Relaxometry

Tuesday 13 May 2014

Rahel Heule¹, Peter Bär², Christian Mirkes^3,4, Klaus Scheffler^3,4, Siegfried Trattnig², and Oliver Bieri^1
1Division of Radiological Physics, Department of Radiology, University of Basel Hospital, Basel, Switzerland, ²MR Centre of Excellence, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria, ³MRC Department, Max Planck Institute for Biological Cybernetics, Tübingen, Germany, ⁴Department of Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany

Quantitative imaging at high to ultra-high fields suffers from prominent B1 field inhomogeneities that affect quantification accuracy. Recently, a 3D triple echo steady-state (TESS) approach has been presented that offers fast B1-insensitive T2 quantification. In this work, the sensitivity to subject motion of 3D-TESS is reduced by investigating a rapid 2D technique suited for brain applications. The feasibility and reliability of 2D TESS-T2 relaxometry is demonstrated in human brain scans at high (3 T) and ultra-high (7 T and 9.4 T) fields. The results accentuate the potential of TESS-T2 to act as valuable measure for the detection of brain tissue alterations.

Bruno Madore¹, Cheng-Chieh Cheng², and Chang-Sheng Mei^1
1Department of Radiology, Harvard Medical School, Brigham and Womens' Hospital, Boston, MA, United States, ²Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan

From 3D data acquired over no more than a few minutes, the present method aims to evaluate all of the main physical MR parameters: T1, T2, T2*, M0, B0 and B1. A single pulse sequence is employed, and the various MR parameters can be evaluated one at a time and/or through linear equations, as opposed to numerically solving larger and non-linear systems of equations involving many or all parameters at once. As few as only two MR scans may be acquired, using different nominal user-input flips angles and/or different repetition times. Simulated and phantom results are presented.

Yoonho Nam¹, Jongho Lee², Dosik Hwang¹, and Dong-Hyun Kim^1
1Department of Electrical and Electronic Engineering, Yonsei University, Seoul, Korea, ²Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States

Myelin water imaging has been proposed as a potential biomarker for demyelinating diseases. In this study, we demonstrated that the multi-component model with frequency offsets offers substantially reliable MWF results that are less affected by the number of echoes used in the analysis. Additionally, we revealed that the MWF map generated from early echoes is less sensitive to B0 field inhomogeneity and, hence, provides wider brain coverage. Lastly, we performed a test-retest scan and demonstrated that the frequency offset model with early echoes provides more reproducible results.

Hyo Min Lee^1,2, Daeun Kim¹, Sung Suk Oh¹, Joon Yul Choi¹, Se-Hong Oh¹, and Jongho Lee^1
1Radiology, University of Pennsylvania, Philadelphia, PA, United States, ²Bioengineering, University of Pennsylvania, Philadelphia, PA, United States

The signal characteristics of a novel myelin water imaging method, direct visualization of short transverse relaxation time component (ViSTa), have been explored. The results show that the phase evolution and magnetization transfer effects of ViSTa match well with those of myelin water and are substantially different from those of GRE. These results, in addition to short T2* characteristics of ViSTa, further support the origin of ViSTa signal to myelin water.

Mengchao Pei^1,2, Thanh D. Nguyen³, Nanda D. Thimmappa³, Carlo Salustri³, Fang Dong², Mitchell A. Cooper⁴, Jianqi Li⁵, Martin Prince³, and Yi Wang^3
1East China Normal University, Shanghai, Shanghai, China, ²Yifu Inc, Jiaxing, Zhejiang, China, ³Radiology, Weill Cornell Medical College, New York, NY, United States, ⁴Cornell University, Ithaca, NY, United States, ⁵East China Normal University, Shanghai, China

We propose a novel fast and accurate method for calculating transverse relaxation times called Auto Regression on Linear Operations (ARLO). T2^*mapping using simulated and in vivo data showed ARLO delivered comparable accuracy compared to the non-linear least squares based Levenberg-Marquardt (LM) algorithm and better accuracy for lower SNR and shorter T2^* compared to the Log-Linear (LL) algorithm. ARLO is approximately 100 and 10 times faster than LM and LL, respectively, enabling rapid whole-organ T2^* mapping.

André Ahlgren¹, Ronnie Wirestam¹, Freddy Ståhlberg^1,2, and Linda Knutsson^1
1Department of Medical Radiation Physics, Lund University, Lund, Sweden, ²Department of Diagnostic Radiology, Lund University, Lund, Sweden

Brain segmentation based on multi-component modelling of quantitative MRI data has yielded great interest recently. Those methods are attractive due to their simplicity in modelling and processing. In this work, we present a novel method to segment gray matter, white matter, and cerebrospinal fluid, based on a spoiled gradient-recalled echo (SPGR) sequence acquired with varying flip angles (VFA). The method, dubbed ‘SPGR-SEG’, yielded robust and realistic segmentation maps in good agreement with a reference method based on inversion recovery data.

Timo Liimatainen¹, Djaudat Idiyatullin², Jinjin Zhang², Hanne Hakkarainen¹, Silvia Mangia², Michael Garwood², and Shalom Michaeli^2
1A.I.Virtanen Institute, University of Eastern Finland, Kuopio, FI, Finland, ²Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

The general procedure of generating tissue contrast which is characterized predominantly by slow motion by altering steady state in SWIFT with RAFFn preparation pulses is described. It is shown that high rotating frame relaxation contrasts obtained with RAFFn provide enhanced sensitivity to slow motion in tissue and is associated with myelin in the brain.

Thanh D. Nguyen¹, Kofi Deh¹, Ashish Raj¹, Martin Prince¹, Yi Wang¹, and Susan A. Gauthier^2
1Radiology, Weill Cornell Medical College, New York, NY, United States, ²Neurology and Neuroscience, Weill Cornell Medical College, New York, NY, United States

An adiabatic T2prep design based on the modified BIR-4 pulse is proposed for multicomponent T2 relaxometry of the brain at 3T. When compared to the conventional composite refocusing T2prep, our results show that the proposed BIR-4 design provides more accurate T2 weighting against increased field inhomogeneities at 3T, enabling fast and reliable whole brain myelin water mapping in 10 minutes.

Diego Hernando¹, Ihab Kamel², Li Pan³, Ivan Pedrosa^4,5, Shreyas Vasanawala⁶, Takeshi Yokoo^4,5, Qing Yuan⁴, and Scott B. Reeder^1,7
1Radiology, University of Wisconsin-Madison, Madison, WI, United States, ²Radiology, Johns Hopkins University, MD, United States, ³Corporate Technology, Siemens Corporation, Baltimore, MD, United States, ⁴Radiology, UT Southwestern Medical Center, Dallas, TX, United States, ⁵Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States, ⁶Radiology, Stanford University, CA, United States, ⁷Medicine, University of Wisconsin-Madison, Madison, WI, United States

Recently developed R2* relaxometry techniques may enable rapid, accurate and robust liver iron quantification. However, the reproducibility of these techniques across multiple sites and MRI platforms has not been established, precluding their widespread dissemination. In this work, we studied the reproducibility of R2* mapping on a phantom with different iron concentrations, at four sites and on eight different scanning platforms including 1.5T and 3T. Results demonstrate excellent reproducibility across sites and platforms at each field strength over a wide range of R2* values.

Peter van Gelderen¹, Xu Jiang¹, Jacco A de Zwart¹, and Jeff H Duyn^1
1AMRI, LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States

To investigate the possibility of using T₁ contrast to selectively image myelin water, inversion-recovery prepared multi-gradient-echo imaging was performed on human subjects at 7T. Multi-component fitting of the T₂* decay curve allowed distinguishing between water inside and outside the myelin sheath and quantifying individual T₁-decay time constants. When properly accounting for imperfect inversion efficiency, no substantial difference between apparent T₁ of the different compartments was found, suggesting a relatively rapid exchange of water within and outside the myelin sheath.