of rodents. , 1966, Journal of applied physiology.

[9]  W. Powers,et al.  Experimental hypoxemic hypoxia: Changes in R2* of brain parenchyma accurately reflect the combined effects of changes in arterial and cerebral venous oxygen saturation , 1998, Magnetic resonance in medicine.

[10]  B. Rosen,et al.  Functional mapping of the human visual cortex by magnetic resonance imaging. , 1991, Science.

[11]  D. Prough,et al.  Validation in Volunteers of a Near-Infrared Spectroscope for Monitoring Brain Oxygenation In Vivo , 1996, Anesthesia and analgesia.

[12]  J. Frahm,et al.  Cerebral blood oxygenation in rat brain during hypoxic hypoxia. Quantitative MRI of effective transverse relaxation rates , 1994, Magnetic resonance in medicine.

[13]  K Kuppusamy,et al.  Quantitative measurements of regional cerebral blood volume using MRI in rats: Effects of arterial carbon dioxide tension and mannitol , 1997, Magnetic resonance in medicine.

[14]  Weili Lin,et al.  In vivo validation of the bold mechanism: A review of signal changes in gradient echo functional MRI in the presence of flow , 1995, Int. J. Imaging Syst. Technol..

[15]  D. Prough,et al.  The Influence of Carbon Dioxide and Body Position on Near-Infrared Spectroscopic Assessment of Cerebral Hemoglobin Oxygen Saturation , 1996, Anesthesia and analgesia.

[16]  B. Rosen,et al.  Measurement of regional blood oxygenation and cerebral hemodynamics , 1993, Magnetic resonance in medicine.

[17]  T. L. Davis,et al.  EPI Imaging of Global Increase of Brain MR Signal with Breath‐hold Preceded by Breathing O2 , 1995, Magnetic resonance in medicine.

[18]  R S Balaban,et al.  Comparison of EPI gradient‐echo contrast changes in cat brain caused by respiratory challenges with direct simultaneous evaluation of cerebral oxygenation via a cranial window , 1994, NMR in biomedicine.

[19]  J C Gore,et al.  Physiologic basis for BOLD MR signal changes due to hypoxia/hyperoxia: Separation of blood volume and magnetic susceptibility effects , 1997, Magnetic resonance in medicine.

[20]  O Henriksen,et al.  Signal changes in gradient echo images of human brain induced by hypo‐ and hyperoxia , 1995, NMR in biomedicine.

[21]  E. Moser,et al.  Proton NMR relaxation times of human blood samples at 1.5 T and implications for functional MRI. , 1997, Cellular and molecular biology.

[22]  Eunice Chace Greene.  Anatomy of the Rat , 1936, Nature.

[23]  Ravi S. Menon,et al.  Functional brain mapping by blood oxygenation level-dependent contrast magnetic resonance imaging. A comparison of signal characteristics with a biophysical model. , 1993, Biophysical journal.

[24]  Relationship of peripheral venous hematocrit to brain hematocrit. , 1969, Journal of applied physiology.

[25]  G. J. Crystal,et al.  Blood volume and hematocrit in regional circulations during isovolemic hemodilution in dogs. , 1989, Microvascular research.

[26]  P. Gaehtgens,et al.  Hemorheological Aspects of the Pathophysiology of Cerebral Ischemia , 1986, Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism.

[27]  N B EVERETT,et al.  Distribution of Blood (Fe59) and Plasma (I131) Volumes of Rats Determined by Liquid Nitrogen Freezing , 1956, Circulation research.

[28]  R. Weisskoff,et al.  MRI susceptometry: Image‐based measurement of absolute susceptibility of MR contrast agents and human blood , 1992, Magnetic resonance in medicine.

[29]  B R Rosen,et al.  Mr contrast due to intravascular magnetic susceptibility perturbations , 1995, Magnetic resonance in medicine.

[30]  Albert Macovski,et al.  Estimating oxygen saturation of blood in vivo with MR imaging at 1.5 T , 1991 .

[31]  D. Becker,et al.  Mannitol causes compensatory cerebral vasoconstriction and vasodilation in response to blood viscosity changes. , 1983, Journal of neurosurgery.

[32]  J C Gore,et al.  A general model of microcirculatory blood flow effects in gradient sensitized MRI. , 1994, Medical physics.

[33]  R. Turner,et al.  Echo‐planar time course MRI of cat brain oxygenation changes , 1991, Magnetic resonance in medicine.

[34]  O. Yu,et al.  NMR relaxation rates and blood oxygenation level , 1995, Magnetic resonance in medicine.

[35]  B. Siesjö,et al.  The influence of acute normovolemic anemia on cerebral blood flow and oxygen consumption of anesthetized rats. , 1975, Acta physiologica Scandinavica.