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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.

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.

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.

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.

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).

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.

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.

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.

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.

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.