Susceptibility Weighted Imaging at 7T

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


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


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)


Mark Haacke’s website – www.mrimaging.com


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


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


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


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


Applying a phase mask


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


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


Negative phase mask – not so impressive

Control Negative Phase Mask

2mm mIP’s


Other phase mask options


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.


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


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


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


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

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


3.1 5.1 7.1 9.1

11.1 13.1 15.1


mIP’s at varying TE

Control

Negative phase mask

Positive phase mask

TE/ΔTE=3.8/3.0


Full brain venograms

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



T2*W FFE – MultiVein MultiVane

CARTESIAN MULTIVANE


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


Related topic

Positive Contrast SWI (PFL Hamburg, Hannes Dahnke)


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)


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


4. T1_3D_iso1mm 07:14


5. T1_TRA_2mm 02:52


6. T2s_TRA_2mm 04:10


7. T2s_SAG_4mm 04:18


8. T2s_TRA_4mm 04:17


9. T2_TRA_GRASE 06:23


10. SWI 9echo 03:58


11. MULTI-FLIP 03:30


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


Other future work…

Susceptibility Weighted Imaging at 7T

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