CODEWITHSUNDEEP
dicom
ananth_adroit
ananth_adroit

Reputation: 347

how to measure the distance in dicom

I want to know how to measure the distance between two pixels in dicom . already done some google found pixel spacing (0028,0030) need to find the distance . could some one clearly explain ....

thanks

Upvotes: 3

Views: 9292

Answers (2)

smocking
smocking

Reputation: 3709

Assuming that you're trying to measure distances in the subject/animal/phantom/whatever, it all depends on whether you want to measure distances between different slices or just in the same slice.

Volumetric DICOM series typically have a slice spacing (0012,0088) in addition to the pixel spacing which you need to take into account. Note that there is also such a thing as slice thickness, which is distinct and should not be used for calculating distances, as there can be a gap or overlap between consecutive slices.

It is helpful to define a voxelspacing vector as follows (pseudocode):

voxelspacing.x = first element of PixelSpacing (0028,0030), i.e. before "\"
voxelspacing.y = second element of PixelSpacing (0028,0030), i.e. after "\"
voxelspacing.z = SliceSpacing (0018,0088) or 0 if 2D and/or not specified

Some brain-dead manufacturers and de-identification tools break the slice spacing tag in which case you'll have to calculate it from another source, such as difference in consecutive slice location, patient image position, etc, but that's another matter.

Moving on, you now have the distance in millimeters between voxels for each dimension. You can then calculate the real-world euclidean distance given voxel coordinates in pointA and pointB:

delta = (pointA - pointB) * voxelspacing
distance = sqrt(delta.x^2 + delta.y^2 + delta.z^2);

Where all the operators are element-wise. It is critical to individually multiply the voxel coordinates with their respective spacings before computing distance, because voxels are typically not isotropic.

Upvotes: 15

Rob
Rob

Reputation: 2472

You need to know the dot pitch of the monitor. For example a jumbotron has huge pixels (guessing), so the distance is larger than it would be for a typical desktop monitor. Ask the manufacturer of the monitor for this information. After that use pythogorean theorum. sqrt(a^2 + b^2) = c c being the total distance and a/b are x and y distances. to find a and be you would find the coordinates of one pixel and subtract from the other. a = (x1-x2) b = (

Upvotes: -5

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