Functional MRI and Diffusion Tensor Imaging

Transcription

1 Functional MRI and Diffusion Tensor Imaging Andrew Steven March 23, 2018 Ochsner Neuroscience Symposium None Disclosure 1

2 Objectives Review basic principles of BOLD fmri and DTI. Discuss indications and clinical applications. Share image-rich examples of the techniques in practice. Stimulate discussion and foster interdepartmental collaboration. Disclaimer Not comprehensive Multiple applications focus on pre-surgical evaluation Techniques and images vendor specific fmri is not currently available Acknowledge: Wilson Altmeyer, MD 2

3 BOLD fmri What is BOLD? A) New scent of AXE body spray. B) The opposite of most radiology reports. C) Blood Oxygen Level Dependent contrast. -Predicated on neurovascular coupling -Dynamic task based assessment -Identify eloquent cerebral cortex 3

4 Neurovascular Coupling BOLD fmri Neuronal Acvity O 2 extraction Cerebral blood flow Deoxyhemoglobin (T2* dark signal) Oxyhemoglobin (T2* bright signal) Dilution of deoxyhemoglobin T2* Signal 4

5 BOLD fmri REST ACTIVATION Functional Neuroradiology 2011, Faro et.al. Hemodynamic Response Curve 2 to 5 seconds MRI T2* Signal Neuronal Activity CBF dominates O2 extracon Time CBF normalizes CBV still elevated 5

6 Typical fmri experiment (paradigm). MRI T2* Signal 20 seconds duration 2 sec T2* sequence 10 brain volumes acquired ACTIVATION 20 seconds REST 20 seconds Repeat: 8 times TOTAL: 320 seconds ~6 minutes per paradigm ~160 brain acquisitions Time 6

7 Voxel by voxel correlation coefficient analysis Random noise T2* signal time No signal True correlation T2* signal time signal Results: 7

8 Post-processing p =7 x p = 6 x p = 0.5 Threshold 8

9 Paradigm Selection Right hand motor activity 9

10 Left foot motor activity produces activations at the right paracentral lobule. Little Bo Peep lost her. 10

11 A + 11

12 fmri of Vision X fmri auditory task 12

13 Uses Presurgical Evaluation 1. Determine hemispheric language dominance 2. Define relationship between lesion and eloquent cerebral cortex Surgical Navigation 1. Activation maps can be imported to navigation system to aid in surgical guidance 2. May speed awake electrocortical stimulation mapping Low Grade Glioma Neurographics. Volume 5, Issue 4, pages

14 Anterior Displacement PMC Finger Tapping Low Grade Glioma Neurographics. Volume 5, Issue 4, pages

15 Left hemisphere language dominance Epilepsy patient, normal MRI 15

16 Left hemisphere language dominance Word Generation Sentence Completion AVM 16

17 Spetzler Martin Grade I Diffusion Tensor Imaging and Tractography 17

18 Diffusion imaging is based on the inherent Brownian motion of water molecules. Any alteration in the diffusivity of water can create contrast. Diffusion imaging is based on the inherent Brownian motion of water molecules. Any alteration in the diffusivity of water can create contrast. 18

19 R MCA infarct b = 560 b = 560 Diffusion imaging is sensitive to the motion of water molecules that are aligned with the motion-probing gradients. 19

20 X Diffusion-Weighting Y Diffusion-Weighting Z Diffusion-Weighting x y z phase read slice RF Diffusion Ellipsoid v 1, λ 1 v 2, λ 2 v 3, λ 3 20

21 When diffusion is random, or equal in all directions the tensor is spherical. FA is low (0). When influenced by organized structures, as in white matter tracts, the ellipsoid becomes elongated. FA is high(1). Fractional Anisotropy Note low signal intensity in gray matter structures. (Basal ganglia) FA = 0 And high signal along white matter tracts (Corpus callosum) FA = 1 21

22 Quantitative FA Principle Direction Color FA x = Color FA map. Blue=CC Red=TV Green=AP 22

23 3D fusion Jellison B J et al. AJNR Am J Neuroradiol 2004;25:

24 Hypertensive microhemorrhage Tractography 24

25 Fused fmri, color FA, and T1 post contrast Seeds Typically seeds are drawn in a region of interest. In this case the internal capsule. The computer estimates tracts by connecting high FA voxels with similarly strongly oriented voxels. 25

26 The placement of additional seeds can help isolate specific tracts. Subcortical white matter of the precentral gyrus. Seed 2 Connecting the two regions of interest isolates the corticospinal tract. Seed 2 Seed 1 26

27 The tracts can be displayed in a variety of manners including 3D models Low Grade Glioma 27

28 T2 FA CST intact T2/color FA fusion Large circumscribed T2 hyperintense lesion (low grade glioma) approaches the CST at the level of the internal capsule DTI exhibits minimal displacement of the CST, but preserved FA suggesting a lack of tumor infiltration High Grade Glioma 28

29 Glioblastoma 29

30 Finger Tapping Sentence Completion 30

31 Successful resection No permanent deficit. Conclusions Complimentary techniques: BOLD fmri used to assess eloquent cortex DTI and tractography interrogate white matter tracts Individualized experiments requires communication and collaboration Not just pretty pictures or science fiction 31

32 Questions, Comments, Cases? 32