Improving data acquisition parameters of 31P in vivo spectra for signal analysis in the time domain.

To obtain reliable NMR quantitation, experimental cautions concerning data acquisition must be taken when using automatic predictive calculations. For this study, 2000 31P in vitro and in vivo spectra were processed, using the enhancement procedure with linear prediction using singular value decomposition (EPLPSVD) method, and analyzed. The effects of quadrature detection modes (simultaneous or sequential), of the number of time-domain samples used are investigated and experimental conditions such as sample motions and spectral width are discussed.

Dental materials and magnetic resonance imaging.

Radiologists may encounter patients with fixed dental prostheses that may produce image distortion on MRI scans of the face and jaw. In this work, we assessed the MRI appearances of dental prosthetic materials in vitro, including precious alloys, nonprecious alloys, ceramic prostheses, dental amalgam, and composite materials. For in vivo studies, these materials were placed in the patient's mouth. Nonprecious alloys produce large image deformations, whereas precious alloys had no effect on MRI images. The in vivo study showed the anatomical zones that were most affected on MRI scans. The size of these zones produced by the presence of nonprecious alloys is influenced by the volume of the prosthesis and is related to the scanning sequence used.

Dipolar contrast for dense tissues imaging.

A new type of contrast called dipolar contrast is obtained by a decrease in the dipolar line broadening of protons. This contrast is usable for dense tissue NMR imaging and more generally for the study of dipolar linked protons in biological tissues. The sequence used is based on a variant of the Magic Sandwich Echoes (MSE) technique. In vitro experiments on a tendon sample are used to reinforce the image intensity of regions where the direct proton dipolar interaction exists.

Self-referencing subtractive angiography by modified stimulated echo in magnetic resonance imaging.

In magnetic resonance imaging, the modified stimulated echo sequence (MSTE) method significantly reduces the signal from stationary nuclei. This sequence was successfully applied to transverse imaging, improving the contrast of moving materials. With the results reported here, it will be shown that projective angiography using MSTE is also feasible without the usual subtraction of two separated images. Another advantage is selectivity with respect to velocity.

Spatial or flow velocity phase encoding gradients in NMR imaging.

We describe time modulated field gradient sequences able to selectively phase encode spatial location or flow velocity in NMR Signals. Two flow conditions are presented: constant flow velocity and simple harmonic flow superposed on steady flow. In each case we show that specific modulated gradients are available in order to discriminate between stationary and mobile protons. The methods are presented in the one dimensional case. The advantages of the phase modulation for flow analysis are the following: the method is sensitive to flow direction, unaffected by the T2, and the stationary and flow parameters are quantifiable factors.

Correlation between magnetic resonance imaging disturbances and the magnetic susceptibility of dental materials.

OBJECTIVES: The purpose of this study was to correlate the size and the orientation of image disturbances observed on specific samples of dental materials with their magnetic susceptibility. The measurement of the magnetic susceptibility was performed in the 10(-5) or 10(-6) range using MRI to establish a classification of dental materials. METHODS: Cylindrical dental alloy samples incorporating gold, silver, and palladium were placed in a Pyrex beaker filled with distilled water. Images were performed at 0.13 Tesla using two-dimensional Fourier transformation and projection reconstruction at 360 degrees imaging methods. The magnetic susceptibilities were obtained by measuring distances between spots having the highest intensity on the image. RESULTS: A very discriminating classification may be established on MRI criteria. This method permits one to determine the dia- or para-magnetic character of the dental materials tested. Only palladium-based alloys have been detected to be paramagnetic with kappa > 0. One of the silver-based alloys did not induce detectable distortion because its susceptibility was very close to that of distilled water. Based on this MRI data, the use of this material may be recommended for applications that may be subjected to MRI evaluation. SIGNIFICANCE: With the increasing use of MRI as a diagnostic tool, it is useful to establish a classification of prosthetic biomaterials compatible with MRI.

In vitro magnetic resonance imaging of rodent teeth.

OBJECTIVE: The anatomic structure of rat teeth was studied and observed using magnetic resonance imaging with high spatial resolution. STUDY DESIGN: The right part of the low mandible of two rats of 3 and 12 weeks old were analyzed. Images with different orientations were performed in a 2 Tesla magnetic field using the spin-echo imaging technique. RESULTS: Highly spatially resolved images revealed details of teeth, and anatomic differences between a young and an adult rat were demonstrated. CONCLUSION: Magnetic resonance imaging is well suited to image the buccal area and may be a useful tool for the diagnosis of dental diseases.

Disturbances caused by dental materials in magnetic resonance imaging.

Nuclear Magnetic Resonance (NMR) is the latest addition to medical imaging technology. This technique plays an important role in head and neck diagnosis. Radiologists may encounter patients with fixed dental prostheses that may produce image distortion on MRI scans of the face. The MRI appearances of dental prosthetic materials was studied in vitro, including precious alloys, non-precious alloys, ceramic prostheses, dental amalgam and composite materials. It was found that non-precious alloys produce large image deformations, whereas precious alloys had no effect on MRI images. An in vivo study showed the anatomical zones that were most affected on MRI scans.

Dosimetry of 60Co and 192Ir gamma-irradiated agarose gels by proton relaxation time measurement and NMR imaging, in a 0-100 Gy dose range.

Localized irradiation of the skin and subcutaneous tissues with large single doses of gamma rays can induce immediate effects characterized by erythema, desquamation, and necrosis. Correlations between the evolution of the lesions and dosimetry studies have to be established by biophysical methods. NMR studies of the effects of an irradiated Fricke solution might be a means of controlling the delivered irradiation doses. After exposition to ionizing radiations, ferrous ions are transformed into ferric ions. Both are paramagnetic ions, and proton spin-lattice relaxation is accelerated depending on the oxidation reaction. In this study, solution of ammonium ferrous sulfate in an acid environment was incorporated into a gelling substance made with agarose, so that T1 weighted image contrast could be used to detect ferric ion formation. Experiments with 192Ir and 60Co gamma rays with doses in the 0 to 100 Gy range were conducted with Fe2+ concentrations of 0.5, 1, 1.5, and 2 mM in a gelling substance containing 4% agarose. A relationship was established between the amount of Fe3+ created and the spin-lattice proton relaxation rate, which led to a straightforward dose-effect relation. The use of such high doses allowed us to reproduce realistic conditions of accidental overexposure. A linear relationship was obtained between the doses absorbed and the NMR parameters measured (T1 and relative image intensity).

Biomedical engineering degrees at Lyon 1 University.

Biomedical diploma degrees have a long tradition at Lyon 1, Claude Bernard University. Since 2004, the transition towards the LMD system leaded to a unified Bachelor and Master Degree in Biomedical Engineering. A next evolution plans the creation of a Biomedical Engineering Department in the future Polytechnic School of Claude Bernard University. This department will form professionals in Biomedical Engineering, Medical Physics and for academic employment in Universities and research structures.

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, optimi zing 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 (LOD(m), LOD(c)) 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.

NMR planar micro coils for micro spectroscopy: design and characterisation.

The goal of this study is to determine the concentration sensitivity and the limit of detection of a SNMR receiver planar micro coil with ellipsoidal geometry 1000x500 microm, fabricated using an electroplating technique and used as SNMR receiver coil at 200 MHz. The maximum signal intensity on the NMR images and simulation of RF field distribution allows defining an active volume of 0.8 microL. The localised spectroscopy based on a PRESS sequence shows that the concentration sensitivity is closed to S(C)=2.33 M(-1) and the limit of detection LOD=0.8 M. This micro-system offers the possibility of new investigation techniques based on implantable micro coils used for in vivo study of local cerebral metabolites occupying a small volume (microL to nL order).

Metabolite concentrations of healthy mouse brain by Magnetic Resonance Spectroscopy at 7 Tesla.

In vivo1H short echo-time Magnetic Resonance spectra are made up of overlapping spectral components from many metabolites. Typically, they exibit low signal-to-noise ratio. Metabolite concentrations are obtained by quantitating such spectra. Quantitation is difficult due to the superposition of metabolite resonances, macromolecules, lipids and water residue contributions. A fitting algorithm invoking extensive prior knowledge is needed. We quantitated1H in vivo mouse brain spectra obtained at 7 Tesla using the time-domain QUEST method combined with in vitro metabolite basis set signals. Brain metabolite concentrations estimated from eight mouse brain signals are compared to previously reported results.

[Recent developments in technics of nuclear magnetic resonance imaging]. / Récents développements des techniques en imagerie par RMN.

Three main aspects of presently developed nuclear magnetic resonance imaging techniques are pointed out in this short review: first, the importance of Fourier transform as reconstruction technique is recalled; secondly, the problem of the choice of the magnetic field value is raised and third, new trends in magnetic imaging are noticed such as the use of nuclei other than hydrogen or the improvement of phase contrast methods.

Proton spectral editing in the inhomogeneous radiofrequency field of a surface coil using modified stimulated echoes.

It is shown that the modified stimulated echo sequence, [theta](+/- x +/- y)-t1-[theta](+ x)-t2/2-[2 theta](+ x)-t2/2- [theta](+ x)-t1-Acq(+/- x +/- y), denoted as MSTE[2 theta]x according to the exciter phase of the 2 theta pulse, is able to perform proton spectral editing without difference spectra. On the other hand, this sequence appears to be suitable for spatial localization. Sensitivity and spatial selectivity of MSTE and conventional stimulated echo sequence (STE) are briefly compared. MSTE is applied to editing lactate in the rat brain using the locally restricted excitation of a surface coil.

A hybrid bird cage resonator for sodium observation at 4.7 T.

A bird cage resonator operating at 52.9 MHz is described. The particularity of the presented design is due to fixed capacitors between conductors. Tuning is performed by adjusting a self-capacitance system without breaking the coil symmetry. This structure denoted as "hybrid" is suitable for biological lossy samples.

Projection-reconstruction methods: fast imaging sequences and data processing.

New, rapid two- and three-dimensional imaging sequences based on steady-state gradient echoes and projection-reconstruction (PR) techniques are proposed. Quantitative studies show that fast PR sequences and classical, fast gradient-echo Fourier transform sequences lead to identical contrasts. In order to minimize inhomogeneity effects, a particular focus has been placed on echo-time reduction. The use of a weighting window permits one to acquire severely truncated echoes; partial k-space scanning may be considered.

A new approach for on-resonance magnetization transfer parameter optimization.

On-resonance radio frequency pulse sequences for magnetization transfer are optimized using a frequency domain approach. The method presented here was developed using binomial pulses and it is demonstrated that a simple analysis leads to accurate sequence parameters that can be used directly for magnetic resonance imaging. With thus optimized parameters it is possible to produce an efficient saturation of protons having short transverse relaxation time while protons with long transverse relaxation time are kept nearly unaffected by the radio frequency. The method is particularly well suited to the design of new magnetization transfer sequences and to the estimation of the limits of the accuracy of a T2 selection. Additionally in vitro tests have been performed on beef tendon oriented with a zero fiber to field angle.