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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.

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.

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.

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.

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.

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.

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.

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.

Christian Brekken¹, Asta Håberg¹, Tina Pavlin¹, Pål Erik Goa, ¹², Atle Bjørnerud³, 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.

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