The Commissures

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What are they?

The commissures are fibre tracts connecting the two hemispheres. There is a posterior commissure, which connects midbrain and diencephalon structures, and lies just in front of and above the superior colliculi, below the pineal gland. The posterior commissure is not always easy to see on a high detailed structural scan, and it is very unlikely you will be able to discern it on functional images.The anterior commissure (AC) connects the middle and inferior temporal gyri of the two hemispheres, and runs across the midline just in front of the fornix. It is relatively easy to see on most structural scans.
连接两个半球的是纤维束。有一个后连合，连接中脑和间脑结构，位于上丘的前面和上面，松果体下面。后连合并不总是很容易在高细节的结构扫描中看到，你也不太可能在功能图像上看到它。前连合(AC)连接两个半球的中间和下颞回，并在穹窿前穿过中线。这是相对容易看到的大多数结构扫描。

Why the commissures?

The commissure have become key landmarks, because Talairach and Tournoux chose them to determine the standard alignment of the brain for their famous atlas. To align a scan to Talairach space, a brain has to be set so that the anterior and posterior commissures are on a horizonatal line.

Where are they?

Below is a little schematic (from Chris Rorden's MriCro tutorial) of a sagittal brain view. The anterior commissure is shown in red, and the posterior commissure in yellow.

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The image below shows the anterior commissure on an iconic brain from the MNI series (see the MNI space page for details). The AC is at the virtual intersection of the red lines.

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The AC is best seen on slice 91 in X, 131 in Y and 67 in Z of the iconic brain image.

Below is an image showing the PC on the same brain, again at the (truncated) intersection of the red lines. The PC can best be seen at slices X 91, Y 103 and Z 70. Note that this brain is not exactly oriented according to the Talairach system, as the two commissures are not on the same axial plane.

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SPM 做AC原点校正

coronal(冠状面，正视图)
Axial(轴状面，俯视图)
sagittal(矢状面，左视图)
1、roll：调整roll值使得十字准线的垂直线粗略的通过coronal视图的中间。roll调整使得图像绕y-axis旋转
2、yaw：调整yaw值使得十字准线的垂直线粗略的通过axial视图的中间。yaw调整使得图像绕z-axis旋转
（1、2一般微调或者不调整）
3、调整好roll和yaw后寻找最中间的sagittal视图：胼胝体（中间白色部分）最长最厚最清晰（里面几乎没有黑色）尽量把十字准线的交点放在AC上（红色的点）、黄色的点为PC（后连合）前面图
4、调整pitch（pitch调整使得图像绕x-axis旋转) 使得sagittal十字准线的横线穿过前连合（AC：红色的点）后连合（PC：黄色的点），如上图

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原文链接：https://blog.csdn.net/QW_sunny/article/details/62052282