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

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

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

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

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

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

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

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

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

GUI

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)

REFERENCES MR Imaging of Diffusion of He-3 Gas in Healthy and Diseased Lungs – Saam et.al. MRM 44: 174-179 (2000 ) Dynamic functional lung MRI using hyperpolarized gases Albert, M.S.; BMES/EMBS Conference, 1999. Proceedings of the First Joint, Volume: 2, 13-16 Oct. 1999, Pages: 1327 vol.2