Atkinson, D

Jones, A

Muthurangu, V

Steeden, JA

English

UCL Discovery

WORKSHOP PRESENTATION Open AccessVelocity unwrap for high resolution slice-selectiveFourier Velocity Encoding using spiral SENSEJennifer A Steeden1*, David Atkinson2, Alexander Jones1, Vivek Muthurangu1From 15th Annual SCMR Scientific SessionsOrlando, FL, USA. 2-5 February 2012BackgroundIn patients with stenoses, it is desirable to accuratelymeasure peak velocity (Vmax). Unfortunately, phase-contrast MR (PCMR) tends to underestimate peak velo-cities. Fourier Velocity Encoding (FVE) can measurepeak velocities in MRI, but is not commonly used dueto long acquisition times.We have developed a FVE sequence that combinesspiral trajectories with parallel imaging (SENSE), partial-Fourier acquisition and a novel velocity-unwrap techni-que. The aim of this study is to validate this sequence.MethodsFVE was performed using a uniform-density spiral tra-jectory with 16 interleaves (table 1). Parallel imagingwas applied (R=4) and reconstructed using an iterativeSENSE algorithm. Partial-Fourier was performed in kv(67%) with a homodyne reconstruction.Velocity-unwrap: By acquiring the centre half of kv-positions, reconstructed data is aliased in v-space.Acquiring one additional kv-position with the fullVENC, and reconstructing this using traditional PCMRprovides information about the direction of flow (on apixel-by-pixel, frame-by-frame basis). This allows accu-rate unfolding of velocity data.In-vitro: A pulsatile flow pump was connected to atube phantom (diameter 13mm) with a stenosis of6mm. At 15 different flow rates, Vmax was measuredusing; 1) ultrasound (US), 2) low-resolution PCMR (lr-PCMR), 3) high-resolution PCMR (hr-PCMR), 4) FVEwith SENSE and partial-Fourier with 21 reconstructedvelocities (FVE21) and 5) FVE with SENSE and partial-Fourier, plus velocity-unwrap giving 41 reconstructedvelocities (FVE41). SNR estimates were comparedbetween FVE21 and FVE41.In-vivo: Six patients with stenoses were also assessed(3M:3F; 31±21years).ResultsIn-vitro: There were no statistically significant differ-ences between Vmax measured using US and FVE (table2). However both PCMR sequences showed statisticallysignificant underestimation of Vmax compared to US.This is particularly true of lr-PCMR, which underesti-mated Vmax by >0.5m/s.In-vivo: As in-vitro, PCMR underestimated Vmax.There were no statistical differences between Vmaxmeasured using US and FVE sequences. However therewas a trend towards FVE21 overestimating Vmax.ConclusionsFVE allows more accurate assessment of Vmax thanPCMR as it measures a velocity spectrum per pixel,rather than the average velocity. We have demonstratedthat it is possible to achieve high resolution FVE withina short breath-hold by combining spiral trajectories, par-allel imaging, partial-Fourier and velocity-unwrap. Thissequence was shown to be significantly more accuratethan PCMR in-vitro and in-vivo. Furthermore using thenovel velocity-unwrap technique there was a trendtowards higher accuracy due to higher velocity resolu-tion. Thus, the sequence may be able to replace US inassessment of Vmax.FundingJAS: EPSRC PhD+.VM: BHF.Author details1Institude of Cardiovascular Science, UCL, London, UK. 2Centre for MedicalImaging, UCL, London, UK.Published: 1 February 20121Institude of Cardiovascular Science, UCL, London, UKFull list of author information is available at the end of the articleSteeden et al. Journal of Cardiovascular Magnetic Resonance 2012, 14(Suppl 1):W25http://www.jcmr-online.com/content/14/S1/W25© 2012 Steeden et al; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative CommonsAttribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction inany medium, provided the original work is properly cited.doi:10.1186/1532-429X-14-S1-W25Cite this article as: Steeden et al.: Velocity unwrap for high resolutionslice-selective Fourier Velocity Encoding using spiral SENSE. Journal ofCardiovascular Magnetic Resonance 2012 14(Suppl 1):W25.Submit your next manuscript to BioMed Centraland take full advantage of: • Convenient online submission• Thorough peer review• No space constraints or color figure charges• Immediate publication on acceptance• Inclusion in PubMed, CAS, Scopus and Google Scholar• Research which is freely available for redistributionSubmit your manuscript at www.biomedcentral.com/submitTable 1 Institude of Cardiovascular Sciencelr-PCMR hr-PCMR FVE21 FVE41TE/TR (ms) ~2.2/5.0 ~2.2/5.0 ~2.5/9.3 ~3.5/10.3Readouts Cartesian Cartesian Spiral: 16 interleaves Spiral: 16 interleavesMatrix Size 128 256 192 192Image FOV (mm) 320 320 450 450kv positions acquired - - 14 15Reconstructed velocity levels - - 21 41Total Scan Duration (heartbeats) 15 108 15 15Spatial resolution (mm) ~2.5 ~1.3 ~2.3 ~2.3Temporal resolution (ms) ~40 ~30 ~37 ~41Velocity resolution (cm/s) - - 30-75 18-38Table 2Echo lr-PCMR hr-PCMR FVE21 FVE41In-vitroPeak velocity (cm/s) 441±144 375±133^ 398±136^ 447±140 443±144Bias* (cm/s) - -66 -42 +7 +3Limits of agreement* (cm/s) - -26 to -105 -10 to -75 +28 to -14 +17 to -12Correlation coefficient* (r) - 0.9926 0.9949 0.9977 0.9987Estimated SNR - - - 5.2±2.6 4.4±3.9In-vivoPeak Velocity (cm/s) 255±71 228±42 234±644 266±67 257±62Bias* (cm/s) - -27 -21 +10 +1Limits of agreement* (cm/s) - +67 to -121 +63 to -106 +74 to -53 +47 to -46Correlation coefficient* (r) - 0.7717 0.8269 0.8957 0.9463* Calculated with echo ^Value is significantly different (ANOVA) from echo (P<0.05)Steeden et al. Journal of Cardiovascular Magnetic Resonance 2012, 14(Suppl 1):W25http://www.jcmr-online.com/content/14/S1/W25Page 2 of 2

Velocity unwrap for high resolution slice-selective Fourier Velocity Encoding using spiral SENSE

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Velocity unwrap for high resolution slice-selective Fourier Velocity Encoding using spiral SENSE

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