Susceptibility Weighted Imaging at 7T

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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 - PowerPoint PPT Presentation

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Brian WelchMR Clinical ScienceIACSM 2007April 24, 2007

Susceptibility Weighted Imaging at 7T

2MR Clinical Science, Brian Welch, April 24, 2007

7T human midbrain

T1W TFETR/TE=19/9.6

TSE_IRTR/TI/TE=4000/60/10

3MR Clinical Science, Brian Welch, April 24, 2007

7T human brain – high resolution sagittal

High Res. Sagittal Protocol3D T1W TFEinversion delay = 1816 msecTFE factor = 1800.33 x 0.33 x 4.0 mm3

24 slicesTR/TE=19/9.6Scan Time = 7:23

4MR Clinical Science, Brian Welch, April 24, 2007

SWI Background and ReferencesPrimarily 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)

5MR Clinical Science, Brian Welch, April 24, 2007

Mark Haacke’s website – www.mrimaging.com

6MR Clinical Science, Brian Welch, April 24, 2007

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

TEHctYBdo 31cos12 20

7MR Clinical Science, Brian Welch, April 24, 2007

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

8MR Clinical Science, Brian Welch, April 24, 2007

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

9MR Clinical Science, Brian Welch, April 24, 2007

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

10MR Clinical Science, Brian Welch, April 24, 2007

Applying a phase mask

11MR Clinical Science, Brian Welch, April 24, 2007

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 PIPEMRM 2004

12MR Clinical Science, Brian Welch, April 24, 2007

7T 2D FFE high-pass phase image

2D FFE ProtocolRF-spoiled, flow compensatedSENSE factor 20.5 mm x 0.63 mm in-planethick/gap = 3 mm/2 mm 20 slicesTR/TE/FA/NSA=349/12/20/4Scan Time = 3:25

13MR Clinical Science, Brian Welch, April 24, 2007

Negative phase mask – not so impressive

Control Negative Phase Mask

2mm mIP’s

14MR Clinical Science, Brian Welch, April 24, 2007

Other phase mask options

15MR Clinical Science, Brian Welch, April 24, 2007

7T human brain – SWI

SWI Protocol

3D FFERF-spoiled, flow compensation0.5 x 0.5 x 1.0 mm3

30 slicesTR/TE/FA=30/14.8/18Scan 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.

16MR Clinical Science, Brian Welch, April 24, 2007

7T human brain – SWI

SWI Protocol

3D FFERF-spoiled, flow compensation1 x 1 x 1 mm3

80 slicesTR/TE/FA=20/18/16Scan 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

17MR Clinical Science, Brian Welch, April 24, 2007

7T SWI (multi-echo) with Buckeye06

Protocol3D FFERF-spoiled, flow compensation7 echoesSENSE factor 21 x 1 x 1 mm3

128 slicesTR/TE/ΔTE/FA=24/3.8/3.0/12Scan Time = 4:44

3.9 6.9 9.9 12.9 15.9 18.9

21.9

18MR Clinical Science, Brian Welch, April 24, 2007

7T T2* mapping

M0 T2*

T2* [msec]

0.0

100.0

SWI Protocol3D FFERF-spoiledflow compensation7 echoesSENSE factor 21 x 1 x 1 mm3

128 slicesTR/TE/FA=24/3.9+n*3.0/12Scan Time = 4:44

*2/

0ˆ TteMtS

19MR Clinical Science, Brian Welch, April 24, 2007

7T SWI (multi-echo) – full brain coverage

Protocol3D FFERF-spoiled, flow compensation7 echoesSENSE factor 21 x 1 x 1 mm3

140 slicesTR/TE/ΔTE/FA=20/3.1/2.0/10Scan Time = 4:15

3.1 5.1 7.1 9.1

11.1 13.1 15.1

20MR Clinical Science, Brian Welch, April 24, 2007

mIP’s at varying TE

Control

Negative phase mask

Positive phase mask

TE/ΔTE=3.8/3.0

21MR Clinical Science, Brian Welch, April 24, 2007

Full brain venograms

Protocol3D FFERF-spoiled, flow compensationSENSE factor 21 x 1 x 1 mm3

140 slicesTR/TE/ΔTE/FA=20/3.1/2.0/10Scan Time = 4:15

22MR Clinical Science, Brian Welch, April 24, 2007

T2*W FFE – MultiVein MultiVane

CARTESIAN MULTIVANE

23MR Clinical Science, Brian Welch, April 24, 2007

2D T2W TSE 3D T1W TFE 3D T2*W FFE

Acquisition Matrix Size 512 x 512 x 8 512 x 512 x 26 512 x 512 x 21

TR/TE [msec] 3500/60 5.6/2.9 32/19

k-space lines/vanes 24 128 (x 26 kz) 24 (x 21 kz)

Number of vanes 34 7 34

Vane acquisition time 240 msec26 x 3000 msec

(TFE shot interval) = 78.0 sec

24 x 21 x 32 msec = 16.1 sec

Cartesian/Multivane acquisition time [mm:ss]

5:22/7:56 5:11/9:05 5:44/9:15

24MR Clinical Science, Brian Welch, April 24, 2007

Related topic

Positive Contrast SWI (PFL Hamburg, Hannes Dahnke)

25MR Clinical Science, Brian Welch, April 24, 2007

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)

26MR Clinical Science, Brian Welch, April 24, 2007

7T “Clinical” ExamCard (WIP)

43:50

1. SCOUT SHC16 00:29

2. REF SHC16 4x4x4 01:55

3. B1MAP 3DFFE 04:44 2.0 x 2.0 x 2.0

4. T1_3D_iso1mm07:14 1.0 x 1.0 x 1.0 SENSE 2.5

5. T1_TRA_2mm 02:52 0.5 x 0.5 x 2.0 SENSE 2.0

6. T2s_TRA_2mm 04:10 0.5 x 0.5 x 2.0 SENSE 2.0

7. T2s_SAG_4mm04:18 0.33 x 0.33 x 4.0 SENSE 2.0

8. T2s_TRA_4mm 04:17 0.33 x 0.33 x 4.0 SENSE 2.0

9. T2_TRA_GRASE 06:23 0.5 x 0.5 x 2.0 SENSE 2.0

10.SWI 9echo 03:58 1.0 x 1.0 x 1.0 SENSE 2.0

11.MULTI-FLIP 03:30 1.0 x 1.0 x 2.0 SENSE 2.0

10 cm = 100 mm slice coverage for axial and sagittal orientations, except isotropic 1mm which covers 172 mm

27MR Clinical Science, Brian Welch, April 24, 2007

4. T1_3D_iso1mm 07:14

28MR Clinical Science, Brian Welch, April 24, 2007

5. T1_TRA_2mm 02:52

29MR Clinical Science, Brian Welch, April 24, 2007

6. T2s_TRA_2mm 04:10

30MR Clinical Science, Brian Welch, April 24, 2007

7. T2s_SAG_4mm 04:18

31MR Clinical Science, Brian Welch, April 24, 2007

8. T2s_TRA_4mm 04:17

32MR Clinical Science, Brian Welch, April 24, 2007

9. T2_TRA_GRASE 06:23

33MR Clinical Science, Brian Welch, April 24, 2007

10. SWI 9echo 03:58

34MR Clinical Science, Brian Welch, April 24, 2007

11. MULTI-FLIP 03:30

35MR Clinical Science, Brian Welch, April 24, 2007

7T human brain – T1 mapping

M0 T1

T1 [sec]

2.5

0.0

cos1

1sinˆ

1

1

/

/

0 TTR

TTR

e

eMS

Multi-Flip Protocol

3D RF-spoiled FFE5 angles {20,16,12,8,4}1.5 x 1.5 x 2.5 mm3

40 slicesTR/TE=14/3.9Scan Time = 6:56

36MR Clinical Science, Brian Welch, April 24, 2007

Other future work…