Search PubMed⌕ Search

Biomedical subjects

D Harder

Publications and source records attributed to D Harder.

At least 19 recordsLinked to original sources
PubMed1992

Non-invasive determination of systolic blood pressure by heart sound pattern analysis.

A new concept of non-invasive blood pressure measurement by heart sound pattern analysis is described. The known diagnostic criterion of the 'accentuated' second heart sound of a hypertensive patient is here converted into a computer-aided pattern-recognition process for the second heart sound, applicable over the entire scale of blood pressure. After a 'learning phase', during which the second heart sound is recorded, analysed and correlated with a set of systolic blood pressure values of the individual patient, the computer is able to determine systolic blood pressure of the same patient from the acoustic spectrum of the second heart sound with sufficient precision. The method is in principle suited for automatically repeated blood pressure measurements, but further development is still needed for conversion into a widely practicable procedure.

Blood Pressure↗
PubMed1991

Dosimetry and physical treatment planning for iodine eye plaque therapy.

The dosimetry of eye plaques loaded with iodine-125 seeds (type 6702) was performed by means of computer calculations and measurements with thermoluminescent dosimeters (TLD). Measurements of the depth dose distribution (2-25.5 mm) along the transverse axis of a single seed were performed in water equivalent phantom material. The transverse axis attenuation and geometry factor F(r) was obtained by applying a least squares fit to the measured data. Based on the resulting radial dose function, a computer program was developed which calculates dose distributions within the eye for arbitrary loading and placement of the eye plaque. The computational results were verified by TLD measurements in an eye phantom.

Brachytherapy↗
PubMed1990

Algorithms for the evaluation of radiation induced chromosome aberration yields per cell from flow karyotypes.

CHO-K1 cells were irradiated in G0/G1-phase with 150 kV X-rays. Single chromosomes isolated from metaphase cells and stained with DNA intercalating dye DAPI were analyzed in the ICP 22 with a modified flow chamber. In order to study dose-dependent changes in the flow karyotypes, they were split into peak- and background-portions by an iterative fit algorithm. As in a first approach, estimates of the frequencies of chromosome lesions were derived from an evaluation of the dose-dependent reduction in peak contents. The number of radiation-induced lesions per chromosome was found to be proportional to its length. As a second approach, the number of fluorescence events in the histogram background was corrected for non-chromosomal debris and evaluated interms of chromosome aberration frequency per cell, which was consistent with the yields of dicentric chromosomes and acentric fragments observed in microscopic investigations. As a third approach, lesion frequencies were calculated from the corrected background light sum in the karyotypes, utilizing a Monte Carlo model to simulate the effect of aberration formation on the flow histogram. The results indicate that the number of chromosome lesions observed by flow cytometry can be quantitatively related to the yield of structural chromosome aberrations detected by microscopic analysis. Dose-effect relations and split-dose kinetics are given as examples demonstrating the usefulness of this technique in radiobiology. Time saving compared to microscopic analysis was of the order of 90%.

Algorithms↗
PubMed1990

[Development and dosimetry of a 125 iodine applicator for brachytherapy of intraocular tumors].

Due to the low gamma energy (27-35 ke V), iodine 125 is especially suitable for brachytherapy of intraocular tumors. 125I is available as encapsulated seeds. Applicators can be individually loaded with these seeds to accommodate the shape of the tumor as much as possible. To measure the depth-dose distribution LiF thermoluminence detectors (TLDs, 1 mm3) are embedded in an RW-1 eye phantom at various distances and directions from the high active plaque positioned at the top of the phantom. To obtain the three-dimensional dose distribution, the TLDs are read after exposure for the appropriate time period. Based on experimental measurements of the 125I plaque, a computer program is developed to calculate the dose distribution within the eye and the radiation time for intraocular tumors. These results are very similar to those obtained when using mathematical equations published in the literature. In summary, three-dimensional dose distribution at various distances from an 125I eye plaque has been experimentally determined using a new method. This is an important prerequisite for introducing 125I plaques into the treatment of intraocular tumors.

Brachytherapy↗
PubMed1989

[Lymphomatoid papulosis resembling ecthyma. A case report].

A 54-year-old female patient recurrently developed disseminated papules, red-brown in color and partly ulcerous, which spontaneously disappeared after 3-6 weeks. Histological examination revealed dense infiltration of atypical lymphocytes with epidermotropism. Immunohistological analysis showed predominantly helper T-cells (CD 4). Accordingly, we established the diagnosis of lymphomatoid papulosis. There was no evidence of malignant lymphoma.

Biopsy↗
PubMed1989

[Dosimetry of ruthenium applicators with an eye phantom and small volume thermoluminescence detectors].

Even though 106Ru/106Rh applicators have been in clinical use over more than two decades for the radiotherapy of malignant uveal melanomas, the dosimetry of emitted beta radiation is still a physical problem. The dose rate at the applicator surface and the depth dose in tissue equivalent material can be determined only within +/- 30% error. Using new cubic-shaped thermoluminescence detectors (TLD) with small volume the dose distribution is examined in water equivalent material (RW-1). The spatial resolution is 14 times better compared to the previous technique. From dose measurements in an eye phantom the homogeneity of nuclide deposition and the depth dose distribution of a 106Ru/106Rh applicator are determined.

Brachytherapy↗
PubMed1986

Membrane ATPase mechanism of K+-return relaxation in arterial muscles of stroke-prone SHR and WKY.

These studies compared the importance of electrogenic Na+-K+ active (ATP driven) transport, changes in K+ conductance, and passive Ca2+-Na+ countertransport in the large relaxation that occurs in the rat caudal and basilar artery on return to K+ from K+-free solutions. Furthermore, we compared the importance of these three membrane electrical mechanisms in stroke-prone spontaneously hypertensive rats (SP-SHR) versus their normotensive Wistar-Kyoto control rats (WKY) in basilar (cerebral) and caudal arteries. We found that in both basilar and caudal arteries the hyperpolarization and relaxation that occurred on return to K+ after exposure to a 0 K+ (extracellular) solution was consistently greater in SP-SHR than in WKY. The change in membrane potential occurring on transition to 0 K+ in arteries maintained at low temperature (16 degrees C), used as an estimate of the change in K+ conductance during the K+ transition, was not different in either basilar or caudal arteries between SP-SHR and WKY. Thus the hyperpolarization on return to K+ at body temperature would depend primarily on the level of activity of the membrane ATPase, referred to as the Na+ pump. We also sought to compare the passive (but electrogenic) Ca2+-Na+ countertransport mechanism between strains for both arteries, but we were unable to detect any evidence of the predicted hyperpolarization-contraction on transition from 145 to 10 mM extracellular Na+. Furthermore, the return to extracellular Na+ solution failed to show the depolarization-relaxation predicted by the Ca2+-Na+ countertransport mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗
PubMed1978

Systematic optimization of the double-scatterer system for electron beam field-flattening.

The scattering foil widely used for field flattening in electron therapy produces a distortion of the electron spectrum which significantly reduces the slope of the descending part of the depth dose curve. It is already known that this effect can be drastically reduced by replacing the scattering foil by a two-foil scatterer. The second foil, fit with a radial thickness profile, acts as a compensator, attenuating the central part and enhancing the peripheral part of the beam by electron scattering. Calculations of the optimal foil combinations and radial thickness profiles are presented and numerical values of smooth (Gaussian) and three-step profiles for various field sizes are provided. The results are applicable to a variety of electron energies and scattering foil materials.

Electrons↗
PubMed1978

[Calculation of the dose distribution of high-energy electrons within and behind tissue inhomogeneities of any width. II. Influence of multiple scattering (author's transl)].

The algorithn proposed in 1976 to allow for the influences of tissue inhomogeneities in electron beam dose distributions has been improved. A factor adopted from Sternheimer corrects for differences in lateral displacement by multiple scattering within the inhomogeneity resp. the equivalent layer of the homogeneous medium. The algorithm has been tested by direct comparison with Monte Carlo computations for the example of cylindrical cavities in carbon at Eo=10 MeV and resulted in a very close approximation.

Carbon↗
PubMed1977

The RBE of 30 kV X-rays for the induction of dicentric chromosomes in human lymphocytes.

The frequency of dicentric chromosomes induced by the irradiation of human lymphocytes in Go phase was determined with hard (150 kV) and soft (30 kV) X-rays. When a linear-quadratic dose-effect relation was used to fit the experimental data, a significant linear contribution was found for 30 kV X-rays. The RBE of 30 kV compared with 150 kV X-rays approaches the value 3 at a 30 kV X-rays dose of 20 rad and decreases with increasing dose. From the results it may be concluded that chromatids with primary breaks, undergoing second order reactions and thus forming dicentric chromosomes, are produced by traversals of low-energy electrons through chromatin material.

Adult↗
PubMed1976

[Calculation of dose distribution of fast electrons within and behind tissue inhomogeneities of any width].

A new algorithm allowing for the effects of tissue inhomogeneities on dose distributions of high-energy electrons is presented for the purposes of treatment planning computations. Starting from the electron dose distribution for homogeneous tissue the doses contributed by the partial beam hitting the tissue inhomogeneity are substituted by those arising from a partial beam which was alterated by stopping, scattering and changed distances in the inhomogeneity. Since actual data for partial beams of limited cross-section are used and the scatter contributions from the rest of the total beam into and behind the inhomogeneity remain unchanged, good approximation compared to measured values is achieved.

Electrons↗
PubMed1976

[The new radiologic units of measurement gray and becqerel (author's transl)].

The general conference on weights and measures in June 1975 introduced the new names of units, the Gray (for ionizing radiations) and the Becqerel (for activity of a radioactive substance), on an international level. The reasons for this change--the units hitherto valid are the Rad and the Curie--and the international efforts at durability of the new regulations are reported.

Health Physics↗