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

Magnetic Resonance Imaging in Concussion: a structural approach Paul Polak, M.A.Sc MRI Physicist Buffalo Neuroimaging Analysis Center Buffalo, NY Saturday, October 12, 2013

Saturday, October 12, 2013

Saturday, October 12, 2013

Why Advanced Imaging?

Saturday, October 12, 2013

Why Advanced Imaging?

normal Saturday, October 12, 2013

acute (1 week) concussion

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 Saturday, October 12, 2013

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

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MRI 101: The Basics • Concerned with contrast between tissue types – ie. white and grey matter; tumour and healthy

Density-weighted

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T1-weighted

T2-weighted

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

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MRI 101: The Basics • Partial voluming – Time – Noisy images

1 mm (through screen) Saturday, October 12, 2013

5 mm

9 mm

Traumatic Brain Injury (TBI): brain structure

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TBI: Mechanism • Holbourn 1945 • Brain – Non-rigid – Grey matter denser – structures slide past each other Holbourn, A. (1945). The mechanics of brain injuries. British medical bulletin, 3(6), 147–149. Saturday, October 12, 2013

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), 163–85.

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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

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Saturday, October 12, 2013

Saturday, October 12, 2013

Saturday, October 12, 2013

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

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

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DTI: how it works • Measures in tissue: – Directional mobility of water molecules – Magnitude of movement

• Directional – isotropic vs. anisotropic

• So what? – measure of myelin integrity

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DTI: how it works

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DTI: how it works

Saturday, October 12, 2013

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 T2-weighted, non-diffusion scan (b = 0) – 6 directional diffusion scans (xx, yy, zz, xy, xz, yz)

• More directions is better – More time

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DTI: how it works • 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 Saturday, October 12, 2013

DTI: how it works

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DTI: measurements • Rank diffusion directions based on quantity – λ1 primary direction diffusion – axial diffusivity (AD) – λ2, λ3 secondary, tertiary directions diffusion – • radial diffusivity (RD) = (λ2 + λ3)/2

• Fractional Anisotropy (FA) – 0 (isotropic) to 1 (isotropic) – anisotropic: λ1 >> λ2, λ3 – isotropic: λ1 ≈ λ2 ≈ λ3 Saturday, October 12, 2013

DTI: measurements

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DTI measurements • DAI associated with: – Reduced FA – Increased RD – Increased MD

• Why?

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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)

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

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• 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. 2012. “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): 329–42. doi:10.1007/s11682-012-9175-2.

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Saturday, October 12, 2013

Saturday, October 12, 2013

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

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• T1 weighted clinical image left, SWI on right • paramagnetic haemosiderin/iron present in Saturday, October 12, 2013

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. 184-94.

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Saturday, October 12, 2013

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. 1183-96.

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Saturday, October 12, 2013

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

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Saturday, October 12, 2013

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. 3232-42, Nov. 2010.

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Saturday, October 12, 2013

MRS and TBI • Vagnozzi 2008 – Slow rate of NAA recovery 1st 15 days – Theorized: • “biochemical priorities”

Vagnozzi, Roberto, S Signoretti, and Barbara Tavazzi. 2008. “Temporal Window of Metabolic Brain Vulnerability to Concussion: a Pilot 1H-magnetic Resonance Spectroscopic Study in Concussed Athletes-part III.” Neurosurgery 62 (6): 1286–1296. doi:10.1227/01.NEU.0000316421.58568.AD. Saturday, October 12, 2013

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

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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

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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.

Saturday, October 12, 2013