Improved Accuracy of Variable Flip Angle T1 Measurements
Using Optimal Radiofrequency and Gradient Spoiling
Vasily L. Yarnykh1
1University of Washington, Seattle, Washington, USA
A variable flip angle (VFA) method is widely used for in vivo T1 mapping due to its time efficiency and easy 3D implementation with a large anatomical coverage. Practical implementations of VFA are typically based on a radiofrequency (RF) spoiled gradient echo (GRE) sequence. Incomplete spoiling was recently identified as a critical source of errors in the VFA method. Such errors are caused by the dependence of the optimal phase increment in the RF spoiling scheme on T2 of the object. This study demonstrates the way to overcome this problem by using a combination of RF and gradient spoiling and also presents a general methodology for theoretical analysis of spoiling phenomena.
An RF Pulse with Spoiled Sidebands Improves the
Accuracy of T1 Measurement in DCE-MRI
Dustin K. Ragan1, James Andrew Bankson1
1M. D. Anderson Cancer Center, Houston, Texas, USA
Quantitative studies using DCE-MRI depend upon accurate measurement of T1, however, accuracy is limited by the accuracy of the expected flip angle, which is in turn limited by the slice profile. Through simulation, we demonstrate the effects of slice profile errors on the measurement of quantitative pharmacokinetic parameters with several realistic and hypothetical pulses. We propose a novel pulse that generates a slice with suppressed sidelobes, minimizing their effects on T1 quantification. In phantom we show a marked improvement in the accuracy of T1 measurement with a two-point gradient echo technique compared to a conventional sinc pulse.
Robust Simultaneous δ R2 and δ R2*
Estimation for Vessel Size Imaging
Stefanie Winkelmann1, Julien Sénégas1, Janine Ring2, Thorsten Persigehl2, Christoph Bremer2, Hannes Dahnke1
1Philips Research Europe, Hamburg, Germany; 2University Hospital Münster, Münster, Germany
Recently it was shown that the mean vessel size of a tumor can be estimated from the local change of R2* and R2 induced by an iron-oxide based blood-pool agent. However, the fast wash-out characteristics of available contrast agents demand the rapid and simultaneous quantification of δ R2* and δ R2. We present a new MR sequence with a dedicated post-processing algorithm to achieve accurate δ R2* and δ R2 maps that are insensitive to large scale B0 and B1 field inhomogeneities as well as slice imperfections. The approach yielded very accurate and reproducible δ R2 and δ R2* maps in phantom and animal experiments.
Orientation Dependence of White Matter T2* Contrast at 7
T : A Direct Demonstration
Christopher John Wiggins1, Valdis Gudmundsdottir1, Denis Le Bihan1, Vincent Lebon1, Myriam Chaumeil1
1CEA/NeuroSpin, Saclay, France
By manipulating the position of the head of a macaque, it is demonstrated that some of the white matter T2* contrast seen in long TE images at 7T is strongly dependent on the orientation of the tissue relative to the main magnetic field.
Modified PROPELLER Approach for T2-Mapping of the
Jie Deng1, 2, Andrew C. Larson1
1Northwestern University, Chicago, Illinois, USA
T2 mapping in the abdomen using SE or 2DFT-TSE sequences is challenging due to motion. The SE sequence requires long imaging times. TSE sequences can reduce imaging time but may be inaccurate due to stimulated echo accumulation. Furthermore, echoes not occurring at the effective TE may result in complex T2W signal contribution. Multi-shot TSE-based PROPELLER techniques have been shown to be less sensitive to motion artifacts. In this study we modified the PROPELLER sequence and acquisition approach to perform T2 mapping of the abdomen. We demonstrate that our modified PROPELLER approach permits robust acquisition of accurate, high-quality abdominal T2 maps.
Simultaneous T2- And T1-Mapping for Cardiac Applications
Ulrike Blume1, Christian Stehning2, Stephen Sinclair1, Sergio Uribe1, Vicky Parish1, Tim Lockie1, Reza Razavi1, Tobias Schaeffter1
1King's College London, London, UK; 2Philips Research Europe, Hamburg, Germany
Cardiac MRI can depict areas of acute and chronic myocardial infarction by using different imaging sequences. In this work we propose free breathing navigator gated and ECG-triggered interleaved T2- and T1-mapping sequence which can be applied to acquire quantitative maps of heart in only one scan. First results are shown in phantoms and in vivo in 7 healthy volunteers and one patient with an acute myocardial infarction. The method has the potential to differentiate between acute and chronic MI by estimating the concentration of Gd from Δ R1 in the necrotic tissue and to assess edema from T2-maps.
Gleaning Multi-Component T1 and T2
Information from Steady-State Imaging Data
Sean CL Deoni1, 2, Brian K. Rutt3, Tarunya Arun1, Carlo Pierpaoli4, Derek K. Jones5
1University of Oxford, Oxford, UK; 2Institute of Psychiatry, London, UK; 3Robarts Research Institute, London, Canada; 4National Institutes of Health, Bethesda, USA; 5Cardiff University Brain Research Imaging Centre, Cardiff, UK
Driven Equilibrium Single Pulse Observation of T1 and T2 (DESPOT1 and DESPOT2) are rapid, accurate and precise methods for quantifying the longitudinal and transverse relaxation times. An implicit assumption in the methods, however, is that of single-component relaxation which is not true in a variety of biological tissues, including human white and grey matter. In this work, we extend the DESPOT1 and DESPOT2 methods to include multi-component relaxation and demonstrate the ability to quantify component-specific T1, T2, volume fraction and mean residence time values over the whole-brain at high resolution.
Volumetric Simultaneous T1, T2, T2* and Proton
Density Mapping in One Minute Using Interleaved Inversion Recovery SSFP
and Multi Gradient Echo Imaging
Christian Stehning1, Stefanie Winkelmann1, Julien Sénégas1, Hannes Dahnke1
1Philips Research, Hamburg, Germany
A fast method for a simultaneous quantification of T1, T2, T2* and proton density is presented. The scan time is approximately one minute for a volumetric coverage of the brain. The sequence allows for rapid quantitative MRI, and represents a fast localizer scan for the generation of synthetic MR images with user-defined contrast.
Quantitative Diffusion, Perfusion and T2 Brain MRI of
the α -Syntrophin Knockout Mouse in the Resting State
Christian Brekken1, Asta Hĺberg1, Tina Pavlin1, Pĺl Erik Goa, 12, Atle Bjřrnerud3, Olav Haraldseth1, 2, Ole Petter Ottersen4, Erlend A. Nagelhus4
1NTNU, Trondheim, Norway; 2St.Olavs Hospital HF, Trondheim, Norway; 3The National Hospital, Oslo, Norway; 4University of Oslo, Oslo, Norway
The predominate water protein.
Characterizing White Matter Damage in Rat Spinal Cord
with Quantitative MRI and Histology
Piotr Kozlowski1, Disha Raj1, Jie Liu2, Clarrie Lam2, Andrew Yung1, Wolfram Tetzlaff2
1UBC MRI Research Centre, Vancouver, Canada; 2ICORD, Vancouver, Canada
DTI and quantitative T2 MRI were used to characterize ex vivo the white matter damage 3 and 8 weeks following dorsal column transection (DC Tx) injury of the cervical rat spinal cord. MRI parameters were correlated with histology. Myelin water fraction (MWF) showed stronger correlation with myelin staining than transverse diffusivity. Both longitudinal diffusivity (Dlong) and fractional anisotropy correlated significantly with axonal count at 3 weeks post-injury, while only Dlong displayed significant correlation 8 weeks post-injury. This study demonstrates that quantitative MRI can accurately characterize white matter damage in DC Tx model of injury in rat spinal cord