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Biomedical subjects

A Briguet

Publications and source records attributed to A Briguet.

At least 19 recordsLinked to original sources
PubMed1996

Magnetic resonance imaging for the determination of magnetic susceptibility of materials.

A magnetic resonance imaging method for volume magnetic susceptibility estimate of materials immersed in a liquid containing resonant nuclei is proposed. The method uses either the standard spin-echo Fourier imaging technique or the projection-reconstruction technique. Image distortions of cylindrical macroscopic susceptibility inhomomogeneities are analyzed and a correlation is established between the susceptibility value and the size of image deformation along the read gradient. For measurements, the susceptibility of the liquid surrounding the sample (here deionized water) serves as a reference, and characteristic distances between particular points, usually highlights in the distorted image, are related to the susceptibility difference between the two media. Different samples, mainly prosthetic materials with a large susceptibility range from 5 to 200 ppm in absolute value, have been investigated, and the accuracy of susceptibility determination is discussed.

Magnetic Resonance Imaging↗
PubMed1994

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.

Animals↗
PubMed1994

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.

Artifacts↗
PubMed1992

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.

Electron Spin Resonance Spectroscopy↗
PubMed1992

Automatic in vivo NMR data processing based on an enhancement procedure and linear prediction method.

A new data processing method for in vivo NMR data quantitation is presented. This method (EPLPSVD) is based on the enhancement procedure (EP) proposed by J. A. Cadzow (IEEE Trans. Acoust. Speech Signal Process. 36, 49, 1988) followed by the usual linear prediction method using the singular value decomposition (LPSVD). The evaluation of this protocol is performed using synthesized 31P signals with different signal-to-noise ratios. A Monte-Carlo simulation as a function of signal-to-noise ratio (SNR) has proved that EPLPSVD leads to unbiased estimated values of parameters. Then the Cramer-Rao method yields reliable confidence intervals for the estimated parameters. The estimates of NMR parameters using EPLPSVD are reliable and accurate for SNR > or = 1.2 while the LPSVD method failed for SNR < or = 4. This protocol is applied to analyze automatically a series of 31P free induction decays obtained from the human gastrocnemius muscle during exercise. Spectral parameters with their confidence intervals, curves of relative intensity variations in phosphocreatine and inorganic phosphate, and pH curves are automatically provided.

Adenosine Triphosphate↗
PubMed1992

Simultaneous imaging of proton and fluorine at moderate field.

Simultaneous imaging of proton and fluorine nuclei distributed in a unique sample has been performed by multiplexing the receiver coil's frequency for nmr signal acquisition. Implementation of the technique and modifications of a conventional spectrometer are described for operating at 0.13 T.

Analog-Digital Conversion↗
PubMed1992

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.

Ceramics↗
PubMed1991

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.

Adult↗
PubMed1990

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.

Animals↗
PubMed1989

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.

Angiography↗
PubMed1985

[Recent developments in technics of nuclear magnetic resonance imaging].

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.

Fourier Analysis↗
PubMed1984

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.

Blood Circulation↗
PubMed1982

Estimating meconium (fetal feces) concentration in human amniotic fluid by nuclear magnetic resonance.

Measurements are reported of NMR relaxation times (T2) on hydrogen in water of isotonic NaCl solutions and of normal human amniotic fluid in which known concentrations of meconium (fetal feces) were dissolved. Magnetic fields for resonance of 23.5 X 10(3) and 0.6 oersteds were used. From the measured T2 values, reliable estimates of meconium concentrations could be obtained that might be considered estimates of fetal distress. Observed minor variation of T2 values was probably due to the mucopolysaccharides comprising 80% of the meconium weight. Advantages of this technique for possible clinical use in obstetrics include small volume of sample required (0.1 ml), lack of necessity for sample filtration or centrifugation, and shortness of time required for analysis (less than 30 min).

Amniotic Fluid↗