[Dcmlib] dicom image orientation

[Mathieu Malaterre]

Greg Book wrote:
> I have some questions about the image orientation of dicom images. The 
> part I'm having the most trouble with is the direction cosines and how 
> it affects the encoding from the HFS, HFP, etc.
> According to the dicom documentation, the patient orientation determines 
> how the data is encoded: positive X direction points to the patient's 
> outstretched left arm, positive Y points from antierior to posterior 
> direction, and positive Z points from feet to head. Do the cosines 
> change this encoding?
> For example, if the patient is head-first supine, then axial slices are 
> acquired, and if the slices are not rotated... How do the directions 
> change? Is X still pointing to the patient's left arm?
> Now... if the slice box were rotated around the patient's feet/head 
> direction by 180º, how would that change the cosines?
> 
> My ultimate goal is to have a 3D cube on my image viewer that shows how 
> the current view relates to the patient's R/L, A/P, and H/F sides.
> I'm not sure if knowing the orientation description (Heart Coronal, etc) 
> will be helpful. I'm interested in how the cosines can be transformed 
> into a cube with the 6 patient directions on it.

Greg,

	See gdcmOrientation implementation or:

http://www.dclunie.com/medical-image-faq/html/part2.html#DICOMOrientation

and

C.7.3.1.1.2

Patient Position

Patient Position (0018,5100) specifies the position of the patient 
relative to the imaging equipment space. This attribute is intended for 
annotation purposes only. It does not provide an exact mathematical 
relationship of the patient to the imaging equipment.

When facing the front of the imaging equipment, Head First is defined as 
the patient's head being positioned toward the front of the imaging 
equipment. Feet First is defined as the patient's feet being positioned 
toward the front of the imaging equipment. Prone is defined as the 
patient's face being positioned in a downward (gravity) direction. 
Supine is defined as the patient's face being in an upward direction. 
Decubitus Right is defined as the patient's right side being in a 
downward direction. Decubitus Left is defined as the patient's left side 
being in a downward direction. The Defined Terms are: HFP HFDR FFDR FFP 
= Head First-Prone = Head First-Decubitus Right = Feet First-Decubitus 
Right = Feet First-Prone HFS HFDL FFDL FFS = Head First-Supine = Head 
First-Decubitus Left = Feet First-Decubitus Left = Feet First-Supine


Mathieu