脑死亡:采用动脉自旋标记评估脑血流
Background:The cardinal requirements to diagnose brain death include coma, absence of brain stem reflexes, and apnea. Additional tests may be needed to declare a person brain dead when the results of any components of clinical testing cannot be evaluated reliably. Arterial spin labeling (ASL) offers a noninvasive means for measuring cerebral blood flow (CBF) and determining brain death. Case Report:Woman, 48, was admitted to the emergency department having experienced nuchal rigidity, tonic seizure, and loss of consciousness. No pupil reaction to light was observed 5 hours after lumbar puncture for diagnostic purposes. In addition, the patient had apnea. Magnetic resonance imaging (MRI) showed tonsillar impaction in the foramen magnum, loss of signal void in the bilateral internal carotid arteries (suggesting a lack of flow), severe swelling in the gyri, and extensive intravenous thrombi filling the vessel lumens. On the twentieth day in the hospital clinical examinations to determine brain death produced results consistent with that diagnosis. At 22days an electroencephalogram demonstrated electrocerebral silence consistent with brain death. Neurologists requested that conventional or radionuclide angiography be done to determine CBF, but the family refused further invasive tests. At 23days unavoidable MRI using the ASL technique was performed, revealing severe perfusion defect in the entire brain. The mean value of CBF in the gray matter was 7.9mL/100g/min. The accepted lower limit of CBF required by the human brain is 10 to 15mL/100g/min for regional CBF. The patient showed no improvement by day 25. Mechanical ventilation and other life support were removed in the operating room after 1month of hospitalization, with organ donations made to five other patients. Conclusions:ASL is completely noninvasive and provides valuable information concerning absolute CBF. With ASL MRI, protons in arterial water are labeled magnetically in the vessels feeding the brain, then flow through the vascular tree and exchange water with unlabeled brain tissue. By subtracting an image in which incoming arterial spins are labeled from an image without spin labeling, a perfusion-weighted image is generated. ASL has proven validity in gray matter but tends to underestimate CBF in white matter. The ASL technique offers potential as a noninvasive imaging tool for determining CBF and thus brain death
来源: ScienceDirect
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