Hi

You need to compute the distance along a line that passes through

the parallel slices perpendicularly.

Given two slices, compute the distance from the origin (0,0,0) of

the top left hand corner of each along the normal to the slice

orientation, and subtract one distance from the other to give the

distance between the center plane of each slice, i.e., the

reconstruction interval.

For each slice, the normal to the slice orientation is the cross

product of the row and column unit vectors (first three and second

three values of Image Orientation (Patient), respectively).

For each slice, the distance from the origin (0,0,0) of the top

left hand corner is the dot product of the Image Position (Patient)

(i.e., a vector from the origin to the top left hand corner of the

image) and the normal to the slice orientation (i.e., the dot

product is the magnitude of the origin to the top left hand corner

vector component along the direction of the normal).

For multiple slices, you may want to first sort them by distance

from the origin along the normal in case they are not already in

ascending order, and you may want to check that the reconstruction

interval is the same between successive sorted slices (i.e., they

are evenly spaced), and you may want to check that they are all

parallel (i.e., that they have the same values for Image Orientation

(Patient)).

For examples of how to do this and similar related things, see:

com.pixelmed.geometry.GeometryOfSlice

com.pixelmed.geometry.GeometryOfVolume

com.pixelmed.dicom.GeometryOfSliceFromAttributeLis t

com.pixelmed.dicom.GeometryOfVolumeFromAttributeLi st

David

vasmvr@yahoo.com wrote:

> Hi all,

> I have a question about image position (0020,0032):

> I have to import Dicom Data set of CT image (MEDIA STORAGE SOP

> CLASS UID 1.2.840.10008.5.1.4.1.1.2) and I need to know the step

> between the axials to a correct reconstruction of the volume. I think

> I can't use the tag 0018,0050 Slice thickness because is a 2 value

> field and i suppose not all Dicom images can have this value, so I

> have to use image position (0020,0032) tag. But which is the way to

> undestand and use that values?

>

> For example I can have a series of CT axial with this value:

>

> 0.0/0.0/0.0

> 0.0/0.0/0.5

> 0.0/0.0/1.0

> 0.0/0.0/1.5

> Patient position (0020,0037) for all images is 1.0/0.0/0.0/0.0/1.0/0.0

>

> or a series of CT axial with this value:

>

> 73.949997/0.0/-110.28971

> 73.949997/0.0/-109.88914

> 73.949997/0.0/-110.48856

> 73.949997/0.0/-110.08798

>

> Patient position (0020,0037) for all images is 1.0/0.0/0.0/0.0/1.0/0.0

>

> or a series of CT axial with this value:

>

> 66.699997/47.013481/-163.11487

> 66.699997/47.760445/-162.80463

> 66.699997/47.507408/-162.49438

>

> Patient position (0020,0037) for all images is

> 1.0/0.0/0.0/0.0/0.774564/0.632496

>

> Is there a relationship between Patient position and Image position to

> retrieve the value of the step?

>

> I hope someone can help me....

>

> Thanks in advance

>

> Vasmvr