Hi,<br><br> I'm quite new to ITK and DICOM, and I'd like to make sure I understand things right - they seem quite important. <br><br>* Is it true, that while using DICOM files, every image I'm dealing with comes in a right-hand coordinate system?<br>
<br>* I've learned that the X values grow to the left hand side of the patient, z goes from toes to head, and y grows to the posterior of the patient. Or does that depend on the C.7.6.1.1.1 Patient Orientation? I do not think I understand this concept of Patient Orientation, maybe since I do not have any DICOM which would include such a tag. <br>
<br>* Now there is a Image Orientation tag in every (?) DICOM file which contains the direction cosines of the first row and column of the image. It is a string a\b\c\d\e\f. This means, that the image I'm dealing with is translated with respect to the patient by a matrix [a b c; d e f; 0 0 0]. So when I have a Image Orientation equal to 1\0\0\0\1\0 that means I do not have to rotate/translate anything, since cos(0) = 1.<br>
<br>* Image Position is the position of the centre of the first voxel, in mm (?). Seems easy. It is negative, at least in the case of the DIOCMs I'm dealing with, but I think that's nothing unusual. What I do not understand is what is it relative to? Is this to make sure that I have consecutive slices in the right position? Could it happen, that SliceA Image Postion is equal to 10\10\z while SliceB being the next in the sequence has been shifted and its position is e.g. 11\10\(z + Slice Thickness)? That would be quite a mess to worry about.<br>
<br>* What is Slice Location? How is it related to the previously mentioned data? I'm pretty sure it is :)<br><br>* Browsing through the archive I've seen this link: <a href="http://www.itk.org/Wiki/Proposals:Orientation#DICOM_LPS_Orientation_-_Lower_Limb_Graphical_Example">http://www.itk.org/Wiki/Proposals:Orientation#DICOM_LPS_Orientation_-_Lower_Limb_Graphical_Example</a> Do I understand that right, that the nuerosurgeon and radiologists always have a different perspective? The radiologists sees the right-hand side of the patient on the left, while the neurosurgeon on the right. If so, it is reflected in the Image Orientation tag, isn't it? That's quite a responsibility for both the physician and developer, as far as I know there's enough of symmetry in the human body to cause confusion.<br>
<br>* Last but not least, I'm transferring data from an itk Image to an unsigned char array, to display that using OpenGL (for now I'm using just a IntensityWindowingImageFilter). Now, the image appeared upside down. Image Orientation is 1\0\0\0\1\0. Is this upside down issue due to the fact, that in my OpenGL app the y values are growing from bottom to top while in the DICOM file it's the other way round? I'm using temporary glPixelZoom(1, -1) to 'fix it', but I'd like to make sure it's right. I've been looking at the <br clear="all">
QtImageViewer example (from InsightApplications/Auxiliary) but that didn't clarify much.<br><br>Thanks for any hints, it's quite confusing at first glance, all this positions, orientations, etc, and I think it might be desirable to understand them 100% right.<br>
<br>Regards,<br> Kornel<br>