Claudia Lenz¹, Oliver Bieri¹, Klaus Scheffler¹, and Francesco Santini^1
1Radiological Physics, University of Basel Hospital, Basel, Switzerland

Only recently, actual flip angle imaging (AFI) has been introduced as a fast and robust 3D method for mapping the B1 transmit field by measuring the spatial variations of the effective flip angle. The AFI pulse sequence consists of a dual TR conventional spoiled gradient echo pulse sequence, where TR2 > TR1. In this work, a second echo has been added to the standard AFI timing diagram, which enables additional B0 mapping by reconstructing phase difference maps based on the phase images of the two acquired echoes. In vivo results of fast simultaneous B1 and B0 mapping using dual echo AFI are presented.

Martijn Anton Cloos^1,2, Nicolas Boulant¹, Guillaume Ferrand², Michel Luong², Christopher J Wiggins¹, Denis Le Bihan¹, and Alexis Amadon^1
1LRMN, CEA, DSV, I2BM, NeuroSpin, Gif-Sur-Yvette, ile-de-France, France, ²CEA, DSM, IRFU, Gif-Sur-Yvette, ile-de-France, France

Currently, B₁⁺-mapping is particularly difficult due to the combination of time and conservative specific absorption rate (SAR) constraints applicable to parallel transmission studies involving human subjects. Measuring relative B₁⁺-maps in the low-tip-angle regime provides a low SAR solution. Inherently, this method requires a relatively long TR (0.2-1.0s) to remain in the domain where the signal intensity is linearly dependent for a large range of flip-angles. Considering 3D tailored excitation pulses, such TR values require too much time for transmit-array B₁⁺-mapping and pulse validation. To tackle the aforementioned problems, an optimized version of this method for the quantification of non-selective excitation pulses is presented.

Rolf Pohmann^1
1Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany

B1 mapping was shown

Kay Nehrke¹, and Peter Börnert^1
1Philips Research Laboratories, Hamburg, Germany

Fast B1-mapping is an essential prerequisite for multi-element transmit applications like e.g. RF-shimming or multi-dimensional RF pulse design. However, the acquisition speed of B1-mapping sequences is typically limited by SAR constraints, relaxation times, or characteristic sequence properties. In this work, a novel STEAM-based preparation sequence is presented, which employs the recently introduced Bloch-Siegert B1-mapping approach. The preparation sequence stores the Bloch-Siegert phase shift along the longitudinal magnetization, which allows the fast readout of the stimulated echo by a subsequent train of small angle pulses. The flexibility and versatility of this concept is demonstrated in experiments on phantoms and in vivo.

Angela Lynn Styczynski Snyder¹, Curt Corum², Steen Moeller², Nathan Powell³, and Michael Garwood^2
1Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States, ²Department of Radiology, University of Minnesota, ³Department of Neuroscience, University of Minnesota

A frequency-swept RF pulse and modulated gradients can be used to move a resonance region through space to generate sequential excitation and subsequent echo formation with time-dependence, which allows image formation without use of the Fourier transform. This two-dimensional time encoding (2DTE) has the unique and important property that each region in space can be treated independently, which is potentially of great benefit for solving problems that are inherently spatial in nature, such as compensating for B0 and B1 inhomogeneities, which is of increasing interest for higher field strengths.

Volker Sturm¹, Thomas Christian Basse-Lüsebrink^1,2, Thomas Kampf¹, Guido Stoll², and Peter Michael Jakob^1
1Experimental Physics 5, University of Würzburg, Würzburg, Germany, ²Neurology, University of Würzburg, Würzburg, Germany

A novel method for B₁⁺ mapping based on the Bloch-Siegert (BLS) shift was recently introduced. BLS-based B₁⁺ mapping employs off-resonant pulses before signal acquisition to encode B₁ information into the signal phase. In the present study, BLS B₁⁺ mapping was extended to CPMG-based Multi-Spin-Echo (MSE). Through only one experiment, this method simultaneously provides the data needed for B₁⁺ mapping with the data necessary for T₂-quantification. Ex vivo phantom and in vivo experiments were performed to investigate the proposed method.

Travis Benjamin Smith¹, and Krishna S Nayak^1
1Electrical Engineering, University of Southern California, Los Angeles, CA, United States

Reduced field-of-view imaging enables accelerated acquisitions or finer resolutions than standard prescriptions. Outer volume suppression reduces signals outside a region of interest and attenuates aliasing energy when a reduced field-of-view is prescribed. We present a new design for B1-insensitive outer volume suppression and demonstrate its performance at 3 Tesla in a phantom and in vivo with cardiac-gated scans.

Stephan Orzada^1,2, Stefan Maderwald^1,3, Benedikt A. Poser^1,4, Sören Johst^1,2, Mark E. Ladd^1,2, Stephan Kannengiesser⁵, and Andreas K. Bitz^1,2
1Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, NRW, Germany, ²Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, NRW, Germany, ³University of Duisburg-Essen, Essen, NRW, Germany, ⁴Donders Institute for Brain, Cognition and Behaviour, Centre for Cognitive Neuroimaging, Radboud University Nijmegen, Nijmegen, Netherlands, ⁵Siemens Healthcare Sector, Erlangen, Germany

High static field strengths of 7 Tesla and above are challenging due to the severe B1 inhomogeneities caused by the short wavelength. Several methods have been proposed to tackle this problem including RF Shimming and Transmit SENSE. Recently, a technique called Time-Interleaved Acquisition of Modes (TIAMO) has been proposed to reduce the impact of B1 inhomogeneity. In this work the influence of TIAMO on the image contrast as well as on the time-averaged SAR at 7 Tesla is addressed in detail, showing that TIAMO is superior to RF shimming in terms of image homogeneity and SAR.

Johannes Thomas Schneider^1,2, Martin Haas², Wolfgang Ruhm¹, Juergen Hennig², and Peter Ullmann^1
1Bruker BioSpin MRI GmbH, Ettlingen, Germany, ²Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany

Recently, first examples of 3D Parallel Spatially Selective Excitation (PEX) have been presented. This technique allows the restriction of the generated transverse magnetization to specified 3D target volumes, while outside these volumes the magnetization is fully restored into the longitudinal direction by the end of the pulse. Exploiting this feature, Multiple Inner-Volume Imaging (MIVI) allows interleaved excitation and data acquisition of multiple different inner-volumes within one repetition time. Compared to successive imaging of multiple inner-volumes in individual experiments, MIVI results in reduced scan times and/or enhanced SNR due to prolonged T1-relaxation periods.

Martin Haas¹, Jeff Snyder¹, Johannes T Schneider^1,2, Peter Ullmann², Denis Kokorin^1,3, Hans-Peter Fautz⁴, Jürgen Hennig¹, and Maxim Zaitsev^1
1Department of Radiology Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²Bruker BioSpin MRI GmbH, Ettlingen, Germany, ³International Tomography Center, Novosibirsk, Russian Federation, ⁴Siemens Healthcare, Erlangen, Germany

Spatially selective excitation of an arbitrarily shaped three-dimensional target volume is demonstrated on a human MR scanner at 3T, accelerated by means of 8-channel parallel transmission. The good excitation fidelity and effective restoration of magnetization outside the volume of interest to the longitudinal direction allows for a reduction of the readout field of view in all three dimensions, resulting in an increase of resolution by a factor of two in all three directions while maintaining the measurement time.

Cem Murat Deniz^1,2, Dong Chen³, Leeor Alon^1,2, Ryan Brown¹, Hans-Peter Fautz⁴, Daniel K Sodickson¹, and Yudong Zhu^1
1Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, New York, NY, United States, ²Sackler Institute of Graduate Biomedical Sciences, NYU School of Medicine, New York, NY, United States, ³Center for Mathematical Science, Technical University of Munich, Munich, Germany, ⁴Siemens Medical Solutions, Erlangen, Germany

Tailored inner-volume excitation on whole-body scanners is currently limited by long 3D RF pulses. Effective pulse length reduction with parallel transmission requires careful selection of the excitation k-space trajectory. In this work, two methods of determining sparse excitation trajectories were compared for parallel transmit pulse design in the small-tip angle and large-tip-angle regimes: a) an Orthogonal Matching Pursuit (OMP) algorithm, and b) a one-step basic thresholding approach. Good inner-volume excitation with a pulse length of less than 9ms was achieved using an eight-channel transmitter on a whole-body human 7T scanner.

Ziqi Sun¹, Sergey Petryakov¹, George Caia¹, Alex Samouilov¹, and Jay L Zweier^1
1Davis Heart & Lung Research Institute, The Ohio State University, Columbus, Ohio, United States

Adiabatic inversion pulses have been widely used in slice- and whole-volume spin inversion in perfusion-weighted MRI. To date, no reports are available for using selective adiabatic inversion pulses for localized volume inversion in perfusion measurements. In this study, we proposed a 3D volume localization using adiabatic inversion pulses for FAIR imaging on a flow phantom. In comparison to the conventional slice-inversion FAIR technique, the perfusion rate measured using the localized volume-inversion FAIR method is in the acceptable accuracy and generates enhanced T1-weighting contrast.

Martin Haas¹, Jeff Snyder¹, Peter Ullmann², Jürgen Hennig¹, and Maxim Zaitsev^1
1Department of Radiology Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²Bruker BioSpin MRI GmbH, Ettlingen, Germany

Multi-dimensionally selective RF excitation suffers from artifacts related to the typically long pulse duration. In particular, applications in MR spectroscopy would significantly benefit from shorter pulses due to increased bandwidth. Previous approaches to mitigate this problem using segmented selective excitation across several repetitions have been limited to small tip angles. In this work, a segmented RF design algorithm for large tip angle pulses, with additional parallel transmit acceleration, is described for multi-dimensionally selective excitation and demonstrated in simulations and a phantom. The method is based on a segment-wise optimal control optimization and not limited to 2D or a particular segmentation.

Borjan Gagoski¹, Khaldoun Makhoul^2,3, Dieter Ritter⁴, Kawin Setsompop^2,3, Josef Pfeuffer⁴, Himanshu Bhat⁵, Philipp Hoecht⁵, Michael Hamm⁵, Ulrich Fontius⁴, Lohith Kini¹, Joonsung Lee¹, Lawrence L Wald^2,6, and Elfar Adalsteinsson^1,6
1Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, ²A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, ³Harvard Medical School, Boston, MA, United States, ⁴Siemens Healthcare, Erlangen, Germany, ⁵Siemens Healthcare, Charlestown, MA, United States, ⁶Harvard-MIT Division of Health Sciences and Technology, MIT, Cambridge, MA, United States

Parallel RF transmission (pTx) offers significant flexibility over single-channel excitations for creating arbitrarily shaped spatial excitation patterns, which can be designed for undersampled spiral-based excitation k-space trajectories played during the pTx RF waveform. In this work we validate the feasibility of using 7T 8-channel pTx for flexibly shaped saturation bands that suppresses a user-defined spatial shape, in combination with a B1+ mitigated pTx slice-selective "spokes" excitation.

Ingmar Graesslin¹, Sebastian Boetzl¹, Ulrich Katscher¹, Kay Nehrke¹, Bjoern Annighoefer², Giel Mens³, and Peter Börnert^1
1Philips Research Laboratories, Hamburg, Germany, ²TU Hamburg-Harburg, Hamburg, Germany, ³Philips Healthcare, Best, Netherlands

Zoom imaging allows an increase of the spatial resolution in the targeted region of interest (ROI) without increasing the scan time. Alternatively, maintaining spatial resolution, zoom imaging allows a reduction of the scanning time by reducing the field of view (FOV) to the ROI. For both techniques, potential backfolding artefacts from body regions outside the reduced FOV can be suppressed via local excitation. This local excitation can be performed by multi-dimensional RF pulses, which can be accelerated using spatial transmit sensitivity encoding instead of full gradient encoding. This paper presents (first) zoom imaging volunteer experiments carried out on an 8-transmit channel 3T MRI system, with a fully integrated real-time SAR validation prior to the scan allowing the safe use of spatially selective Transmit SENSE RF pulses and their fast calculation for optimal workflow.

Tiejun Zhao¹, Hai Zheng², Yik-Kiong Hue³, Tamer Ibrahim^2,3, Yongxian Qian³, and Fernando Boada^2,3
1Siemens Medical Solutions, Pittsburgh, Pennsylvania, United States, ²Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, ³Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Parallel transmission was recently proposed as one of the methods to accelerate multidimensional selective excitation using multiple coils driven with independent waveforms. The parallel excitation could be a potential solution for mitigating or solving the RF and SAR problems at the ultra-high field (e.g, 7T). One of the popular methods was proposed by Grissom et al. In this work, we propose two novel methods that the artifacts due to finite gradient raster step can be successfully compensated to avoid tilted and excitation errors. Significant improvement can be obviously seen from both simulations and experiments on 7T scanner.

Hai Zheng¹, Tiejun Zhao², Yongxian Qian³, Tamer Ibrahim^1,3, and Fernando Boada^1,3
1Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, ²Siemens Medical Solutions, Pittsburgh, Pennsylvania, United States, ³Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Hardware and experimental imperfections can severely impact the excitation patterns in ultra high field parallel transmission. In this work, we propose a new eddy current correction method combining existing eddy current characterization method for parallel transmission RF pulse design to compensate the overall distortion induced by gradient and RF coils as well as the system delay to reduce the distortions in parallel transmission. Our proposed compensation method is a straightforward and easy to implement, but yields an evident improvement in the performance.

Xiaoping Wu¹, Gregor Adriany¹, Kamil Ugurbil¹, and P-F. Van de Moortele^1
1CMRR, Radiology, University of Minnesota, Minneapolis, MN, United States

Jing Chen¹, Jing An², and Yan Zhuo^1
1State Key Laboratory of Brain and Cognitive Science, Inst. of Biophysics, Chinese Academy of Sciences, Beijing, China, People's Republic of, ²Siemens Healthcare, MR Collaboration NE Asia, Siemens Mindit Magnetic Resonance, China, People's Republic of

This work describes an interleaved spatial-spectral RF pulse for use with large excitation/suppression difference frequency, for example, exciting water while suppressing fat on a 7T system. The excitation is divided into three repetitions to fill the excitation k-space in an interleaving pattern. Interleaving allows driving the gradient at a lower slew rate. Therefore, this method has the advantages of less eddy current distortion, relative ease of implementation, and thinner slice thickness.

Rene Gumbrecht^1,2, Elfar Adalsteinsson^3,4, Paul Müller², and Hans-Peter Fautz^1
1Siemens Healthcare, Erlangen, Germany, ²Department of Physics, Friedrich-Alexander University, Erlangen, Germany, ³Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, ⁴Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States

For ultra high field strengths of 7T and above, peak RF power and SAR are limiting factors for high performance imaging. One way to keep these quantities low is to prolong the RF pulses. However, long RF pulses are prone to B0 homogeneities because the bandwidth of such pulses is reduced. In this work, we investigate the potential of prolonging large-tip-angle composite RF pulses for power and SAR reduction by using pTx pulse design methods which account for local B0 field variations.

Nicolas Boulant¹, Martijn Cloos¹, and Alexis Amadon^1
1NeuroSpin, CEA Saclay, Saclay, France

The design of the strongly modulating pulses, developed by the same authors and initially non-selective, has been adjusted to create selective pulses by using average Hamiltonian theory. Such a theory formulates an approximate analytical expression of the dynamics which allows navigating quickly in some pulse parameter space. Once a pulse is found to perform sufficiently well using that approximation, it can be modified with a few iterations by calculating more accurately the spin evolution. Using that technique, in-vivo results are reported which show good mitigation of the B1 inhomogeneity problem over an axial slice in the human brain at 7T.

Hui Liu^1,2, and Gerald B. Matson^1,3
1Center for Imaging of Neurodegenerative Diseases (CIND), Veterans Affairs Medical Center, San Francisco, CA, United States, ²Northern California Institute for Research and Education, San Francisco, CA, United States, ³University of California, San Francisco,CA, United States

Although high-field MRI offers increased signal-to-noise (SNR), the non-uniform tipping produced by conventional RF pulses leads to spatially varying contrast such as a bright center, and sub-optimal S/N, thus complicating the interpretation of the MR images. The aim of this research was to develop non-slice-selective (NSS) RF pulses with immunity to B1 inhomogeneity and resonance offset for a full range of tip angles. To accomplish this, we developed an optimization routine to design RF pulses with a desired range of immunity to B1 inhomogeneity and to resonance offset. Simulations were validated by phantom tests and an in vivo human study. The resulting pulses were more efficient (in terms of length) than previous pulses in the literature. These pulses have promise for 3D MRI experiments at high field.

Ziqi Sun^1
1Davis Heart & Lung Research Institute, The Ohio State University, Columbus, Ohio, United States

Selective adiabatic excitation pulses have been utilized to generate pseudo-echoes to improve image contrast and quality. In this study, pseudo-echo images were obtained using a customized CPMG pulse sequence incorporated with selective adiabatic refocusing pulses that alternate frequency sweep directions between each of the echoes. Apparent T2 time constants were measured from the pseudo-echo images using the customized CPMG sequence. T2-weighting was significantly increased using the sequence in comparison to the CPMG sequence using amplitude modulated selective refocusing pulses.

Seung-Kyun Lee¹, Mika W Vogel², William A Grissom², Graeme C McKinnon³, and Patrick H Le Roux^4
1GE Global Research, Niskayuna, NY, United States, ²Advanced Medical Applications Laboratory, GE Global Research, Munich, Bavaria, Germany, ³Applied Science Lab, GE Healthcare, Waukesha, WI, United States, ⁴Applied Science Lab, GE Healthcare, Palaiseau, France

In parallel transmit, phase-relaxed RF pulse design significantly improves image quality in gradient echo and spin echo images. Here we present a simulation study showing that phase-relaxed 90-180 RF pulses can also be used in fast spin echo imaging with Le Roux’s quadratic phase modulation implemented on all transmit channels.

Vincent Gras¹, Zaheer Abbas¹, and Nadim Jon Shah^1,2
1Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Forschungszentrum Jülich GmbH, Jülich, Germany, ²Faculty of Medicine, Department of Neurology, RWTH Aachen University, Aachen, Germany

Mapping of the proton density (PD) is a common MRI application, with interesting perspective in medical research. At 3 Tesla, PD imaging supposes an accurate correction of the sample-dependent RF non-uniformity, which is measured using a dedicated protocol termed B1 mapping. Such measurement is possible if one assumes 1) the linear relationship between flip angle and B1 and 2) the NMR reciprocity principle. From these 2 assumptions, it follows a unique correction scheme. In this work, the accuracy of the correction is evaluated to 2%, setting an upper limit to the precision of the PD measurement achievable with this general approach.

Vincent Gras¹, Zaheer Abbas¹, Anna-Maria Oros-Peusquens¹, Klaus Hans Manfred Möllenhoff¹, Fabian Keil¹, Miriam Rabea Kubach¹, and Nadim Jon Shah^1,2
1Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Forschungszentrum Jülich GmbH, Jülich, Germany, ²Faculty of Medicine, Department of Neurology, RWTH Aachen University, Aachen, Germany

A 1.5T and 3T quantitative water content imaging protocol is proposed, extending a previously developed method, suited to 1.5T only. The benefit of working at 3T is a noticeable gain in SNR compared to 1.5T, although refinements are needed for the accuracy to be preserved. The gradient echo approach, envisaged in this work, allows for the detection of myelin water, exhibiting short relaxation times. Furthermore, the required short scanning time, 15 minutes, is particularly suited to the clinical practice. The accuracy of the method is evaluated to 2%, making this method eligible for the detection of cerebral oedema of various origins. This method is presented and in vivo results at 1.5T and 3T are shown.

Stephan William Anderson¹, Jennifer Ellis-Ward², Erskine Hawkins³, James A Hamilton⁴, Carl J O'Hara⁵, Lawreen H Connors⁶, Jorge A Soto¹, David C Seldin², and Hernan Jara^1
1Radiology, Boston University Medical Center, Boston, MA, United States, ²Hematology and Medical Oncology, Boston University Medical Center, ³Boston University School of Medicine, ⁴Physiology and Biophysics, Boston University Medical Center, ⁵Pathology and Laboratory Medicine, Boston University Medical Center, ⁶Biochemistry, Boston University School of Medicine

Purpose: To evaluate the effects of amyloid deposition on T2 and apparent diffusion coefficient (ADC) measurements in human autopsy specimens of myocardium, liver, spleen, and kidney of patients with AL amyloidosis using 11.7T MRI. Methods: T2 and ADC values of tissues with amyloid deposition were compared to control specimens. Results Significant differences in T2 and ADC values were seen when comparing control and involved specimens of myocardium, spleen and kidney (all p<0.002). Conclusion: Deposition of amyloid protein in human autopsy specimens substantially affects ADC values in myocardium, liver, spleen, and kidney and T2 values in myocardium, spleen and kidney.

Neville D Gai¹, Christian Stehning², Marcelo Nacif¹, and David A Bluemke^1,3
1Radiology & Imaging Sciences, National Institutes of Health, Bethesda, MD, United States, ²Philips Research Europe, Hamburg, Germany, ³NIBIB, Bethesda, MD, United States

The MOLLI technique for T1 mapping has found favor in cardiac imaging due to its relative robustness to motion. A subsequent work explored optimization of parameters based purely on performing phantom scans while varying scan parameters. Such an approach could fail to be comprehensive in the covered parameter space or parameters affecting accuracy. Here, we develop Bloch simulation based characterization of MOLLI and evaluate T1 accuracy for several scan parameters. We corroborate T1 values obtained from simulation with values obtained from scanning phantoms. Based on simulations and scanning, it is shown that the simulation is a valuable tool in understanding the accuracy of T1 values given different scan conditions.

Thomas Christen¹, Heiko Schmiedeskamp¹, Matus Straka¹, Roland Bammer¹, and Greg Zaharchuk^1
1Department of radiology, Stanford University, Stanford, California, United States

We compared in this study three different EPI-based approaches for measuring T2’ : (1) a subtraction of T2 from T2* relaxation rates that are derived from separate multiecho sequences; (2) an asymmetric spin echo (ASE) sequence; (3) a combined multiple gradient echo and spin echo (SAGE) sequence. The results obtained in the brain of 4 subjects suggest that the different approaches give similar T2’ values. They however showed spatial differences. The highest-quality maps were obtained with the ASE method. The SAGE approach, while containing spatial artifacts, could be used in a dynamic approach with high time resolution.

Neville D Gai¹, Christian Stehning², Saman Nazarian³, Evrim Turkbey¹, and David A Bluemke^1,4
1Radiology & Imaging Sciences, National Institutes of Health, Bethesda, MD, United States, ²Philips Research Europe, Hamburg, Germany, ³Division of Cardiology, Johns Hopkins University, Baltimore, United States, ⁴NIBIB, Bethesda, MD, United States

T1 mapping can differentiate between diffuse fibrosis and normal myocardium. Several longitudinal cardiac studies do not have a dedicated T1 mapping scan as part of the protocol. However, segmented Look-Locker (LL) with b-SSFP is typically used as a scout scan. T1 values may then be derived from such a scan. Certain diseases exhibit fatty infiltration as part of their etiology. Based on simulations and scanning, we show that fat T1 quantification so obtained can be highly erroneous based on the scan parameters used. Therefore, conclusions based on observed cardiac T1 values in cases where fatty infiltration is substantial might be fraught with complications.

Haosen Zhang¹, Kevin Hitchens¹, Qing Ye¹, EriK B. Schelbert², and Chien Ho^1
1Pittsburgh NMR Center for Biomedical Research, Department of Biological Science, Carnegie Mellon University, Pittsburgh, PA, United States, ²Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States

In this study, an inversion recovery (IR)-prepared segmented gradient echo sequence was developed to sample the T1 recovery curve in Look-Locker scheme at 7 T. Via a multi-variable regression algorithm corrected for the saturation effect induced by the á-train, we have obtained more accurate T1 values than with the conventional three-parameter fit (average error of -0.53% vs. -5.4% separately, compared to T1s measured with IR-SE) in agarose phantoms simulating human myocardium and blood.

Peter van Gelderen¹, Jacco A de Zwart¹, Jongho Lee¹, Pascal Sati², Daniel S Reich², and Jeff H Duyn^1
1Advanced MRI section, LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States, ²Translational Neuroradiology Unit, Neuroimmunology Branch, NINDS, National Institutes of Health, Bethesda, MD, United States

A number of methods have been proposed to determine the myelin distribution in human brain, which may report on pathology. One potentially promising method is measurement of the T₂^* relaxation curve ,which may be affected by restricted mobility of myelin associated water. Here we investigated this possibility using multi-gradient echo MRI at 3T and 7T in normal brain. In myelin-rich regions, we observed relaxation characteristics more consistent with effects from susceptibility variations rather than from mobility restrictions. This may complicate the interpretation, as susceptibility effects are affected by additional factors independent of myelin content.

Jerry S. Cheung¹, Enfeng Wang^1,2, XiaoAn Zhang², Emiri Mandeville³, Eng H. Lo³, A. Gregory Sorensen¹, and Phillip Zhe Sun^1
1Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, MGH and Harvard Medical School, Charlestown, MA 02129, United States, ²Department of Radiology, 3rd Affiliated Hospital, Zhengzhou University, China, People's Republic of, ³Neuroprotection Research Laboratory, Department of Radiology and Neurology, MGH and Harvard Medical School, Charlestown, MA 02129, United States

Transverse relaxation time (T₂) is a basic but very informative MRI parameter, widely used in imaging to examine a host of diseases including multiple sclerosis, stroke, and tumor. When the repetition time (TR) is very long, T₂ can be derived by fitting T₂-weighted images as a function of echo time (TE). However, short TR is often used to minimize scan time, which may introduce non-negligible errors in T₂ measurement. Our study proposed a fast RF-enforced steady state (FRESS) spin echo MRI sequence, which saturates the magnetization after the spin echo and ensures a TE-independent steady state for accurate T₂ mapping.

Arezou Koohi¹, and Vasiliki N Ikonomidou^1
1Electrical and Computer Engineering, George Mason University, Fairfax, VA, United States

This study presents the application of Tissue Specific Imaging (TSI), a double inversion recovery variant that produces three single tissue type images, to the quantitative mapping of tissue T₁ values. The methodology presented, which can add value to the application of TSI, is stable over a wide range of T₁ values, up to 4500 ms for usually encountered signal-to-noise ratio values.

Stefan Kirsch¹, and Lothar R Schad^1
1Computer Assisted Clinical Medicine, Heidelberg University, Mannheim, Germany

Measurement of the transversal relaxation time T₂ is one of the most established techniques to characterize material samples or biological tissue by means of NMR. If molecular motion is restricted, direct spin-spin interactions become relevant and extremely short T₂ values are expected. Here we present a slice-selective MRI method for mapping of submillisecond T₂. The method utilizes a spin echo preparation followed by slice-selective ultra-short echo time imaging. Mapping of submillisecond T₂ could be useful in studies on material samples, short T₂ biological tissue like bone, tendon or cartilage and on quadrupolar nuclei like ²³Na, ³⁵Cl, and ¹⁷O.

Jung-Jiin Hsu^1
1Radiology, University of Miami School of Medicine, Miami, Florida, United States

The accuracy of the T₁ measurement depends on the accuracy of the flip angle (FA). The FA is non-uniform in a slice across the slice-thickness direction, which can result in serious T₁ measurement error. Although it has been recognized that measuring the FA regional inhomogeneity in a volume is important, the effect of the slice profile is still less known. In this work, the slice-profile effect is studied systematically for various common experimental conditions. The results provide essential guidelines for experiment design and scan parameter selection for the T₁ measurement with steady-state magnetization (e.g., DESPOT).

Yoonho Nam¹, Eung-Yeop Kim², Dosik Hwang¹, and Dong-Hyun Kim^1
1Electrical & Electronic Engineering, Yonsei University, Seoul, Korea, Republic of, ²Radiology, Yonsei University, Seoul, Korea, Republic of

Myelin water imaging is a useful tool for studying white matter diseases. So far, a multi-exponential T2 analysis using multi-echo spin echo sequence has been mostly used for myelin water imaging. But, using a multi-echo spin echo sequence has some limitations such as high SAR, small coverages. Therefore, several studies have been conducted using multi-echo gradient echo sequences recently. However, T2* decay curve measured by gradient echo sequence can be easily distorted by macroscopic field inhomogeneity. In this study, the bmGESEPI method was applied for myelin water imaging to remove the effects of macroscopic field inhomogeneity.

Moritz Cornelius Berger¹, Wolfhard Semmler¹, and Michael Bock^1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

Fast saturation recovery turboFLASH imaging introduces a saturation-time dependent filter on the magnetization-prepared k-space. To mitigate these filtering effects for reliable T1 measurements, multiple k-space segmentation schemes were simulated to characterize the tradeoff between the accuracy of T1 determination and total measurement time.

Yong Chen^1,2, Wen Li^1,2, and Xin Yu^1,2
1Department of Biomedical Engineering, Case Western Reserve Univ, Cleveland, OH, United States, ²Case Center for Imaging Research, Case Western Reserve Univ, Cleveland, OH, United States

In this study, we developed a novel method for rapid T2 mapping of mouse heart in vivo. Our results demonstrate that a high temporal resolution of ~15 seconds can be achieved by combining a fast multi-echo spin-echo sequence with a model-based compressed sensing reconstruction.

Adrienne E Campbell^1,2, Anthony N Price³, Bernard M Siow¹, Jack A Wells¹, Mark F Lythgoe¹, and Roger J Ordidge^2
1Centre for Advanced Biomedical Imaging, Division of Medicine and Institute of Child Health, University College London, London, United Kingdom, ²Department of Medical Physics and Bioengineering, University College London, London, United Kingdom, ³Robert Steiner MRI Unit, Imaging Science Department, Hammersmith Hostpital, Imperial College London, London, United Kingdom

A time-efficient multi-slice ECG gated Look-Locker sequence is developed for multi-slice T1 mapping in the mouse heart. With this sequence, multi-slice T1 maps can be generated for the mouse heart in less than 10 minutes. Multi-slice T1 mapping was tested in phantoms and in a CD-1 mouse, and it was found that T1 measurements agreed with single-slice T1 measurements within 4% for the phantom and within 10% in vivo. This sequence will have great applicability for multi-slice arterial spin labelling perfusion measurements to study cardiac disease models.