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Biomedical subjects

A Leroy-Willig

Publications and source records attributed to A Leroy-Willig.

16 recordsLinked to original sources
PubMed1992

Single-input double-tuned Foster-type probe circuit.

Synthesizing two different values of inductance from a given sample coil for use in a single-input double-tuned circuit is possible by means of three extra LC elements. A detailed analysis with derived equations shows how to calculate the circuit component values and what to expect from this kind of probe. It also derives the upper limit of the trap coil/sample coil inductance ratio beyond which no solution exists to double-tune the 31P-1H probe. The general expression for the channel efficiency shows that the latter is a function not only of the inductance of the coils, but also of their quality factor and of the operating frequencies. A numerical example is given illustrating good agreement between experiment and theory provided high quality rf capacitors are used.

Humans↗
PubMed1992

Magnetic resonance imaging to monitor pathology of caudate-putamen after excitotoxin-induced neuronal loss in the nonhuman primate brain.

We used MR imaging to locate and monitor in vivo the pathological events taking place 2 to 4 weeks after unilateral striatal injections of ibotenic acid (IA) in the Papio papio baboon. As early as 2 weeks after IA injections, excitotoxic lesions in the caudate and the putamen were directly visualized on T1-weighted images as small areas of low signal intensity. On T2-weighted images, the lesion sites were visualized as areas of high-intensity signal, spreading over larger areas than the corresponding regions in T1-weighted images. These alterations of T2-values in the lesioned striatum persisted 4 weeks after surgery. However, as the striatal degeneration progressed from 2 to 4 weeks after lesion, the size of the areas of high signal intensity on T2-weighted images decreased, whereas the same regions appeared essentially unmodified on T1-weighted images. A marked enlargement of the ipsilateral lateral ventricle (a characteristic of excitotoxic striatal lesions) could be detected 4 weeks after surgery, on both axial T1- and T2-weighted images. Comparisons of MR images with postmortem anatomical data indicated that areas of increased T1 values corresponded to regions of severe neuronal depletion (a direct result of the excitotoxic lesion), whereas areas of increased T2 values corresponded to regions of increased content in astrocytes and ferritin and probably in the early period following lesion (2 weeks) to a superimposed edema.

Animals↗
PubMed1992

Temperature changes induced in human muscle by radio-frequency H-1 decoupling: measurement with an MR imaging diffusion technique. Work in progress.

To investigate temperature increases in tissues during magnetic resonance (MR) imaging or spectroscopy, the authors measured temperature changes in vitro and in vivo (leg of a volunteer) in a condition simulating hydrogen-1 decoupling in MR spectroscopy. Noninvasive measurements were obtained by using the temperature dependence of the translational diffusion coefficient of water. Temperature was measured at 0.5 T (86 MHz) by using a stimulated-echo sequence that included intense gradient pulses and a procedure reducing sensitivity to bulk tissue motion. Calibration curves of the diffusion coefficient against thermocouple-measured temperature were obtained for a gelatin phantom and bovine muscle. Temperature changes were 5.3 degrees C +/- 0.5 at 2.5 cm from the coil in gelatin and 7.7 degrees C +/- 0.5 at 0.7 cm in bovine muscle. The temperature changed by 4.9 degrees C +/- 1.9 at 2.2 cm from the coil in the calf muscle of a volunteer. The H-1 decoupling protocol can be adapted (modifications in transmission power, duty cycle) to reduce heating effects to below safety recommendations.

Animals↗
PubMed1991

Exercise-induced muscle modifications: study of healthy subjects and patients with metabolic myopathies with MR imaging and P-31 spectroscopy.

Exercise-induced variations in proton signal intensity at magnetic resonance (MR) imaging and in intracellular pH were studied in the forearm muscles of healthy subjects and patients with muscular glycogenoses. The relative increase in T2 was measured from MR images obtained at 0.5 T, and end-exercise pH was measured with surface coil phosphorus-31 spectroscopy at 2 T. Eight healthy subjects showed a relative increase in T2 ranging from 20% to 44% in the flexor digitorum superficialis muscle and a drop in pH ranging from 0.35 to 1.1. Seven patients with muscular glycogenosis (six with McArdle disease and one with phosphofructokinase deficiency) showed only a slight variation in T2 (0%-17%) and no decrease in pH. Variations in T2 and in end-exercise pH were found to be correlated, perhaps reflecting the stimulation of muscular perfusion caused by acidosis.

Adult↗
PubMed1990

Spectroscopic MRI: a tool for the evaluation of systemic lipid storage disease.

Spectroscopic MR imaging allows to measure the lipid content of a region inside the human body. This technique has been applied to the case of a woman with a severe multisystemic triglyceride storage disease. Lipid contents of liver, pancreas, kidneys, left ventricle, skeletal muscles (calves, thighs, arms) were measured by using the Dixon spectroscopic imaging sequence. In some heterogeneous muscles, localized proton spectra were recorded. Results agreed with clinical findings (muscle weakness, normal renal and cardiac function, diabetes). These techniques could help to quantify the severity of the disease and to follow up its evolution under therapy.

Adult↗
PubMed1989

In vivo MR spectroscopic imaging of the adrenal glands: distinction between adenomas and carcinomas larger than 15 mm based on lipid content.

The usefulness of MR spectroscopic imaging for discriminating between lipid and water was applied to the in vivo differentiation of adrenal adenomas from carcinomas. By using the Dixon sequence in 20 patients, the lipid content of 22 adrenal tumors larger than 15 mm was determined. The mean percentage of lipid in 15 adenomas was 13.4% (standard deviation, 8%), compared with 3.5% lipid (standard deviation, 2%) in seven carcinomas. Only one lesion would have been misclassified on the basis of in vivo measurements of lipid content. After surgery, in vitro MR spectroscopy was used to determine the percentage of lipid in excised samples of nine of the 22 tumors. These in vitro measurements confirmed the in vivo results on lesions larger than 20 mm in diameter. Respiratory artifacts appeared to decrease the accuracy of in vivo measurements in smaller lesions. In vivo MR spectroscopic imaging of adrenal tumors appears to be useful for differentiating between adrenal carcinomas and adenomas.

Adenoma↗
PubMed1989

[Magnetic resonance imaging of the adrenal glands].

MRI is one of the most recent techniques of medical imaging. While it gives excellent results at the level of the skull, spine and pelvis, its use remains limited at thoracic and abdominal level because of movements which produce a deterioration in the image. However, the retroperitoneal space and in particular the adrenals may be explored under satisfactory conditions. The indications and results of this technique are discussed, based on the experience of adrenal examination in 90 cases.

Adenoma↗
PubMed1988

Parallel-plate split-conductor surface coil: analysis and design.

A split-conductor circular parallel-plate resonator with one end shorted to ground can be used to one's advantage as a surface coil for NMR imaging experiments. It can be easily constructed by a printed-circuit method and possesses a relatively high loaded Q with negligible frequency detuning. From the proposed equivalent circuit, an equation was derived that relates the self-resonance frequency of the resonator to the split distance measured from a reference point. An example of a 101-mm-diameter surface coil operating at 26 MHz for 31P in vivo spectroscopy is given to illustrate the concordance between calculated and experimental results. Complementary equations and formulas are also included to assist researchers in designing their own antennas to meet specific requirements.

Magnetic Resonance Imaging↗
PubMed1988

[Magnetic resonance imaging in the diagnosis of adrenal pathology].

M.R.I. allows a good delineation of adrenals, due to the high contrast with fat and to the use of frontal planes. We showed on post operative adrenal lesions samples that the lipid percentages, high in normal and hyperplasic glands, was still high in most benign adenomas, and very low (under 5%) in adrenal carcinomas. MRI, with Dixon sequence, allows to evaluate this lipid percentage in adrenal lesions. Post-operative controls show a good agreement between in vivo and in vitro measurements. This simple technique should allow to discriminate between malignant and benign adrenal cortex lesions.

Adenoma↗
PubMed1987

In vitro adrenal cortex lesions characterization by NMR spectroscopy.

Percentage of lipid content of 22 adrenal cortex lesions and their water proton longitudinal relaxation time were measured in vitro at 60 MHz. Although water relaxation times obtained on benign and malignant samples overlap each other, measurements of the percentage of lipids performed on the same tissues allow us to distinguish the two pathologies. The specific tool of characterization should be possible to obtain through in vivo spectroscopic imaging techniques.

Adenoma↗
PubMed1986

[Demonstration by spectroscopy NMR at 1,5 Tesla of changes in lipid/water ratio in pathology of the adrenal cortex].

By NMR proton spectrometry with a main field of approximately 1.5 Tesla the authors have studied on pieces obtained at surgery changes of the lipid/water ratio in the cortex of diseased adrenal glands. On the basis of 58 samples taken from 20 different glands they show that this ratio is comparable in hyperplasias and adenomas but quite significantly reduced in carcinomas. They are therefore of the opinion that this ratio might serve as a malignancy index in spectroscopic imaging of patients bearing tumors of the adrenal cortex.

Adenoma↗
PubMed1985

The slotted cylinder: an efficient probe for NMR imaging.

The slotted cylinder, an inductive structure with low self-inductance, low electric field, has been studied as a probe for NMR imaging applications. A theoretical calculation allows us to map the magnetic field and to evaluate electrical parameters of the structure. Several implementations, including new designs, have been experimentally tested over a wide range of frequencies (4-40 MHz), and compared to a classical coil probe. This study demonstrates the efficiency of the slotted cylinder for NMR imaging. It is optimized for large conductive samples when imaging at high frequencies (for human head, above 20 MHz).

Magnetic Resonance Spectroscopy↗
PubMedDate not supplied

[Osteonecrosis of the femoral head. MRI study of 60 cases].

Normal and pathologic femoral heads have been studied by MRI at 1.5 Tesla. The study was centered upon avascular necrosis (53 lesions). Twenty normal subjects and three patients with algodystrophy were examined. The osteonecrosis patterns were established from known lesions. A low signal rim surrounds an upper polar zone of conserved (Type I) or decreased (Type II) signal. The lesions age correlates significantly with their type: amongst type I lesions, 6 are asymptomatic and the 21 others have a mean age of 5.5 months; Type II lesions have a mean age of 12.7 months. Fourteen lesions were not seen on plain radiographs and six were not detected by bone scan. The older lesions with femoral head deformation are better depicted by standard radiologic techniques. Conservatively MRI is the most efficient examination for recent avascular necrosis lesions.

Adolescent↗