Forster B B, MacKay A L, Whittall K P, Kiehl K A, Smith A M, Hare R D, Liddle P F
Department of Radiology, Vancouver Hospital and Health Science Centre-UBC Site.
Can Assoc Radiol J. 1998 Oct;49(5):320-9.
There are 2 principal techniques of functional MRI (fMRI): the blood-oxygen-level dependent (BOLD) technique, which is the favoured method because no intravenous contrast medium is required, and the dynamic or exogenous technique. The BOLD technique takes advantage of the fact that the change from diamagnetic oxyhemoglobin to paramagnetic deoxyhemoglobin that takes place with brain activation results in decreased signal intensity on MRI. Commercially available scanners can be used to conduct single-slice BOLD fMRI experiments, but echo-planar hardware is needed for multislice wholebrain experiments. Sequence choices in BOLD fMRI include spin-echo and gradient-echo sequences, to which rapid acquisition with relaxation enhancement and echoplanar techniques may be applied. Optimal imaging parameters (echo time, slice thickness, field of view and flip angle) are important in maximizing signal-to-noise ratios. Various statistical techniques and software programs have been developed to interpret the large amounts of data gathered from BOLD fMRI experiments, which presents one of the biggest challenges in performing this technique with clinical MR units. Controversy exists regarding the effects of draining veins on cortical mapping, of inflow of blood into the imaging slice or volume, and of motion artifact. BOLD fMRI has demonstrated good correlation with positron emission tomography, magneto-encephalography and electrocorticographic recordings of motor responses. It has been used to study cortical activity of visual, motor, auditory and speech tasks as well as brain centres for smell, motor imagery, complex motion and memory. As such, it holds promise for the study of brain function, but must be subjected to larger studies comparing it with the gold standard of electrocorticographic mapping.
功能磁共振成像（fMRI）有两种主要技术：血氧水平依赖（BOLD）技术，这是一种更受青睐的方法，因为无需静脉注射造影剂；以及动态或外源性技术。BOLD技术利用了这样一个事实，即随着大脑激活，从抗磁性的氧合血红蛋白转变为顺磁性的脱氧血红蛋白会导致MRI信号强度降低。商用扫描仪可用于进行单切片BOLD fMRI实验，但多层全脑实验需要回波平面硬件。BOLD fMRI中的序列选择包括自旋回波和梯度回波序列，可应用快速采集与弛豫增强以及回波平面技术。优化成像参数（回波时间、切片厚度、视野和翻转角）对于最大化信噪比很重要。已经开发了各种统计技术和软件程序来解释从BOLD fMRI实验中收集的大量数据，这是在临床MR设备上执行该技术时面临的最大挑战之一。关于引流静脉对皮质映射的影响、血液流入成像切片或体积的影响以及运动伪影存在争议。BOLD fMRI已证明与正电子发射断层扫描、脑磁图和运动反应的皮质脑电图记录具有良好的相关性。它已被用于研究视觉、运动、听觉和言语任务的皮质活动以及嗅觉、运动想象、复杂运动和记忆的脑中心。因此，它在脑功能研究方面具有前景，但必须进行更大规模的研究，将其与皮质脑电图映射的金标准进行比较。
