2例病灶内可见囊性低密度区。

Cystal low density were demonstrated in 2 lesions.

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原先病灶侧（左侧）的病灶缩小为一处小的低密度区。

The left-sided lesion now has shrunk to a small hypointense area.

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脾原发恶性淋巴瘤，呈局灶性低密度区和不均匀强化。

Primary lymphoma of spleen had presented part range low density regions and uneven enhancement .

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So, for example, we have this average level, and then it can go high where we have the peak, or it can go very low. We can also discuss sound waves, so again it's just the periodic variation of some property -- in this case we're talking about density, so we have high density areas and low density areas.

例如这是平均位置，在峰的位置水位高，在谷水位低，我们也可以,讨论声波它也是某种,量的周期变化，在这里我们,讨论的是密度,我们有高密度区和低密度区。

麻省理工公开课 - 化学原理课程节选