Measurement of Cerebral Oxygen Extraction Fraction Using Magnetic Resonance Imaging Technique
Date Issued
2005
Date
2005
Author(s)
Mo, Yuan-Heng
DOI
zh-TW
Abstract
Cerebrovascular disease is the second most common cause of death among adults in Taiwan, just behind the cancer for many years. It also contributes to most case of morbidity and brings a great burden to society. According its etiology, cerebrovascular disease can be subcategorized as ischemic and hemorrhagic stroke.
Many hemodynamic changes will consequently happens while ischemia. As cerebral perfusion pressure falls, cerebral blood flow (CBF) is initially maintained by arteriolar dilation. When vasodilatory capacity has been exceeded, cerebral autoregulation fails, and CBF begins to decrease rapidly. A progressive increase in oxygen extraction fraction (OEF) preserves cerebral oxygen metabolism. When the increase in OEF is no longer able to maintain the energy needs of the brain, cortical dysfunction may be observed. If there is no improvement in perfusion, permanent injury is the destiny. If we can differentiate irreversibly damaged tissue from functionally impaired but viable tissue, beneficial treatment for select patients may be possible. Increase in OEF seems to be a good physiologic indicator for possible area of ischemic penumbra.
Hypothermia is regarded as a therapy to protect brain tissue during surgery and appears to improve the clinical course of patients with acute ischemic stroke and traumatic brain injury. The beneficial effects owing to reduced aerobic demand and decline of cerebral metabolic rate of oxygen make tissue more tolerable to ischemia. Other protective mechanisms include reduce the increased intracranial pressure, maintenance of mitochondrial function, inhibition of neuroexcitatory transmitter release. However, the relationship between hypothermia and OEF is unclear.
Positron emission tomography (PET) is the imaging modality of choice for measurement of CBF, CMRO2 and even OEF. But it has great disadvantage in its availability, time-consuming, poor spatial resolution and radiation. During the last 10 years, major advances in Magnetic Resonance Imaging (MRI) have made it possible to visualize early changes in patients suffering from ischemic stroke. The combination of DWI and PWI has promising future in identifying ischemic areas potentially salvageable. Recently, a novel MRI sequence based on the BOLD contrast is used to assess the extent of deoxygenation in ischemic tissue and to derive the OEF.
Our preliminary results show that significantly decreased cerebral oxygen extraction fraction and CO2 production of rabbits after hypothermia and normal volunteers have similar OEF value as previous reports using noninvasive MR technique. We believe this technique provide a possible immediate imaging modality to monitor the physiological change in study of ischemic stroke.
Subjects
磁振造影
大腦
氧氣被利用率
MRI
brain
oxygen extraction fraction
SDGs
Type
text
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