最近看文献，只知道vbm经过modulate后是volume，不经过modulate是的density，不过具体表示了什么还不是很清楚。而且为什么经过modulate就是体积也不是太清楚。下面一段话是文章中的，没太理解，请指点下，谢谢。还有，用哪一个指标比较好也没有具体的说法吧（体积还是密度？），是不是喜欢用哪种就用哪种？有没有什么经验呢？
Gray matter values for unmodulated images are typically referred to as gray matter density. The term density indicates that cortical thickness and/or white matter volume averaging in a particular area influences the size of the gray matter values. Gray matter values for Jacobian modulated images are referred to as gray matter volume. Gray matter volume reflects the influence of regional volumes on the size of the gray matter values, as well as cortical thickness and/or volume averaging.
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谢谢，假如GMD指该体素内灰质的含量，那么GMV究竟代表了
不好理解，密度这个指标更容易理解一些。