Efficient Trajectories

Thursday 15 May 2014

Jiang Du¹, Vipul Sheth¹, Shihong Li¹, Michael Carl², Scott Vandenberg³, Jody Corey-Bloom⁴, and Graeme Bydder^1
1Radiology, University of California, San Diego, San Diego, CA, United States, ²General Electric, Global MR Applications & Workflow, San Diego, CA, United States, ³Pathology, University of California, San Diego, La Jolla, CA, United States, ⁴Neurosciences, University of California, San Diego, La Jolla, CA, United States

Myelin is a lamellar membranous structure consisting of alternating protein and lipid layers. Researchers have been working for decades to develop MRI techniques to assess myelin in vivo. The non-water protons in myelin and tightly bound water have very short T2s and are “invisible” with conventional clinical sequences. We have implemented a 2D adiabatic inversion recovery prepared dual echo ultrashort echo time (2D IR-dUTE) acquisition with a TE of 8 us. In this study we aimed to morphologically and quantitatively evaluate myelin and tightly bound water in white matter of the brain of normal volunteers at 3T.

Peder Eric Zufall Larson¹, Misung Han¹, Sarah J. Nelson¹, Daniel B. Vigneron¹, Roland Krug¹, and Douglas A. C. Kelley^2
1Radiology and Biomedical Imaging, University of California - San Francisco, San Francisco, CA, United States, ²Neuro Apps and Workflow, GE Healthcare, Corte Madera, CA, United States

Detection of short-T2 (< 1ms) semi-solid tissue components, such as in tendons, calcified cartilage, the meninges, and myelin, is limited with Cartesian MRI acquisitions due minimum TEs. Two promising approaches for imaging these components are ultrashort echo time (UTE) and zero echo time (ZTE) pulse sequences. ZTE and UTE MRI acquired at 7T in the brain, ankle, and knee demonstrated similar tissue contrast with matched acquisition parameters. UTE offers advantages of slab or slice selection and supports variable TEs. ZTE provides a shorter TE, is practically insensitive to gradient infidelity, and is relatively quiet due to slow gradient switching.

Jinjin Zhang^1,2, Djaudat Idiyatullin¹, Curtis Corum¹, Naoharu Kobayashi¹, and Michael Garwood^1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States, ²School of Physics and Astronomy, University of Minnesota, minneapolis, Minnesota, United States

A gradient-modulated SWIFT sequence (GM-SWIFT) is compared with standard SWIFT sequence. GM-SWIFT is shown to reduce RF amplitude, SAR, or acquisition time, by up to 70%, 90% and 45%, respectively, while maintaining image quality. Also, the choice of gradient modulation influences the lower limit of the short T2 sensitivity, which can be exploited to suppress unwanted image haze from ultra-short T2 signals in the rigid plastic materials of the coil housing. In summary, GM-SWIFT reduces RF power requirements and provides a way to choose sequence parameters for balancing RF amplitude, SAR, scan time, and image quality considerations.

Cheng Li¹, Jeremy F. Magland¹, Alan C. Seifert¹, and Felix W. Wehrli^1
1Radiology, University of Pennsylvania, Philadelphia, PA, United States

Zero-echo Time (ZTE) imaging is a promising technique for detecting short-T2 nuclei. However, a well-known problem with ZTE imaging is the presence of a spatial encoding gradient during excitation causing the hard pulse to become spatially selective, resulting in blurring and shadow artifacts. In this work, an approach is proposed to correct the artifacts by applying quadratic phase-modulated RF excitation and iterative reconstruction. Results from simulations and in vivo studies demonstrate the effectiveness of the method. The proposed method may contribute toward establishing ZTE MRI as a routine 3D pulse sequence for short-T2 imaging on clinical scanners.

Qi Peng^1
1Gruss MRRC, Radiology, Albert Einstein College of Medicine and Montefiore Medical Center, Bronx, New York, United States

A major technical difficulty for UTE imaging is the suppression of long-T2 signal to obtain positive contrast from ultra-short-T2 components. Variations of pre-pulse suppression and echo subtraction are currently the two approaches used to enhance short-T2 to long-T2-species contrast. A Low flip-Angleb-SSFP UTE (LA-bUTE) sequence is introduced to achieve up to 50% of long-T2 signal suppression without time penalty. It is also demonstrated that full suppression of long-T2-tissue can be achieved when combine LA-bUTE with traditional pre-saturation pulses with only slight increase on scan duration.

Ryan K Robison¹, Michael Schär^1,2, Dinghui Wang¹, Zhiqiang Li¹, Nicholas R Zwart¹, and James G Pipe^1
1Neuroimaging Research, Barrow Neurological Institute, Phoenix, Arizona, United States, ²Philips Healthcare, Cleveland, Ohio, United States

The FLORET trajectory is an efficient and easy to design sequence based upon a Fermat spiral design. Advantages of FLORET include high SNR efficiency, relatively benign aliasing artifacts, and faster traversal out from the center of k-space. This work utilizes FLORET in UTE imaging and compares its image quality to that obtained in 3D radial UTE acquisitions.

Kie Tae Kwon¹, R Reeve Ingle¹, Holden H Wu², William R Overall³, Juan M Santos³, Bob S Hu⁴, and Dwight G Nishimura^1
1Electrical Engineering, Stanford University, Stanford, CA, United States, ²Radiology, UCLA, California, United States, ³HeartVista, Inc, California, United States, ⁴Palo Alto Medical Foundation, Palo Alto, CA, United States

2D multislice interleaved spiral imaging for coronary magnetic resonance angiography (MRA) has been shown to be capable of imaging multiple slices with sub-mm in-plane resolution and high temporal resolution within a breath-hold. However, an important issue with this sequence is blood-lesion contrast. In this work, we developed a spiral-ring version of the sequence, which is aimed for first-pass coronary MRA for potentially better blood-muscle and blood-lesion contrast. The preliminary in vivo datasets demonstrated the feasibility of the spiral-ring trajectory for first-pass coronary MRA.

Wei-Tang Chang¹, kawin Setsompop¹, Jyrki Ahveninen¹, John Belliveau¹, Thomas Witzel¹, and Fa-Hsuan Lin^2
1Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ²Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, Taiwan

Using simultaneous acquisition from multiple channels of a radio-frequency (RF) coil array, magnetic resonance inverse imaging (InI) achieves functional MRI acquisitions at a rate of 100 ms per whole-brain volume. InI accelerates the scan by leaving out partition encoding steps and reconstructs images by solving under-determined inverse problems using RF coil sensitivity information. Hence, the correlated spatial information available in the coil array causes spatial blurring in the InI reconstruction. Here, we propose a method that employs gradient blips in the partition encoding direction during the acquisition to provide extra spatial encoding in order to better differentiate signals from different partitions.

Hing-Chiu Chang¹, Chun-Jung Juan², Hsiao-Wen Chung³, Shayan Guhaniyogi¹, and Nan-Kuei Chen^1
1Brain Imaging and Analysis Center, Duke University Medical Center, Durham, North Carolina, United States, ²Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, ³Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan

The IDEAL based fat-water separation has not yet been applied to chemical-shift ADC mapping, because of several major technical challenges. Such as original IDEAL framework may be not compatible with EPI data in presence of significant pixel displacement due to chemical-shift effect. To address these technical challenges to enable chemical-shift ADC mapping, we first evaluate the IDEAL framework in the presence of large chemical-shift effect using both original and our modified frameworks. Second, we integrated 1) interleaved EPI sequence and 2) multiplexed sensitivity encoding (MUSE) to reliably enable quantification of chemical-shifting ADC mapping in parotid glands.

Samantha J Holdsworth¹, Stefan Skare², Kristen Yeom³, and Michael E Moseley^1
1Lucas Center for Imaging, Department of Radiology, Stanford University, Palo Alto, CA, United States, ²Clinical Neuroscience, Karolinksa Institute, Stockholm, Sweden, ³Lucile Packard Children's Hospital, Department of Radiology, Stanford University, Palo Alto, CA, United States

The fluid attenuating inversion recovery (FLAIR) MRI method is an important technique for the differentiation of brain and spine lesions. However the FLAIR-FSE sequence typically used in the clinics can be long and prone to motion. Here, we show preliminary patient data using a faster readout-segmented (rs)-EPI-FLAIR implementation. With a better selection of imaging parameters, rs-EPI-FLAIR may be a useful rapid alternative to conventional FLAIR and EPI-FLAIR in the clinics.