1. Processing Diffusion Weighted MRI Images
Diana R. Palsetia
Shilpa R. Panth
ECE 533

2. INTRODUCTION
Lung MRI using Hyperpolarized Helium-3 - visualize defects in the lung
In Diffusion Weighted Imaging (DWI) water protons diffuse
The path traveled by the proton along any one direction can be given by:
Where is observation time
ADC Apparent Diffusion Co-efficient is proton displacement
DWI-MRI on human lung ADC values probe lung microstructure
HHe3 MRI is a recently developed technique to visualize defects in the lung.
DWI MRI is a technique that relates the image intensities to the relative mobility of endogenous tissue water molecules.
The diffusion of the water molecules provides information about the structure of the lung

3. PROBLEM DW Images – High Signal Intensity in the major airways
High Signal intensity skews ADC mean value of lung parenchyma
Segment out the airways
In diffusion weighted images as you see in the figure there is high signal intensity in the major airways. In order to probe the lung microstructure we calculate the ADC value from the lung. The high signal in the airways contribute to the ADC mean and skews the ADC mean.
In order to obtain the true ADC mean value from the lung parenchyma we need to segment out the airways.
Diffusion weighted Image of central slice showing the major airways

4. APPROACH Thresholding Erosion/Dilation Binary Mask
Multiply with Original Image
To segment out the major airways we applied
Threshold
Eroded and Dilated the thresholded image
Created a binary mask from it
Again applied erosion or dilation and
Finally multiplied it with the original image

5. THRESHOLDING Applied Threshold based on the maximum intensity value
Thresholded Image
Original Image
On the left is the original image and on the right the thresholded image. As you can see in the thresholded image some parts of the lung parenchyma have been thresholded.
Applied Threshold based on the maximum intensity value
Lost some lung parenchyma

6. EROSION - DILATION b a b a Dilated Image Eroded Image Eroded Image
This slide shows the difference between applying erosion and then applying dilation or vice versa
In both the cases we have lost some lung parenchyma
Eroded Image
Dilated Image

7. BINARY MASK Application of Binary mask on:
- Dilation followed by erosion (Figure 1)
- Erosion followed by dilation (Figure 2)
The binary mask obtained after the application dilation followed by erosion and then erosion followed by dilation
Figure 2: Binary Mask after Erosion and Dilation
Figure 1: Binary Mask after Dilation and Erosion

8. RESULT
Multiplying the original image with the image obtained from the mask
- Erosion followed by Dilation
- Dilation followed by Erosion
The results obtained after multiplying the original image with the images obtained from the mask.
As you can see in the images the airways are still present along with that we have lost some amount of lung parenchyma too
The reason these segmentation techniques do not give the desired results is that the major airways are difficult to delineate from the lung parenchyma.
Erosion followed by dilation
Dilation followed by erosion

9. SOLUTION Original Image Manually segmented image
By selecting the region manually using a MR specific tool we were able to segment out the major airways in order to perform the ADC calculations.
Original Image
Manually segmented image

10. GUI

11. CONCLUSION / FUTURE WORK
Manual segmentation provided better results compared to automation based on the analysis
FUTURE WORK
Combine the manual regional analysis with the GUI (not in the scope of the project)

12. REFERENCES
MR Imaging of Diffusion of He-3 Gas in Healthy and Diseased Lungs – Saam et.al. MRM 44: (2000 )
Dynamic functional lung MRI using hyperpolarized gases
Albert, M.S.; BMES/EMBS Conference, Proceedings of the First Joint, Volume: 2, Oct. 1999, Pages: 1327 vol.2