# ITK Image Direction vs DICOM Image Orientation (Patient)
**URL:** https://discourse.itk.org/t/itk-image-direction-vs-dicom-image-orientation-patient/6364
**Category:** Beginner Questions
**Tags:** python, simpleitk
**Created:** [December 17, 2023, 8:22pm UTC](https://discourse.itk.org/t/itk-image-direction-vs-dicom-image-orientation-patient/6364 "2023-12-17T20:22:29Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@aditya](https://discourse.itk.org/u/aditya)
#### Post date: [December 17, 2023, 8:22pm UTC](https://discourse.itk.org/t/itk-image-direction-vs-dicom-image-orientation-patient/6364/1 "2023-12-17T20:22:29Z")
I am working with a directory containing sagittal DICOM images.
Here is how I obtain Image Orientation (DICOM tag 0020,0037) using pydicom.
```auto
from pydicom import dcmread
import os
dcm_dir = r"path/to/dicom/dir/sagittal_acq"
ds = dcmread(os.path.join(dcm_dir,"000000.dcm"))
ds.ImageOrientationPatient
Out[88]: [0, 1, -1e-016, 0.05582152223083, 0, -0.9984407632183]
```
In the following code, I read the contents of this directory into an ITK Image and get the Direction. However, the Direction differs from original DICOM (0020,0037).
```auto
import SimpleITK as sitk
reader = sitk.ImageSeriesReader()
dicom_names = reader.GetGDCMSeriesFileNames(dcm_dir)
reader.SetFileNames(dicom_names)
image_from_dcm = reader.Execute()
sitk.DICOMOrientImageFilter_GetOrientationFromDirectionCosines(image_from_dcm.GetDirection())
Out[92]: 'PIR'
image_from_dcm.GetDirection()
Out[91]:
(-5.573448326015114e-18,
0.055821522230826974,
-0.9984407632182459,
1.0,
-4.81482486096809e-35,
-5.582152223082697e-18,
-3.1160423441667093e-19,
-0.9984407632182459,
-0.055821522230826974)
```
Is there a way to get Direction from ITK Image that matches DICOM Orientation 0020,0037?
As Image row is oriented from A to P (as shown by DICOMOrientImageFilter\_GetOrientationFromDirectionCosines), I expected the direction cosines of row (1st three elements) from ITK’s GetDirection to be [0,1,0], which is what I get with ds.ImageOrientationPatient[:3].
I tested the same with HFS and FFS oriented DICOM files and the Direction obtained from getDirection() matches DICOM.
For example, for FFS scan I get the following which matches DICOM Orientation 0020,0037
```auto
img_ori = image_from_dcm.GetDirection()
img_ori
Out[8]: (-1.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, -1.0)
sitk.DICOMOrientImageFilter_GetOrientationFromDirectionCosines(img_ori)
Out[9]: 'RPI'
```
Thanks!
---
### Author:  [@zivy](https://discourse.itk.org/u/zivy)
#### Post date: [December 18, 2023, 1:19am UTC](https://discourse.itk.org/t/itk-image-direction-vs-dicom-image-orientation-patient/6364/2 "2023-12-18T01:19:59Z")
Hello @aditya,
The DICOM tag 0020,0037 “Image Orientation Patient” lists the x axis, first three numbers, followed by the y axis, last three numbers. These are the columns of the direction cosine matrix (see [the standard](https://dicom.nema.org/medical/dicom/current/output/html/part03.html#sect_C.7.6.2.1.1)). These correspond to the first two columns of the direction matrix returned by the `GetDirection` method, which returns the matrix in row major order (first three numbers are first row…). If you look at that matrix you will see that the first column is `[0, 1.0, 0]` and the second column is `[0.055821522230826974, 0, -0.9984407632182459]` which match the values in the DICOM tag.
---
### Author:  [@aditya](https://discourse.itk.org/u/aditya)
#### Post date: [December 18, 2023, 3:08am UTC](https://discourse.itk.org/t/itk-image-direction-vs-dicom-image-orientation-patient/6364/3 "2023-12-18T03:08:37Z")
Got it. Thank you so much @zivy
---
### Author:  [@zx-lhb](https://discourse.itk.org/u/zx-lhb)
#### Post date: [April 9, 2024, 7:47am UTC](https://discourse.itk.org/t/itk-image-direction-vs-dicom-image-orientation-patient/6364/4 "2024-04-09T07:47:25Z")
hi, I used getDirection method to get the returned direction was
but the dicom orientation tag was
it seems the direction maxtrix first colums was [1,0,0], why didn’t the orientation correspond to the first two columns of the direction matrix?