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Comparison of Robarts ’ 3T and 7T MRI Machines for Obtaining fMRI sequences Jacob Matthews

Comparison of Robarts ’ 3T and 7T MRI Machines for Obtaining fMRI sequences Jacob Matthews April 4, 2012 Supervisors: Rhodri Cusack, PhD Annika Linke , Postdoctoral Fellow. Medical Biophysics 3970. Overview -Introduction -Objectives -Approach, Hypothesis, and Methods

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Comparison of Robarts ’ 3T and 7T MRI Machines for Obtaining fMRI sequences Jacob Matthews

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  1. Comparison of Robarts’ 3T and 7T MRI Machines for Obtaining fMRI sequences JacobMatthews April 4, 2012 Supervisors: Rhodri Cusack, PhD Annika Linke, Postdoctoral Fellow Medical Biophysics 3970

  2. Overview -Introduction -Objectives -Approach, Hypothesis, and Methods -Results, Discussion -Conclusions Medical Biophysics 3970

  3. Brief Introduction to MRI and fMRI Medical Biophysics 3970

  4. Magnetic Resonance Imaging (MRI) • Imaging modality based on nuclear magnetic resonance properties of tissues • Atoms have nuclear spins which create magnetic dipoles • Can be caused to precess about an axis • Recovery from precession can be measured and is unique for each tissue type Medical Biophysics 3970

  5. Magnetic Resonance Imaging (MRI) • Three Magnetic Fields • B0 field used to align the spins of atoms • B1 field oscillates to create RF pulse at the resonance frequency of target atoms • Causes precession of atom spin axes • During recovery atoms “Echo” back an RF pulse • Gradient fields encode spatial information Medical Biophysics 3970

  6. Magnetic Resonance Imaging (MRI) Medical Biophysics 3970

  7. Magnetic Resonance Imaging (MRI) Medical Biophysics 3970

  8. Magnetic Resonance Imaging (MRI) • Magnetization Prepared Rapid Acquisition Gradient Echo (MPRAGE) • High Contrast, high spatial resolution 3D Structual • T1-weighted • Fats appear brighter than water • Stereotypical MRI image Medical Biophysics 3970

  9. Functional Magnetic Resonance Imaging (fMRI) • Relies on BOLD Contrast (Blood Oxygen Level Dependent) • Activate brain region with task • O2 consumption increases • Local blood flow increases • Ratio of oxyhemoglobin to deoxyhemoglobin increases • Detected as weak transient increase in signal Medical Biophysics 3970

  10. Functional Magnetic Resonance Imaging (fMRI) • Echo Planar Imaging (EPI) • Fast repetitive imaging sequence • Records entire volume in 1-2 seconds • Weaker spatial resolution Medical Biophysics 3970

  11. Objectives Medical Biophysics 3970

  12. Objectives • Obtain equivalent images sets from both machines given the constraints of the hardware involved • Compare, both qualitatively and quantitatively, the image sets from each machine, to evaluate their use for fMRI scans Medical Biophysics 3970

  13. Approach, Hypothesis, and Methods Medical Biophysics 3970

  14. Approach • Obtain image sets • Compare SNR Measurements • Run ICA analysis on the data set Medical Biophysics 3970

  15. Hypothesis • From Boltzmann Distribution, an increase in field strength should accentuate the difference in parallel and anti-parallel spins, increasing the signal to noise ratio Medical Biophysics 3970

  16. Methods • Obtained two sets (3T and 7T) of MRI images • MPRAGE sequence (Structural) • EPI sequence (fMRI time series) • Resting • With Movie Stimuli • Analysis done with SPM and AA Matlab Software Packages Medical Biophysics 3970

  17. Methods • Spatial Analysis • SNR using mean signal of ROI and standard deviation of image as noise • Temporal Analysis • Individual Component Analysis (ICA) • Auditory Component correlated with 3T, 7T, and prior Group 3T study data Medical Biophysics 3970

  18. Results, and Discussion Medical Biophysics 3970

  19. Results – Some Images • 3T MPRAGE Structural Medical Biophysics 3970

  20. Results – Some Images • 7T MPRAGE Structural Medical Biophysics 3970

  21. Results – Some Images • 3T EPI fMRI Medical Biophysics 3970

  22. Results – Some Images • 7T EPI fMRI Medical Biophysics 3970

  23. Results – Spatial SNR • 7T EPI fMRI Medical Biophysics 3970

  24. Results – ICA • 3 sets of data used • 3T EPI time course • 7T EPI Time Course • 3T Group Analysis • 20 Subject Study acquired in Cambridge Medical Biophysics 3970

  25. Results – ICA Medical Biophysics 3970

  26. Results – ICA • Run twice with slightly different parameters Medical Biophysics 3970

  27. Results – ICA • ICA - Moviecut Medical Biophysics 3970

  28. Results – ICA • Results – ICA • Component 2 – Group Study Medical Biophysics 3970

  29. Discussion • Correlation used to identify auditory component (p<0.05) Medical Biophysics 3970

  30. Results – ICA • Time Courses Medical Biophysics 3970

  31. Results – ICA • Power Spectrum for Auditory Component Medical Biophysics 3970

  32. Results – ICA • Statistical correlations for auditory component • 3T – 7T: r = .73, p<.0001 • 3T – Group: r = 0.82, p<.0001 • 7T – Group: r = 0.87, p<.0001 • 3T – Sound Envelope: r = .33, p<.0001 • 7T – Sound Envelope: r = .39, p<.0001 Medical Biophysics 3970

  33. Discussion – Problems with 7T • Problems with 7T data format • Different software delivers data differently • AA matlab scripts designed for 3T data • Problems with 7T images • Prone to inhomogeneity in the B1 field • Certain brain regions unusable • Problems with 7T data collection • Higher SAR (specific absorption rate in W/kg) than 3T scanner • Very small head bore (60 cm diameter) • Movie presentation made difficult Medical Biophysics 3970

  34. Discussion – Continuing Analysis • More thorough Spatial SNR in other ROIs • Temporal SNR • ICA run and correlated with other components • Quantization of field Inhomogeneity • Correction for field Homogeneity • Expansion of current data set to include more scanning variables (T times, sequences) • Application to other studies Medical Biophysics 3970

  35. Conclusions Medical Biophysics 3970

  36. Conclusions • Spatial SNR showed expected increase for 7T, although not statistically proven • ICA showed 7T auditory component signal better correlated with sound envelope • ICA showed 7T auditory component signal better correlated with group study data Medical Biophysics 3970

  37. Acknowledgments • Rhodri Cusack, PhD • Annika Linke, Postdoctoral Fellow • Cusack Lab group • Conor Wild, PhD Candidate • Bobby Stojanoski, PhD • Robarts MRI Operating Team Medical Biophysics 3970

  38. Questions? Medical Biophysics 3970

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