Correct using of Image position tag (0020,0032) - DICOM

This is a discussion on Correct using of Image position tag (0020,0032) - DICOM ; 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 ...

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Thread: Correct using of Image position tag (0020,0032)

  1. Correct using of Image position tag (0020,0032)

    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

  2. How to compute reconstruction interval, was Re: Correct using ofImage position tag (0020,0032)

    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


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