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Biomedical subjects

C Boesch

Publications and source records attributed to C Boesch.

At least 91 records · Page 5Linked to original sources
PubMed1995

The dynamics of brain concentrations of phenylalanine and its clinical significance in patients with phenylketonuria determined by in vivo 1H magnetic resonance spectroscopy.

Cerebral concentrations of phenylalanine (PHE) were measured by means of quantitative in vivo 1H MR spectroscopy in 8 adult patients treated early for phenylketonuria type I. A 1.5-Tesla routine magnetic resonance scanner, localization sequence with short echo time (20 ms), and a fully automated data processing scheme were used. Baseline plasma PHE concentrations were 1.04 (0.70-1.39) mmol/L PHE with concurrent brain PHE concentrations of 0.27 (0.13-0.41) mmol/kg of wet weight resulting in a plasma/brain ratio of 4.12. Plasma and brain concentrations correlated significantly (Kendall tau b = 0.91, p < 0.01). During an oral load with a single dose of 100 mg L-PHE per kg of body weight in four patients, plasma levels steeply increased. Concurrent brain PHE increase was less steep, was significantly delayed, and still continued up to 20 h postload. Despite the proven rise in plasma and brain concentrations of PHE, neuropsychologic examinations revealed no impairment of attentional and fine motor abilities from preload up to 20 h postload.

Adult↗
PubMed1994

Electrocardiogram acquisition during MR examinations for patient monitoring and sequence triggering.

We have developed a method for measuring the electrocardiogram (ECG) continuously during MR examinations. In contrast to ECG acquisition by wires, our new method is to amplify and convert the ECG into an optical signal directly above the patient's heart. The optical signal is transmitted out of the magnet bore by optical fiber. The small and fixed dimensions of the ECG amplifier avoid interactions with the MR system because of shorter electrical structures and smaller enclosed areas. Tests of the proposed device in a 1.5 Tesla MR system show that continuous and reliable ECG monitoring and sequence triggering are possible.

Adult↗
PubMed1994

Quantitative MR imaging of lumbar intervertebral disc and vertebral bodies: methodology, reproducibility, and preliminary results.

Since relaxation times are influenced by the hydration of the tissue and the chemical environment of the water molecules, T1 and T2 measurements (quantitative MRI) could be used as an indicator for the water content and the biochemical composition of lumbar intervertebral discs. The discriminating power of quantitative MRI for tissue characterization in individuals (for clinical diagnosis) and in cohorts (e.g. for investigations on disc physiology or composition) relies on the reproducibility in relation to the expected tissue differences. We therefore investigated the reproducibility in vitro (lumbar spine phantom) and in vivo (10 volunteers). To estimate the differences between normal and pathologic tissues in vivo, 100 normal and 20 herniated intervertebral discs were examined by quantitative MRI in a first application of our method. The relaxation times were calculated from a set of 20 images obtained with five single-slice/multi-echo sequences at different TR values on a commercial whole-body system (1.5 T). We have found a satisfactory reproducibility in vitro (T1: 1.9%; T2: 6.2%), while the reproducibility was less satisfactory in vivo (T1: 16.4%; T2: 13.4%). Calculated from theses values, differences in relaxation times of various tissues must exceed 486 ms for T1 and 24 ms for T2 (tolerance limits) to allow discrimination with a 95% confidence in individuals. We observed statistically significant (p = 0.001) mean differences between normal (n = 100) and herniated (n = 20) intervertebral discs (delta T1: 196 ms; delta T2: 15 ms). Although statistical significant in cohorts, a discrimination of normal and herniated intervertebral discs is limited by quantitative MRI in individuals, since the differences are smaller than the tolerance limits necessary for a reliable clinical diagnosis. However, our results indicate that variations in the disc hydration and/or composition can be noninvasively detected by quantitative MRI in studies of cohorts with sufficient accuracy.

Adolescent↗
PubMed1993

Determination of saturation factors in 31P NMR spectra of the developing human brain.

In order to assess the influence of longitudinal relaxation on previously reported variations in 31P NMR signals during brain development, we used an accelerated two-point technique to determine T1 at 2.35 Tesla in 8 min. Comparison between 10 normal neonates (age range 37-46 weeks postconception) and 10 healthy infants (age range 80-157 weeks postconception) indicated that T1 does not vary substantially during the first year of life, except in the phosphomonoester (PME) region of the spectra. T1 of total PME decreases with age which we could explain by its variable multicomponent nature: The signal from (unresolved) components at the downfield shoulder of PME (attributed mostly to phosphorylethanolamine at 6.72 ppm) with a T1 of at least 6.4 s decreases with age relative to contributions from other phosphomonoester compounds resonating predominantly at the upfield side of the peak (approximately 6.3 ppm), with T1 below 2.9 s. Because the T1 heterogeneity of PME may depend on its relative composition, quantitative 31P NMR spectroscopy may require an assessment of the influence of longitudinal relaxation on the signal amplitudes in each measurement.

Brain↗
PubMed1993

Quantitative MR imaging of lumbar intervertebral disks and vertebral bodies: influence of diurnal water content variations.

The influence of diurnal water content variation on T1 and T2 and relative proton density (Nr) in intervertebral disks and vertebral bodies was studied in 10 healthy adult volunteers. T1, T2, and Nr were calculated from a set of 20 images obtained at 1.5 T with five single-section, multiecho sequences at different repetition times. Volunteers were randomized into study (one measurement in the morning and one in the evening) and control (two consecutive measurements in the morning) groups. In the study group, evening mean T1 and Nr in intervertebral disks and in vertebral bodies were significantly (P < .001) less than measured in the morning. Mean T2 in vertebral bodies significantly (P < .05) increased between morning and evening measurements. Diurnal variations were significantly less pronounced in degenerative than in normal intervertebral disks. No significant changes occurred in the control group. Relaxation time and Nr measurements allow sufficiently accurate estimation of diurnal water content variation in cohorts of vertebral bodies and intervertebral disks.

Adolescent↗
PubMed1992

[Hemodynamic study of intravenous milrinone in 26 patients with NYHA class III or IV cardiac failure].

The hemodynamic effects of milrinone (WIN 47203) were studied in 26 NYHA Class III or IV patients. The compound was administered intravenously using a protocol including an initial push dose of 50 micrograms/kg in 10 min, followed by a 24 hour infusion at the dose of 0.5 microgram/kg/min. Maximal response was obtained after 15 min and persisted during the infusion: cardiac index increased from 2.08 +/- 0.36 l/min/m2 to 3.09 +/- 0.68 l/min/m2, while capillary pressure fell from 25 mmHg to 16-17 mmHg. These variations were significant (p = 0.01). Heart rate was stable. Mean peripheral blood pressure fell modestly (6%). Systemic vascular resistance fell by 30% and pulmonary vascular resistance by 20%. All these results confirmed the beneficial effect of this inotropic agent administered intravenously. The increase in ventricular premature contractions noted by many justifies the careful surveillance of these patients by monitoring.

Adult↗
PubMed1991

Temporal and spatial analysis of fields generated by eddy currents in superconducting magnets: optimization of corrections and quantitative characterization of magnet/gradient systems.

We propose methods for the spatial and temporal characterization of time-dependent magnetic fields generated by eddy currents after switching gradients. For an on-line determination of the temporal variations of the fields, we extract two terms from the unresolved signal of an extended sample, describing the time evolution of a frequency shift gamma delta Bz(t) and of a decay constant k(t). This procedure allows us to optimize interactively the multiexponential pre-emphasis as well as any spectral volume selection method with respect to eddy currents. Additionally, we suggest an imaging sequence which allows us to determine the spatial distribution of eddy current fields at a chosen time-point after any gradient sequence to be tested. Expansion of these eddy currents fields into spherical harmonic functions proves the existence of a higher order terms, which cannot be corrected by a standard pre-emphasis device, where time constants and amplitudes are adjusted on the X, Y, Z, and Z0 coils. The proposed numerical analysis gives a tool to characterize any magnet/gradient system quantitatively with respect to eddy current performance.

Magnetic Resonance Imaging↗
PubMed1991

MRI of two infants with tuberous sclerosis.

Two children (4 1/2 and 9 months of age) suffering from tuberous sclerosis were examined with MRI, using a 2.35-Tesla magnet. Both patients showed the typical brain lesions of tuberous sclerosis, namely, subependymal nodules projecting into the lateral ventricles and parenchymal hamartomas. However, in one child the examination revealed subcortical foci of low signal intensity on T2-weighted images and of high signal intensity on T1-weighted images, which could represent fat-containing hamartomas.

Brain↗
PubMed1991

MR imaging of the brainstem: normal postnatal development.

Magnetic resonance imaging (MRI) of the mesencephalon during the first four years of life allowed normal maturational processes of the various midbrain structures in vivo to be followed. Using T2-weighted SE sequences, we found 5 characteristic age dependent patterns on axial tomograms taken at the level of the superior colliculi, that let us derive a grading system for normal development of the quadrigeminal plate, the cerebral peduncles, the reticular substantia nigra and the red nuclei. A subsequent statistical analysis of these age dependent changing patterns on T2-weighted MRI of 60 neonates, infants and small children yielded normal age ranges for each of the 5 maturational stages of the midbrain. Grading the changing pattern of midbrain structures during early postnatal life into 5 distinct maturational stages allowed not only monitoring of normal differentiation, e.g. myelination of the brainstem in vivo, but may also help to distinguish between normal, delayed and abnormal development of the mesencephalon on routine MRI.

Brain Stem↗
PubMed1991

Magnetic resonance imaging in infantile encephalopathy with cerebral calcification and leukodystrophy.

Three children, one pair of siblings and a sporadic case, with "infantile (familial) encephalopathy with cerebral calcification and leukodystrophy" are reported. Neuroimaging studies demonstrated extensive bilateral calcifications particularly in paraventricular location and within the cerebral white matter. MRI, performed in two infants, confirmed marked white matter involvement with diffuse delay of myelination. This condition can be added to the growing list of leukodystrophies.

Brain↗
PubMed1991

Contribution of magnetic resonance imaging in the evaluation of microcephaly.

Magnetic resonance imaging (MRI) was performed in 33 children using a 2,35 T MR system. The intention was to determine the various types of morphological abnormalities seen in primary microcephaly and the frequency with which they occur. MRI findings were typical for cytomegalovirus infection in six patients. Cerebral malformations were found in 14 cases and patchy white matter lesions in both hemispheres in two subjects. MRI appeared to be abnormal in eight of the remaining 11 children. However, we were unable to provide an exact interpretation of the findings. All the children with MRI abnormalities with the exception of two were neurodevelopmentally deviant. Thus, MRI revealed abnormalities in the majority of infants with primary microcephaly and neurodevelopmental disturbances. It appears to be more sensitive than cranial ultrasound and computed tomography.

Brain↗
PubMed1990

Application of interlaced orientation slices in orthogonal planes for system characterization and as a basis for standardized brain sections in multiple-oblique positions.

Interlaced acquisition of orthogonal spin-echo orientation slices yields saturated intersection lines, which are available for a system characterization (spatial distortions, slice thickness, chemical shift displacement). Additionally, these scout images contain complete information for a transformation of the gradient coordinate system into the oblique coordinate system of the patient, bearing standardized planes for improved image interpretation and quantitative examinations.

Brain↗
PubMed1990

A method for rapid evaluation of saturation factors in in vivo surface coil NMR spectroscopy using B1-insensitive pulse cycles.

For a rapid determination of saturation factors in surface coil NMR spectroscopy, the recently published (90 degrees-tau-180 degrees-tau-90 degrees-tau-) SUFIR sequence was modified with adiabatic pulse cycles. Signals were acquired after each of the two 90 degrees pulses and they were stored in different memory blocks. The deleterious offset-dependent saturation effects inherent in adiabatic 90 degrees excitation pulses were minimized by suitable combinations of adiabatic pulses that sweep from either side of the spectrum onto resonance, and by setting the carrier frequency in the middle of the spectrum. The practical use of the proposed method is illustrated with the determination of 31P NMR saturation factors in human calf muscle.

Humans↗
PubMed1990

Non-invasive 31P magnetic resonance spectroscopy revealed McArdle disease in an asymptomatic child.

A Turkish couple suffering from McArdle disease (myophosphorylase deficiency) and their two sons aged 5 and 9 years, respectively, were studied using 31phosphorus magnetic resonance spectroscopy (31P MRS). During exercise both sons showed the same pathological pattern as their parents. In contrast to healthy volunteers, intracellular pH (pHi) as measured by 31P MRS every 10 s during exercise, never fell below the lower 95% confidence limit (6.94) of pHi at rest (7.06), but tended to be raised. It is of special interest that the 5-year-old boy was completely asymptomatic, although the enzyme defect seems to be fully expressed at the cellular level.

Adult↗