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R Luypaert

Publications and source records attributed to R Luypaert.

16 recordsLinked to original sources
PubMed1992

Contrast behavior between microadenoma and normal pituitary gland after gadolinium injection as a function of time at 1.5 T.

The behavior of contrast enhancement between a microadenoma and the normal pituitary gland after gadolinium injection was evaluated in 12 operatively confirmed cases using a repetitive sequence of four coronal T1-weighted spin echo series (T1 SE) (continuous acquisition, TR = 400 ms), followed by conventional coronal T1 SE (TR = 600 ms) and a three-dimensional fast low-angle shot sequence. The first and second acquisitions were useful with respect to delayed scans only in 3 cases (25%). Nevertheless, in these cases confident diagnosis could also be made on pre-contrast studies, which diminishes the real advantage of this finding. For a 1.5 T MRI unit we advocate starting with coronal T1 SE 30 s after a rapid injection of gadolinium.

Adenoma↗
PubMed1991

Absolute quantification of 31P muscle metabolites using NMRS with an internal standard and a high-Q, double-tuned coil.

31P-nuclear magnetic resonance spectroscopy (NMRS) is used to determine absolute concentrations of 31P metabolites in rat muscle. A technique exploiting tissue water 1H as internal concentration reference and a highly sensitive, double-tuned coil is described and evaluated experimentally. On KH2PO4 solutions of known concentration and varying coil loading it is shown to allow neutralization of systematic errors due to conductive losses, which normally range up to 20% or more. In vivo application in the determination of the absolute concentrations of ATP, PCr and Pi in eight rat thighs yields results that are in good agreement with literature values.

Adenosine Triphosphate↗
PubMed1990

Pituitary microadenomas: diagnosis with two-and three-dimensional MR imaging at 1.5 T before and after injection of gadolinium.

The usefulness of different magnetic resonance (MR) imaging sequences (coronal and sagittal spin-echo [SE] and three-dimensional fast low-angle shot [3D FLASH]) in the detection of pituitary microadenomas before and after gadolinium injection was prospectively evaluated in 28 patients with surgical confirmation. When evaluated separately, the most useful sequences in the detection of these microadenomas were coronal pregadolinium T1-weighted SE, coronal pregadolinium 3D FLASH, coronal postgadolinium T1-weighted SE, and coronal postgadolinium 3D FLASH. The combination of pre- and postgadolinium T1-weighted sequences with pre-and postgadolinium 3D FLASH sequences produced the highest number of true-positive findings (90%) and the lowest number of false-positive findings (5%). When a 1.5-T imaging unit with a high signal-to-noise ratio allowing useful three-dimensional acquisition is used, the authors advocate a coronal T1-weighted SE sequence, followed (if necessary) by a coronal 3D FLASH sequence, both without injection of gadolinium, in the diagnosis of pituitary microadenomas. When no confident diagnosis is reached, the same sequences should be performed after the injection of gadolinium. The sagittal pre- and postgadolinium T1-weighted SE and long-TR SE sequences are useful only in specific cases.

Adenoma↗
PubMed1990

31P-NMR spectroscopy and the metabolic properties of different muscle fibers.

To study the in vivo recruitment of different fiber types and their metabolic properties, 31P-nuclear magnetic resonance spectroscopy (31P-NMRS) of the human calf muscle was performed in seven normal sedentary subjects. In the exhaustive exercise protocol used, the work load was increased every minute during 5 min. This resulted in a prominent split of the Pi resonance in all subjects, indicating pH compartmentation in the muscles studied. From the chemical shift of the Pi peaks relative to phosphocreatine (PCr) at the end of the exercise, intracellular pH (pHi) averaged 6.92 +/- 0.05 (SD) in compartment 1 and 6.23 +/- 0.15 in compartment 2. The recovery of both Pi resonances after exercise could be followed easily in five of these subjects. The recovery rate of the Pi peak is a good estimate of the oxidative metabolism at the end of the exercise. A monoexponential regression analysis showed that the mean initial recovery rate S0 was 2.49 +/- 0.17%/s in compartment 1 and only 0.87 +/- 0.12%/s in compartment 2, indicating aerobic function three times higher in compartment 1 at the end of exercise. The mean relative ATP fraction dropped significantly (P less than 0.001), from 20.0 +/- 1.0% of the total 31P signal integral before exercise to 14.0 +/- 1.6% at the end of exercise. The simultaneous visualization of two compartments, in good order, one with high pHi and fast recovery and another with low pHi and slow recovery, is rationalized by the different metabolic behavior of type I and II fibers in human calf muscle in response to exhaustive exercise. This study demonstrates that 31P-NMRS is an excellent noninvasive procedure to quantify aerobic metabolism in both fiber types simultaneously.

Adenosine Triphosphate↗
PubMed1988

Evaluation of time interval difference digital subtraction fluoroscopy in patients with cystic fibrosis.

In this study the potential of thoracic subtraction fluoroscopy has been evaluated on the basis of our experience with this functional imaging modality in patients presenting with cystic fibrosis. The method, which consists of subtracting dynamic digital fluoroscopic images of the breathing chest in the time interval difference (TID) mode, applies to the study of the lucency variations during the respiratory cycle and provides dynamic functional information about ventilation and/or perfusion and diaphragmatic kinetics, without any injection and with minimal irradiation. To assess the validity of the TID procedure, our results were compared with standard roentgenography, clinical data, and scintigraphic findings, with emphasis on the latter. The limitations and advantages of TID compared with scintigraphy are discussed. Three groups of discrepancies emerge which do not discredit TID. TID offers rather the advantage of providing anatomic pictures and unique dynamic information, which is emphasized.

Cystic Fibrosis↗
PubMed1988

Reproducibility of CT bone densitometry: operator versus automated ROI definition.

Intrasubject reproducibility with repeated determination of vertebral mineral density from a given set of CT images was investigated. The region of interest (ROI) in 10 patient scans was selected by four independent operators either manually or with an automated procedure separating cortical and spongeous bone, the operators being requested to interact in ROI selection. The mean intrasubject variation was found to be much lower with the automated process (0.3 to 0.6%) than with the conventional method (2.5 to 5.2%). In a second study, 10 patients were examined twice to determine the reproducibility of CT slice selection by the operator. The errors were of the same order of magnitude as in ROI selection.

Algorithms↗
PubMed1985

Radionuclide evaluation of left ventricular synergic pumping efficiency during acute myocardial infarction.

The clinical value of an index of left ventricular synergic pumping efficiency (EFF) was evaluated in 50 patients with uncomplicated myocardial infarction in which radionuclide ventriculography was performed within 72 h of the onset of the infarction and between 7 and 13 days post infarction. EFF was defined as the ratio of global left ventricular stroke volume to the magnitude of all intraventricular blood pool variations measured on a pixel by pixel basis. EFF correlated better with a subjectively evaluated wall motion index (r = 0.84) than did the ejection fraction (EF) measurements (r = 0.69). In all patients, but most significantly in patients with inferoposterior infarctions, EFF measurements in the acute phase were a better predictor of the predischarge ventricular performance than the EF measurements. The left ventricular EFF is a reliable parameter to quantitate the effect of regional wall motion disturbances on global ventricular function in a standardized manner.

Adult↗
PubMedDate not supplied

Absolute quantification of 31P liver metabolites in rat using an external reference and a surface spoiling magnetic field gradient.

A simple method for measuring absolute concentrations of 31P metabolites in rat liver using an external reference is described. It neutralizes systematic errors due to conductive losses by calibration of the matching capacitor and selects liver signals via an electrically driven, surface spoiling magnetic field gradient. The technique avoids the chemical shift problems associated with linear field gradient localization methods at 4.7 T and allows combination with the double standard method for absolute metabolite concentration determination. Application of the method to the in vivo measurement of the absolute concentrations of ATP and P(i) in eight rat livers yields results that are in good agreement with literature values. Absolute phosphomonoester concentrations were also obtained, but no literature data were available.

Adenosine Triphosphate↗