Bulte Daniel P, Drescher Knut, Jezzard Peter
FMRIB Centre, Department of Clinical Neurology, University of Oxford, United Kingdom.
Magn Reson Med. 2009 Feb;61(2):391-8. doi: 10.1002/mrm.21862.
MRI may be used to measure fractional changes in cerebral oxygen metabolism via a metabolic model. One step commonly used in this measurement is calibration with image data acquired during hypercapnia, which is a state of increased CO2 content of the blood. In this study some commonly used hypercapnia-inducing stimuli were compared to assess their suitability for the calibration step. The following stimuli were investigated: (a) inspiration of a mixture of 4% CO2, 21% O2 and balance N2; (b) 30-s breath holding; and (c) inspiration of a mixture of 4% CO2 and 96% O2 (i.e., carbogen). Measurements of BOLD and cerebral blood flow made on nine subjects during the different hypercapnia-inducing stimuli showed that each stimulus leads to a different calibration of the model. We argue that of the aforementioned stimuli, inspiration of 4% CO2, 21% O2 and balance N2 should be preferred for the calibration as the other stimuli produce responses that violate assumptions of the metabolic model.
磁共振成像（MRI）可通过代谢模型用于测量脑氧代谢的分数变化。这种测量中常用的一个步骤是用高碳酸血症期间采集的图像数据进行校准，高碳酸血症是血液中二氧化碳含量增加的一种状态。在本研究中，对一些常用的诱发高碳酸血症的刺激进行了比较，以评估它们在校准步骤中的适用性。研究了以下刺激：（a）吸入4%二氧化碳、21%氧气和其余为氮气的混合气体；（b）屏气30秒；（c）吸入4%二氧化碳和96%氧气的混合气体（即卡波金）。在不同的诱发高碳酸血症刺激期间对9名受试者进行的血氧水平依赖（BOLD）和脑血流量测量表明，每种刺激都会导致模型的不同校准。我们认为，在上述刺激中，吸入4%二氧化碳、21%氧气和其余为氮气的混合气体在校准中应是首选，因为其他刺激产生的反应违反了代谢模型的假设。
