I have a basic question for the DICOM protocol.
I know how I can calculate the orientation labels of every slice of a DICOM image (A,P,L,R,H,F). But when I got for example an Axial slices with numbers from 0001 to 0024 I need to know if the slice order is from Head to Feet or from Feet to Head.
How can I calculate that ?
Answer
Patient Position (0018, 5100) will tell you if the patient was scanned head-first supine, feet-first prone, head-first prone, etc. Instance Number (0020, 0013), also commonly known as slice number, contains no information about spatial location and isn't even guaranteed to be unique. Slice Location (0020, 1041) is useful, if it exists, but you can't count on it always existing because it's a Type 3 (optional) attribute. To have a robust solution, you need to use Image Position Patient (0020, 0032) together with Image Orientation Patient (0020, 0037) and Patient Position (0018, 5100) to properly order the slices in space. Image Position Patient gives you a vector from the origin to the center of the first transmitted pixel of the image. Image Orientation Patient gives you vectors for the orientation of the rows and columns of the image in space. Patient Position tells you how the patient was placed on the table relative to the coordinate system.