the aorta, the aortic arch is here.

主动脉主动脉弓在这
Remember from our pictures of the heart?

还记得看过的一张心脏的照片么
You can't see it entirely because behind it is another white object

后面还有一个白色物体所以看不完整
that's sort of the midline here, that's the bones of the spine.

在中间线的位置这就是脊椎骨
In this region here, they're all superimposed

在这个区域影像都是叠加的
so you can't really tell how much of this absorption

所以没法具体说清
comes from the aortic arch and how much of it comes from the spine.

主动脉弓和脊椎各吸收了多少X射线
This is one problem with X-rays,

这是X线成像的一个缺点
that you're not seeing

在这个例子中就是
a three dimensional image of the chest in this case;

你无法看到胸腔的三维影像
you're seeing a projected image.

你看到的只是投影
You're only looking in one direction, really,

实际上你只是从单一的方向来看