Phase Contrast MRA with Simultaneous Fat-Water
Kevin Michael Johnson1, Alexey Samsonov1, Oliver Wieben1
1University of Wisconsin - Madison, Madison, Wisconsin, USA
We present a novel approach capable of performing phase contrast (PC) imaging with fat/water separation in order to minimize image degradations from fat signal. The technique is demonstrated with a modified undersampled 3D radial sequence For non-contrast enhanced abdominal MRA and offers an alternative for patients excluded from CE-MRA because of risk for NSF. In volunteers, PC images show superior visualization of 2nd and 3rd order branches of the renal arteries as compared to clinically used contrast enhanced exam.
Generalized k-Space Decomposition for Non-Cartesian
Ethan K. Brodsky1, 2, James H. Holmes1, Huanzhou Yu2, Scott B. Reeder1
1University of Wisconsin - Madison, Madison, Wisconsin, USA; 2GE Healthcare, Menlo Park, California , USA
Combination of chemical shift based water/fat separation methods with non-Cartesian acquisitions has been very limited due to the blurring and artifacts caused by chemical shift. While the bulk shift of fat associated with chemical shift artifacts in spin-warp imaging is well-understood and clinically acceptable, the phase roll accumulated by off-resonant spins in non-Cartesian sequences is far more destructive to image quality. IDEAL is a multipoint chemical-shift-based water/fat decomposition technique. Performing IDEAL in k-space allows off-resonant fat signal to be rephased, eliminating distortion and enabling imaging techniques with long readouts, such as spirals or low-bandwidth PR imaging, which were previously not clinically useful without fat suppression.
Bipolar Multi-Echo Water-Fat Separation:
Phase Correction Using Parallel Imaging
Huanzhou Yu1, Charles A. McKenzie2, Ann Shimakawa1, Scott B. Reeder3, Jean H. Brittain4
1GE Healthcare, Menlo Park, California , USA; 2University of Western Ontario, London, Canada; 3University of Wisconsin, Madison, Wisconsin, USA; 4GE Healthcare, Madison, Wisconsin, USA
Three-point water-fat separation techniques have seen a recent increase in clinical use. To improve scan efficiency, recent implementations employ a “bipolar” multi-echo approach, where all echoes are collected in one sequence repetition with alternating gradient polarities. However, the echoes collected with opposite gradient polarities are associated with different phase errors, disrupting the inter-echo phase consistency that is critical for water-fat separation. In this work, we introduce a novel method to correct for the phase error by utilizing parallel imaging reconstruction. A nonlinear phase error can be removed from the bipolar multi-echo data and thus uniform water-fat separation can be achieved.
|Fat/Water Separation Using a Concentric Rings
Hochong H. Wu1, Jin Hyung Lee1, Dwight G. Nishimura1
1Stanford University, Stanford, California , USA
In this work, we present a time-efficient fat/water separation method based on the concentric rings k-space trajectory. Similar to multi-echo acquisitions, rings in the center of k-space are sampled through multiple revolutions to characterize fat/water phase evolution differences at multiple time points. By taking advantage of the unique circularly-symmetric sampling nature of rings, we can extract fat/water phase information at intermediate time points in addition to the number of actual revolutions. Experimental results show that fat/water images can be obtained from appropriate processing of this time-efficient acquisition.
IDEAL with Turbo-PROP
Donglai Huo1, Zhiqiang Li2, Eric Aboussouan1, John P. Karis3, James G. Pipe1
1Barrow Neurological Institute, Phoenix, Arizona , USA; 2GE Healthcare, Waukesha, Wisconsin, USA; 3Southwest Neuro-Imaging, Phoenix, Arizona , USA
Turbo-PROP was developed to provide wider blades for diffusion-weighted and T1-weighted imaging. We propose to reconstruct separate images from different echoes in Turbo-PROP. These images can be synthesized to get a final high-quality image, and at the same time can be used to separate the water and fat signals based on the phase difference with the IDEAL algorithm. Compared with the regular FSE IDEAL approaches, our method can significantly reduce the scan time, and provide the possibility of reliable motion correction (by PROPELLER).
Multi-Echo Tricks Acquisition (META): A High Spatio-Temporal
Resolution Multi-Point Dixon Sequence for Dynamic Contrast Enhanced MRI
Manojkumar Saranathan1, Dan Rettmann1, Ersin Bayram2, Ramesh Venkatesan3, Anthony T. Vu2, Zachary Slavens2, Naoki Takahashi4, Christine Lee4, Akira Kawashima4, James Glockner4
1Global Applied Science Lab, GE Healthcare, Rochester, Minnesota, USA; 2GE Healthcare, Waukesha, Wisconsin, USA; 3GE Healthcare, Bangalore, India; 4Mayo Clinic, Rochester, Minnesota, USA
Dynamic contrast enhanced MRI (DCEMRI) is widely used in clinical abdominal and pelvic MRI for tissue characterization and visualization of focal lesions. The technique affords adequate spatial resolution but temporal resolution is often insufficient for visualizing hypervascular tumors such as neuro-endocrine metastases and hepato-cellular carcinoma (HCC). Optimal timing of contrast arrival in the organ of interest is critical in capturing “arterial” phases. Furthermore, traditional fat suppression methods perform suboptimally at 3T due to Bo and B1 inhomogeneities. We report a new DCEMRI technique called META (Multi-Echo Tricks Acquisition) that combines a multi-echo TRICKS scan with a two-point Dixon fat-water reconstruction algorithm to generate fat-only and water-only images at very high spatio-temporal resolution.
IDEAL Water-Fat Decomposition with
Multipeak Fat Spectrum Modeling
Huanzhou Yu1, Ann Shimakawa1, Charles A. McKenzie2, Jean H. Brittain3, Scott B. Reeder4
1GE Healthcare, Menlo Park, California , USA; 2University of Western Ontario, London, Canada; 3GE Healthcare, Madison, Wisconsin, USA; 4University of Wisconsin, Madison, Wisconsin, USA
Previous multi-point water-fat separation methods used a simple model that assumes both water and fat have a single resonant frequency. However, fat spectrum has a number of side-peaks, typically resulting in incomplete separation of water and fat. In this work, a more accurate multipeak model of fat is integrated in the IDEAL water-fat separation technique. A spectrum self-calibration algorithm is developed to estimate the relative amplitudes of three primary fat peaks directly from the 3-pt data, thereby reducing the method’s sensitivity to potential spectrum variation. The improvement in water-fat separation with multipeak-IDEAL is demonstrated in a variety of in-vivo applications.
Hierarchical IDEAL – Robust Water-Fat Separation at
High Field by Multiresolution Field Map Estimation
Jeffrey Tsao1, Yun Jiang1
1Novartis Institutes for BioMedical Research, Cambridge, Massachusetts, USA
A hierarchical approach to field-map estimation and a new least-squares calculation technique are proposed for robust water-fat separation at high field using the IDEAL acquisition of 3 images at equally spaced but asymmetric echo times.
Noise Considerations in Water-Fat Separation with
Bipolar Multi-Echo Sequences
Wenmiao Lu1, Huanzhou Yu2, Ann Shimakawa2, Marcus Alley1, Scott Reeder3, Brian Hargreaves1
1Stanford University, Stanford, California , USA; 22Global Applied Science Laboratory, GE Healthcare, Menlo Park, California , USA; 3University of Wisconsin-Madison, Madison, Wisconsin, USA
Bipolar multi-echo sequences provide an efficient means to acquire multiple echoes in a single repetition for water-fat separation. One major problem is that the chemical-shift-induced misregistration between water and fat exists in opposite readout directions between even and odd echoes. Separating water/fat signals in k-space eliminates the chemical-shift induced misregistration. However, the k-space separation results in different noise amplification for different k-space locations. We characterize the colored noise present in separated water/fat images with a noise amplification factor, and demonstrate the utility of the noise amplification factor in choosing imaging parameters or regularization parameters in the case of ill-conditioned separation.
Linear Phase Error Correction for Improved Water and
Fat Separation in the Dual-Echo Dixon Techniques
Jingfei Ma1, Zachary Slavens2, Wei Sun2, Ersin Bayram2, Lloyd Estowski2, Ken-Pin Hwang3, James Akao2, Anthony T. Vu2
1University of Texas M. D. Anderson Cancer Center, Houston, Texas, USA; 2GE Healthcare, Waukesha, Wisconsin, USA; 3GE Healthcare, Houston, Texas, USA
The presence of unusually large linear phase errors may pose challenges to phase correction that is needed for Dixon water and fat separation. In this work, we propose a two-step process that first corrects linear phase errors with a modified Ahn-Cho algorithm and then applies a previously-developed region growing algorithm to correct the residual nonlinear components. We demonstrate that successive application of the two-step process provides a “1-2 punch” to the phase errors and can overcome water and fat separation failures occasionally encountered when the region growing based algorithm alone is applied to the dual-echo Dixon processing.