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Susceptibility Weighted Imaging at 7T

Susceptibility Weighted Imaging at 7T. Brian Welch. MR Clinical Science. IACSM 2007. April 24, 2007. 7T human midbrain. T1W TFE TR/TE=19/9.6. TSE_IR TR/TI/TE=4000/60/10. 7T human brain – high resolution sagittal. High Res. Sagittal Protocol 3D T1W TFE inversion delay = 1816 msec

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Susceptibility Weighted Imaging at 7T

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  1. Susceptibility Weighted Imaging at 7T Brian Welch MR Clinical Science IACSM 2007 April 24, 2007

  2. 7T human midbrain T1W TFE TR/TE=19/9.6 TSE_IR TR/TI/TE=4000/60/10

  3. 7T human brain – high resolution sagittal High Res. Sagittal Protocol 3D T1W TFE inversion delay = 1816 msec TFE factor = 180 0.33 x 0.33 x 4.0 mm3 24 slices TR/TE=19/9.6 Scan Time = 7:23

  4. SWI Background and References Primarily associated with E. Mark Haacke, Ph.D. • Professor of Radiology, Wayne State University, Detroit, MI • Director, Magnetic Resonance Imaging Institute for Biomedical Research (http://www.mrimaging.com) U.S. Patents (http://www.uspto.gov) • 6,501,272 - MR Methods, some post-processing • 6,658,280 - post-processing, CNR optimization Selected SWI Publications • Small Vessels in the Human Brain: MR Venography with Deoxyhemoglobin as an Intrinsic Contrast Agent, JR Reichenbach, EM Haacke, et al. Radiology 204:272-277(1997) • High-resolution BOLD venographic imaging: a window into brain function, JR Reichenbach, EM Haacke. NMR Biomed 14:453-467(2001) • Susceptibility Weighted Imaging (SWI), EM Haacke, JR Reichenbach, et al. MRM 52(3):612-618(2004) • Magnetic Susceptibility-Weighted MR Phase Imaging of the Human Brain, A Rauscher, JR Reichenbach, et al. AJNR 26:736-743(2005)

  5. Mark Haacke’s website – www.mrimaging.com

  6. Why the interest in SWI at 7T? • Phase accrual per unit time is a function of static field strength • Shorter echo times mean shorter scan times or better coverage • 40-50 msec at 1.5T • 20-25 msec at 3.0T • 9-11 msec at 7.0T • Increased SNR • Popular topic at 2007 ISMRM Workshop on Advances in High Field MR • ~6 invited presentations • many posters

  7. Possible Clinical Applications for SWI • Small vessel (vein) imaging • Microhemorrhage • Mineralization, e.g. iron • Occult vascular disease • Stroke • Traumatic brain injury • Tumor vascularization • Multiple sclerosis • Anatomical imaging of the midbrain

  8. Typical SWI Protocol • 3D gradient echo • High resolution (0.5 mm – 1.0mm in-plane, 1.0-2.0 mm slice thickness) • RF spoiled (“T1 Enhancement”) • Full flow compensation • TE – long enough for susceptibility-induced effects to evolve • TR – shortest • Save magnitude, real and imaginary parts for post-processing

  9. SWI Post-Processing Steps • Low-pass filter original image • Produce high-pass image from complex division of original image by low-pass filtered image • Create phase mask from high-pass phase image with negative or positive weighting • Operate on original magnitude images with phase mask images • Perform minimum intensity projections (mIP’s) across neighboring slices

  10. Applying a phase mask

  11. Low pass filtering using pyramidal k-space window • Most SWI publications refer to convolution with a Hanning window - requires padding to avoid aliasing across image volume boundaries • Simplier approach is to apply a triangular/pyramidal window in k-space (borrowed from Jim Pipe’s PROPELLER processing) JG PIPE MRM 2004

  12. 7T 2D FFE high-pass phase image 2D FFE Protocol RF-spoiled, flow compensated SENSE factor 2 0.5 mm x 0.63 mm in-plane thick/gap = 3 mm/2 mm 20 slices TR/TE/FA/NSA=349/12/20/4 Scan Time = 3:25

  13. Negative phase mask – not so impressive 2mm mIP’s Control Negative Phase Mask

  14. Other phase mask options

  15. 7T human brain – SWI SWI Protocol 3D FFE RF-spoiled, flow compensation 0.5 x 0.5 x 1.0 mm3 30 slices TR/TE/FA=30/14.8/18 Scan Time = 7:18 High-pass filtered phase from original complex-divided by low-pass filtered (pyramidal filter in k-space). Positive phase mask multiplied with magnitude data 4 times.

  16. 7T human brain – SWI SWI Protocol 3D FFE RF-spoiled, flow compensation 1 x 1 x 1 mm3 80 slices TR/TE/FA=20/18/16 Scan Time = 6:07 High-pass filtered phase from original complex-divided by low-pass filtered (pyramidal filter in k-space). Positive phase mask multiplied with magnitude data 4 times. 20 mm mIP’s

  17. 7T SWI (multi-echo) with Buckeye06 3.9 6.9 9.9 12.9 15.9 18.9 21.9 Protocol 3D FFE RF-spoiled, flow compensation 7 echoes SENSE factor 2 1 x 1 x 1 mm3 128 slices TR/TE/ΔTE/FA=24/3.8/3.0/12 Scan Time = 4:44

  18. 7T T2* mapping T2* [msec] 100.0 SWI Protocol 3D FFE RF-spoiled flow compensation 7 echoes SENSE factor 2 1 x 1 x 1 mm3 128 slices TR/TE/FA=24/3.9+n*3.0/12 Scan Time = 4:44 0.0 M0 T2*

  19. 7T SWI (multi-echo) – full brain coverage 7.1 3.1 5.1 9.1 Protocol 3D FFE RF-spoiled, flow compensation 7 echoes SENSE factor 2 1 x 1 x 1 mm3 140 slices TR/TE/ΔTE/FA=20/3.1/2.0/10 Scan Time = 4:15 11.1 13.1 15.1

  20. mIP’s at varying TE TE/ΔTE=3.8/3.0 Control Negative phase mask Positive phase mask

  21. Full brain venograms Protocol 3D FFE RF-spoiled, flow compensation SENSE factor 2 1 x 1 x 1 mm3 140 slices TR/TE/ΔTE/FA=20/3.1/2.0/10 Scan Time = 4:15

  22. T2*W FFE – MultiVein MultiVane CARTESIAN MULTIVANE

  23. Related topic Positive Contrast SWI (PFL Hamburg, Hannes Dahnke)

  24. Conclusions • SWI data collection is straightforward using existing Philips protocol options • Full brain, high-res SWI data can be acquired at 7T in a short time • SWI post-processing consists of simple steps, though best results yielded using a method inconsistent with published approaches • SWI may be a method waiting for an application • Current plans to include SWI as part of an IRB-approved protocol to image pathology (patients recruited from hospital MR center)

  25. 7T “Clinical” ExamCard (WIP) 10 cm = 100 mm slice coverage for axial and sagittal orientations, except isotropic 1mm which covers 172 mm • SCOUT SHC16 00:29 • REF SHC16 4x4x4 01:55 • B1MAP 3DFFE 04:44 2.0 x 2.0 x 2.0 • T1_3D_iso1mm 07:14 1.0 x 1.0 x 1.0 SENSE 2.5 • T1_TRA_2mm 02:52 0.5 x 0.5 x 2.0 SENSE 2.0 • T2s_TRA_2mm 04:10 0.5 x 0.5 x 2.0 SENSE 2.0 • T2s_SAG_4mm 04:18 0.33 x 0.33 x 4.0 SENSE 2.0 • T2s_TRA_4mm 04:17 0.33 x 0.33 x 4.0 SENSE 2.0 • T2_TRA_GRASE 06:23 0.5 x 0.5 x 2.0 SENSE 2.0 • SWI 9echo 03:58 1.0 x 1.0 x 1.0 SENSE 2.0 • MULTI-FLIP 03:30 1.0 x 1.0 x 2.0 SENSE 2.0

  26. 4. T1_3D_iso1mm 07:14

  27. 5. T1_TRA_2mm 02:52

  28. 6. T2s_TRA_2mm 04:10

  29. 7. T2s_SAG_4mm 04:18

  30. 8. T2s_TRA_4mm 04:17

  31. 9. T2_TRA_GRASE 06:23

  32. 10. SWI 9echo 03:58

  33. 11. MULTI-FLIP 03:30

  34. 7T human brain – T1 mapping T1 [sec] 0.0 Multi-Flip Protocol 3D RF-spoiled FFE 5 angles {20,16,12,8,4} 1.5 x 1.5 x 2.5 mm3 40 slices TR/TE=14/3.9 Scan Time = 6:56 2.5 M0 T1

  35. Other future work…

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