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2D-CSI in a fraction of the time using multiple receiver coils. Simon J. Doran 1 , Adam J. Schwarz 2 and Martin O. Leach 2 1 Department of Physics, University of Surrey, Guildford, Surrey, UK 2 Institute of Cancer Research & Royal Marsden NHS Trust, Sutton, Surrey, U.K. Acknowledgements. - PowerPoint PPT Presentation
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2D-CSI in a fraction of the time using multiple receiver coils
Simon J. Doran1, Adam J. Schwarz2
and Martin O. Leach2
1Department of Physics, University of Surrey,
Guildford, Surrey, UK2Institute of Cancer Research & Royal Marsden NHS
Trust, Sutton, Surrey, U.K.
Funding from Cancer Research Campaign [CRC]National Institutes of Health (NIH)NHS (South Thames)
Acknowledgements
Background
• Use of phased array receiver coils in surface coil studies - improves SNR- improves coverage (e.g. ~volumetric coverage)
• Spatial receive profiles of the coil array elements already employed in imaging schemes to reduce the total acquisition time
• Aim of this study is to develop such techniques for application to chemical shift imaging (CSI) spectroscopy acquisitions, primarily for application to extra-cranial tumours.
Reduced imaging time with phased arrays: Ra-Rim method
Advantages:
• Works for arbitrary array sensitivity profiles. (Orthogonal coil basis functions [as in SMASH] not required).
• Don’t require pure coil sensitivity maps. Any sequence can be used for the reference.
Reduced imaging time with phased arrays: Ra-Rim method1
1 Ra and Rim (1993) MRM 30 142-145
For C coils, acquire:
MxN reference image: R ( M x N x C )
Mx(N/L) folded image: I ( M x N/L x C )
These are related to each other via the array sensitivity function, which is the same for both.
Folded images acquired in fraction of time
N N / L
E.g. L = 2
Reconstruction scheme
To find relationship x jl between desired (unfolded) and
reference image, solve the matrix equation
I jc = R j
c l x jl for x j
l, for each j
(i.e. N/L times).
Desired image obtained as Icfinal = Rc x
Foldedimage
Referenceimage
Unknown to be found
Pixel numberin fold direction
Coil number Foldingparameter
Application to CSI
• Additional complex, chemical shift dimension in undersampled data set.
• Use imaging (rapidly acquired gradient echo) reference data for coil sensitivity maps.
16 x 16 x 1024 x 4 2D-CSI [for comparison] 8 x 16 x 1024 x 4 undersampled 2D-CSI 16 x 16 x 1 x 4 reference images
(in practice rebinned from clinical 256 x 256 images)
• Three compartment phantom
• Siemens Vision, body-phased-array (C=4)
• (No k-space apodisation)
Extension to CSI
Spatial dimensions 16 x 16
Spectral dimension1024
Repeat the basic Ra-Rim1024 times, once on eachplane.
Phantom & coil arrangement
Transverse section Side view
20mMCho
50mM Cho
oil
Coil elements
Reconstruction of undersampled images
Folded T1w
Reference
Reconstructed T1w
Reference images from individual elements
Acquired at 256x256
k-space truncated to 16x16 for registration with CSI
CSI metabolite images : oil
Folded CSI (oil CH2) Reconstructed
Full CSI
Rebinned ref. image
CSI metabolite images : water
Folded CSI (water)
Rebinned ref. image
Reconstructed
Full CSI
Folded spectra from within oil and choline balls
Unfolded Reference from full 16x16 CSI
Unfolded spectrum from within oil and choline balls
CH2
CH3
(water)
choline residuallipid
Conclusions
• Ra-Rim method has been extended to reduce acquisition time in CSI spectroscopic studies in (pseudo-) abdominal sites, using product coil and rapidly acquired image data as coil sensitivity reference.
• ‘Unfolding’ process moves aliased signal to its correct location.
• Further work is need both to quantify the minor differences seen between restored (unfolded) and reference CSI signals and to improve the method.
Funding from Cancer Research Campaign [CRC]National Institutes of Health (NIH)NHS (South Thames)
Acknowledgements