Problem StatementApproachAnalysisConclusion/Future WorkReferencesAppendix A: Erosion-Dilation CodeAppendix B: Dilation – Erosion codeAppendix C - ADCGUICourse Project Workload Analysis TableECE533 - ProjectPROCESSING OF DIFFUSION WEIGHTED MRI Images ByShilpa R. PanthDiana R. Palsetia1Table of ContentsProblem Statement...............................................................................................................5Approach..............................................................................................................................6Analysis...............................................................................................................................7Conclusion/Future Work....................................................................................................13References..........................................................................................................................14Appendix A: Erosion-Dilation Code.................................................................................15Appendix B: Dilation – Erosion code................................................................................18Appendix C - ADCGUI.....................................................................................................21Course Project Workload Analysis Table...........................................................................342BACKGROUNDThe human respiratory system consists of the nose leading into the trachea, the trachea divide into the bronchi which enter the right and left lung respectively. The bronchi divide into the bronchioles and finally into the alveoli (Figure 1). The alveoli resemble small balloons; it is in the alveoli that the exchange of gases takes place. In diseases like emphysema the alveoli rupture causing a decrease in the amount of gas being exchanged. This causes the person to experience difficulty in breathing. The gold standard in measuring lung function is spirometry. This technique does not provide us with visual images of the lung. The only information we obtain from spirometry is measures of lung volume.IntroductionMagnetic resonance imaging (MRI) is an imaging technique used primarily in medical settings to produce high quality images of the insides of the human body. Clinical MRI uses the magnetic properties of hydrogen and its interaction with both a large external magnetic field and radio waves to produce high resolution images. Hyperpolarized Helium-3 ( 3HHe) lung MRI is a recently developed technique to visualize lung function and physiology. 3Figure 1: The Human Respiratory SystemThe water content in the lung being very low, the lung is not an ideal candidate for protonMRI. Figure 2 shows a proton MRI image. The signal outside the lung is higher than inside since the water content in the tissue is higher. Figure 3: is the image of the lung obtained using 3HHe.The lung parenchyma is clearly seen along with the bronchi. 3HHe MRI technique is capable of producing high spatial resolution MR images of the lung air spaces after inhalation of laser polarized helium gas. This technique is capable ofdifferentiating the healthy lungs from those with diseases such as chronic obstructive pulmonary disease, asthma, emphysema and cystic fibrosis. The contrast in these MR images is determined by regional spin density of the helium and reflects the gas distribution in the ventilated portion of the lung. The application of diffusion MR imaging methods to 3HHe imaging presents the opportunity to probe the lung microstructure.Diffusion-weighted MRI (DW-MRI) is a technique used for relating image intensities to the relative mobility of endogenous tissue water molecules. Two equal and opposite largemagnetic field gradients are applied before the data is acquired. In the absence of any motion of the water molecules, the magnetic spins will be de-phased by the first gradient,and then completely re-phased by the second gradient. However, because the actual motion of the water molecules is that of a random walk, the second gradient will not completely re-phase the spins. The signal intensity will therefore be exponentially attenuated proportional to the mean diffusion length. Areas with relatively high mean diffusion length will appear dark on the MRI images relative to areas with low mean diffusion length [3]. As water protons diffuse and thus interact with the lattice and spin micro environment, their traveled path (L) along anyone direction can be described as thefollowing:)ADC(T2L2where Tis the observation time (typically 20-50 ms for most clinical scanners) and theproton displacement is expressed by an Apparent Diffusion Coefficient(ADC).4Figure 2: Proton MRI image of the lungFigure 3: 3HHe image of the lungDiffusion weighted imaging is performed on the human lung to obtain the Apparent Diffusion Coefficient (ADC) values. In the lung, diffusive movement of 3HHe atoms is restricted by bronchial and alveolar walls, to a degree, which is dependent on the dimensions of the respective airspace and the local gas composition. The use of DW-MRIallows determination and mapping of Apparent Diffusion Coefficient (ADC) of 3HHe. The ADC in lung parenchyma is related to alveolar size, and has consequently been found to increase with age and emphysema. Calculating the ADC values, provide knowledge of the activity of the lung. For example, if there are ruptured alveoli in a person’s lung, there is increased air space in the lung that implies an increase in ADC value. This increase in ADC value is due to the increased area available for the proton to diffuse (i.e. the proton is not confined by alveoli) an indicator of emphysema.Problem StatementThe diffusion weighted images have high signal in the major airways (see Figure 4) biasing the ADC parameters to be calculated. The high signal intensity values vary between slices and subjects. Normally in DWI we obtain 18 or 20 images from which we calculate ADC maps. 9 or 10 ADC maps along with histograms are obtained. The whole lung ADC (including major airways) calculated shows substantially larger ADC values compared to the ADC values from the lung parenchyma. The trachea being larger in size than the alveoli contains more gas giving high signal in the MRI image.In order to obtain the ADC mean from the lung parenchyma we need to segment out the major airways. This implies high signal from the airways skews the ADC values. We
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