Relaxometric & Water/Fat Imaging
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Wednesday 9 May 2012
Room 201  10:00 - 12:00 Moderators: H. Harry Hu, Mariya Doneva

10:00 0358.   A Novel Reconstruction Approach Using Model Consistency Condition for Accelerated Quantitative MRI (MOCCA)
Alexey Samsonov1
1Radiology, University of Wisconsin, Madison, Wisconsin, United States

In this work, we put forward a MOdel Consistency Condition for Accelerated imaging (MOCCA) derive a novel, practical method for improved reconstruction of parametric image series and quantitative maps from undersampled data. The novel method reconstructs parametric image series sampled below the Nyquist limit using prior knowledge of a signal evolution in the parametric dimension. The method is resilient to data errors such as noise and poor representation of signal evolution in the parametric dimension caused by imaging imperfections such as motion artifacts. The method was validated on T1/T1 relaxometry data.

10:12 0359.   
A Model-based Reconstruction Technique for Parameter Mapping of Saturation Prepared Radially Acquired Data
Johannes Tran-Gia1, Daniel Stäb1, Dietbert Hahn1, and Herbert Köstler1
1Institute of Radiology, University of Würzburg, Würzburg, Germany

A model-based image reconstruction algorithm for parameter mapping of the apparent relaxation parameter T1eff after saturation preparation is presented. For radial trajectories, every acquired projection contains information about the image contrast. By incorporating a signal model into the image reconstruction, it is possible to use this information to resolve the signal evolution with a high temporal resolution, yielding the relaxation parameters T1eff. The functionality of the algorithm and the accuracy of the quantified parameters are demonstrated in phantom studies as well as in in-vivo measurements.

10:24 0360.   
A Bayesian Algorithm Using Spatial Priors for Multi-Exponential T2 Relaxometry from Multi-Echo Spin Echo MRI
Dushyant Kumar1, Thanh Nguyen2, Susan Gauthier3, and Ashish Raj2
1Neuroradiology, University of Hamburg, Hamburg, Hamburg, Germany, 2Radiology, Weill Cornell Medical College, Newyork, NY, United States,3neurology, Weill Cornell Medical College, Newyork, NY, United States

Problem: Because of the ill-posedness of the inverse problem with more unknowns than number of echoes, the accurate quantification of myelin water fraction (MWF) from T2-relaxometry requires high SNR (~500-1000). Methods: The voxelwise conventional regularization is performed followed by implementation of the spatial smoothness over local neighborhood using proposed spatial approach. Results: The inferred MWF-map has significantly reduced spatial variations resulting in better tissue-differentiation and is superior to conventionally regularized version based on various criteria. Conclusions: Spatial constraints allow the handling of lower SNR data which may allow better MWF reproducibility for longitudinal or multi-site studies and warrants further evaluation.

10:36 0361.   Highly accelerated 3D spiral acquisition for whole brain myelin water mapping using a hybrid SPIRiT-PCA reconstruction
Thanh D. Nguyen1, Mitchell Cooper1,2, Pascal Spincemaille1, Bo Xu1,2, Ashish Raj1, Susan A. Gauthier3, and Yi Wang1,2
1Radiology, Weill Cornell Medical College, New York, NY, United States, 2Biomedical Engineering, Cornell University, Ithaca, NY, United States,3Neurology and Neuroscience, Weill Cornell Medical College, New York, NY, United States

Recently an SNR efficient 3D T2prep spiral sequence has been developed to provide whole brain coverage in 24 min at 1.5T. We propose to develop a hybrid reconstruction method which combines Iterative Self-consistent Parallel Imaging Reconstruction (SPIRiT) and Principal Component Analysis (PCA) to exploit the spatiotemporal redundancy in multi-component T2 relaxometry to accelerate whole brain coverage from 24 min down to 6.5 min. Comparable myelin water fractions were obtained with the accelerated spiral data at 3T. SPIRiT-PCA may be a promising approach to bringing myelin quantification closer to clinical practice.

10:48 0362.   
Indirect Echo Compensated T2 Mapping from Highly Undersampled Radial FSE Data with SERENADE
Chuan Huang1, Ali Bilgin2, and Maria I Altbach3
1Mathematics, University of Arizona, Tucson, Arizona, United States, 2Biomedical Engineering, University of Arizona, 3Radiology, University of Arizona

With the goal of fast T2 mapping, a radial FSE technique, where T2 maps are reconstructed from highly undersampled data, was developed. As all T2 mapping techniques based on multiple refocusing pulses, the accuracy of T2 estimation is compromised by the presence of indirect echoes. Recently a slice resolved extended phase graph algorithm for T2 estimation from decay curves contaminated by indirect echoes was proposed. However, the application of this algorithm to highly undersampled data is challenging because the decay curves need to be reconstructed from limited data. A direct model-based algorithm results in a highly non-linear system which is difficult to solve. In this work, SlicE Resolved ExteNd phAse graph baseD rEconstruction of principal component coefficient maps (SERENADE) algorithm is proposed to obtain accurate T2 decay curves hence accurate T2 estimates from data acquired in a short period of time.

11:00 0363.   
Absolute Quantification of In Vivo Water and Fat Content
Yifan Cui1, Issac Y. Yang2, Trevor Wade2, Curtis N. Wiens1, Abraam S. Soliman3,4, and Charles A. McKenzie1,2
1Physics and Astronomy, University of Western Ontario, London, Ontario, Canada, 2Medical Biophysics, University of Western Ontario, London, Ontario, Canada, 3Biomedical Engineering, University of Western Ontario, London, Ontario, Canada, 4Imaging Research Laboratories, Robarts Research Institute, University of Western Ontario, London, Ontario, Canada

Accurate measurement of in vivo fat fraction has been demonstrated with IDEAL. However, knowing the absolute (instead of relative) fat and water content is valuable for understanding the source of fat fraction changes. Existing methods for absolute fat and water quantification are limited to single coil data acquisition and have not been demonstrated in vivo. We have extended these methods with rapid B1+ measurement and corrections for coil array sensitivity, validated the accuracy of fat and water content measurement with these corrections and demonstrated the use of this new method for in vivo imaging.

11:12 0364.   
A Closed-form Formula for Multipoint Water-Fat Imaging with Flexible Echo Increments
Dinghui Wang1, and James G. Pipe1
1Neuroimaging Research, Barrow Neurological Institute, Phoenix, AZ, United States

We introduce a new closed-form multipoint water-fat reconstruction algorithm with flexible echo time increments. Two sets of possible solutions of water, fat and field map are computed from images acquired at N (N>2) echo times. Under the assumption of the local smoothness of the field map, the solutions for water, fat are resolved by thresholding, region-growing and bilinear fitting of the field map. An implementation with multi-coil spiral imaging has demonstrated the feasibility of this method.

11:24 0365.   Water-Fat Identification in Dual-Echo Dixon Imaging
Holger Eggers1
1Philips Research, Hamburg, Germany

While the separation of two signal components with fixed difference in resonance frequency is usually straightforward in dual-echo Dixon imaging, establishing their correspondence to water and fat signals is more intricate. To increase the robustness and to decrease the complexity of the separation, a direct identification of water or fat signals is desirable. In the present work, an approach to such a direct identification in dual-echo Dixon imaging is proposed, which exploits the spectral complexity of fat for a differentiation between water and fat signals. Its potential is analyzed theoretically and demonstrated experimentally on high-resolution pelvic imaging.

11:36 0366.   
3D balanced SSFP Dixon imaging with Band-Reduction at 3T
Brady Quist1,2, Brian A. Hargreaves1, Bruce L. Daniel1, and Manojkumar Saranathan1
1Department of Radiology, Stanford University, Stanford, CA, United States, 2Department of Electrical Engineering, Stanford University, Stanford, CA, United States

Balanced steady-state free precession (bSSFP) can offer fast 3D imaging with T2-like contrast, and multiple acquisitions can be used to avoid banding artifacts due to static magnetic field variations. Simulations of multi-peak fat models show that the bSSFP profile of fat varies with echo and repetition time, which can complicate Dixon separation methods, particularly in combination with phase-cycling. The effect is demonstrated, and robust fat/water separation with banding reduction was demonstrated in the breast at 3T by performing the Dixon reconstruction on the complex sum of two 3D phase-cycled images.

11:48 0367.   
Water-Fat Separation with a Bipolar Multiecho 3D Concentric Cylinders Trajectory
Kie Tae Kwon1, Holden H. Wu1,2, and Dwight G. Nishimura1
1Electrical Engineering, Stanford University, Stanford, CA, United States, 2Cardiovascular Medicine, Stanford University, Stanford, CA, United States

For water-fat separation using Dixon techniques, a bipolar multi-echo sequence acquires data more efficiently than a comparable unipolar multi-echo sequence, and also enables more robust field map estimation by shortening echo-spacings, which is crucial for reliable water-fat separation. In this work, a variation of the bipolar multiecho sequence was implemented with a 3D concentric cylinders trajectory. The concentric cylinders sequence requires fewer excitations than a comparable 3DFT sequence, thereby enabling a further scan time reduction while maintaining robustness to off-resonance effects.