Jiawen Chen¹, Piya Pal¹, and Eric Ahrens^2
1Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, CA, United States, ²Department of Radiology, University of California San Diego, La Jolla, CA, United States

To accelerate the imaging speed and improve the signal-to-noise ratio of three-dimensional, whole body ¹⁹F MRI, we describe an ultrafast compressed sensing data acquisition scheme adapted for a zero echo time (ZTE) pulse sequence, with data reconstruction via a sparsity-promoting algorithm using a nonuniform fast Fourier transform (NUFFT) sensing operator. These methods are well suited for MRI of labeled cells using ¹⁹F tracer agents, particularly paramagnetic metallo-perfluorocarbon nanoemulsions. In phantom data and an in vivo immunotherapy mouse model, we show the feasibility of boosting MRI detection sensitivity by greater than an order of magnitude without increasing total scan time.

Clara J. Fallone¹ and Atiyah Yahya^1,2
1Department of Oncology, University of Alberta, Edmonton, AB, Canada, ²Department of Medical Physics, Cross Cancer Institute, Edmonton, AB, Canada

Magnetic resonance spectroscopy measures of the olefinic resonance (≈ 5.3 ppm) enables estimation of fat unsaturation levels. In spinal bone marrow, the olefinic peak is significantly overlapped by that of water (≈ 4.7 ppm).  Previously, STEAM with a TE of 100 ms was demonstrated to resolve the olefinic resonance from that of water in spinal bone marrow at 3 T.  In this work, we show that an inversion recovery with short-TE STEAM (20 ms) suppresses the water signal, resolving the olefinic resonance and yielding a signal to noise ratio 3.3x larger than that obtained with long-TE STEAM.

Qiuhong He^1,2, Hong Yuan^2,3, and Yen-Yu Ian Shih^1,2,4
1Center for Animal MRI, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, ²Biomedical Research Imaging Center (BRIC), University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, ³Department of Radiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, ⁴Department of Neurology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States

We have developed the phase-incrementing MRSI (pi-MRSI) method to resolve overlapping biomarker images in the presence of a frequency encoding gradient during acquisition time.  We report here the pi-SEE-HSelMQC experiments on a pre-clinical Bruker 9.4T spectrometer.  The choline-selective and lactate CH-selective RF pulses in the pulse sequence were phase incremented by 10° in opposite signs in synchronization with the phase-encoding steps.  In vivo two-dimensional pi-SEE-HSelMQC imaging of lactate and choline acquired from the PC3 human prostate cancer xenograft in a nude mouse showed opposite image offsets, shifted away from spurious signals.  The pi-SEE-HSelMQC method completely suppresses lipid and water. 

Komlan Payne¹ and Xiaoliang Zhang^1
1Jacobs School of Medicine & Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, NY, United States

Decoupling performance between coil elements is one of the factors that limits the transmit B₁ field efficiency and SNR. However, mutual coupling between coil elements is an inevitable electromagnetic interaction that alters the isolated current distribution and impedance of individual elements. In contrast to linear arrays, decoupling challenge of quadrature arrays is more pronounced. In the pursuit of low inter-coupling, a high-impedance technique is adopted. A quadrature hybrid coil composed of loop and microstrip is used in a planar configuration. By employing the high-impedance method, sufficient decoupling between quadrature coils is obtained without the use of additional decoupling network.

Molin Zhang¹, Nicolas Arango¹, Jason Stockmann², Jacob White¹, and Elfar Adalsteinsson^1,3,4
1EECS, MIT, Cambridge, MA, United States, ²Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, ³Harvard-MIT Health Sciences and Technology, MIT, Cambridge, MA, United States, ⁴Institute for Medical Engineering and Science, MIT, Cambridge, MA, United States

Shim arrays provide nonlinear, time-varying fields that can extend the possibility of linear gradient field for RF excitations. In this work, we explore the possibility of designing a selective refocusing 180° pulse for a restricted slice pattern of 1.2cm thickness, aimed at application for the fetal brain. We use an auto-differentiable Bloch simulator framework for the design, but without the presentence of crusher gradients. Decomposition property is employed to overcome the undetermined initial magnetization. The selective refocusing profile achieves selective refocusing for 85% of voxels in the ROI (My< -0.9). 

Gregory Peng¹, Can Wu², and Qi Peng^1
1Department of Radiology, Albert Einstein College of Medicine, Bronx, NY, United States, ²Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, United States

Phase-cycling (PC) has been proposed as an effective method to minimize the impact of B0 and B1 field inhomogeneities in quantitative T1rho mapping, which needs both positive and negative longitudinal magnetization T1rho preparations. We propose here a simple magnetization inversion with an adiabatic inversion RF pulse before an established T1ρ preparation module to achieve an opposite PC. This approach has been shown to be much less sensitive to B0/B1 field imperfections compared with a traditional approach of reversing the phase of the last 90° RF pulse.

Qi Peng¹ and Can Wu^2
1Department of Radiology, Albert Einstein College of Medicine, Bronx, NY, United States, ²Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, United States

T1ρ dispersion imaging based on repeated T1ρ measurements at multiple spin-lock frequencies allows characterization of different dynamic processes of tissues. The clinical potential of this techniques is however limited by the total scan time needed to obtain reliable and consistent quantitative measurements. In this work, we propose an unpaired, interleaved phase-cycling scheme for T1ρ dispersion imaging, which almost reduces total scan time by a half compared with the traditional paired PC approach. This method, when combined with other advanced imaging and reconstruction techniques, could potentially enable high-resolution T1rho dispersion imaging acquired within clinically acceptable scan duration. 

Esteban Denecken^1,2,3, Cristobal Arrieta^1,3, Hernán Mella^1,3, and Sergio Uribe^1,3,4
1Biomedical Imaging Center, Pontificia Universidad Católica de Chile, Santiago de Chile, Chile, ²Department of Electrical Engineering, School of Engineering, Pontificia Universidad Católica de Chile, Santiago de Chile, Chile, ³ANID – Millennium Science Initiative Program – Millennium Nucleus for Cardiovascular Magnetic Resonance, Santiago de Chile, Chile, ⁴Department of Radiology, School of Medicine, Pontificia Universidad Católica de Chile, Santiago de Chile, Chile

Phase-contrast in areas with a significant fat signal is subject to chemical shift artifacts where the fat signal interferes with the neighboring water signal. The purpose of this work is to present a novel method that combines phase-contrast with T2*-IDEAL water-fat separation to obtain water-fat concentrations and velocity images from a single acquisition. We validate our method using a numerical phantom with different combinations of water-fat concentrations, velocity, and noise, and MRI of a 2D axial section of the neck acquired in volunteers. PDFF comparisons showed a significant agreement between phase-contrast T2*-IDEAL and standard methods.

 

Qing-San Xiang^1
1Radiology, University of British Columbia, Vancouver, BC, Canada

Elliptical signal model for bSSFP imaging has found various applications such as banding artifact removal and quantitative mapping of physical parameters. Typically, four or more phase-cycled acquisitions are needed and thus impose a limiting factor in term of total scan time. In this work, it is found that the phase-cycled bSSFP system can be unlocked using a general analytical solution with only three acquisitions, leading to a significant reduction of total scan time. Mathematical frame work is presented, followed by validation with simulated data. Future work includes further demonstration, optimization, and applications with phantoms and in vivo subjects.

Travis Salzillo¹, Alex Dresner², Brigid McDonald¹, Ashley Way¹, Sara Ahmed ¹, Lauren Andring¹, Kelsey Corrigan¹, Gohar Manzar¹, Alison Yoder¹, Abdallah Mohamed¹, Chelsea Pinnix¹, Jason Stafford³, Jihong Wang⁴, and Clifton Fuller^1
1Radiation Oncology, MD Anderson Cancer Center, Houston, TX, United States, ²Philips Healthcare, Best, Netherlands, ³Imaging Physics, MD Anderson Cancer Center, Houston, TX, United States, ⁴Radiation Physics, MD Anderson Cancer Center, Houston, TX, United States

In order to improve head and neck radiotherapy treatment planning, a series of 3D fat-suppressed T2-weighted sequences were developed with varying pulse sequence parameters. One non-fat-suppressed and five fat-suppressed sequences were acquired on five patients, and on each image, four structures were segmented by six radiation oncology physicians (observers). Robust and comprehensive analysis was performed to assess qualitative and quantitative image quality metrics. This included geometric distortion, SNR and CNR measurements, structure conspicuity, interobserver segmentation variability, and qualitative image quality rankings. The results of these were used to determine the optimal fat-suppressed sequence for head and neck radiation treatment planning.

Curtis A Corum^1,2, Stanley J Kruger², Mathews Jacob³, Vincent A Magnotta², and James H Holmes^2
1Champaign Imaging LLC, Shoreview, MN, United States, ²Radiology, University of Iowa, Iowa City, IA, United States, ³Electrical and Computer Engineering, University of Iowa, Iowa City, IA, United States

Missing point estimation has been a part of Fourier Transform NMR and MRI since the beginning. FID based imaging sequences, such as the ZTE (zero echo time) sequence, are missing needed data points corresponding to the region around the center of K-space. In multi-channel ZTE acquisitions, this estimate must be made for each channel. Missing data can be estimated by separate reference scans (WASPI and PETRA) but require extra time. In dynamic acquisitions missing points are optimally estimated from the data itself. Here we investigate applying a method borrowed from solid state NMR to estimate the missing points.