NMR imaging of water flow in packed beds

Measurements by magnetic resonance imaging (MRI) of water flow within granular porous media are presented in this study. Our goal was not only to obtain visualizations of velocity field in porous media but rather to make accurate measurements of interstitial and averaged velocities in bead packs. Two situations were examined: the first for a packed bed with a large beads diameter where it was possible to visualize the interstitial velocities and the second with a packed bed with a small beads diameter where only averaged interstitial velocities were measured

Free-breathing myocardial T2 measurements at 1.5T

POSTER PRESENTATIONInternational audienc

Effect of physiological Heart Rate variability on quantitative T-2 measurement with ECG-gated Fast Spin Echo (FSE) sequence and its retrospective correction

International audienceObject: Quantitative T-2 measurement is applied in cardiac Magnetic Resonance Imaging (MRI) for the diagnosis and follow-up of myocardial pathologies. Standard Electrocardiogram (ECG)-gated fast spin echo pulse sequences can be used clinically for T-2 assessment, with multiple breath-holds. However, heart rate is subject to physiological variability, which causes repetition time variations and affects the recovery of longitudinal magnetization between TR periods. Materials and methods: The bias caused by heart rate variability on quantitative T-2 measurements is evaluated for fast spin echo pulse sequence. Its retrospective correction based on an effective TR is proposed. Heart rate variations during breath-holds are provided by the ECG recordings from healthy volunteers. T-2 measurements were performed on a phantom with known T-2 values, by synchronizing the sequence with the recorded ECG. Cardiac T-2 measurements were performed twice on six volunteers. The impact of T-1 on T-2 is also studied. Results: Maximum error in T-2 is 26% for phantoms and 18% for myocardial measurement. It is reduced by the proposed compensation method to 20% for phantoms and 10% for in vivo measurements. Only approximate knowledge of T-1 is needed for T-2 correction. Conclusion: Heart rate variability may cause a bias in T-2 measurement with ECG-gated FSE. It needs to be taken into account to avoid a misleading diagnosis from the measurements

SIGNAL-TO-NOISE IMPROVEMENT IN MID-FIELD MRI SURFACE COILS - A DEGREE IN PLUMBING

International audienceAbstract: From a series of standard SE imaging sequences, performed on a Bruker 0.28 T imaging system, with the assistance of a healthy volunteer, the image signal-to-noise (S/N) ratio obtained from a 23-cm square surface coil has been shown to increase by up to 38% as the tube gauge is increased from 4 to 18 mm. The reason did not lie solely in the much improved Q factor of the unloaded coils. Despite a more than twofold increase in the unloaded Q factor, the loaded coil Q values only increased by 8%. It would appear, however, that the resistive, dielectric and inductive noise components are all reduced, and hence contribute to the observed improved S/N. The reduction in pure ohmic losses accounts for a quarter of the improved S/N, while the reduced inductive and dielectric losses provide the remaining three quarters. No independent quantification of the two latter noise sources was attempted, although a reduced dielectric contribution is confirmed qualitatively by a reduction in the negative frequency shift of the resonance frequency as a function of increasing coil gauge when the coil is loaded

NMR imaging of water flow in packed beds

Measurements by magnetic resonance imaging (MRI) of water flow within granular porous media are presented in this study. Our goal was not only to obtain visualizations of velocity field in porous media but rather to make accurate measurements of interstitial and averaged velocities in bead packs. Two situations were examined: the first for a packed bed with a large beads diameter where it was possible to visualize the interstitial velocities and the second with a packed bed with a small beads diameter where only averaged interstitial velocities were measured

Nonrigid registration improves MRI T-2 quantification in heart transplant patient follow-up

International audienceBackgroundTo evaluate the use of a nonrigid registration technique for detecting acute heart transplant rejection by MRI T-2 quantification. MethodsMyocardial T-2 quantification was achieved in 279 consecutive examinations from 78 different patients. The protocol consisted of 10 successive black-blood fast spin echo sequences with varying echo times, and a postprocessing based on image registration and exponential fitting. An automatic nonrigid registration method was applied to correct for myocardium misalignment. Finally T-2 values were compared with those obtained with a conventional rigid registration followed by manual correction. ResultsNonrigid registration was feasible in 98% of the datasets and was judged of higher quality compared with conventional processing (P<0.001). No significant difference was found in the clinical outcome (average septal T-2) between nonrigid and conventional registration (P=0.66). Interobserver variability was improved with 95% limits of agreement of 2.7 ms (against 3.7 ms with conventional registration). The quality of T-2 fitting, as assessed by the coefficient of determination R-2, was significantly improved (P<0.001). ConclusionNonrigid registration improves T-2 quantification in heart-transplant patient follow-up.J. Magn. Reson. Imaging 2015;42:168-174

NMR imaging of water flow in packed beds

Measurements by magnetic resonance imaging (MRI) of water flow within granular porous media are presented in this study. Our goal was not only to obtain visualizations of velocity field in porous media but rather to make accurate measurements of interstitial and averaged velocities in bead packs. Two situations were examined: the first for a packed bed with a large beads diameter where it was possible to visualize the interstitial velocities and the second with a packed bed with a small beads diameter where only averaged interstitial velocities were measured

Nuclear magnetic resonance spectroscopy of phosphorus in Becker's dystrophy

National audienc

P-31 NMR-SPECTROSCOPY IN MYOTONIC-DYSTROPHY

International audienc