DSA (digital subtraction angiography) have two important tags:

```
(0018, 1110) Distance Source to Detector
(0018, 1111) Distance Source to Patient
```

The DSA image is perspective projection to an object, likes:

where S is the source, N is the distance source to patient `(0018, 1111) `

, and F is the distance source to detector `(0018, 1110)`

.

`P`

is a point inside of the imaging object, and `P'`

is the point in DSA image. If the position of `P`

is (w_x, w_y, w_z) , and the position of `P'`

is (x, y) , we can have:

\frac {w_x-o_x}{N-o_y} = \frac {x-o_x}{F}

My question is: what should (o_x, o_y, o_z) be? Is it the image position `(0020, 0032)`

? Or how can I obtain this point?

In addition, the image position `(0020, 0032)`

is a absolute point in a world coordinate, where is the original point (0, 0, 0)?

Any suggestion is appreciated~~~