1 / 19

Correction of Partial Volume Effects in Arterial Spin Labeling MRI

By: Tracy Ssali Medical Biophysics 3970z April 4 th 2012 Supervisors : Keith St. Lawrence, PhD Udunna Anazodo , PhD candidate. Correction of Partial Volume Effects in Arterial Spin Labeling MRI. Introduction.

cirila
Download Presentation

Correction of Partial Volume Effects in Arterial Spin Labeling MRI

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. By: Tracy Ssali Medical Biophysics 3970z April 4th 2012 Supervisors: Keith St. Lawrence, PhD UdunnaAnazodo, PhD candidate Correction of Partial Volume Effects in Arterial Spin Labeling MRI

  2. Introduction • Brain Tissue consists of Grey Matter (GM) White Matter (WM) and Cerebral Spinal Fluid (CSF) • Perfusion in the brain is indicative of function • Irregular flow in grey matter is indicative of disease state [1] • Arterial Spin Labeling is a novel technique used to measure perfusion in the brain

  3. Theory – Why ASL MRI? • Established techniques require radioactive exogenous tracers which cannot be used on certain patient populations, and require long clearance times.[2] • ASL MRI uses magnetized water molecules in arterial blood as a tracer to measure tissue perfusion non-invasively

  4. Theory - ASL MRI • Creating the control image • Creating the tagged image • Arterial blood is magnetically labeled using radiofrequency pulses • A delay time is allowed for the blood to reach the brain • When the labeled water interacts with the magnetic field, it affects the signal being produced

  5. ASL Image ≈ CBF Theory – How ASL MRI Works Subtract Adapted from Wolf and DetreNeurother Vol. 4, 346–359, July 2007

  6. Theory - Partial Volume Effects • Perfusion images are taken in quick succession • Information from the labeled blood must be captured before it relaxes • Blood water has a half life of around 1-2s[3] Pettersen Br J Radiology 2006

  7. Theory – Partial Volume Effects (Cont’d) • Point spread blurring • Resolution is not fine enough to resolve GM, WM and CSF • Voxel size is approximately 3 x 3 x 3mm [2]

  8. Theory – Separating the Signals • Partial Volume Effects (PVE) correction • Estimates the partial signal contribution based on the contrast information from anatomical MRI image volume

  9. Theory – Partial Volume Effects Correction • Kernel Regression Algorithm • Based on the size of the kernel the algorithm assesses a radius around the centre point to reassign a partial volume

  10. Theory – Signal to Noise Ratio (SNR) • Signal – Mean signal of GM, WM or CSF • Noise – Standard deviation 40 20 Deibler et al AJNR march 2008

  11. Objective • To measure the signal to noise ratio before and after the partial volume effects correction

  12. Methods • 5 Chronic Regional Pain Syndrome Patients (CRPS) • Image Preprocessing • Remove the pixels representing the skull • Motion correction Wolf and DetreNeurother Vol. 4, 346–359, July 2007

  13. Methods (Cont’d) • PVE correction • Implemented an In-house written MATLAB code created by Asllani et al. [2] • Images from 5CRPS were processed using a kernel size of 5 and 9 • Kernel filter • Adjust the kernel size from to 5, 7, 9, 11 and 15 • 1 patient’s data

  14. K = 5 Results & Discussion Significant decrease (P<0.05) in the SNR Variation in the voxels due to the noise could have prevented the code from working as intended

  15. K = 9 Results & Discussion Inconsistent Results There is no significant difference (P>0.05) It is likely that the algorithm is not functioning as intended

  16. Subject 5Results & Discussion Larger kernel have a greater SNR Small kernel sizes are sensitive to noise and variance

  17. Conclusion • The SNR decreased after the PVE correction • Kernel size needs to be chosen carefully • Our in-house implementation of the PVE correction needs to be fine tuned

  18. References • [1] Tracy, Melzer R. "Arterial Spin Labelling Reveals an Abnormal Cerebral Perfusion Pattern in Parkinson’s Disease." Brain 134.3 (2011): 845-55. • [2] Asllani, Iris, AjnaBorogovac, and Truman R. Brown. "Regression Algorithm Correcting for Partial Volume Effects in Arterial Spin Labeling MRI." Magnetic Resonance in Medicine 60.6 (2008): 1362-371. • [3] Xu, Guofan, Howard A. Rowley, Gaohong Wu, David C. Alsop, AjitShankaranarayanan, Maritza Dowling, Bradley T. Christian, Terrence R. Oakes, and Sterling C. Johnson. "Reliability and Precision of Pseudo-continuous Arterial Spin Labeling Perfusion MRI on 3.0 T and Comparison with 15O-water PET in Elderly Subjects at Risk for Alzheimer’s Disease." NMR in Biomedicine 23.3 (2010): 286-93. Print.

  19. Thank you Questions?

More Related