Fagaly R L
Applied Physics Group, General Atomics, San Diego, California 92186.
Adv Neurol. 1990;54:11-32.
In considering what type of MEG system is needed, there are four main considerations: 1. Ambient magnetic noise at the intend site(s). The need to reject external noise will determine the need for a shielded room. Here, manufacturer's claims can be compared in terms of magnetic field sensitivities (BN/square root Hz) at the measurement site. There are several tradeoffs to consider. A relatively quiet environment may allow use of a less expensive eddy-current-shielded room combined with second-derivative gradiometer coils. A more harsh environment might need an MSR, but a gain in sensitivity may be afforded by using first-derivative gradient coils. A truly hostile environment could require multiple eddy-current shields combined with an MSR using three or more layers of mu-metal. 2. Head coverage and spatial resolution. The number of channels will roughly determine the number of times the Dewar(s) must be moved to cover the entire region of interest. Until MEG systems are available that can cover the entire head, coverage will be an important factor. Spatial resolutions (related to the diameter of the pickup coils and their spacing) should be adequate for all intended measurements. 3. Required sensitivity. Since the objects to be studied are current dipoles, magnetic field sensitivities (in fT/square root Hz) are not appropriate. This should be in terms of sensitivity to a current dipole measured in ampere-meters (Eq. 10) as a function of depth below the bottom of the Dewar tail. 4. Data acquisition systems and system software. Major considerations include the following: At what rate is data to be gathered? What is the total amount of data to be gathered in a single session? Must the data be processed real-time? How is the data to be interpreted? How is the data to be displayed? By examining these factors, it should be possible to compare available systems for neuromagnetic measurements and determine which system is appropriate for your needs.
在考虑需要何种类型的脑磁图（MEG）系统时，有四个主要考量因素：1. 预期测量地点的环境磁噪声。抑制外部噪声的需求将决定是否需要屏蔽室。在此，可以根据测量地点的磁场灵敏度（BN/√Hz）来比较制造商的宣称。有几个权衡因素需要考虑。相对安静的环境可能允许使用成本较低的涡流屏蔽室，并结合二阶导数梯度计线圈。环境更恶劣时可能需要磁屏蔽室（MSR），但使用一阶导数梯度线圈可能会提高灵敏度。真正恶劣的环境可能需要多层涡流屏蔽与使用三层或更多层坡莫合金的磁屏蔽室相结合。2. 头部覆盖范围和空间分辨率。通道数量将大致决定为覆盖整个感兴趣区域必须移动杜瓦瓶的次数。在能够覆盖整个头部的脑磁图系统出现之前，覆盖范围将是一个重要因素。空间分辨率（与拾取线圈的直径及其间距有关）应足以满足所有预期测量。3. 所需灵敏度。由于要研究的对象是电流偶极子，磁场灵敏度（以fT/√Hz为单位）并不合适。这应以对电流偶极子的灵敏度来衡量，该灵敏度以安培 - 米为单位测量（式10），作为杜瓦瓶尾部底部以下深度的函数。4. 数据采集系统和系统软件。主要考量因素包括以下几点：数据采集的速率是多少？单次采集的数据总量是多少？数据必须实时处理吗？数据如何解读？数据如何显示？通过审视这些因素，应该能够比较现有的神经磁测量系统，并确定哪种系统适合您的需求。
