Tome (大部头的书)在希腊语中是层面的意思。大部分颅脑影像中的标准观察层面是水平面或“轴面”。颅脑的左侧被显示在影像的右侧，也就是说象从身体的“低位器官”的角度仰视颅脑所看到的那样。其它一些标准的观察层面还有冠状面和矢状面。非断层扫描成像的方式有X光片及磁共振血管造影，这些成像方式的图像是由被成像物体上的单一的点的投影组成。
Tome is Greek for slice. The standard slice orientation in most brain imaging is transaxial or "axial". Left is shown at right. Note that, like the "lower organs", we look up to the brain. Other standard planes of view are coronal and sagittal. Non-tomographic images represent "projections" from a single point of view and include bolus contrast x-ray angiograms and MR angiograms.
断层扫描图像是由一定数目的小点所构成,这些小点被称为像素,每一个像素 每一个像素代表一个从1(黑色)至256(白色)中的灰度级。 每个断层的厚度一般是3毫米或是5毫米，这样就可以产生一个三维的体积元素，形状象一个鞋盒，也称为体素。 象素的强度代表体素中组织所平均厚度。
Tomographic images are made up of little squares called "pixels" (picture elements), each of which takes a grey-scale value from 1 (black) to 256 (white). Each pixel represents brain tissue which is about 1 mm. on each of two sides. The thickness of the slice is often 3 or 5 mm, thus creating a three-dimensional volume element, or "voxel", which is shaped like a shoe box. Pixel intensity represents an average from tissue within the voxel.
MRI (magnetic resonance imaging) When protons (here brain protons) are placed in a magnetic field, they become capable of receiving and then transmitting electromagnetic energy. The strength of the transmitted energy is proportional to the number of protons in the tissue. Signal strength is modified by properties of each proton's microenvironment, such as its mobility and the local homogeneity of the magnetic field. MR signal can be "weighted" to accentuate some properties and not others.
如果另加一个磁场，这个磁场空间中的不同点上的磁力都在精细地发生变化，那么空间中的每一点都有一个唯一的频率来接收和发射信号。这就为构筑一幅图像提供了可能。就象一架钢琴，它代表了频率的空间编码(举例)。更多有关磁共振的细节请点这里。
When an additional magnetic field is superimposed, one which is carefully varied in strength at different points in space, each point in space has a unique radio frequency at which the signal is received and transmitted. This makes constructing an image possible. It represents the spatial encoding of frequency, just like a piano. (example). More details of MR here.
SPECT/PET (single photon/positron emission computed tomography) When radiolabeled compounds are injected in tracer amounts, their photon emissions can be detected much like x-rays in CT. The images made represent the accumulation of the labeled compound. The compound may reflect, for example, blood flow, oxygen or glucose metabolism, or dopamine transporter concentration. Often these images are shown with a color scale. (example)
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