Magnetic Resonance Imaging in Concussion: a structural approach. Paul Polak, M.A.Sc MRI Physicist Buffalo Neuroimaging Analysis Center Buffalo, NY

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1 Magnetic Resonance Imaging in Concussion: a structural approach Paul Polak, M.A.Sc MRI Physicist Buffalo Neuroimaging Analysis Center Buffalo, NY

4 Why Advanced Imaging?

5 Why Advanced Imaging? normal acute (1 week) concussion

6 MRI 101: The Basics Components Static magnetic field (the magnet) Radiofrequency pulses (RF) Magnetic gradients (responsible for the loud banging noise) Pulse sequence (software to control timing

7 4 components + hydrogen resonance to create images 1 H prevalence Water Fat Muscle MRI 101: The Basics

8 MRI 101: The Basics Concerned with contrast between tissue types ie. white and grey matter; tumour and healthy Density-weighted T1-weighted T2-weighted

9 MRI 101: The Basics Pixel: smallest coherent element of a 2- D picture (picture element) Voxel: 3-D volumetric pixel slice thickness

10 Partial voluming Time Noisy images MRI 101: The Basics 1 mm (through screen) 5 mm 9 mm

11 Traumatic Brain Injury (TBI): brain structure

12 Holbourn 1945 Brain Non-rigid Grey matter denser structures slide past each other TBI: Mechanism Holbourn, A. (1945). The mechanics of brain injuries. British medical bulletin, 3(6),

13 TBI : Diffuse Axonal Injury (DAI) Strich 1956 diffuse degeneration of cerebral white matter Diffuse Axonal Injury (DAI) Caused by traumatic shearing forces when brain accelerates/decelerates Structures moving past each other strain axons Axons have some tensile strength Strich, S. J. (1956). Diffuse degeneration of the cerebral white matter in severe dementia following head injury. Journal of neurology, neurosurgery, and psychiatry, 19(3),

14 TBI: DAI DAI most likely in corpus callosum, brain stem, basal ganglia, thalamus Axons stretch / damaged as denser brain structures slide over each other Wasserman 2007 grey / white matter boundaries Wasserman, J. R., Feldman, J. S., & Koenigsberg, R. A. (2007). Diffuse Axonal Injury. emedicine.com

18 Dr. Michael D. Noseworthy, Ph.D., P.Eng McMaster University, Co-Director, McMaster School of Biomedical Engineering Director, Imaging Research Centre St. Joseph s Healthcare, Hamilton, ON

19 Advanced MRI Techniques Diffusion Tensor Imaging (DTI) Susceptibility Weighted Imaging (SWI) Magnetic Resonance Spectroscopy (MRS)

20 Measures in tissue: DTI: how it works Directional mobility of water molecules Magnitude of movement Directional isotropic vs. anisotropic So what? measure of myelin integrity

21 DTI: how it works

22 DTI: how it works

23 DTI: how it works Compare images with diffusion weighting with an image without any (b = 0 image) Minimum number of full brain scans: 7 1 T 2 -weighted, non-diffusion scan (b = 0) 6 directional diffusion scans (xx, yy, zz, xy, xz, yz) More directions is better More time

24 Diffusion scans Identical to the b = 0 except for the diffusion weighting If water can diffuse along direction, represented by drop in signal intensity in that voxel DTI: how it works

25 DTI: how it works

26 DTI: measurements Rank diffusion directions based on quantity λ 1 primary direction diffusion axial diffusivity (AD) λ 2, λ 3 secondary, tertiary directions diffusion radial diffusivity (RD) = (λ 2 + λ 3 )/2 Fractional Anisotropy (FA) 0 (isotropic) to 1 (isotropic) anisotropic: λ 1 >> λ 2, λ 3 isotropic: λ 1 λ 2 λ 3

27 DTI: measurements

28 DAI associated with: Reduced FA Increased RD Increased MD Why? DTI measurements

29 DTI and TBI DTI scans often used in group-wise comparisons ie. Multiple Sclerosis patients vs. controls Difficulty in assessing DAI in TBI with DTI: Previous comparison scan? (Is there one?) Controls? Timing? Method of injury (group-wise insensitive)

30 FA Analysis z-score potholes analysis Individual FA scans from TBI patients compared to controls Significantly different voxels in TBI patients highlighted

31 Lipton 2012 Lipton, Michael L, Namhee Kim, Young K Park, Miriam B Hulkower, Tova M Gardin, Keivan Shifteh, Mimi Kim, Molly E Zimmerman, Richard B Lipton, and Craig a Branch Robust Detection of Traumatic Axonal Injury in Individual Mild Traumatic Brain Injury Patients: Intersubject Variation, Change over Time and Bidirectional Changes in Anisotropy. Brain Imaging and Behavior 6 (2) (June): doi: /s

34 SWI: how it works Paramagnetic materials (iron, deoxygenated blood) distorts local magnetic field Causes a localized drop in signal intensity Useful for detecting hemorrhages, iron stores, venous vasculature

35 T1 weighted clinical image left, SWI on right paramagnetic haemosiderin/iron present in

36 T. Babikian, M.C. Freier, K. a Tong, J.P. Nickerson, C.J. Wall, B. a Holshouser, T. Burley, M.L. Riggs, and S. Ashwal, Susceptibility weighted imaging: neuropsychologic outcome and pediatric head injury., Pediatric neurology, vol. 33, Sep. 2005, pp

38 C.A. Chastain, U.E. Oyoyo, M. Zipperman, E. Joo, S. Ashwal, L.A. Shutter, and K.A. Tong, Predicting outcomes of traumatic brain injury by imaging modality and injury distribution., Journal of neurotrauma, vol. 26, Aug. 2009, pp

40 MRS: how it works Concentrations of 1H containing nuclei in the brain N-acetylaspartate (NAA) Creatine (Cr) Choline (Cho) Lipids Lactate Glutamate and Glutamine

42 R. Vagnozzi et al., Assessment of metabolic brain damage and recovery following mild traumatic brain injury: a multicentre, proton magnetic resonance spectroscopic study in concussed patients., Brain : a journal of neurology, vol. 133, no. 11, pp , Nov

44 MRS and TBI Vagnozzi 2008 Slow rate of NAA recovery 1 st 15 days Theorized: biochemical priorities Vagnozzi, Roberto, S Signoretti, and Barbara Tavazzi Temporal Window of Metabolic Brain Vulnerability to Concussion: a Pilot 1H-magnetic Resonance Spectroscopic Study in Concussed Athletes-part III. Neurosurgery 62 (6): doi: /01.neu ad.

45 Conclusions and Challenges Diffusion Tensor Imaging (DTI) Assess axonal integrity in vivo Need controls (z-score) or pre-tbi images Group-wise comparisons usually insensitive

46 Conclusions and Challenges Susceptibility Weighted Imaging (SWI) hemorrhages Specialized image reconstruction software Still unclear in TBI not every event has hemorrhage Magnetic Resonance Spectroscopy (MRS) NAA -> neuronal and axonal integrity Prescription difficult (where to put it?) Voxel size

47 The Buffalo Neuroimaging Analysis Center (BNAC) is located in The Jacobs Neurological Institute at Buffalo General Hospital, part of the University of Buffalo and Buffalo Niagara Medical Campus in downtown Buffalo, NY, USA.

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