Eddy Solomon, Gilad Liberman, Zhiyong Zhang , Lucio Frydman

This study presents a new diffusion tool based on a novel single-shot 2D MRI method called xSPEN. xSPEN is characterized with unusual resilience to field heterogeneities, but extending it to DTI requires to overcome the strong intrinsic diffusion weighting of this technique. To achieve this we formulated xSPEN’s diffusion weighting using a novel, spatially localized b- matrix analysis, and devised a novel diffusion-weighting scheme that overcomes xSPEN’s original limitations. These methods were numerically validated and applied to new DTI xSPEN sequences with which we mapped diffusion in often unreachable human head regions, including optic nerve and olfactory bulb regions. 

Daniele Mascali, Keith Jamison, Emily Kittelson, Kâmil Ugurbil, Essa Yacoub, Shalom Michaeli, Melissa Terpstra, Federico Giove, Silvia Mangia

High sampling rate is pivotal for differentiating neuronal-related from spurious correlations in resting-state-fMRI (rsfMRI). Acquiring multi-echoes (ME) during an EPI readout increases contrast-to-noise, but it can compromise temporal resolution even when combined with multiband (MB). Therefore, whether MBME-EPI is ultimately beneficial for rsfMRI remains unclear. To address this, we collected data at 3T with 2-mm resolution using MBME-EPI and the human-connectome-project MB-single-echo-EPI. Data were evaluated for spectral amplitude, consistency and specificity. MBME-EPI showed significant gains in all quantities when physiological noise and sampling rate were matched between time-series. However, there was no clear gain when different sampling rates were considered.  

Zaheer Abbas, Farida Grinberg, Ezequiel Farrher, Krzysztof Dzieciol, Elene Iordanishvili, Nadim Jon Shah

Two methods – distributions of total free water (FW) content and unrestricted, isotropic water fraction (IWF) were studied in order to establish a possible link between them. MRI protocols were set in order to obtain quantitative FW maps as well as IWF distributions, based on a free water elimination DTI method. Joint histograms reveal strong correlation and suggest the way FW can complement the information obtained from IWF. Combining both modalities (FW and IWF distributions) in presence of pathologies may help to define the pathophysiological basis of different disorders and identify predictors of clinical symptoms.

Thomas Lindner, Naomi Larsen, Olav Jansen, Michael Helle

Selective Arterial Spin Labeling (ASL) is established to perform non-contrast enhanced flow territory mapping. In super-selective pCASL only one artery of interest is labeled while the efficiency in contralateral arteries is near zero.  To obtain a holistic picture of all brain perfusion territories, the label and control experiments have to be repeated for each artery, prolonging scan time. In this study, it is hypothesized that due to the (almost) negligible signal contribution of non-tagged arteries, selective perfusion images can be calculated from a single scan that is performed without the acquisition of control images.

Chuanchen Zhang, Changhu Liang, Chuanying Shi, Mingzhen Wu, Bin Zhang

The goal of the present study was to evaluate ZTE acquisitions for the inferior alveolar neurovascular bundle (IANB) identification. For this purpose, 15 volunteers were scanned using a standard 3D ZTE sequence with a voxel size of 0.8×0.8×0.8 mm on a 3 Tesla MR unit. Both subjective and objective analyses were performed on all acquired IANB images. The results indicate that ZTE-MRI is feasible for the IANB imaging without the use of contrast material.

Xiaopeng Zong, Weili Lin

Pulsatility of blood flow in human perivascular spaces may play an important role in clearing metabolic waste from the brain.  However, flow measurement within small arterioles using MRI are hampered by the limited spatial resolutions of MRI.  We report an approach that can accurately measure flow in sub-voxel tubular structures such as arterioles by combining time of flight and phase contrast MRI.  The accuracy of our method were first demonstrated in a flow phantom study.  Then, flows of penetrating arterioles were obtained in human subjects.  Our results demonstrate the importance of correction of partial volume effects in measuring arteriole flow.

Cheng-Chieh Cheng, William Scott Hoge, Tai-Hsin Kuo, Bruno Madore

A novel quantitative imaging method based on steady-state signals was proposed to simultaneously resolve MR-related parameters.  A special, two-flip angle acquisition was implemented to account for the fluctuations in B₁⁺ field. Furthermore, we developed a motion-resistant sampling scheme to lessen the impact of motion on steady-state signal for in vivo brain scans. A 3D brain imaging that extracts main MR-related parameters such as T₁, T₂, T₂*, M₀, B₀, and B₁⁺ was performed here in less than 12 minutes.

Gregory Simchick, Amelia Yin, Hang Yin, Qun Zhao

The treatment of obesity is clinically significant as it is related to many serious heart diseases and diabetes. Therefore, it is very advantageous to be able to non-invasively monitor whether or not a treatment is effective. Presented here is a method using magnetic resonance imaging (MRI) based water-fat separation, quantitative susceptibility mapping (QSM), and transverse relaxation rate ($$$R_{2}^{*}$$$) to dynamically monitor brown adipose tissue (BAT) activation and the white adipose tissue (WAT) beiging process. In a mouse model, increases in susceptibility between 40-164% and increases in $$$R_{2}^{*}$$$ between 32-71% were observed in intracapsular BAT and inguinal WAT indicating metabolic changes related to BAT activation and WAT beiging.

Eric Van Reeth, Hélène Ratiney, Sophie Gaillard, Michael Tesch, Olivier Beuf, Steffen Glaser, Dominique Sugny

Optimal control RF pulse design has recently been proposed to address the optimization of image contrast in MRI - in order to explore the theoretical contrast bound of a given imaged system. Their use has recently been validated on a real MRI scanner to contrast various in vitro samples. This abstract extends these results to in vivo applications, and shows that contrasts obtained with standard weighting strategies on rat and mouse brains can be improved or inverted. This demonstrates both the interest and flexibility that one can get when using optimal contrast pulses for in vitro and in vivo applications.

Christopher Hasselwander, William Grissom

RF encoding using the Bloch-Siegert shift has the potential to replace conventional gradient encoding with cheaper RF gradients, and can directly replace gradient pulsing in common MRI sequences. However, current implementations require large frequency offsets to prevent on-resonance excitation, which subsequently requires high RF power for encoding as well as separate imaging and encoding RF coils. Here we show that frequency-swept encoding RF pulses enable the use of a single RF coil for imaging and encoding since the frequency offset can be brought much closer to resonance. 

Jinjin Zhang, Michael Garwood, Djaudat Idiyatullin

Recent advances in nanotechnology have allowed for the effective use of iron oxide nanoparticles (IONP) in magnetic nanoparticle hyperthermia for cancer therapy and in cell tracking for immunotherapy. Noninvasive imaging techniques for tracking and quantifying IONPs in-vivo will be necessary for accurate assessment. In this study, we have tested four representative ultra-short T2 sensitive MRI pulse sequences, UTE, ZTE, SWIFT and MB-SWIFT, to compare their performance for measuring IONPs at clinically relevant high concentration range. Multiple performance metrics were evaluated, compared, and summarized. 

Samy Abo Seada, Jo Hajnal, Shaihan Malik

Multiband pulses can have long durations, which can be reduced by applying the VERSE approach to optimize the combination of gradient and RF pulse to make full use of available hardware performance. The resulting time-varying gradients are demanding and can lead to excitation errors on non-ideal gradient systems. In this work we incorporated the measured gradient impulse response function (GIRF) into an iterative VERSE design method and validated the result using simulation and experiments.

Umesh Rudrapatna, Fabian Fluerenbrock, Terence Nixon, Robin de Graaf, Christoph Juchem

Despite numerous improvements in MRI technology, the fundamental gradient hardware has always been designed to generate linear and orthogonal fields. This mould was broken with the advent of DYNAmic Multi-coiIl TEchnique (DYNAMITE), which uses non-linear and non-orthogonal B$$$_{0}$$$ fields for shimming and imaging. Besides vastly expanding the field shaping possibilities, this new technology also promises faster switching and lower eddy currents. For widespread uptake of this technology, proving its suitability for performing widely used contemporary scans like EPI is a must. In this work we share our results from the first successful implementation of DYNAMITE-EPI.

Benjamin Zahneisen, Murat Aksoy, Julian Maclaren

Motion and geometric distortions of EPI acquisitions remain challenging as motion during an fMRI scan affects the stability of the time series in two ways: Rigid motion displaces voxels by “moving” the spins. A change in head orientation and the complex interplay of external and internal susceptibility differences lead to a change in the off-resonance field. In combination with an EPI readout this change in off-resonance field leads to an “apparent” voxel displacement. Here, we propose the simultaneous acquisition of a blip-down navigator with the original blip-up host-EPI sequence which is used to derive a snapshot of dynamic off-resonance changes.

Neville Gai, John Butman

Phase contrast (PC) imaging is commonly employed for mapping velocities in cerebral arteries. This requires a dedicated sequence along with acquisition of two sets of image data. In addition, PC imaging can be compromised by residual eddy currents, motion, selection of velocity encoding value (VENC) and imaging plane in relation to the vessel. In this work, a magnitude based method exploiting the inflow effect was employed to determine velocity in the carotid arteries. A standard 3D T1w SPGR sequence was used eschewing the need for a dedicated sequence. By measuring signal in ROIs at two locations of the artery and jugular vein, velocity independent of B1 inhomogeneity can be derived. The effect of B1+ field was also taken into account. It was shown that the velocity estimated with this technique shows significant correlation with PC based velocity while showing no significant differences in the right and left CAs in 12 volunteers.

Naoharu Kobayashi, Djaudat Idiyatullin, Gregor Adriany, Michael Garwood

In vivo human brain imaging under highly inhomogeneous B₀ field of 250 kHz off-resonance variation over 20 cm is demonstrated. The B₀ field inhomogeneity was generated by mounting a head gradient coil at 36 cm off the isocenter of a 90-cm 4T magnet. Brain imaging was performed with 3D missing-pulse steady-state free precession using the inhomogeneous field gradient for spatial (readout) encoding. Frequency-modulated pulses were employed to excite the widely distributed spin frequencies in the inhomogeneous field with easily achievable RF peak power (~1 kW). By providing combined T₁, T₂, and high diffusion weighting, images with clear delineation of brain anatomy were produced.

Zhiqiang Li, Dinghui Wang, James Pipe

In the conventional MR setting, each contrast is typically acquired with a different scan/sequence, often resulting in long scan time and inter-scan misregistration. Simultaneous multi-contrast imaging has advantages such as good registration, reduced scan time, etc. In this project we propose a hybrid spiral SE technique for simultaneous T1, T2, and PD imaging, with fast scan speed and improved image quality.

Xiaoying Cai, Yang Yang, Xiaodong Zhong, Daniel Weller, Michael Salerno, Frederick Epstein

Cine displacement encoding with stimulated echoes (DENSE) is an accurate strain imaging technique that generally requires breath-holding. We have recently developed a free-breathing method with image-based navigators (iNAVs) that makes use of the localized signal generation property of stimulated echoes (STE) to facilitate the estimation of heart motion due to respiration. However the non-localized echo due to T1 relaxation presents challenges. We propose to use principle component analysis (PCA) to separate the STE and T1-relaxation echo signals and improve the accuracy of motion estimation with iNAVs for free-breathing cine DENSE.

Xiaocheng Wei, Yongchuan Lai

Discrimination between signals from fat and water is of great importance in clinical practice. Chemical saturation, the most widely used fat suppression method, has degraded performance in an in-homogeneity transmit field, and may jeopardize the diagnosis effectiveness. In this abstract, we proposed an improved fat saturation method employing multiple chemical saturation segments. Phantom and volunteer evaluation results show that new method has much less residual lipid signal and can achieve more uniform lipid saturation over big field of view under inhomogeneity condition. Which support the conclusion that proposed method has superior transmit field inhomogeneity immunity.

Chenxi Hu, Dana Peters

Standard parameter mapping methods such as T1 and T2 mapping suffer from long scan time and low resolution due to the need to sample multiple images along the relaxation curve. Here we propose a novel acquisition and reconstruction strategy to improve efficiency by undersampling each k-space frame in the phase-encoding direction. By shifting the undersampling pattern circularly in each time frame, the relaxation signal at spatially distinct voxels is modulated and combined into a single signal, which can be used to reconstruct the parameters by solving a small-size nonlinear equation. This technique is especially suitable for applications where multiple TIs or TEs are needed, and can improve either resolution or acquisition time.

Yulia Shcherbakova, Cornelis A.T. van den Berg, Pim T.S. Borman, Chrit T.W. Moonen, Lambertus W. Bartels

The ellipse fitting approach for simultaneous estimation of the relaxation times T₁ and T₂ from phase-cycled balanced steady-state free precession (PC-bSSFP) has been so far limited to the 3D acquisition mode due to sensitivity to slice profile imperfections. In this work we present the results of a 2D approach which is based on a RF excitation pulse optimization. This minimally affects the ellipse fitting leading to minimal corruption of  T₁ and T₂ quantification from 2D PC-bSSFP data.

Daiki Tamada, Takashi Watanabe, Tomoyuki Takeguchi, Hitoshi Kanazawa

A prepulse for resetting longitudinal and transverse magnetization is proposed in order to accelerate magnetic resonance fingerprinting (MRF) with Cartesian sampling. A pulse sequence was developed based on a steady-state free precession sequence in which the prepulse consists of a set of radio frequency (RF) pulses and gradient spoilers. Simulation and experimental results demonstrated that the prepulse enables fast MRF in the presence of additional sequence modules, such as respiration triggering.

James Korte, Bahman Tahayori, Peter Farrell, Stephen Moore, Leigh Johnston

It is known that steady-state ring-locked trajectories are formed on an elliptical manifold under a constant amplitude and constant frequency excitation envelope. Here we demonstrate that the excitation envelope can be expressed in terms of the spin-system parameters and a target steady-state trajectory, providing control of the magnetisation on the steady-state ellipsoid when spin-system parameters, such as the relaxation constants, are known. Conversely, we exploit this relationship between excitation parameters and unknown relaxation constants to develop a volume relaxometry technique, which can potentially be extended to relaxation mapping due to the elliptical nature of balanced SSFP.

Simone Coppo, Bhairav Mehta, Dan Ma, Yun Jiang, Mark Griswold

Magnetic Resonance Fingerprinting (MRF) is a newly developed approach for accurate and efficient multi parameter mapping. This work proposes a balanced steady state free precession (bSSFP) based MRF framework which introduces different phase cycling (phc-MRF) to compensate for banding artifact induced by B₀ inhomogeneity. The phc-MRF was tested in both phantoms and in vivo. The preliminary results show the robustness of the phc-MRF to banding artifacts while maintaining the precision of parameter estimation and B₀ sensitivity.

Maria Eugenia Caligiuri, Gaetano Barbagallo, Tobias Kober, Umberto Sabatini, Aldo Quattrone, Andrea Cherubini

Reliable in vivo assessment of human substantia nigra (SN) requires highly trained operators and different MRI sequences. Advanced techniques have recently facilitated SN identification, but their acquisition in routine clinical practice may not be feasible. MP2RAGE allows for quantitative T1 mapping with an acceptable acquisition time (< 10 minutes). Moreover, SN can be seen on T1 maps, but not on standard MPRAGE. In this study, we tested the feasibility of semi-automated SN identification on MP2RAGE-derived T1 maps by using a thresholding approach, and compared SN volume and T1 values between healthy controls and patients with Parkinson's disease.

Hanwen Liu, Emil Ljungberg, Erin MacMillan, Laura Barlow, Shannon Kolind, John Kramer, Cornelia Laule

In-vivo microstructural information of myelin in the spinal cord is desirable for studying spinal cord injury and neurodegenerative diseases. We used myelin water imaging combine with Spinal Cord Toolbox to create a standard microstructure template specific to myelin content, so-called myelin water atlas, for healthy cervical spinal cord. The resulting atlas is able to distinguish myelin content in 7 different spinal cord pathways and agrees with well-known anatomical characteristics. Our work shows the potential of using a myelin water atlas as a microstructure reference to visualize demyelination in spinal cord injuries or diseases.

Saeko Sunohara, Satoshi Yatsushiro, Mitsunori Matsumae, Kagayaki Kuroda

To visualize the distribution of the pressure gradients of the cardiac- and respiratory-driven cerebrospinal fluid (CSF), asynchronous two-dimensional phase-contrast velocity imaging was performed in 9 healthy subjects. The pressure gradients were calculated by the Navier–Stokes equations after the total CSF motion was classified into either cardiac or the respiratory components in the frequency domain. In the prepontine, the pressure gradients in the caudal-to-cranial direction were 14.9 ± 3.17 Pa/m for cardiac components and 1.28 ± 0.46 Pa/m for respiratory components; the cardiac pressure gradient was also significantly larger than the respiratory pressure gradient in other regions.

Pim Borman, Rob Tijssen, Bas Raaymakers, Chrit Moonen, Clemens Bos

Golden angle radial sampling allows for flexible sliding window reconstructions while minimizing motion sensitivity and undersampling artifacts. Simultaneous MultiSlice (SMS) can be used to increase the spatial coverage without decreasing the framerate. Here we show that the golden angle profile ordering is in principle not compatible with the in-plane phase cycling scheme required by SMS. It follows that these are only compatible for a certain number of spokes, namely when the number of spokes is part of the Fibonacci sequence and the SMS factor is a divisor of this number.

Valery Vishnevskiy, Georg Spinner, Christian Stoeck, Constantin von Deuster, Sebastian Kozerke

Intravoxel Incoherent Motion (IVIM) imaging is an attractive approach for contrast-agent free in vivo perfusion measurement in the heart. Since the data is acquired during free breathing, nonrigid respiratory motion is considerable and needs to be corrected before estimation of IVIM parameters. In order to provide accurate image registration, an approach with parametric total variation regularization of displacements and low-rank structure of aligned images stack is presented. The proposed method allows for robust IVIM parameter estimation and improves mean squared residuals of the IVIM model by 24% on average compared to state-of-the-art non-rigid registration methods.

Wenjian Huang, Hao Li, Jue Zhang, Xiaoying Wang, Jing Fang

A supervised DCE-MR images classification strategy is proposed in this study. First, the training set was obtained by an automated seeds extraction procedure. Subsequently, support vector machine (SVM) and random walk algorithms were employed as two separate classification approaches to achieve image segmentations, respectively. The automated segmentations and a repeated manual segmentation were compared quantitatively with a reference manual segmentation. The average similarity indexes for SVM, random walker and repeated manual segmentation were 0.78, 0.76 and 0.72, respectively. The results indicate that the proposed strategy yield a satisfied similarity with manual segmentation and is more stable than the manual segmentation. 

Peter Koken, Thomas Amthor, Mariya Doneva, Holger Eggers, Karsten Sommer, Jakob Meineke, Peter Börnert

Efficient, highly under-sampled spiral acquisition is preferred in magnetic resonance fingerprinting (MRF). However, although the spiral is very efficient in terms of sampling, it is sensitive to all kinds of off-resonance effects resulting in signal blurring. This effect leads to geometric distortion and matching errors, reducing accuracy significantly. To overcome these limitations, the present work proposes to combine spiral-based MRF with field map-based deblurring, e.g. by conjugate phase reconstruction (CPR). The basic feasibility of this approach for under-sampled MRF is shown in phantom and in-vivo experiments, underlining the effectiveness of this simple correction approach paving the way for even more efficient MRF sampling.

Camille Van Assel, Gabriel Mangeat, Benjamin De Leener, Nikola Stikov, Caterina Mainero, Julien Cohen-Adad

Partial Volume Effect (PVE) hampers the accuracy of studies aiming at mapping MRI signal in the cortex due to the close proximity of adjacent white matter (WM) and cerebrospinal fluid (CSF). The proposed framework addresses this issue by disentangling the various sources of MRI signal within each voxel, assuming three classes (WM, gray matter, CSF) within a small neighbourhood. MRI scans of 17 healthy subjects suggest robust estimations of PVE, allowing accurate extraction of MRI metrics using surface-based analysis. This method can be particularly useful for probing pathology  in outer or inner cortical layers, which are subject to strong PVE with adjacent CSF or WM.

Michael Perrins, Lucy Hiscox, Calum Gray, Scott Semple, Lucy Barclay, Rachael Kirkbride, Lisa Salisbury, Colin Brown, Timothy Walsh, Edwin van Beek, Neil Roberts, David Griffith

Muscle wasting is common during critical illness.  In this study, thigh muscles of previously mobile patients surviving an episode of severe critical illness were imaged by Magnetic Resonance Imaging (MRI) during convalescence and compared to healthy controls. We present preliminary findings of the first clinical study using Magnetic Resonance Elastography (MRE) to measure muscle stiffness (kPa) and muscle cross-sectional area (mm²) for Intensive Care Unit (ICU) patients. A statistically significant reduction in muscle area and muscle stiffness in patients was found when compared to the healthy control group. There was a significant cross-sectional muscle area increase following ICU patient discharge.

Matthias Schloegl, Stefan Spann, Christoph Aigner, Martin Holler, Kristian Bredies, Rudolf Stollberger

Dynamic arterial spin labeling MRI provides important quantitative information about blood arrival time and perfusion. However, the inherently low signal-to-noise ratio requires repeated measurements to achieve a reasonable image quality. This leads to long acquisition times and hence increases the risk of motion artifacts, which impedes clinical applicability. To overcome this limitation we propose to reconstruct the dynamic ASL data employing ICTGV regularization from a reduced number of averages. The performance of the method is evaluated on synthetic and in-vivo ASL data.

Maolin Qiu, Yuqing Wan, R. Todd Constable

MRI with non-linear spatial encoding magnetic fields (SEM) can provide high quality MR images, but there images are usually calculated using iterative optimization procedures. Such reconstruction methods can take a long time to converge, and the results may depend on the initial iteration parameters. We propose a fast, non-iterative image reconstruction method for O-space imaging based on the local K-space and local SEMs and demonstrate its effectiveness for image reconstruction of nonlinear O-space imaging data.

Lavanya Umapathy, Jonathan Brand, Jean-Philippe Galons, Lars Furenlid, Diego Martin, Maria Altbach, Ali Bilgin

Non-invasive imaging techniques that can identify early structural changes due to fibrosis in vivo are of high clinical importance. In this work, a five-level wavelet decomposition of biopsy confirmed normal and fibrotic ex vivo liver tissues is performed and histogram-based features are extracted from the wavelet subbands. A linear classifier is trained using the top 10 features and applied to classify liver fibrosis in Gadolinium-enhanced delayed phase T1-weighted in vivo images. The results show that normal samples yield low posterior probabilities for fibrosis whereas these values are very high for fibrotic samples. 

Nadège Corbin, Elodie breton, Michel de Mathelin, Jonathan Vappou

MR Elastography (MRE) requires substantial data processing involving phase image reconstruction, wave enhancement and inverse problem solving. The objective of this study is to propose an alternative reconstruction method based on direct k-space data processing, particularly adapted to applications requiring fast MRE measurements such as the monitoring of elasticity changes. Elastograms are directly reconstructed from raw MR data without prior phase image reconstruction, circumventing thereby the delicate step of phase unwrapping. The k-space MRE method shows promising results by providing elasticity values similar to the ones obtained with conventional MRE in phantoms and in vivo in porcine liver. 

Vikas Kotari, Vasiliki Ikonomidou

Accurate image registration is essential for both cross-sectional and longitudinal MR studies. In longitudinal studies aligning same contrast intra-subject images, which are the focus of our work, registration is assumed to be a rigid body problem. This assumption is questionable due to global and local changes in brain volume either due to hydration or atrophy. Consequently, misregistration at the voxel level may occur in these studies, which might lead to subject data being discarded. This misregistration is evident particularly around the cortex. Visual inspection of images is used to determine registration accuracy. While this approach is suitable for assessing alignment of landmark structures, it fails to capture the millimteric or sub-millimetric misregistrations. Automatic metrics can precisely estimate the overall performance of a given registration algorithm by employing an evaluation database. However, to estimate the registration accuracy of a given pair of images, such metrics are unsuitable. In this work we propose texture analysis of a subtraction image to evaluate the registration accuracy of a given pair of same contrast, intra-subject images. Once registered, images are intensity normalized, blurred and subtracted. In the event of registration errors, or violation of the rigid body assumption, the subtraction images have artifacts. The texture features of these artifacts are different from the artifact-free (clean) areas of the subtraction images. Using a texture-based classifier, artifact areas in the subtraction images that indicate failed registration are identified. In addition to determining if the registration has failed, our approach can identify the specific locations of misregistration, which can be corrected, leading to a more inclusive subject data.

Corey Baron, Anjali Datta, Dwight Nishimura

At high field strengths, cardiac cine acquisitions acquired with balanced SSFP can suffer from banding artifacts. To mitigate this issue, dynamically phase-cycled cardiac cine was acquired in a single breathhold with undersampling rates of 4 and 6, and images were reconstructed with a phase-cycle banding profile regularization that exploits redundancy between phase-cycles.

Gopal Nataraj, Jon-Fredrik Nielsen, Jeffrey Fessler

This work introduces a new framework for myelin water fraction (MWF) estimation. We use a novel scan design approach to construct a sequence a fast steady-state sequences and optimize corresponding flip angles and repetition times for precise MWF estimation. We quantify MWF and five other parameters per voxel using a novel method based on kernel ridge regression. We obtain MWF maps in vivo that are comparable to those reported in literature, with possibly shorter overall scan time.

Tom Hilbert, Alexis Roche, Cristina Granziera, Guillaume Bonnier, Kieran O’Brien, Tony Stöcker, Pavel Falkovskiy, Reto Meuli, Jean-Philippe Thiran, Gunnar Krueger, Tobias Kober

We construct a database of normal T2 values by spatially normalizing quantitative maps from healthy subjects into a common space. A low standard deviation across all subjects demonstrates good reproducibility of the T2 values in white matter and deep grey matter. Additionally we adopt a standard voxel-based procedure that compares the quantitative T2 map of a patient to the database and test it on three multiple sclerosis datasets. The obtained z-score maps show that white matter lesions can be detected in the limits of the available resolution and the applied smoothing.

Tobias Hoh, Eduardo Coello, Jorge Carretero Benignos, Axel Haase, Rolf Schulte

Magnetic resonance imaging (MRI) temperature mapping of gases is challenging due to limited sensitivity. In this proof of concept study, proton thermometry methods from tissue temperature monitoring were transferred to ¹⁹F gas MRI.

A phase-dependent ¹⁹F resonance frequency shift temperature mapping is proposed for fluorinated gas at 3T based on a spiral readout to overcome limitations of ultra-short relaxation times.

This work demonstrates the feasibility of 2D thermometry in a canonical setup with inert fluorinated gases.

Tie-Qiang Li, Elaine Lui, Patricia Desmond

In this study we have focused on the development and application of PVC techniques for improving the quantification accuracy of STC with 23Na MRI at 3T. Although PVEs are known to induce errors in quantification, it has not been widely used in 23Na MRI. While different PVC algorithms have been proposed in the PET literature, each method has its limitations and relies on simplified assumptions. The proposed hybrid methods, such as GTM+RBV, aimed to overcome such limitations are most robust.

Antonio Carlos Senra Filho, Gareth Barker, Luiz Otávio Murta Junior, Flavio Dell'Acqua

Reconstruction of the cortical surface is of great importance as a biomarker for many brain diseases, and in recent years a number of advances in image processing and analysis have been made in the cortical reconstruction process. However, despite the scientific community employing a range of advanced surface reconstruction algorithms in order to improve quantitative accuracy, cortical thickness measurement is still a challenge. Here, we address the question of whether a better brain extraction procedure can improve the cortical surface reconstruction. Our analyses suggest that a more accurate brain mask directly affects the global cortical thickness estimate, reducing its quantitative uncertainty.

David Owen, Andrew Melbourne, David Thomas, Joanne Beckmann, Jonathan Rohrer, Neil Marlow, Sebastien Ourselin

Arterial spin labelling (ASL) offers valuable measurements of perfusion in the brain and other organs. However, ASL data have low SNR and are prone to partial volume effects. We present a Bayesian model of anatomically-derived spatial correlation in ASL data (ADRIMO), which improves the accuracy of perfusion estimates and hence improves the analysis of ASL data. The method is assessed experimentally by examining ASL images from a cohort of 130 preterm-born adolescents.

Martin Krämer, Karl-Heinz Herrmann, Silvio Schmidt, Otto Witte, Jürgen Reichenbach

High resolution 3D-RARE imaging at 9.4T can be very challenging due to increased artifacts caused by strong T₂- and Gibbs ringing. In this work, we present the combination of two correction algorithms, local subvoxel-shift unringing and T₂-compensation, to reduce effectively both types of artifacts. For this purpose, the local subvoxel-shift algorithm has been extended to the third spatial dimension and evaluated in healthy mice. 

Guillaume Bonnier, Alexis Roche, Tom Hilbert, Gunnar Krueger, Cristina Granziera, Tobias Kober

We propose a new methodology, which is based on the quantification of region-specific brain tissue-properties to provide personalize maps of brain damage in a single patient. To achieve this aim, we used T1, T2, T2* and MTI maps and applied the method to detect brain abnormalities in multiple sclerosis patients.

Johannes Toger, Tanner Sorensen, Krishna Somandepalli, Asterios Toutios, Sajan Goud Lingala, Shrikanth Narayanan, Krishna Nayak

This study presents a test-retest repeatability framework for quantitative speech biomarkers from static MRI and real-time MRI (RT-MRI), and applies the framework to healthy volunteers (n=8). Repeatability was quantified using intraclass correlation coefficient (ICC) and mean within-subject standard deviation (σe). Inter-study agreement was strong to very strong for static anatomical biomarkers, (ICC: min/median/max 0.71/0.89/0.98, σe: min/median/max 0.90/2.20/6.72 mm), poor to very strong for dynamic RT-MRI biomarkers of articulator motion range (ICC: 0.26/0.75/0.90, σe: 1.6/2.5/3.6 mm) and poor to very strong for velocity (ICC: 0.26/0.56/0.93, σe: 2.2/4.4/16.7 cm/s). The introduced framework can be used to guide future development of speech biomarkers.

Yu Li

A new parallel imaging reconstruction framework is proposed to accelerate MRI using both coil sensitivity and data sparsity. This framework uses random undersampling and performs parallel imaging reconstruction with a k-space variant constraint. No calibration data are needed. It is demonstrated that this new approach offers a gain over conventional parallel imaging in imaging acceleration.

Uten Yarach, Hendrik Mattern, Oliver Speck

The quality of EPI image is intrinsically hindered by Nyquist ghost and geometric distortion which are commonly handled by a 1D non-phase encoded reference and a field map based corrections, respectively. In some cases, a 2D phase reference is required, but scan time is increased. The geometric-mismatch between EPI and coil sensitivities is another concern. Here, the 2D phase correction (without prolonging scan time) and the distortion correction are integrated into a single forward operator rather than considering them consecutively. The results show that the stable reduction in Nyquist ghosting and distortion can improve the tSNR of EPI time series.

Yigit Can, Efe Ilicak, Tolga Çukur

Several successful iterative approaches have recently been proposed for parallel-imaging reconstructions of variable-density (VD) acquisitions, but they often induce substantial computational burden for non-Cartesian data. Here we propose a generalized variable-FOV PILS reconstruction 3D VD Cartesian and non-Cartesian data. The proposed method separates k-space into non-intersecting annuli based on sampling density, and sets the 3D reconstruction FOV for each annulus based on the respective sampling density. The variable-FOV method is compared against conventional gridding, PILS, and ESPIRiT reconstructions. Results indicate that the proposed method yields better artifact suppression compared to gridding and PILS, and improves noise conditioning relative to ESPIRiT, enabling fast and high-quality reconstructions of 3D datasets. 

Haifeng Wang, Jonathan Polimeni, Berkin Bilgic, Lawrence Wald , Kawin Setsompop

Slice-GRAPPA (SG) is often used to reconstruct blipped-CAIPI simultaneous multi-slice EPI data, in particular in conjunction with the dual even-odd kernel approach (SG-DK) to mitigate ghosting related reconstruction artifacts. To achieve good performance in blipped-CAIPI acquisition, the CAIPI shift factor should be optimized in a case by case manner to minimize g-factor penalty. The g-factor is influenced by the reconstruction approach and so far a fast analytical g-factor calculation has been developed only for standard SG reconstruction but not SG-DK, where time-consuming Monte Carlo simulation is still needed. Here we propose an analytical g-factor calculation for SG-DK and demonstrate that the proposed method is fast and accurate. Our simulation and experimental results also highlight the superior performance of SG-DK over SG reconstruction, both in mitigating image artifacts and noise penalty.

H. Christian M. Holme, Frank Ong, Sebastian Rosenzweig, Robin Wilke, Michael Lustig, Martin Uecker

We propose an extension to Regularized Non-Linear Inversion (NLINV), which simultaneously  reconstructs multiple images and sets of coil sensitivity profiles. This method, termed ENLIVE (Extended Non-Linear InVersion inspired by ESPIRiT), can be related to a convex relaxation of  the NLINV problem subject to a low-rank constraint. From NLINV, it inherits its suitability for calibrationless and non-Cartesian imaging; from ESPIRiT it inherits robustness to data inconsistencies.

Zechen Zhou, Chun Yuan

In this work, we incorporated the Feature Refinement (FR) scheme into the Self-supporting Tailored k-space Estimation for Parallel imaging reconstruction (STEP) image reconstruction framework to enhance its capability for structural representation in image domain, and developed a novel Weber Local Descriptor (WLD) method to improve the extraction of local image boundaries. With the preliminary experiments, it has been demonstrated that the improved STEP with WLD FR scheme can provide more accurate estimation of image details in comparison to original STEP and existing classic method.

Chaoping Zhang, Alexandra Cristobal-Huerta, Juan Antonio Hernández-Tamames, Stefan Klein, Dirk Poot

We propose a subsampled interleaved parallel acquisition pattern for Autocalibrated Parallel Imaging Reconstruction for GRASE (APIR4GRASE) which considers different echoes during each refocusing of the GRASE as if they originated from different coil channels. APIR4GRASE eliminates ghosting artifacts caused by the phase and amplitude modulations in traditional GRASE split sampling pattern and achieves an additional acceleration factor of 1.3 compared to a fully sampled GRASE k-space. In addition, multiple contrast (spin echo and gradient echo) images are reconstructed. Experiments on a phantom demonstrate the effectiveness of our method.

Gigi Galiana, Nadine Luedicke

FRONSAC encoding, which adds a rapidly oscillating low-amplitude nonlinear gradient to a standard undersampled trajectory based on linear gradients, has been shown to significantly improve k-space coverage and parallel imaging reconstructions.  This abstract further shows that a fixed FRONSAC waveform improves image quality for Cartesian trajectories of various FOV and resolution, while avoiding many of the pitfalls of other highly efficient gradient trajectories.  Results show that FRONSAC provides better reconstruction than Cartesian encoding alone, while offering better resilience to delays and off-resonance effects than non-Cartesian trajectories, such as spiral.  

Yilong Liu, Mengye Lyu, Ed Wu

MR cardiac cine plays a key role in quantifying the cardiac function. The measurement accuracy is highly dependent of both spatial and temporal resolution, which can be improved substantially by acceleration with parallel imaging. SPIRiT, a GRAPPA-like parallel imaging reconstruction, can be applied to cardiac cine by incorporating temporal sensitivity estimation (TSPIRiT). In this study, we propose to enhance MR cardiac cine using TSPIRiT with generalized data fidelity (GDF) based on the assumption that k-space signal in cardiac cine changes smoothly. Results show that the proposed method can provide better tradeoff between SNR and temporal resolution when compared with TSPIRiT and k-t SPIRiT.

Toygan Kilic, Efe Ilicak, Tolga Çukur, Emine Saritas

Recently, compressed-sensing (CS) was proposed to jointly reconstruct undersampled multi-contrast datasets to exploit the common structural features therein. Here, we propose a method to improve joint reconstruction of multi-contrast acquisitions. Inspired by the SPIRiT framework for parallel imaging, our method linearly synthesizes missing data for each contrast from neighboring k-space data for all contrasts. To improve reconstruction quality, the proposed method high-pass filters calibration data to emphasize the weight of intermediate spatial frequencies in the interpolation operator. Phantom and in vivo results at 3T indicate that the proposed method outperforms reconstructions with conventionally estimated interpolators. 

Sen Jia, Yanjie Zhu, Lei Zhang, Yiu-cho Chung, Jing Cheng, Leslie Ying, Xin Liu, Hairong Zheng, Dong Liang

The nonlinear relationship between missing and acquired data in k-space has been proved in nonlinear GRAPPA. In this work, we propose nonlinear SPIRiT which integrates the polynomial kernel method into SPIRiT via a simple second-order virtual coil approach. The proposed method represents the relationship between missing and acquired data in k-space of SPIRiT using a more accurate nonlinear model. In vivo results demonstrated that nonlinear SPIRiT could suppress aliasing artifact or noise better than SPIRiT, and was applicable to more acceleration scenarios than nonlinear GRAPPA.

Joelle Sarlls, S. Lalith Talagala

It has been shown that the temporal SNR (tSNR) of GRAPPA EPI can be improved by using different autocalibration scan (ACS) acquisitions. We evaluated the impact of using FLASH-ACS for high resolution, GRAPPA accelerated EPI at 7T.  We compared the tSNR, ghost levels and distortions characteristics of EPI data reconstructed using SSEPI, MSEPI and FLASH based ACS at different acceleration factors and resolutions. Results showed that the tSNR of GRAPPA accelerated EPI improved by 60-100% when using FLASH-ACS data during image reconstruction.  FLASH-ACS reconstructions also had less residual EPI ghost and identical image distortions compared to SSEPI-ACS and MSEPI-ACS.

Wajiha Bano, Arnold Julian Vinoj Benjamin, Ian Marshall, Mike Davies

The utility of MR parametric mapping is limited due to the lengthy acquisition time. A Maximum Likelihood Estimation (MLE) and Parallel Imaging (PI) method is presented for MR parameteric mapping. The approach is based on a high Signal to Noise ratio (SNR) assumption such that the noise can be modelled as Gaussian and estimates the parameters that maximizes the signal from a multichannel coil. The method was tested on a multi-echo gradient-echo T2* mapping experiment in a phantom and a human brain. Accurate T2* maps were reconstructed up to an acceleration factor of 6 with a small error for phantom and human brain.

Yu Ding, Renjie He, Qi Liu, Renkuan Zhai, Guobin Li, Jian Xu, Weiguo Zhang

We propose a novel method to improve GRAPPA reconstruction when blood vessel pulsation artifacts appear. It removes the artifacts in the ACS lines, and boosts the SNR of GRAPPA reconstruction. Volunteer study confirmed that the proposed method improved image quality of GRAPPA reconstruction in 3T FSE knee scan.

Efrat Shimron, Andrew Webb, Haim Azhari

We introduce a new method combining Compressed Sensing (CS) and parallel MRI (pMRI) for fast MRI acquisition. The method, termed SPID-CS, is advantageous over existing methods since it (1) produces a high-quality initial reconstruction, (2) avoids aliasing related to sub-Nyquist sampling by joining information from different coils, (3) enables flexible k-space sampling, (4) converges much faster than conventional CS and (5) enables clinical real-time reconstruction due to its extremely short runtime. 

Ying Chen, Lisha Yuan, Yi Sun, Jianhui Zhong

Single-shot spatiotemporally encoded (SPEN) MRI is a novel fast imaging scheme with remarkably reduced geometric distortions at high field compared to conventional single-shot EPI. The k-space along SPEN dimension is undersampled, resulting in aliases at regions of rapid profile variation. The feasibility of utilizing sensitivity profiles of array receiver coils to unravel the undersampling aliases is investigated. High resolution relative sensitivity profiles can be obtained from multicoil 2D polynomial fitting of the SPEN reconstructed images without additional reference scans. The effectiveness of the SPEN SENSE strategy is validated by healthy human brain scans at 3T.

Gilad Liberman, Eddy Solomon, Michael Lustig, Lucio Frydman

Spatio-temporal encoding (SPEN) delivers single-scan images with increased robustness to shift and susceptibility artifacts. These acquisitions are usually carried out in a “hybrid” mode that prevents a sufficiently dense sampling along the SPEN domain. Alleviating this resolution loss had so far demanded the acquisition of multiple interleaved scans. The present study demonstrates that by relying on multiple sensors, a similar resolution enhancement can be achieved in a single shot. The principles and potential of the ensuing Super-resolved SPEN with SENSE (SUSPENSE) is demonstrated, with sub-mm single-shot 3T image acquisitions on phantoms and humans.

Franciszek Hennel, Maria Engel, Lars Kasper, Bertram Wilm, Klaas Pruessmann

Spiral readout was used to accelerate the standard T1-weighted 3D head scan based on MPRAGE at 3 Tesla without any compromise on images quality. The encoding model used by the reconstruction included the static magnetic field map as well as the k-space trajectory and a dynamic field correction provided by a field camera. The study demonstrates the utility of state-of-the-art spiral scanning for routine MRI applications.

Jolanda Schwarz, Daniel Brenner, Eberhard Pracht, Tony Stoecker

In this work, a GRAPPA-based reconstruction for wave-CAIPI acquisitions is presented. 16-fold accelerated full brain MPRAGE images with 1 mm isotropic resolution and high image quality are measured in 45 seconds and a clear improvement compared to Cartesian CAIPIRINHA sampling can be observed. It is demonstrated that optimization of the gradient waveforms further improves image quality.

Hassan Shahzad, Hammad Omer

The proposed work presents a combination of GRAPPA and Compressed sensing (POCS) to reconstruct MR images from the highly under-sampled data. Firstly, GRAPPA is applied to the acquired under-sampled data. The output of GRAPPA which contains aliasing artifacts (especially for high acceleration factors) is fed in to POCS which solves for the solution image iteratively and produces a reconstructed image with minimal aliasing artifacts. The reconstruction results are compared with GRAPPA and POCS separately. The results show that the proposed method significantly reduces the aliasing artifacts as compared to GRAPPA or POCS reconstructions.

Nikolaos Kallistis, Kai Tobias Block, Robert Grimm, Hersh Chandarana, Ian Rowe, Steven Sourbron

Golden-angle radial sparse parallell (GRASP) MRI uses temporal regularization in the reconstruction, which risks distorting temporal profiles and reducing DCE-MRI parameter accuracy and precision. The aim of this study is to investigate this issue for liver DCE-MRI by measuring kinetic parameters on data reconstructed at variable temporal resolution. The results depend on temporal resolution according to well-known patterns also observed in simulations and fully sampled data. A systematic error remains at the highest temporal resolution, but this is more likely due to well-known issues of signal saturation. Image reconstruction at lower temporal resolution risks degrading diagnostic image quality due to the mixing of images with different contrast. We conclude that: (1) temporal regularization in GRASP is unlikely to induce significant error in kinetic parameters; (2) images should be reconstructed at high temporal resolution around 2-4s.

Olivia Stanley, Ravi Menon, L Klassen

Fitting the relative B₁^- maps derived from a B₁⁺ shim acquisition to the Helmholtz equations allows for the calculation of absolute B₁^- maps. The sensitivity profiles can then be used to optimally combine coils in subsequent acquisitions. In addition, absolute B₁^- maps allow for the removal of the receive sensitivity from the combined images. This was validated in a GE-EPI sequence and found to produce images with lower phase standard deviation and increased temporal signal-to-noise ratios across the brain. Both of these differences were found to be statistically significant in a Student’s t-test. 

Yulin Chang, Marta Vidorreta, John Detre

Self-consistent parallel imaging (SPIRiT) is a self-calibrated, iterative parallel imaging technique that is not restricted by a particular k-space sampling pattern. 3D SPIRiT takes advantage of the 3D arrangement of a modern receive array to further improve image quality. Although SPIRiT was shown to yield higher image quality than does GRAPPA, especially at acceleration factors higher than 2, its signal-to-noise behavior has not been rigorously studied. In this study we investigate the image quality behavior of 3D SPIRiT and determine the optimal condition for best image quality.

Jing Cheng, Sen Jia, Lei Zhang, Yanjie Zhu, Yuanyuan Liu, Leslie Ying, Xin Liu, Hairong Zheng, Dong Liang

Depicting the vessel wall of intracranial arteries at high resolution and contrast is important to evaluate the intracranial artery disease. This paper propose a feature refinement strategy for improving the reconstruction quality of intracranial artery vessel wall by incorporating the feature descriptor into the reconstruction framework of L1-SPIRiT. Results on in vivo MR data have shown that the feature refinement method is capable of reconstructing the vessel wall with higher contrast than the method without feature refinement, and thus presents great potential for MR vessel wall imaging.

Chen Cui, Abhay Shah, Xiaodong Wu, Dan Thedens , Mathews Jacob

A 3D Rapid, GlObally Optimal Surface Estimation (R-GOOSE) algorithm for fat-water decomposition in MRI is proposed. The fat-water separation is formulated as an optimization problem with data consistency and field-map smoothness penalty. The data consistency only contains exact minimizers from the fully discretized field-map value volume. The proposed method employs a connectivity-reduced graph construction that enables the new formulation to be solved efficiently. The method is validated by the 17 datasets from the 2012 ISMRM Challenge with thirty-fold computational gain compared to our previous method GOOSE while the high quantitative accuracy is maintained. Fat fraction maps obtained from the proposed method also provides a good marker for degenerative muscle diseases in newly collected lower limb datasets. 

Maximilian Diefenbach, Stefan Ruschke, Dimitrios Karampinos

The purpose of this work is to develop a generalized formulation to study the parameter estimation of complex MR signals and its multi-species components.

Slavka Carnicka, Kathryn Keenan, Elizabeth Mirowski, Mark Brown, Christopher Suiter, Tara Fortin, Hannah Erdevig, Karl Stupic, Stephen Russek

Phase-based magnetic resonance thermometry is used for monitoring minimally invasive ablation therapies like focused ultrasound therapy. MRT is prone to errors when applied in tissues with high fat content (e.g. breast tissue, fatty liver) due to heat-induced susceptibility changes. Therefore, there is a need for developing well characterized adipose tissue mimics that could serve as standards for validation of MRT techniques. In this study we showed that all measured adipose tissue mimics are representative of human adipose tissue with similar chemical spectra and thermal dependence of susceptibility shift and are reproducible standards for human adipose tissue validation MRI techniques.

Weitian Chen

In conventional T1rho imaging, the fat signal is usually suppressed to avoid image artifacts and quantification errors. It is desirable to acquire both water and fat images for certain diseases. In this work, we present an approach to use spectrally selective spin-lock pulses to achieve T1rho quantification with simultaneous fat-water imaging. The theoretical analysis is provided with proof on numerical phantoms.  

Naoyuki Takei, Kang Wang, Lloyd Estkowski, Ken Arai, Mitsuhiro Bekku, Hiroyuki Kabasawa, Ersin Bayram

DISCO (Differential Subsampling with Cartesian Ordering) is high spatial-temporal imaging technique with Dixon based fat suppression for 3D volumetric Abdominal imaging. We developed DISCO with frequency selective presaturation pulse for fat suppression (FatSAT) called FatSAT DISCO. The feasibility study explores the computational advantage of FatSAT DISCO in accelerating scan time with compressed sensing technique and demonstrated that it is a promising technique for achieving faster imaging for 4D dynamic MR imaging with robustness to image artifact and light computation demand for clinical use.

Steve Hui, David Yeung, Winnie Chu

Liver fat contents measured by magnetic resonance spectroscopy and chemical-shift water-fat separation imaging were compared in a group of obese adolescents. Distribution of fat in left and right liver lobes was also compared. Results demonstrated that fat contents obtained from both MR modalities were highly correlated and agreed to each other. In obese adolescents with non-alcoholic fatty liver disease, fat distribution was non-uniform between left and right lobes. This study supports the use of fat-fraction map to measure liver fat, which can shorten the scanning time by acquiring information about body adipose tissue and liver fat within a single sequence.   

Brandon Campbell, Gregory Simchick, Hang Yin, Qun Zhao

Determining the volume and distribution of white adipose tissue (WAT) and brown adipose tissue (BAT) by magnetic resonance imaging (MRI) is clinically important. Previous WAT and BAT classification has relied on using fat fraction and proton relaxation time via fixed multi-peak spectroscopic models. However, the recently proposed Multi-Varying-Peak MR Spectroscopy (MVP-MRS) model allows for the selection of appropriate classification features for differentiation between WAT and BAT. Furthermore, these multi-peak features allow prediction of a ‘browning’ or ‘beigeing’ process of WAT by using a Support Vector Machine (SVM) learning algorithm. 

Michael Mendoza, Joseph Valentine, Neal Bangerter

In this work, we present a novel technique that combines the advantages of bSSFP with Dixon reconstruction in order to produce robust water fat decomposition with high SNR in a short imaging time, while simultaneously reducing banding artifacts that traditionally degrade image quality. 

Carlos Sing-Long, Cristobal Arrieta, Curtis Wiens, Diego Hernando, Sergio Uribe

We propose an algorithm based on a Gauss-Newton Trust-Region algorithm that estimates the field map and water and fat concentrations in two steps for all pixels at once. The results are comparable to those obtained with the state-of-art methods.

Noura Azzabou, Harmen Reyngoudt, Pierre Carlier

The purpose of this work was to study the impact of fat model on the quantification of fatty infiltration in skeletal muscle. To this end, we acquired multi-echo 1H-NMRS from 23 subjects affected by an inflammatory myopathy and measured the lipid spectrum of each subject. We also acquired 3D gradient echo volumes at different TEs. Fat and water maps were reconstructed in two cases: (i) with a unique mean fat model (ii) with a fat model specific to each subject. The results of comparison showed a good agreement between both methods and the difference never exceeded 4%.

Xiaoqi Wang, Li Xu, Xiaoguang Cheng

An error analysis was carried, under frame work of Bayesian probability theory, for fat quantification using multiple gradient echo sequences to separate water and fat content in MRI signal. The results confirm that this method is accurate when protocols are carefully designed; this analysis also provides guideline in designing parameter settings to achieve optimal accuracy in fat quantification measurements. 

Jie Ding, Patricia Thompson, Yi Gao, Marilyn Marron, Betsy Wertheim, Maria Altbach, Jean-Philippe Galons, Denise Roe, Fang Wang, Gertraud Maskarinec, Cynthia Thomson, Alison Stopeck, Chuan Huang

Breast density (BD) is a risk factor for breast cancer, which makes the accurate measurement of BD a priority. Mammography is most widely used for BD determination (MG-BD) but ionizing radiation prohibits its use. BD derived from fat-water decomposition MRI (FWMRI-BD) has been proposed. Here we developed an optimized FWMRI-BD measurement (FraG+W) and compared it to MG-BD and a previous FWMRI-BD measurement (Fra80/90). Both FWMRI-BD measures were strongly correlated with MG-BD and exhibited superior test-retest reliability. The proposed automated FraG+W, which quantifies the entire fibroglandular and water content of the breast, is more accurate and reliable than the previous Fra80/90. 

Junying Cheng, Yingjie Mei, Biaoshui Liu, Xiaoyun Liu, Wufan Chen, Yanqiu Feng

The phase information is widely used, for example water-fat separation, susceptibility imaging, etc.   The phase-unwrapping methods are generally needed to estimate the underlying true phase from the principal period (-π, π]. While current phase-unwrapping methods are affected by noise, rapid phase change and disconnected regions. This paper presents an algorithm combined a wrapping identification scheme by thresholding the difference map between the local variations between phasor and wrapped phase, with the local polynominal surface fitting to merge the disconnected components and estimate the phase value of residual pixels in quality guidance region-growing way.  The results demonstrate the proposed method provides an accurate and reliable unwrapped results and has potential application to phase-related MRI in practice.

Nathan Roberts, Diego Hernando, James Holmes, Curtis Wiens, Scott Reeder

The purpose of this work was to characterize the noise distribution of proton density fat fraction estimation and provide alternatives to averaging for unbiased estimation.  Monte-Carlo simulations and phantom experiments were used to validate the theoretically derived noise distribution. Results demonstrated that at low SNR, median and Nelder-Mead fitting algorithm estimators have reduced bias compared to the mean estimator.

Lena Trinh, Pernilla Peterson, Emelie Lind, Lars Olsson, Sven Månsson

The most common method for fat-water separation nowadays is chemical shift-encoded imaging (CSEI). However, when studying fat accumulation in skeletal muscles and high spatial resolution fat fraction (FF) images are desired, CSEI might be challenging due to the increased inter-echo spacing. Here, three alternative methods based on T2-relaxation times, have been explored and compared to CSEI by calculating the muscular fat fraction of ten healthy volunteers. All T2-based methods resulted in qualitatively improved high-resolution FF images compared to CSEI, while a 2-parameter non-linear least square fit showed best quantitative agreement to low resolution CSEI.

Manuel Schneider, Felix Lugauer, Dominik Nickel, Brian Dale, Berthold Kiefer, Andreas Maier, Mustafa Bashir

MRI is not only capable of quantifying the fat content, but also the fatty acid composition of human adipose tissue. Especially for low fat fractions, fatty acid quantification is sensitive to image noise. Including prior information or additional parameter approximations into the quantification method helped to improve the noise propagation behavior, but also introduced a systematic bias. Performing spectral denoising in between image reconstruction and fatty acid quantification kept the systematic bias as well as the noise in the parameter maps low, and hence allows for more flexible protocol selection and shorter acquisition times.

Thobias Romu, Patrik Tunón, Fredrik Uhlin , Micael Gylling, Mårten Segelmark, Anders Fernström, Olof Dahlqvist Leinhard

This work introduces a signal model for imaging of the local hydration of lean tissue, based on water-fat separated MRI. The signal model is calibrated on a healthy cohort and then evaluated on a cohort of hemodialysis patients.

Jong Bum Son, Colleen Costelloe, Ken-Pin Hwang, Tao Zhang, Ersin Bayram, John Hazle, Jingfei Ma

The conventional spin-echo (SE) sequence produces the best available T1-contrast and is often used for imaging of brain, head and neck, and spine. Unfortunately, the inclusion of fat suppression pulses in an SE acquisition substantially reduces the number of slices per TR and therefore the overall scan efficiency.  In this work, we developed a flexible spin-echo triple-echo Dixon (flexible STED) technique that enables SE Dixon imaging with high efficiency. The feasibility of the technique is demonstrated with in vivo post-contrast fat-suppressed T1-weighted imaging of spine.

B. Dustin Pooler, Jeannine Ruby, Diego Hernando, Ann Shimakawa, Scott Reeder

Chemical shift encoded (CSE-MRI) techniques have been previously validated for the measurement of liver proton density fat fraction (PDFF), which serves as a biomarker for liver fat content.  However, current CSE-MRI techniques rely upon 3D volumetric or 2D interleaved acquisitions, both of which are sensitive to motion and require the patient to suspend respiration.  In this study, we demonstrate the feasibility of a "single shot" 2D sequential CSE-MRI technique to freeze motion. 2D sequential CSE-MRI demonstrates superior performance during free breathing when compared to 3D and 2D interleaved acquisitions.

Cheng Hong, Gavin Hamilton, Catherine Hooker, Charlie Park, Calvin Tran, Jeffrey Schwimmer, Scott Reeder, Claude Sirlin

Non-zero proton density fat fraction (PDFF) is commonly observed in the spleen on chemical-shift-encoded MRI. A prospective assessment in 42 research subjects with no visible fat peaks on MR spectroscopy demonstrated small amounts of splenic fat (PDFF up to 4%) using four different MRI-based fat fraction estimation techniques. These measurements were poorly correlated with each other, implying that fat measurements in spleen are likely artifactual rather than representing true splenic fat.

Chloe Hutton, Michael Gyngell, Matteo Milanesi, Michael Brady

We compared standard Dixon and T2* relaxometry with “IDEAL” for measuring liver proton density fat fraction (PDFF) and T2*, surrogate metrics for steatosis and iron burden respectively. Results in 118 UK Biobank study participants showed very good correlation between the two methods. Dixon PDFFs were consistently lower than IDEAL PDFFs, explained by the 20° flip angle used for Dixon, introducing a T1 bias and deviation from true PDFF values. Results also showed improved image quality for IDEAL, highlighting the strength of this technique to serve as a reliable and simultaneous biomarker of liver fat and iron overload.  

Zahra Hosseini, Junmin Liu, Maria Drangova

Multi-echo gradient echo MR imaging enables the generation of quantitative B₀, fat fraction and R₂* maps, from which tissue can be characterized. When applied to cardiac imaging these methods face the challenge presented due to the large susceptibility differences between lung and heart. We present a novel post-processing pipeline for multi-echo GRE phase images that processes the phase data prior to channel combination to enable generation of robust quantitative cardiac maps enabling accurate tissue visualization and characterization.

Krishna Kanth Chitta, Bhanu Prakash KN, Suresh Sadananthan, Sendhil Velan S

Uniform distribution of intensity values for a given tissue type is desirable for accurate segmentation and quantification.  Factors like non-uniform static magnetic field, motion artifacts, and inconsistent RF coil sensitivity introduce intensity inhomogeneity during MR image acquisition.   Several methods for intensity inhomogeneity correction are proposed in the literature. We explored the suitability of Biased fuzzy C-means (BFCM) correction for quantification of abdominal fat from Dixon images.  In our study we formulated a new 2-pass, 2D (intra-slice and inter-slice) BFCM framework for improved segmentation and quantification of abdominal fat.

Kirsten Koolstra, Jan-Willem Beenakker, Peter Koken, Thomas Amthor, Andrew Webb, Peter Börnert

MR imaging of the eye requires a sequence of scans with different contrast to provide the necessary information on ocular conditions. In this study we apply Cartesian MR fingerprinting in the eye at 7T to add quantitative information to the standard clinical protocol, with the final goal of advancing disease diagnosis. 

Christopher Mirfin, Stephen Bawden, Paul Glover, Penny Gowland, Richard Bowtell

We investigate the performance that can be achieved by applying volume and slice shimming on the commonly-used Nova 8-channel transmit/32-channel receive head coil, whilst controlling the total transmit power, as a proxy for global SAR. Under this constraint, our results suggest that shimming on individual axial slices can significantly improve the achievable B1 field uniformity (39.0% ± 3.9%) for the same transmit power as normal quadrature mode.

Daniel Stäb, Markus Barth

3D planes-on-a-paddlewheel (POP) EPI is a non-Cartesian readout scheme realized by rotating EPI readout planes about the phase encoding axis. We show that the additional use of echo-asymmetry allows for significant improvements in spatial resolution without negative effects on echo-time, dropouts and distortions. The concept called POP-ART was evaluated at 7T. Whole brain images were obtained at a spatial resolution of 0.78x0.78x1.0mm³ within less than 1 minute by using an echo-asymmetry of only 28%. Being faster spoiled gradient-echo and providing resolutions not achievable by corresponding Cartesian EPI techniques, the trajectory is of interest for T2* weighted or quantitative susceptibility imaging.

JM Spijkerman, HJ Kuijf, WH Bouvy, MI Geerlings, J Hendrikse, PR Luijten, JJM Zwanenburg

Currently, perivascular spaces (PVS) are mostly investigated with qualitative measures. In this work, PVS in the centrum semiovale were tracked using a semi-automatic method, and PVS length and tortuosity were determined. Univariate and multivariate linear regression was performed for age, number of tracked PVS, PVS length, and PVS tortuosity. The results show that quantitative assessment of PVS beyond counting is feasible, and a significant positive association between PVS length and the number of tracked PVS was found. These quantitative measurements may be more suitable than qualitative methods to investigate PVS. 

Yi-Fen Yen, Kathryn Keenan, Karl Stupic, Andre van der Kouwe, Jonathan Polimeni

We are reporting quantitative T1 values of the NIST T1 phantom at 7T for the first time by using IR-SE method. We also compared the accuracy of T1 mapping by using MP2RAGE and variable flip angle (VFA) methods against the IR-SE T1s at 7T and found MP2RAGE gave more accurate T1 measure than VFA, for T1 of 300 ms to 2000ms (the range of brain T1). Although the accuracy of MP2RAGE at 7T was not as good as that at 3T (also shown), MP2RAGE is a promising technique for accurate brain T1 mapping at 7T within a clinically acceptable scan time. 

Peng Cao, Shuyu Tang, Xucheng Zhu, Andrew Leynes, Angela Jakary, Peder Larson

In this study, we aimed to explore accelerated acquisition of multi-contrast 3D images with different magnetization preparation times. We combined shuffled acquisition in k-space, parallel imaging, compressed sensing and pixel-wise low rank Hankel matrix reconstruction, achieving reconstruction of tens of multi-contrast 3D images from three 3-minute scans.  

Guillaume Bonnier, Kieran O'Brien, Pascal Sati, Mario Fartaria, Jon Polimeni, Alexis Roche, Daniel Reich, Gunnar Krueger, Cristina Granziera

We performed an analysis of the cortex organization of 10 healthy subjects using partial volume information. Tissue concentration were estimated using a novel algorithm applied to 7T MP2RAGE high resolution images (0.75mm), and ultra high resolution (0.35mm). We identified 3 distinct layers characterized by presence of WM-like signal (inner layer), only GM (central layer) and GM/CSF partial volume (outer layer).

S. Johanna Vannesjo, Yuhang Shi, Irene Tracey, Karla Miller, Stuart Clare

Spinal cord imaging would benefit from the SNR increase at ultra-high field, to depict small structures inside the cord. However, higher background field strengths also increase susceptibility-induced B₀ field distortions, causing image distortions and signal dropouts. To improve field homogeneity, we here implement slice-wise first-order shimming in the cervical spinal cord at 7T. The slice-wise shim settings were calculated based on a B₀ field map and a semi-automatically generated spinal cord mask. We demonstrate that the slice-wise shims can improve signal levels in a high-resolution anatomical multi-echo GRE sequence.

Christian Anderson, Charlie Wang, Yuning Gu, Yun Jiang, Dan Ma, Mark Griswold, Xin Yu, Chris Flask

Magnetic Resonance Fingerprinting allows for rapid, simultaneous multi-parametric quantification. The use of a FISP imaging kernel is necessary due to field inhomogeneity in human body and preclinical imaging. We have observed that increases in the applied gradient moment lead to gradient moment size dependent changes in T2 accuracy. By examining different applied gradient moments we illustrate this loss of T2 accuracy while T1 measurement accuracy is maintained. This has implications for FISP MRF design and the implementation of unbalanced gradient moments for quantification.

Xi-Nian Zuo, Yin-Shan Wang, Dan-Yang Sui, Xiu-Xia Xing

We employed the test-retest HCP datasets scanned at both 3T and 7T scanners from a same group of 62 healthy adults to compare differences in common functional metrics of the human connectome between 3T and 7T rfMRI settings in terms of their regional variations, individual variability and test-retest reliability. Our findings revealed metric-specific differences in both spatial patterns and reliability between 3T and 7T scanners whereas 7T improves reliability of global metrics but reduces reliability of local metrics of the functional connectomes.

Ayodeji Adams, Peter Luijten, Jaco Zwanenburg

Cardiac induced brain tissue pulsatility holds potential as a means to study the viscoelastic properties of the aging brain. In this study we measured the brain tissue motion in 8 healthy volunteers with DENSE at both 7T and 3T, and assessed the gain in SNR between field strengths. 4D SNR maps for both field strengths were made and examined with a robust histogram analysis. The mean SNR for all volunteers at 7T and 3T was 21.2 ± 6.3 and 7.1 ± 2.5  respectively. The higher SNR at 7T will likely yield greater accuracy in quantifying brain tissue pulsatility.

Yuta Urushibata, Hideto Kuribayashi, Junko Inoue, Tobias Kober, John Grinstead, Tomohisa Okada

Fluid and white matter suppression (FLAWS) is a technique to suppress cerebrospinal fluid (CSF) and white matter (WM) using the MP2RAGE sequence, which has been introduced for 3T.  In this study, FLAWS was applied at 7T and compared to a SPACE double inversion recovery (DIR).  Inversion times of the sequences were optimized for volunteer brain images at 7T.  FLAWS showed better suppression of CSF and WM, more homogeneous gray matter (GM) delineation, as well as better GM/WM contrast compared with DIR.

Willy Gsell, Uwe Himmelreich, Cindy Casteels, Christophe Deroose, Antonio Gonzalez, Albert Aguilar, Carlos Correcher, Emilio Gimenez, Cesar Molinos, Ramiro Polo, Thorsten Greeb, Ralph Wissmann, Sven Junge, Jose Benlloch

We designed a novel PET insert based on monolithic LYSO crystals. From our first evaluation, we can conclude that sub-millimeter detector spatial resolution, combined with accurate photon DOI determination, make it possible to acquire high resolution reconstructed images. This enables us now to combine simultaneously high resolution and sensitivity PET with high field preclinical MRI to extract simultaneously complex data from anatomical to molecular information and to dynamically follow non-invasively animal models of different pathologies with no compromise in performance of each imaging modality.

Jinhyeok Choi, Hyeonjin Kim

A balanced steady-state-free-precession (bSSFP) sequence may be preferred in magnetic resonance fingerprinting (MRF) for its high SNR. However, as demonstrated recently at 3.0T, the echo formation in bSSFP is hindered by randomly varying flip-angles in a B0-dependent manner, and yet, the destroyed spin-echo-like signal behavior can be restored by tailoring sequence timings according to varying flip-angles such that the spin ensemble is driven into a pseudo-steady-state. Given more severe B0-inhomogeneity at high-field, we explored the efficacy of the pseudo-steady-state-free-precession (pSSFP) sequence in MRF (pSSFP-MRF) at 9.4T. Our results suggest that pSSFP-MRF has great potential for single-scan multiparameter mapping at high-field.

Sankar Seramani, Lydiane Hirschler, Boominathan Ramasamy, Sakthivel Sekar, Kishore Bhakoo, Emmanuel Barbier, Kuan Lee

Arterial Spin Labeling (ASL) is a non-invasive MRI technique which can be used to measure quantitative renal perfusion without the injection of contrast agents. The goal of this study is to compare the performance of pCASL with FAIR in measuring Renal Blood Flow in mouse kidney at Ultra High Field (UHF) MR. Based on our experimental results, pCASL based perfusion measurement shows similar reproducibility when compared to FAIR method. pCASL shows better SNR sensitivity and lower in ROI variation of RBF in the kidney when compared to FAIR based ASL method at 9.4 Tesla.

Ruomin Hu, Matthias Malzacher, Mathias Davids, Andreas Neubauer, Simon Konstandin, Lothar Schad

³⁵Cl MRI has been of interest for both human and animal in vivo applications to visualise chloride homeostatic changes. In this study we performed measurements of resolution phantoms at an isotropic resolution of 0.490 and 0.326 mm using scanner-equipped ultrashort echo time 3D (UTE3D) and newly implemented density-adapted 3D projection reconstruction (DA-3DPR) sequences with subsequent spatial resolution analysis. DA-3DPR images with visibly higher SNR are capable of resolving both gross and fine structures with more reliable signal distributions and more consistent rendition of structure shapes. Moreover, penalty-free radial oversampling leads to more extended artefact-free regions, allowing for smaller FOVs and reduced measurement times.

Sankar Seramani, Lydiane Hirschler, Emmaneul Barbier, Kuan Lee

The objective of this study was to show the feasibility of performing ASL based high resolution perfusion imaging in the mouse brain at 9.4 Tesla. In this work we applied   pCASL with phase optimization technique at the labeling plane to minimize the effect of B0 inhomogenity . We used fcFLASH based technique to measure the labeling efficiency of pCASL sequence and compared the labeling efficiency with FAIR ASL in mouse brain. Based on our results, with the proposed method of phase optimization, labelling slice can be place away from the iso-center of the magnet. This will allow us to place the imaging slice at the isocenter, which has showed significant improvement in the image quality of the mouse brain at ultra-high field strengths.

Yasuhiko Terada

Magnetic resonance fingerprinting (MRF) is a technique that enables simultaneous quantification of tissue parameters in a single scan. So far, MRF has been realized mostly for clinical 1.5 T and 3 T scanners, and a preclinical 7 T scanner. Application to a higher field scanner is limited and challenging because of the increased sensitivity to system hardware imperfections, such as B0 and B1 inhomogeneities and slice-profile imperfection. In this study, we assessed the feasibility of the MRF approach in a preclinical, wide-bore 14.1 T system.

Andrew Leynes, Melanie Morrison, Angela Jakary, Peder Larson, Janine Lupo

To introduce and evaluate a novel strategy for iterative combination of bias-corrected fuzzy c-means (BCFCM) and N4 bias correction for robust bias correction and segmentation in 7 Tesla brain imaging studies.

Joep Wezel, Jan-Willem M. Beenakker

Mascara has been proposed as a simple approach to correct for eye-motion artefacts via detection of induced B₀ changes when blinking. In this study we measure the B₀ changes from 10 different types of mascara. We can differentiate three different categories of mascara, in which in violation of Murphy’s law the cheapest brands result in the strongest B₀ field changes.

Xianchang Zhang, Qi Yang, Qingle Kong, Zhaoyang Fan, Jing An, Rong Xue, Zihao Zhang

TOF-MRA at 7T ultra-high field has been proven to have advantages in imaging the perforating arteries originating from the middle cerebral artery. In this study, a novel method of VOI-based micro-vessel density measurement was developed to quantitatively assess the blood flow in subcortical nuclei. Using this technique, the vascular density (VD) of specific basal ganglia sub-regions can be evaluated. Preliminary results showed that VD values of specific nuclei were different among Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalophy (CADASIL) patients, stroke patients, and healthy volunteers. VOI-based micro-vessel density measurement may be useful in differentiating the etiology of cerebral small vessel diseases.

Arian Beqiri, Hans Hoogduin, Alessandro Sbrizzi, Joseph Hajnal, Shaihan Malik

3D-FLAIR imaging at 7T using a 3D Turbo Spin Echo (TSE) readout is a useful tool for assessment of neurological disorders. The method does however suffer from variation in signal homogeneity due to B₁⁺ inhomogeneities making whole-brain coverage difficult.

In this work, image uniformity is improved by using Direct Signal Control (DSC). The DSC method uses predictions of echo amplitudes to compute optimized RF shims that vary on a pulse by pulse basis throughout the echo train with the aim of homogenising signal properties. Low signal in the centre of the brain and cerebellum is effectively recovered in multiple subjects.

Iris Zhou, Enfeng Wang, Jerry Cheung, Xiaoan Zhang, Giulia Fulci, Phillip Sun

CEST MRI is sensitive to dilute metabolites with exchangeable protons, allowing tissue characterization in diseases such as acute stroke and tumor. CEST quantification using multi-Lorentzian fitting is challenging due to its strong dependence on image SNR, initial values and boundaries. Here we proposed an Image Downsampling Expedited Adaptive Least-squares (IDEAL) fitting algorithm that quantifies CEST images based on initial values from multi-Lorentzian fitting of iteratively less downsampled images. The IDEAL fitting provides smaller coefficient of variation and higher contrast-to-noise ratio at a faster fitting speed compared to conventional fitting. It revealed pronounced CEST contrasts in tumors which were not found using conventional method. The proposed method can be generalized to quantify MRI data where SNR is suboptimal.

Lenka Minarikova, Stefan Zbyn, Olgica Zaric, Stephan Gruber, Armin Nagel, Siegfried Trattnig

In this work, adaptive combine (AC) reconstruction was optimized on breast and knee sodium MRI data, acquired with a 14-channel breast and a 15-channel knee coils. AC reconstruction was compared with the standard sum-of-square (SoS) reconstruction. The optimal reconstruction parameters were: the lowest interpolation factor of two and an overlap of the analysis block of two to eight pixels. Images reconstructed using the AC had lower noise floor when compared to the SoS. However, when a multichannel coil with low noise correlation between elements is used, the advantage of AC reconstruction decreases.