ISMRM 23rd Annual Meeting & Exhibition • 30 May - 05 June 2015 • Toronto, Ontario, Canada

Traditional Poster Session • Relaxation
1664 -1697 Relaxometry

Tuesday 2 June 2015
Exhibition Hall 13:30 - 15:30

1664.   Accelerated and motion-robust in vivo T2 mapping from radially undersampled data using Bloch-simulation-based iterative reconstruction
Noam Ben-Eliezer1,2, Daniel K Sodickson1,2, Timothy M Shepherd1,2, Graham C Wiggins1,2, and Kai Tobias Block1,2
1Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 2Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, NY, United States

Accurate mapping of T2 relaxation values in vivo is highly challenging in clinical settings. This work integrates two techniques: (1) a recently-developed T2 mapping technique – the echo-modulation curve (EMC) algorithm – which is immune to the T2 bias caused by indirect coherence pathways in multi spin-echo protocols, and (2) non-linear model-based reconstruction of radially sampled datasets allowing to overcome undersampling-related aliasing artifacts. The synergistic combination of the two provides accelerated scanner- and parameter-invariant quantification of T2 relaxation, and morphological proton-density information at sub-millimeter spatial resolutions and reduced motion sensitivity.

1665.   Quantitative MR imaging method: All of the main MR parameters can be obtained in little more than a single scan
Bruno Madore1, W. Scott Hoge1, Tai-Hsin Kuo2, and Cheng-Chieh Cheng1
1Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States, 2Philips Healthcare, Taipei, Taiwan

The present method aims to obtain in little more than a single scan all of the main physical MR parameters: T1, T2, T2*, M0, B0 and B1. In principle at least, based on these maps one could generate images of essentially any desired contrast, through well-known signal equations. The approach treats the flip angle as a parameter to be evaluated rather than a known quantity, and all parameters are calculated one at a time and/or through linear equations, as opposed to numerically solving larger and non-linear systems of equations. The method was validated on phantom data, with in vivo results forthcoming.

1666.   Paramagnetic Ion Phantom to Independently Tune T1 and T2
Kathryn E Keenan1, Karl A Stupic1, Elizabeth Horneber2, Michael Boss1, and Stephen E Russek1
1National Institute of Standards and Technology, Boulder, CO, United States, 2University of Colorado, Boulder, CO, United States

Method to independently tune T1 and T2 relaxation times using the paramagnetic ions Ni++ and Mn++ in aqueous solution. These phantoms, when sealed and stored in the MR laboratory exhibit long term stability with 10% change.

1667.   Time-dependent transverse relaxation reveals statistics of structural organization in microbead samples
Alexander Ruh1, Philipp Emerich1, Harald Scherer2, Dmitry S. Novikov3, and Valerij G. Kiselev1
1Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Dept. of Inorganic and Analytical Chemistry, University Freiburg, Freiburg, Germany,3Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States

Transverse relaxation in biological tissues is sensitive to the structural organization of magnetic inhomogeneities on the cellular level. A recently developed theory predicts a reflection of this structural organization in the long-time behavior of the induced relaxation rate as a power law approach to the asymptote. Here we present the first direct experimental verification of such dependence in differently composed media. Specifically, we observe the theoretically expected behavior in a microbead phantom with two different types of structural disorder.

1668.   Effects of formalin fixation on MR relaxation times in the human brain
Christoph Birkl1, Christian Langkammer2, Nicole Golob-Schwarzl3, Marlene Leoni3, Johannes Haybaeck3, Walter Goessler4, Franz Fazekas1, and Stefan Ropele1
1Department of Neurology, Medical University of Graz, Graz, Austria, 2MGH/HST Martinos Center for Biomedical Imaging, Harvard Medical School, Boston, MA, United States,3Department of Neuropathology, Institute of Pathology, Medical University of Graz, Austria, 4Institute of Chemistry, Analytical Chemistry, University of Graz, Austria

Post mortem MRI is commonly used to validate quantitative MRI methods and to improve our understanding of relaxation in tissue. However, formalin which is frequently used to preserve tissue samples for degradation, can substantially affect MR relaxation times, which hampers comparison with in vivo conditions. In this study, we systematically evaluated the influence of formalin fixation on MR relaxation times by combining water content measurements, electrophoresis, and temperature dependent relaxation time measurements. Our results suggest that formalin induced cross-linking is the main reason for the shortening of relaxation times while changes of water content do not play a major role.

1669.   A Structurally Anthropomorphic Brain Phantom
Kyoko Fujimoto1,2, Trent V. Robertson1, Vanessa Douet2, David G. Garmire1, and V. Andrew Stenger1,2
1Department of Electrical Engineering, University of Hawaii at Manoa, Honolulu, HI, United States, 2Department of Medicine, John A. Burns School of Medicine, University of Hawaii, Honolulu, HI, United States

Techniques for better Magnetic Resonance imaging are being continuously developed. Before applying new techniques on subjects and patients in a scanner, they are tested with cylindrical or spherical phantoms. However, results are often not realistic since the human cerebrum has complex structure with multi-contrast tissues and gyrifications. Some phantoms model electrical and functional properties but a phantom with gray and white matter structure does not exit. The purpose of this study is to show the development of an anthropomorphic phantom to obtain calibration data with simulated cerebral tissues to reduce cost and time by not necessitating in-vivo subjects.

1670.   Single-Shot Multi-slice T1 Mapping at High Spatial Resolution – Inversion-Recovery FLASH with Radial Undersampling and Iterative Reconstruction
Xiaoqing Wang1, Volkert Roeloffs1, Klaus-Dietmar Merboldt1, Dirk Voit1, Sebastian Schaetz1, and Jens Frahm1
1Biomedizinische NMR Forschungs GmbH am Max-Planck-Institut fuer biophysikalische Chemie, Göttingen, Germany

Low spatial resolution and long acquisition time have been the two major limitations for T1 mapping’s routine application in clinical MRI. Recently several image space and k-space based reconstruction methods have been proposed to estimate T1 maps from undersampled data, however, most of them dealing with single-shot single-slice T1 mapping. In this work, a single-shot sequential multi-slice acquisition scheme together with a new relaxation model is proposed. After combining it with radial undersampling and iterative reconstruction, our method facilitates accurate, high-resolution multi-slice T1 mapping.

1671.   Simultaneous T1 and T2 mapping using a modified multi-echo spin-echo sequence (MOMSE)
Andreas Petrovic1 and Rudolf Stollberger2
1Institute of Medical Engineering, Universtiy of Technology Graz, Graz, -, Austria, 2Institute of Medical Engineering, University of Technology Graz, -, Austria

In multi-parametric MRI several MR parameters are estimated within one single scan, which reduces acquisition time. In this work we modified a multi-echo spin-echo sequence for simultaneous estimation of M0, T1, and T2 using the Generating Functions formalism. Reducing the refocusing angle allows longitudinal magnetization recovery during the sequence, which is used to create a final “T1 weighted echo”. Simulations, measurements and fitted T2 values are in excellent agreement; however, accuracy of fitted T1 values is limited, requiring a thorough sensitivity assessment. The robust spin echo nature and reduced SAR of this sequence render it applicable at high field scanners.

1672.   A Min-Max CRLB Optimization Approach to Scan Selection for Relaxometry
Gopal Nataraj1, Jon-Fredrik Nielsen2,3, and Jeffrey A. Fessler1,2
1Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, United States, 2Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States,3Functional MRI Laboratory, University of Michigan, Ann Arbor, MI, United States

We describe a CRLB-inspired min-max optimization problem to guide scan design for relaxometry. In essence, our method minimizes the theoretical worst-case (i.e., maximum) standard deviations of T1 and T2 estimates. As an example, we first optimize two DESS acquisitions for T2 relaxometry in the brain. Our results show that predicted and empirical T2standard deviations over WM/GM ROIs recommend similar scan parameter combinations for precise T2 estimation. We then compare a regularized T2 estimate from our suggested scan protocol against one from many acquisitions and find that much T2 content in DESS is well captured with only two scans.

1673.   A simple method (eMoS) for T1 mapping is more accurate and robust than the Variable Flip Angle (VFA) method
Sofia Chavez1,2
1Centre for Addiction and Mental Health, Toronto, Ontario, Canada, 2Psychiatry, University of Toronto, Toronto, Ontario, Canada

The purpose of this work is to present a simplified method (eMoS) that can be used to compute T1 maps from two low flip angle SPGR signal acquisitions if B1 maps are known. A study of the effects of B1 errors and noise on eMoS in contrast to the effect of these on the standard variable flip angle (VFA) method can be used to explain the observed differences in human brain, in vivo, T1 maps. Simulations and human scans are used to demonstrate the improved accuracy and noise robustness of the eMoS relative to the VFA method for T1 mapping.

1674.   Qualtification of rapid decay species with short TE spin echo sequence
Eamon K Doyle1,2, Jonathan M Chia3, Krishna Nayak1,4, and John C Wood1,2
1Biomedical Engineering, University of Southern California, Los Angeles, CA, United States, 2Cardiology, Children's Hospital of Los Angeles, Los Angeles, CA, United States, 3Philips Healthcare, Cleveland, OH, United States, 4Electrical Engineering, University of Southern California, Los Angeles, CA, United States

Evaluation of iron-containing tissues at 3T presents challenges related to ultra-fast, susceptibility-mediated signal decay. We propose a low flip angle spin echo sequence as a method of acquiring data to diagnose liver iron overload when traditional pulse sequences are too slow.

1675.   Whole-Brain Multi-Parameter mapping using Dictionary learning
Sampada Bhave1, Sajan Goud Lingala2, Casey P Johnson1, Vincent A Magnotta1, and Mathews Jacob1
1University of Iowa, Iowa City, Iowa, United States, 2Electrical Engineering, University of Southern California, Los Angeles, California, United States

Quantification of multiple tissue parameters is emerging as a powerful tool in diagnosing various neurological and psychiatric diseases. However the major bottleneck in its routine clinical use is the long acquisition time. In addition, long acquisition times are likely to result in motion induced artifacts. In this work, we propose a dictionary learning based scheme to simultaneously recover T1ρ and T2 maps. The proposed method models the data as a weighted linear combination of basis functions from a dictionary, which is learned from the measured data.

1676.   Fast and Accurate Quantification of T1, T2 and Proton Density using IR bSSFP with Slice Profile Correction and Model Based Reconstruction
Andreas Lesch1, Andreas Petrovic1, Tilman Johannes Sumpf2, Christoph Stefan Aigner1, and Rudolf Stollberger1
1Department for Medical Engineering, Graz University of Technology, Graz, Styria, Austria, 2Biomedizinische NMR Forschungs GmbH, Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany

This work describes multiple parameter quantification using the IR-bSSFP sequence with single coil measurements and parallel imaging. An advanced implementation is shown that address quantification accuracy by slice profile correction, high acceleration by undersampling and integrated parameter determination by model based image reconstruction.

1677.   Inversion Group (IG) Fitting: A New Fitting Algorithm for Modified Look-Locker Inversion Recovery (MOLLI) that allows for Arbitrary Inversion Groupings
Issac Y Yang1, Kai-Ho Fok1, Bernd J Wintersperger2,3, and Marshall S Sussman2,3
1Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada, 2Department of Medical Imaging, University of Toronto, Toronto, Ontario, Canada, 3Joint Department of Medican Imaging, University Health Network & Mt. Sinai Hospital, Toronto, Ontario, Canada

Modified Look-Locker Inversion Recovery (MOLLI) is a common technique for T1 mapping of the heart. However, it requires a lengthy rest period in between inversion groupings to allow for complete magnetization recovery. A new MOLLI fitting algorithm with a new fitting model is presented in this work to allow for arbitrary inversion groupings and rest periods, including no rest period. Phantom and in-vivo experiments verified the technique. T1 values measured using several different inversion grouping/rest period combinations yielded consistent results with the new algorithm, but with a slight loss of precision.

1678.   Plug-n-Play Magnetic Resonance Fingerprinting (PnP- MRF)
Shivaprasad Ashok Chikop1, Antharikshanagar Bellappa Sachin Anchan1, Shaikh Imam1, Amaresha Shridhar Konar1, Rashmi Rao1, Arush Honnedevasthana Arun1, and Sairam Geethanath1
1Medical Imaging Research Center, Dayananda Sagar Institutions, bangalore, Karnataka, India

Plug-n-Play (PnP) MRF is a novel technique based on MRF and provides an opportunity to MR researchers who do not have access to pulse sequence designing to use a comprehensive framework like MRF on clinical scanner using readily available pulse sequence. PnP MRF is implemented using PSIF sequence and is modelled using a data driven model which uses an analytical equation obtaining optimum Contrast to Noise Ratio (CNR) between brain tissues, enabling fast computation of dictionary. The number of MR images required for MRF has been reduced to forty eight in PnP MRF.

1679.   Super-resolution T1 mapping: a simulation study.
Gwendolyn Van Steenkiste1, Dirk H.J. Poot2,3, Ben Jeurissen1, Arnold J. den Dekker1,4, and Jan Sijbers1
1iMinds-Vision Lab, University of Antwerp, Antwerp (Wilrijk), Antwerp, Belgium, 2BIGR (Medical informatics and Radiology), Erasmus Medical Center Rotterdam, Rotterdam, Netherlands, 3Imaging Science and Technology, Delft University of Technology, Delft, Netherlands, 4Delft Center for Systems and Control, Delft University of Technology, Delft, Netherlands

The spin-lattice relaxation time (T1) of tissues can be estimated from a set of T1 weighted images. Even though T1 mapping has a broad range of potential applications, T1 maps are not routinely used in clinical practice. The high acquisition time of the necessary set of high resolution T1 weighted images is not clinically feasible. We propose to use super-resolution in combination with T1 estimation to provide a better trade off between the acquisition time, SNR and spatial resolution of the T1 maps.

1680.   Removing SSFP Banding Artifacts from DESPOT2 Images Using the Geometric Solution
Tobias Charles Wood1, Stephen J Wastling1, and Gareth J Barker1
1Neuroimaging, King's College London, London, London, United Kingdom

We combine the Geometric Solution to bSSFP band-removal with DESPOT2 to speed up calculation of T2 by 4 orders of magnitude, at the expense of increased scan time.

1681.   Ultra-Low Field NMR Relaxometry: Calibration Method and T1-Dispersion below 1000 Hz
Vasileios Zampetoulas1, Lionel M. Broche1, and David J. Lurie1
1Aberdeen Biomedical Imaging Centre,School of Medicine&Dentistry, University of Aberdeen,Foresterhill, AB25 2ZD, Aberdeen, United Kingdom

Fast Field-Cycling (FFC) NMR is a technique that provides information about the molecular dynamics of a range of materials by using the T1-dispersion curve. After the compensation of the stray magnetic fields coming from external sources, the T1-dispersion curve can extend to magnetic fields in the region of μT allowing for the investigation of slow dynamic processes and determination of the local magnetic fields within the sample. With further development, differences in that region of the curve obtained from biological samples can be associated with the early stages of progress of diseases, leading to a new diagnostic tool.

1682.   B1+ Field Mapping Improves Accuracy of T1 Measurements in Phantoms and Normal Breast at 3.0 T
Jennifer G. Whisenant1, Lori R. Arlinghaus1, Richard D. Dortch1, William A. Grissom1, Gregory S. Karczmar2, and Thomas E. Yankeelov1
1Vanderbilt University, Nashville, TN, United States, 2University of Chicago, Chicago, IL, United States

This study evaluated the effect of B1+ correction on T1 measurements calculated from variable flip angle (VFA) data in phantoms and in vivo. Additionally, the accuracy of these measurements was compared to T1 values from inversion recovery (IR) data. On average, 31% error was observed between IR and uncorrected VFA data in both phantoms and in vivo, which was significantly reduced to 6% (P<0.001) when applying a B1+ correction. IR measurements of T1 are very robust, yet the long acquisition times limit clinical utility. Therefore, these data suggest that the VFA method with B1+ correction is a suitable alternative.

1683.   Exponential T2 Fitting with Even Echoes Only or Skipping the First Echo: How Well Does it Work?
Kelly C McPhee1 and Alan H Wilman2
1Physics, University of Alberta, Edmonton, Alberta, Canada, 2Biomedical Engineering, University of Alberta, Edmonton, Alberta, Canada

It is common for researchers to skip the first echo, or skip all odd echoes in the echo train in order to determine T2 from exponential fitting multi-echo spin echo data. Using both simulations and in vivo experiments of slice selective muti-echo spin echo experiments, we find that these alternate exponential fitting schemes do not avoid T2-misestimation. Skipping the first echo may reduce errors to less than 10%, if very wide refocusing pulses are used, provided that the refocusing angles are >150 degrees.

1684.   Proton density mapping: Removing receive-inhomogeneity using multi-coil information and T1 regularization
Aviv Mezer1, Ariel Rokem2, Trevor Hastie2, and Brian Wandell2
1Edmond and Lily Safra Center for Brain Sciences, The Hebrew University, Jerusalem, Israel, 2Stanford university, CA, United States

Proton density is the most basic MRI measure, representing the amount of water protons in each voxel. Water content differs between tissue types, and changes during development and in disease. Using simulation we find that in the presence of noise, combining parallel imaging, smoothness assumptions, and the biophysical regularization together generates the most accurate estimates of both coil sensitivity maps and PD. We confirm the high accuracy when using multiple coils and T1-regularization on data from a phantom and a living human brain.

1685.   Bayesian Monte Carlo Analysis of mcDESPOT
Mustapha Bouhrara1 and Richard G. Spencer1
1National Institute on Aging, NIH, BALTIMORE, Maryland, United States

Stochastic region contraction (SRC) has been proposed as an efficient approach for extracting system parameters from mcDESPOT data. However, the SRC algorithm exhibits a high degree of sensitivity to initial parameter conditions, especially at low-to-moderate signal-to-noise ratios. In this study, we investigated the accuracy and precision of component fraction determination in a bicomponent mcDESPOT model using two Bayesian methods, based respectively on maximum posterior probability and means, and compared the results with those derived using the SRC algorithm. Results show that the estimation of component fractions was markedly improved through use of Bayesian analysis.

1686.   Compensating for Stimulated Echoes in Quantitative T2 Relaxometry
Dushyant Kumar1,2, Susanne Siemonsen1,3, Jens Fiehler1, and Jan Sedlacik1
1Neuroradiology, Universitätsklinikum Hamburg-Eppendorf, Hamburg, Hamburg, Germany, 2Multiple Sclerosis Imaging Section (SeMSI), Universitätsklinikum Hamburg-Eppendorf, Hamburg, Germany, Germany, 3Multiple Sclerosis Imaging Section (SeMSI), Universitätsklinikum Hamburg-Eppendorf, Hamburg, Hamburg, Germany

Problem: The voxelwise T2-decay deviate significantly from multi-exponential (ME) model due to the stimulated emission (SE) resulting from the imperfect slice profile of refocusing pulses and the B1-error and so, following ME model would lead to serious quantification inaccuracy. Methods: A novel post-processing method, combining extended phase graph model and multi-exponential model with nonnegative least-square, is being proposed to compensate for B1 error. The method requires using only QT2R data. Results & Conclusions: Both experimental and simulated results are presented to demonstrate the improvement. A significant improvement in myelin quantification is demonstrated when flip angle error is significant (≥8-10%).

1687.   Optimization of acquisition parameters for Magnetic Resonance Fingerprinting
Amaresha Shridhar Konar1, Rashmi R Rao1, Shaik Imam1, Shivaprasad Chikop1, Sachin Anchan1, and Sairam Geethanath1
1Medical Imaging Research Center, Dayananda Sagar College of Engineering, Bangalore, Karnataka, India

Magnetic Resonance Fingerprinting (MRF) provides simultaneous MR multi-parametric maps. Purpose of this work is to reduce the number of TR/FA and to obtain optimal combinations. PSIF sequence was used to obtain 3D plots for different brain tissue types and a difference plot of GM and WM were generated. 48 TR/FA (through sample size analysis) values were picked from difference plot to achieve high CNR and T1 and T2 maps were obtained by pattern matching algorithm. Mean and Standard deviation of T1 and T2 values for WM, GM, and CSF were calculated that lie in the standard range.

1688.   Comparison of Indirect and Stimulated Echo Compensated T2 Relaxometry Techniques: Extended Phase Graph vs Shinnar-Le Roux Based Modelling
Kelly C McPhee1 and Alan H Wilman2
1Physics, University of Alberta, Edmonton, Alberta, Canada, 2Biomedical Engineering, University of Alberta, Edmonton, Alberta, Canada

Recent works have implemented methods to fit for single component T2 from slice selective multi-echo spin echo experiments with indirect and stimulated echo compensation. These works have made use of either the Extended Phase Graph with Fourier Transform slice approximations, or Shinnar-Le Roux and Bloch simulations to model complete echo pathways. Here, we compare the recently demonstrated SLR based fitting technique with prior flip angle measurement to the EPG based method which is a commonly used correction technique for multi-echo spin echo based T2 measurements. We use simulations and human in vivo experiments to compare these two methods of indirect and stimulate echo compensated T2 fitting.

1689.   Optimizing and Comparing the Efficiencies of Relaxometry Sequences in Quantitative T1 and T2 Imaging
Yang Liu1, John R. Buck1, Shaokuan Zheng2, and Vasiliki N. Ikonomidou3
1Electrical and Computer Engineering, University of Massachusetts Dartmouth, North Dartmouth, MA, United States, 2Department of Radiology, University of Massachusetts Medical School, Worcester, MA, United States, 3Bioengineering, George Mason University, Fairfax, VA, United States

Quantitative MRI estimates MR quantities such as T1 and T2 as precisely and accurately as possible within a relatively short scan time. Although there is extensive relaxometry research for T1/T2 mapping, little effort has been made to statistically quantify T1/T2 estimate efficiencies. This paper establishes a framework to compare different relaxometry sequences on their T1/T2 estimate precisions per unit time. The new metric T1/T2-to-noise ratio (TNR) efficiency defines from the Cramer-Rao bound, a statistical lower bound on the parameter estimate variance. This framework fairly predicts the T1/T2 mapping performances of any relaxometry approaches before phantom or in vivo experiments.

1690.   Sources of Systematic Error in MRI Liver Fat Quantification
Mark Bydder1, Gavin Hamilton2, Ajinkya Desai2, Elhamy R Heba2, Tanya Wolfson2, and Claude B Sirlin2
1CRMBM UMR 7339, CNRS / Aix-Marseille Université, Marseille, France, 2University of California San Diego, CA, United States

This study investigates several sources of systematic errors affecting fat quantification by standard methods (chemical shift imaging). The influence from these different error parameters was assessed.

1691.   Improving Noise Robustness of the Quantitative (q)BOLD Model.
Jan Sedlacik1, Dushyant Kumar1, and Jens Fiehler1
1University Medical Center Hamburg-Eppendorf, Hamburg, Hamburg, Germany

The qBOLD model describes the effect of deoxygenated blood of the capillary network on the signal decay. However, the oxygenation extraction fraction (OEF) and the deoxygenated blood volume (DBV) affect the signal decay very similarly, which allows reliable OEF and DBV estimation only for very high signal to noise ratios (SNR>500). We improved the fitting of the qBOLD model by obscuring the divergent global minimum root mean squared errors (RMSE) by adding noise and finding an effective global minimum by analyzing the local RMSE minima.

1692.   MR Fingerprint assessment of capillary with quadratic coefficient and falling down parameter
Feng Qi1,2, Limiao Jiang1,2, Quek Swee Tian1, and Ng Thian C.1,2
1Diagnostic Radiology, National University of Singapore, Singapore, Singapore, Singapore, 2Clinical Imaging Research Cente, A*STAR-NUS, Singapore, Singapore, Singapore

MR Fingerprint approach can combine multiple de/rephsing mechanisms to resolve microvascular parameters in high spatial resolution. We propose two new biomarkers, quadratic coefficient q and falling down parameter f, to enhance r-v assessment accuracy by building MRF dictionary in q-f feature space (qf-MRF). Feature parameters q-f are acquired by SE-EPI before echo time, which preserve more microstructural information than traditional acquisition of relaxation rate at echo time. qf-MRF requires only 4 EPI readout, costing less than tenth of the scanning time of tradition MRF, while the estimation accuracy is improved by 59% as compared with traditional identical weighting MRF (iw-MRF)

1693.   Fast and Accurate Two-Component Relaxometry with EPG Simulations and Dictionary Searching
Pierre-Yves Baudin1, Benjamin Marty2,3, Ericky C.A. Araujo2,3, Noura Azzabou2,3, Pierre G. Carlier2,3, and Paulo Loureiro de Sousa4
1Consultants for Research in Imaging and Spectroscopy, Tournai, Belgium, 2NMR Laboratory, Institute of Myology, Paris, France, 3NMR Laboratory, CEA/I2BM/MIRCen, Paris, France,4ICube, Université de Strasbourg, CNRS, Strasbourg, France

T2 mapping from Multi-Slice Multi-Echo data is generally performed using a mono-exponential regression. However, the presence of stimulated echoes in the signal severely limits the performance of this approach and better signal models have been proposed, using the Bloch equations or the Extended-Phase-Graph (EPG) formalism. The case of mixed T2 decays – such as water and fat components in fatty infiltrated muscles - has been addressed via a non-negative least-square fitting of an EPG model, at the cost of long processing times. We propose a simpler and faster approach where a 2-component EPG model is explicitly fitted by dictionary searching.

1694.   Rapid calculation of correction parameters to compensate for imperfect RF spoiling in quantitative R1 mapping
Martina F. Callaghan1, Shaihan J Malik2, and Nikolaus Weiskopf1
1Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, London, London, United Kingdom, 2Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom

Quantitative MRI is attractive because of its standardised nature and higher specificity to underlying tissue microstructure. Acquiring spoiled gradient echo datasets with two different flip angles is an efficient approach to mapping the longitudinal relaxation rate with high resolution and whole brain coverage. However, this approach is biased when the transverse magnetisation is not fully spoiled. Correcting this effect relies on simulating the steady state signal taking account of the full suite of sequence parameters, including diffusion effects. Long simulations need to be recomputed for every sequence change. Here we demonstrate a rapid alternative using the extended phase graph approach.

1695.   Performing Dynamic Contrast-Enhanced MRI quality assurance for multi-centre trials using a multi-compartment phantom with physiological T1s
Neil Peter Jerome1, Vasia Papoutsaki1, James A d'Arcy1, Harold G Parkes1, Nandita deSouza1, Martin O Leach1, and David J Collins1
1Radiotherapy & Imaging, The Institute of Cancer Research, Sutton, London, United Kingdom

The inclusion of Dynamic Contrast Enhanced MRI into clinical trials, in particular those run across multiple centres, requires that quality assurance be performed, ensuring that functional parameters derived from different scanners may be usefully combined and compared. For DCE, the stability and noise characteristics are useful metrics for comparison; we present data from a multi-compartment test object with physiological T1s that allow comparison of DCE protocols with varying flip angles, as well as the same protocol acquired at two separate scanners, and demonstrate the usefulness of the test object for quality assurance of DCE-MRI.

1696.   Uncertainty Quantification of Multi-Site T1 Measurements with Polyvinylpyrrolidone (PVP) Phantom and Human Brain Using Wild Bootstrap Analysis
Congyu Liao1, Meng Chen1, Darong Zhu2, Hongjian He1, Song Chen1, Qiuping Ding1, and Jianhui Zhong1
1Center for Brain Imaging Science and Technology, Zhejiang University, Hangzhou, Zhejiang, China, 2Hangzhou First People's Hospital, Zhejiang, China

In this study, T1 mapping of a phantom with different concentration of Polyvinylpyrrolidone (PVP) solutions and a volunteer were acquired in two different 3T scanners using DESPOT1 method, and wild bootstrap analysis was used to assess both intra- and inter-site uncertainty of quantitative T1 measurements.

1697.   The optimal curve-fitting models for liver T2´ measurements iron overload in β-thalassemia major patients
Busakol Ngammuang1, Kittichai Wantanajittikul2, Monruedee Tapanya1, Suchaya Silvilairat3, Pimlak Charoenkwan3, and Suwit Saekho1
1Department of Radiological Technology, Faculty of Associated Medical Sciences, Chiang Mai University, Chiang Mai, Thailand, 2Biomedical Engineering Center, Faculty of Engineering, Chiang Mai University, Chiang Mai, Thailand, 3Department of Pediatrics, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand

T2' is another MRI parameter that reflects solely to the magnetic inhomogeneity and shows high correlations to LIC, T2 and T2*. We compare liver T2' obtained from ROI and pixel based method by three curve-fitting models, mono-exponential, offset and truncation model. Fifteen β thalassemia major patients were study. Results showed that ROI based method with offset curve fitting model potentially provided no significantly difference outcomes to those of pixel based method for liver T2´ measurements.