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Biomedical subjects

B Jung

Publications and source records attributed to B Jung.

At least 19 recordsLinked to original sources
PubMed1989

Resolution of biexponential transverse relaxation in magnetic resonance imaging.

The accuracy in measurements of mono- and biexponential transverse relaxation processes with an MRI unit (0.5 T) was studied with a binary phantom. Comparison with spectrometer measurements (0.5 T) demonstrated that the imager underestimated the T2 values for monoexponential processes. Numerical resolution of biexponential processes also yielded underestimated relaxation times, but the resolution of a slow, constant component from faster components was relatively precise and consistent, provided the T2 ratio was above 2.5 in the T2 range 200-800 ms for a spin-echo sequence with 32 echoes. The effects of signal-averaging, strength of slice-selective gradient, single- versus multi-slice mode and repetition time were of little importance. In coronal slices a spurious biexponentiality occurred occasionally from monoexponential sources. The influence of stochastic noise was of minor importance compared to the effect of systematic noise.

Magnetic Resonance Imaging↗
PubMed1989

Comparison between electrophysiologic and morphologic changes in lead induced peripheral neuropathy in rats.

Compound nerve action potential (CNAP) of the mixed peripheral nerve is composed of A alpha beta, A delta, and C potentials. All components of CNAPs in the sciatic nerve were recorded by stimulating the tibial nerve of both control and lead-poisoned rats. Marked decrease of nerve conduction velocity and prolonged duration were found in A alpha beta and A delta fibers especially in large myelinated A alpha beta fibers. The amplitude decreased in A alpha beta potential, but the area did not change. In C potential produced by activation of unmyelinated fibers, nerve conduction velocity slightly decreased, but the amplitude and area did not significantly change. Pathologic correlates revealed prominent segmental demyelination with significant decrease of large myelinated fiber densities. Minimal axonal degeneration of unmyelinated fibers was present. We can conclude that electrophysiologic changes in the lead-poisoned rats correlate with pathologic changes in them.

Animals↗
PubMed1987

Delayed hypersensitivity responses in children after local cutaneous anesthesia.

The effect of cutaneous analgesia on delayed type hypersensitivity (DTH) reactions as challenged by injections in the skin was assessed by comparing a lidocaine/prilocaine mixture with placebo. Application of 5 g of the mixture 90 min before testing significantly (p less than 0.001) reduced pain but did not influence the DH-reactions as read after 48 hours. Based on these findings, DTH to several antigens were measured in 116 school children, aged 7-15 years. All the children were positive to either tetanus antigen, 7.5 Lf/ml (98% at 48 hours) or mumps test antigen (82%), while positivity to tuberculin 2 TU/ml and candida 1000 PNU/ml were only 11 and 62% respectively. Therefore, DTH tests in an adequately immunized population of children can be limited to two antigens. Application of cutaneous analgesia is recommended as a routine procedure in DTH testing in young children.

Adolescent↗
PubMed1986

Improved formulae for signal amplitudes in repeated NMR sequences: applications in NMR imaging.

An improved formalism describing the dependence of the signal strength on relaxation times and spin densities in pulsed nuclear magnetic resonance experiments is presented. It is especially applicable to repetitive experiments such as occur in imaging applications. Essentially, it includes long-time spin coherence effects not considered in the algorithms usually adopted. Also, some generalizations of classical concepts are made. Validity criteria are studied using numerical simulations. The algorithm assumes a relatively inhomogeneous main magnetic field, but the computer simulations indicate that the inhomogeneity normally present in magnetic resonance imagers is sufficient. The simulations also indicate that the field gradient pulses applied in the spatial encoding procedure do not necessarily interfere seriously with the validity of the formulae, but complicate the choice of optimal formula and may in some circumstances prevent the spin system from reaching a steady state.

Algorithms↗
PubMed1986

T1, T2, and relative proton density at 0.35 T for spleen, liver, adipose tissue, and vertebral body: normal values.

An MRI installation (Magnetom, Siemens, software version B1 of NUMARIS) working at 0.35 T was used to estimate T1, T2, and relative proton density in the spleen, liver, adipose tissue, and vertebral body in 14 healthy volunteers. Two double-echo sequences were applied for all subjects: TR = 500 ms, TE1 = 35 and TE2 = 70 ms; and TR = 1600 ms, TE1 = 35 and TE2 = 70 ms. The images were sampled in regions of interest and appropriate relaxation expressions fitted to the ROI data yielding relaxation parameters and relative proton densities. Relaxation expressions, included in standard software (Siemens), were compared to more elaborate functions, developed in parallel to this study. The latter were found more appropriate, especially for high T1 values, and gave the following mean values for the four tissues (estimated uncertainty of mean in parentheses) T1 (ms) 915(36), 428(5), 261(7), and 501(11); T2 (ms) 79.7(8.8), 51.0(0.2), 59.8(1.0), and 64.7(0.8); and corresponding relative proton density (rho, arbitrary units) 2088(136), 2182(10), 2915(49), and 2136(21). The uncertainty in the values was estimated in the fitting procedure and does not include systematic errors. The relative noise in the ROIs was about 9% and the reproducibility of the ROI mean values about 8%.

Adipose Tissue↗
PubMed1986

Selective properties of trains of real and complex RF micropulses in slice-selective spin-echo MRI.

The spin nutation properties of frequency selective (space selective in combination with a magnetic field gradient) trains of radiofrequency micropulses were studied in a numeric model. Two cases were considered, one simulating the 90 degrees excitation pulse in spin-echo MRI, the other the 180 degrees spin inversion pulse. Image reconstruction according to the 2-D Fourier transform technique requests that the effect of the 180 degree pulse is independent of the initial phase of the spin vector relative to the radiofrequency field. It was found that with a train of phase-stable radiofrequency micropulses with an envelope of the traditional 'sinc' type the result of the spin inversion pulse was depending on the initial phase whereas this was not the case for a train of phase-shifted (complex) micropulses. The complex train of radiofrequency micropulses also had better selective properties both for excitation and spin inversion than the real one.

Electron Spin Resonance Spectroscopy↗
PubMed1986

Subtraction in magnetic resonance imaging.

Subtraction of images recorded with multiple echo, spin echo (SE) techniques was performed in phantom and clinical studies of patients with pituitary adenomas and gliomas. The tissue differentiation was enhanced in the subtracted images.

Adenoma↗
PubMed1986

Cerebrospinal fluid flow studied with gated magnetic resonance imaging during the various parts of the cardiac cycle.

The pulsatile movement of cerebrospinal fluid (CSF) through the Sylvian aqueduct has been studied in two normal volunteers. A standard magnetic resonance scanner was used as well as a routine spin echo sequence. Series of ECG-gated axial images were obtained perpendicular to the long axis of the Sylvian aqueduct. Previously it has been demonstrated by flow phantom experiments that the phase information can be used to obtain a linear relation between phase and flow velocity. By multiplying the CSF flow velocity by the cross-sectional area of the aqueduct of Sylvius obtained in each image, the CSF flow variation during the cardiac cycle could be demonstrated and measured.

Cerebrospinal Fluid↗
PubMed1985

Affinity and efficacy of racemic, (+)-, and (-)-methacholine in muscarinic inhibition of [3H]-noradrenaline release.

The right postganglionic sympathetic nerves of rat isolated perfused hearts (previously loaded with [3H]-noradrenaline) were stimulated electrically with 10 trains of 10 pulses at 10 Hz. The inhibition by methacholine of stimulation-evoked [3H]-noradrenaline overflow into the perfusate (determined in the presence of corticosterone, desipramine, phentolamine, and propranolol) was taken as a measure for activation of presynaptic muscarinic receptors. The evoked [3H]-noradrenaline overflow was inhibited by (+)-, racemic, and (-)-methacholine in a reversible and concentration-dependent manner. The concentration causing 50% inhibition (IC50) was 0.1, 0.26, and 65 microM, respectively, resulting in an isomeric potency ratio IC50 (+)/IC50(-) of 650. The dissociation constant KA of the (+/-)- or (+)-methacholine-presynaptic receptor complex was determined after fractional receptor inactivation according to Furchgott & Bursztyn (1967) with phenoxybenzamine or propylbenzilylcholine mustard as irreversible antagonists of muscarinic receptors. KA for (-)-methacholine was estimated according to Mackay (1966). KA of (+)-, (+/-)-, and (-)-methacholine were 2.5, 4 and 440 microM, resulting in an isomeric affinity ratio KA (+)/KA(-) of 180. The discrepancy between the isomeric IC50 ratio and the isomeric KA ratio is explained by a higher intrinsic efficacy of the (+)-enantiomer compared to the (-)-enantiomer. Thus, (+)-methacholine has to occupy fewer receptors to induce a given inhibition of release than its antipode as revealed by a plot of fractional receptor occupancy vs response. The results show that, in the effector system of presynaptic muscarinic inhibition, methacholine enantiomers differ greatly not only in affinity for the receptor, but also to some extent in the efficiency of signal transmission, and both parameters contribute to the high isomeric potency ratio. The activity of the racemate is fully accounted for by the activity of the (+)-enantiomer.

Animals↗
PubMed1985

A new monooxygenase product from 7-ethoxycoumarin and its relation to the O-dealkylation reaction.

The widely used fluorometric microsomal monooxygenase test for 7-ethoxycoumarin O-dealkylation was reinvestigated with regard to other possible hydroxylation products. By HPLC-analysis no beta-hydroxylation of the ethyl group and no 8-hydroxylation could be detected. Only a small percentage of 6-hydroxylation occurred, but as a new major metabolite 7-ethoxy-3-hydroxycoumarin was found in quantities depending on the microsomal preparation used. The ratio of O-dealkylation to 3-hydroxylation varied according to species, induction, buffer and pH, suggesting that different isozymes of cytochrome P450 were involved. The isozyme mainly responsible for 3-hydroxylation exhibited a great dependence on cytochrome b5 as the donor for the second electron. The fluorometric test does not include 3-hydroxylation due to the virtual absence of an emission spectrum above 450 nm.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1985

Radioprotection of the kidney with degradable microspheres. A pilot study in the dog with repeated irradiation.

The left kidney of 9 dogs was irradiated daily for three days with 300 kVp X-rays. Radioprotection was attempted in 5 of the kidneys by administration of degradable microspheres in the renal artery, immediately before irradiation. Protected kidneys received 3 X 8 or 3 X 12 Gy in midplane dose, unprotected kidneys 3 X 5.2 or 3 X 8 Gy. A protective effect due to induced hypoxia could be demonstrated in creatinine clearance, which was significantly higher in protected than in unprotected kidneys at 7 - 13 weeks after irradiation.

Animals↗
PubMed1984

Morphologic and histochemical studies on the differing radiosensitivity of ductular and acinar cells of the rat submandibular gland.

The submandibular glands of male rats were exposed to 50 Gy X-irradiation as a single dose, with or without pre-treatment with either alpha-adrenergic agonists (noradrenaline, phenylephrine) or a cholinergic antagonist (atropine). The effects were analyzed by morphometric, cytochemical and biophysical methods. When X-irradiated without drug pre-treatment, many serous epithelial cells of the intralobular convoluted ducts displayed morphologic evidence of irreversible radiation damage, in contrast to neighbouring mucous and other cells which were unaffected. The effect was maximal 96 h after irradiation. Serous cells from animals irradiated after pre-treatment with atropine showed much more wide-spread injury than those of animals exposed to X-irradiation only. In contrast , serous cells suffered considerably less damage if their secretory granules had been depleted 1 or 2 h before irradiation with either noradrenaline or phenylephrine. Other epithelial cells showed no modulation of their slight radioresponsiveness by these drugs. The observations were substantiated by morphometry of three cell types: (a) mucous cells, (b) non-granulated serous and intralobular striated duct cells, and (c) granulated serous cells. The findings suggest that the striking radiosensitivity of salivary gland serous epithelial cells is linked to their content of secretory granules. These granules are rich in heavy metals, as demonstrated cytochemically with the sulphide silver method (SSM). Using particle-induced X-ray emission ( PIXE ) spectroscopy, the principal metals were shown to be Zn, Mn and Fe. It is conceivable that membranes which enclose organelles rich in metals with the ability to form redox systems (e.g. Fe2+ in equilibrium Fe3+) show enhanced sensitivity to radiation damage due to the metal-catalyzed induction of lipid peroxidation by ionizing radiation. Disruption of secretory granules would be expected to release lytic enzymes into the cell sap, resulting in autolysis. This hypothesis is supported by the findings that atropine--which increases the number of granulated serous cells--enhances radiosensitivity, while noradrenaline and phenylephrine--which cause degranulation of serous cells--decrease radiosensitivity.

Animals↗
PubMed1984

Variance measurements with two semiconductor dose detectors.

Variance measurements were performed with pairs of semiconductor detectors of different ionization volumes in continuous and pulsed radiation fields. By a statistical analysis the relative variance of the detector was separated from that of the accelerator. The relative variance of the detector signal was shown to be correlated to the detector volume and to the dose per pulse. From the measurements the number of events per pulse within the detector volume was estimated and the number of pulses needed to have a reading with a given precision was estimated.

Cobalt Radioisotopes↗
PubMed1979

Gastrointestinal motility and absorption of calcium during infusion of somatostatin in the rat.

The effect of somatostatin on gastric evacuation, small bowel propulsion and gastrointestinal (GI) absorption of calcium was studied in conscious rats. Nonabsorbable 125I-PVP was deposited in the stomach or in the duodenum and the distribution of the radioactivity along the excised GI specimen was recorded after 15 min. 47Ca in chloride from was administered simultaneously and the amont of radioactivity remaining in the GI speciment at sacrifice could easily be measured. Intravenous infusion of synthetic somatostatin (50 micrograms.kg-1.h-1), which resulted in a manifest although not extreme hypersomatostatinemia had no effect either on gastric evacuation, small bowel propulsion or GI absorption of calcium. The findings do not indicate that somatostatin has a direct effect on GI motility or absorption of calcium.

Animals↗
PubMed1979

Image enhancement by digital-analog filtration. II. Tests of filters.

The function of a device for frequency filtration of roentgenograms with digital filters has been tested with the use of different filters. The image was altered in the expected way, which means that the device is suitable for investigating the possibilities of different filters to improve the diagnostic ability. The results of the tests indicate that improvement should be achieved by low-pass filtration.

Femur↗