Latifa Fakri-Bouchet

Real-time gating system for mouse cardiovascular MR imaging

Mouse cardiac MR gating using ECG is affected by the hostile MR environment. It requires appropriate signal processing and correct QRS detection, but gating software methods are currently limited. In this study we sought to demonstrate the feasibility of digital real‐time automatically updated gating methods, based on optimizing a signal‐processing technique for different mouse strains. High‐resolution MR images of mouse hearts and aortic arches were acquired using a chain consisting of ECG signal detection, digital signal processing, and gating signal generation modeled using Simulink (The MathWorks, Inc., Natick, MA, USA). The signal‐processing algorithms used were respectively low‐pass filtering, nonlinear passband, and wavelet decomposition. Both updated and nonupdated gating signal generation methods were tested. Noise reduction was assessed by comparison of the ECG signal‐to‐noise ratio (SNR) before and after each processing step. Gating performance was assessed by measuring QRS detection accuracy before and after online trigger‐level adjustments. Low‐pass filtering with trigger‐level adjustment gave the best performance for mouse cardiovascular imaging using gradient‐echo (GE), spin‐echo (SE), and fast SE (FSE) sequences with minimum induced delay and maximum gating efficiency (99% sensitivity and R‐peak detection). This simple digital gating interface will allow various gating strategies to be optimized for cardiovascular MR explorations in mice. Magn Reson Med 57:29–39, 2007.

Evaluation of coils for imaging histological slides: Signal-to-noise ratio and filling factor

To investigate the relative gain in sensitivity of five histology coils designed in‐house to accommodate tissue sections of various sizes and compare with commercial mouse head coils.

Investigation of NMR limits of detection for implantable microcoils

Although NMR has the ability to investigate biological systems non-destructively, its low sensitivity primarily has hampered their investigation compared to other analytical techniques. Therefore, optimizing radio frequency (RF) coils to improve sensitivity do offer benefits in MR spectroscopy (MRS). Sensitivity may be improved for mass- and volume- limited samples if the size of the detection RF coils matches the sample size. In this paper, the mass- and concentration-limit of detection (LODm, LODc) for an implantable microcoil will be estimated by MRS measurements and then compared with their analytical values. For a sample containing a solution of several cerebral metabolites, for the Choline case, the LODm is 5.7-10-9 mol and LODc of 3.8 mM. These preliminary results enable to open largely the biomedical applications based on cerebral metabolism investigation on small animal experiments.

Measurements of the radiofrequency field in magnetic resonance coils

This design note describes an inexpensive system used to control the radiofrequency field generated by magnetic resonance coils. The device is built around three main modules, a sequencer, a modulator and a phase-sensitive detector. This system permits one to detect the radiofrequency field at each point of the region of interest using a pick-up coil, without the requirement of a magnetic resonance spectrometer. Examples of radiofrequency field distributions obtained at 85 MHz are given.

In vivo animal NMR studies using implantable micro coil

This study aims at developing in vivo exploration based on NMR (Imaging and Spectroscopy) using implantable micro coils ldquoNeedle coilsrdquo. Analysis of highly localized tissue of few nanolitres with this ldquominimardquo invasive method is possible. Reinforced by acquisition and signal processing methodology, it aims at pushing the limits of in vivo detection, thus opening the way to a number of biomedical applications. To the best of our knowledge, no in vivo study has been done with such ldquohigh-tech micro coilsrdquo. Axial MRI slices, allow measurements of the lesion dimensions, compared to the micro coil size and to stereotaxic coordinates determined with the rat atlas and histological control. These first results validate the reproducibility of micro coil implantation under stereotaxic conditions, the biocompatibility aspect and the good micro coil performance in situ. This micro system offers the possibility of new investigation techniques with chronic implantation based on micro coils used for in vivo study of local cerebral metabolites occupying a small volume.

Electrothermal Modeling for 3-D Nanoscale Circuit Substrates: Noise

We apprehend, here, some insights into 3-D integration modeling, from a physical point of view, concerning electrical and temperature domains in transient regimes, applied to multilayered silicon substrates, as well as an insight into noise study. This paper is motivated by the need to develop more general analytical coupled solutions in these fields, manageable by the industry. It is also a track for a synthesis beginning. First of all, we calculate the spreading impedance. For this, our approach is twofold: compact Green kernels or a transmission line matrix method, with contacts over or into the multilayered substrate, is derived by solving Poissons equation analytically. All the resolution of the equation system is done in the reciprocal domain, extracting real value only at the end of the calculation process. It permits to extract 3-D impedances between any two embedded contacts of any shape, real or virtual; this is original, to the best of our knowledge. Indeed, we calculate 3-D time-dependent temperature maps, from heat equation, from any contact into the bulk. We propose not only to couple the two master equations, Poisson and heat, but to show that our methodology, applied to these two equations, can also be addressed to noise propagation. We investigate our models on both analytical and numerical methods. These extended models should enable extracting substrate impedances and parasitic elements, in 3-D.

MRI of Histological Tissue: Effect of Passive Gadolinium-Staining

across groups. However, when the proportion of 1.5T and 3T scans differed across patient groups the segmentation biases were apparent (Figure 1A & B, highlighted in green) and reduced the reliability of the results. These biases reduced as the proportion of 1.5T and 3T images in each patient group gets closer to the situation where they are matched across patient groups. Including field strength as a covariate reduced the biases but also reduced the amount of significant results. Conclusions: This study shows that field strength influences VBM assessments of atrophy: combining data acquired at 1.5T and 3T in VBM studies is however possible as long as the proportion of different field strengths is matched across patient groups.

High-Resolution 1H NMR Micro spectroscopy using an Implantable Micro-coil

This study presents a new concept of implantable micro coil (1000 times 500 mum2) fabricated using an electroplating technique, used as receiver coil at 200 MHz for the measurement of small volumes and concentrations samples by NMR spectroscopy. Our goal is to determine its concentration sensitivity Sc and its limit of detection LOD. The MRI and simulation of RF field distribution allows defining an active volume of 0.8 muL. The spectroscopic results show that the Sc is closed to 0.2691 mM-1 and LOD of 11.1 mM. This micro-system offers the possibility of new investigation techniques like local cerebral metabolites occupying small volumes (muL to nL).