1

Department of Electrical Engineering, University of Southern CalDepartment of Electrical Engineering, University of Southern Californiaifornia

In vivo assessment of carotid wall shear rate using spiral Fourier velocity encoding

In vivo assessment of carotid wall shear rate using spiral Fourier velocity encoding

JLA JLA CarvalhoCarvalho, JF Nielsen, KS , JF Nielsen, KS NayakNayak

April 21st, 2009

Declaration of Conflict of Interest or Declaration of Conflict of Interest or RelationshipRelationship

Joao Carvalho:

I have no conflicts of interest to disclose with regard to the subject matter ofthis presentation.

Wall shear stress (WSS)Wall shear stress (WSS)

•• Prognostic value in carotid artery Prognostic value in carotid artery diseasedisease–– Low WSS Low WSS Zarins et al 1983, Circ Res 53:502

–– High WSS High WSS Thubrikar and Rubicsek 1995, Ann Thorac Surg 59:1594

–– Oscillatory WSS Oscillatory WSS Ku et al 1985, Arterioscler Thromb Vasc Biol 5:293

•• No gold standardNo gold standard

Wall shear stress andWall shear stress andwall shear ratewall shear rate

•• WSS = WSS = μμ ×× WSRWSR

blood viscosity wall shear rate

Wall shear rate (WSR)Wall shear rate (WSR)•• Radial gradient of velocity (Radial gradient of velocity (dv/drdv/dr) near the wall) near the wall

Ai et al 2008, Am J Physiol Cell Physiol 294:1576

shear rate(dv/dr)

MR flow MR flow quantitationquantitationphase contrast

one velocityvalue: e.g. 60 cm/s

Fourier velocity encoding (FVE)

→→ within a within a voxelvoxel

velocity distribution

kx

kv

kx

kv

2

WSR w/ phaseWSR w/ phase--contrast MRIcontrast MRI

2 min

20 min

resolution: 0.33 × 0.33 × 3 mm3

WSR w/ Fourier velocity encodingWSR w/ Fourier velocity encodingFrayne and Rutt 1995, MRM 34:378

•• 2DFT2DFT--FVE: prohibitive scan timeFVE: prohibitive scan time

velocity distribution velocity profile

Spiral FVESpiral FVE•• 77×× faster faster than 2DFTthan 2DFT--FVEFVE

S(kx,ky,kv) → s(x,y,v)FT−1

Carvalho and Nayak 2007, MRM 57:639

Spiral FVE: timeSpiral FVE: time--velocity distributionsvelocity distributions

ECA ICA

CCA

Experimental methodsExperimental methods

•• Hypothesis:Hypothesis:–– WSR measurement using spiral FVEWSR measurement using spiral FVE

•• Validation:Validation:–– Simulation using CFD dataSimulation using CFD data

•• Demonstration:Demonstration:–– Healthy subjects @ 3THealthy subjects @ 3T

•• Reconstructed in Reconstructed in MatlabMatlab

Validation resultsValidation results

Ai et al 2008, Am J Physiol Cell Physiol 294:1576

velocity map

CFD simulation

true WSR

linearregression

s(x,y,v)

modeling

estimated WSR

Frayne

3

Validation resultsValidation results

•• 10% precision for 50% of the 10% precision for 50% of the voxelsvoxels•• 20% precision for 80% of the 20% precision for 80% of the voxelsvoxels•• 30% precision for 95% of the 30% precision for 95% of the voxelsvoxels

In vivoIn vivo experiments experiments –– Spiral FVESpiral FVE

• GE Signa 3T EXCITE HD system– 40 mT/m amplitude– 150 T/m/s slew rate

•• Resolution:Resolution:–– Spatial: 1.4 mmSpatial: 1.4 mm–– Velocity: 5 cm/sVelocity: 5 cm/s–– Temporal: 24 msTemporal: 24 ms

•• Scan time: Scan time: 2 minutes per slice2 minutes per slice–– 5 slices5 slices

In vivoIn vivo resultsresults Oscillatory pattern of WSROscillatory pattern of WSR

•• Common carotidCommon carotid

peak flow

ConclusionConclusion•• First First in vivo in vivo results using Frayneresults using Frayne’’s methods method

–– Spiral FVE: 7Spiral FVE: 7×× faster than 2DFTfaster than 2DFT--FVEFVE•• High temporal resolution High temporal resolution →→ oscillatory patternoscillatory pattern•• High dimensionalityHigh dimensionality →→ scan time can be reducedscan time can be reduced

–– Currently: 2 minutes per sliceCurrently: 2 minutes per slice•• Limitations:Limitations:

–– VoxelVoxel shape, intrashape, intra--voxelvoxel weighting, offweighting, off--resonanceresonance–– Slice must be perpendicular to wallSlice must be perpendicular to wall

AcknowledgementAcknowledgement•• CFD dataCFD data

–– LisongLisong Ai & Ai & TzungTzung HsiaiHsiai (BME/USC)(BME/USC)•• FundingFunding

–– AHA (0435249N)AHA (0435249N)–– The USC Graduate SchoolThe USC Graduate School

•• Travel fundsTravel funds–– Brazilian Government (MEC/CAPES)Brazilian Government (MEC/CAPES)–– University of Brasilia (FGA,ENE,GPDS)University of Brasilia (FGA,ENE,GPDS)

http://mrel.usc.edujoaoluiz@gmail.com – http://www.ene.unb.br/~joaoluiz/