Dicom protocol and CT scan and sorting according to z position of axial slices?

1
votes

I have a CT scan of the chest where I can't seem to figure out how to determine how to sort the aixal slices such that the first slices are the ones closet to the head.

The scan has the following dicom parameters:

Patient Position Attribute (0018,5100): FFS (Feet First Supine) Image Position (Patient) (0020,0032): -174-184-15 (one slice) Image Orientation (Patient)(0020,0037): 1\0\0\0\1\0

The most cranial slice (anatomically, closet to the head) has z position 13 and the most caudal (lower) -188.

However, when the Patient Position is FFS shouldn't the slice with the lowest z position (e.g. -188) be the one being the one most cranially (anatomically, i.e. closet to the head) located?

Can anyone enlighten me?

Kind regards

1
dicom

1 Answers

0
votes

DICOM very clearly defines, that the x-axis has to go from the patients right to the left, the y-axis has to go from front to back, and the z-axis has to go from foot to head. So the lower z-position of -188 has to be closer to the feet than the higher position of 13. You should always rely on this.

Patient Position Attribute is rather some informational annotation. If you do all the math yourself, then you can ignore it. If a viewer does not do the math (there are a lot of them) and just loads the images and shows them sored by ImageNumber, then the Position Attribute is the info to annotate, if the image with ImageNumber 1 is the one closer to the head or the one closer to the feet. Meaning: when the patient went throught the ct scanner, which one was the first imate aquisitioned: the one of the head or of the feet.