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Biomedical subjects

K R Diller

Publications and source records attributed to K R Diller.

At least 55 records · Page 3Linked to original sources
PubMed1987

Computer automated cell size and shape analysis in cryomicroscopy.

Computer vision techniques have been developed for quantitative analysis of size and shape changes in cells frozen on a cryomicroscope. The analysis is based on implementation of standard serial edge detection algorithms in conjunction with a shape transform to isolate individual cells in complex scenes which may include adjacent and overlying ice crystals. In the present study the sensitivity of the automated analysis procedure is evaluated for images obtained by various microscope optical systems for progressive degrees of subject blurring by defocusing. Size measurements in calibration trials for freezing latex spheres with extracellular ice in the field of view were least sensitive for bright field images, although the most consistent data was obtained by differential interference contrast microscopy. In all cases phase contrast images produced the least accurate data. An example analysis is presented for the freezing of pancreas beta-cells.

Algorithms↗
PubMed1984

Automated computer evaluation of time-varying cryomicroscopical images.

A system has been developed to perform automatic computerized recognition, tracking, and quantitative morphological analysis of viable cells in freezing solutions. Cryomicroscopical image sequences of freezing cells are digitized and analyzed by computer. Image-processing techniques are used which are insensitive to contrast fluctuations from image to image, and which perform well even in noisy, cluttered images. The generalized Hough transform is used for shape detection, and a heuristic graph-search boundary completion algorithm is applied for shape extraction. The extracted cell shape may be analyzed for changes in cross-sectional area, perimeter length, shape deformation, and other metrics of interest. Knowledge from the shape-extraction phase is used to form a prediction of what shape the cell will be in the next image frame, and thus what to look for in the next shape-detection phase. This combination of knowledge-feedback with a powerful shape-detection technique produces an automatic, dynamic shape-recognition scheme capable of accurate recognition and analysis of the cells regardless of how deformed they may become during the freezing sequence. Example performance of the system is illustrated for a series of micrographs of freezing granulocytes.

Blood Preservation↗
PubMed1984

Intracellular freezing of human granulocytes.

Human granulocyte suspensions were exposed to controlled freezing regimens on a cryomicroscope, and the incidence of intracellular freezing was measured as a function of cooling rate and extracellular nucleation temperature. The presence of intracellular ice was assessed by analysis of serially recorded images of the freeze-thaw process and by correlation with measured patterns of change in the cell volume. For granulocytes suspended in autologous plasma, a threshold was described for intracellular freezing as an empirical function of cooling rate (B) and extracellular nucleation temperature (Tn): B (degrees C/min) = 1.1 Tn (degrees C) + 12.3.

Blood Preservation↗
PubMed1984

A unidirectional temperature gradient stage for solidification studies in aqueous solutions.

A low temperature light microscope stage has been designed and fabricated for quantitative analysis of the solidification of aqueous solutions. Thermal boundary conditions are controlled during freezing so as to enable direct comparison of data with complementary theoretical models. Evolution of the temperature distribution within the system is monitored by a one-dimensional thermocouple array, and growth of the phase interface is measured via a displacement transducer. The two-dimensional solution concentration field is assessed by computer densitometric analysis of the grey scale distribution for a light absorbing solute. Experimental and theoretical analyses of freezing processes with the stage correlate well, and the data base is shown to be internally consistent by independent thermal and mechanical measures of the interface velocity.

Computers↗
PubMed1984

Measurement of the water permeability of single human granulocytes on a microscopic stopped-flow mixing system.

The water permeability (Lp) of human granulocytes was measured for individual isolated cells with a novel, microscopic stopped-flow mixing system. Changes in volume were monitored as a cell was introduced suddenly into an osmotically active solution. Permeability values were determined as a function of solution osmolality from the volume versus time curves for mixing into both hypotonic and hypertonic solutions within the range of 145 to 833 mOsm. The calculated reference permeability at 25 degrees C was 1.15 micrometers/atm.min with an osmotic coefficient of 0.46 Osm/kg.

Cell Membrane Permeability↗
PubMed1983

Osmotic response of individual cells during freezing. II. Membrane permeability analysis.

An analytical model is presented to simulate the freezing of individual yeast cells. In addition the model is solved numerically on a digital computer to obtain values for cell volume as a function of temperature, based on the thermal protocol during freezing, and the transport parameters of the cell membrane. The numerical procedure was modified to enable values for the membrane hydraulic permeability reference coefficient, Lpg, and activation energy, ELp, to be deduced by nonlinear analysis of complementary experimental data (10). It was observed that the apparent values of both Lpg and ELp increase with cooling rate, from Lpg = 0.0116 micrometer 3 micrometers-2 atm-1 min-1 and ELp = 19.4 kJ mol-1 for 9 degrees K/min to Lpg = 2.11 micrometers 3 micrometer-2 atm-1 min-1 and ELp = 101 kJ mol-1 for 35 degrees K/min. The deduced permeabilities fall within the range of values determined in a prior study by Levin (6). Analysis with the model also indicates that the turgor pressure exerts a negligible effect on yeast exposed to freezing stress.

Cell Membrane Permeability↗
PubMed1983

Osmotic response of individual cells during freezing. I. Experimental volume measurements.

The osmotic response of yeast to freezing was measured as a function of cooling rate and degree of extracellular supercooling. Thirteen experimental trials were conducted on a cryomicroscope in which incremental size changes of individual cells were recorded photographically, and the corresponding volume variations were measured using a digital computer image analysis algorithm. Plots were obtained of normalized cell volume as a function of temperature. Cellular dehydration during freezing was progressively inhibited with increasing values of cooling rate and extracellular supercooling. Normalized cell volume changes were not a function of the relative initial cell size. A constant volume plateau occurred for conditions under which intracellular ice formation was expected.

Cell Membrane↗
PubMed1983

A finite element model of burn injury in blood-perfused skin.

The burn process resulting from the application of a hot, cylindrical source to the skin surface was modeled using the finite element technique. A rotationally symmetric 125-element mesh was defined within the tissue beneath and outlying to an applied heating disk. The disk temperature and duration of contact were varied, respectively, between 50 and 100 degrees C for up to 30 s. Natural convection with ambient air was assumed for areas of skin surface not in direct contact with the disk. The simulated thermal history was used in a damage integral model to calculate the extent and severity of injury in the radial and axial dimensions.

Animals↗
PubMed1983

Analysis of the water permeability of human granulocytes at subzero temperatures in the presence of extracellular ice.

The plasma membrane water permeability of human granulocytes in the presence of extracellular ice was determined experimentally on a cryomicroscope. Transient volumes of individual cells were measured at constant subzero temperatures subsequent to ice nucleation. Permeability values were deduced by adjustment of multiple parameters in a model to obtain an optimal fit to the data. The permeability was determined to be a function of both temperature and intracellular solute osmolality, with a reference value at 0 degrees C of 0.407 micrometers/atm.min and temperature and solute coefficients of 218kJ/mol and 1.09 Osm/kg.

Cell Membrane Permeability↗
PubMed1983

A finite element model for phase change heat transfer in a composite tissue with blood perfusion.

This paper describes a finite element model of the thermal response of a human to extreme subfreezing environments and the transient temperature fields that are produced at specific locations within the body. This analysis includes the effects of latent heat of fusion from the liquid to the solid phase and of blood perfusion in selected tissues during the freezing process. A highly simplified physiological model is assumed. This type of analysis can be used as a predictive tool in many applications such as cryosurgery and cryopreservation of organs. The finite element model described herein has many advantages over standard numerical techniques such as finite difference methods for analyzing heat transfer problems. This method can treat very general geometries with many different tissue types, each having unique thermal properties, and unique blood perfusion and metabolic rates. This model can incorporate either convective thermal resistance at the body surface or a prescribed temperature history as a boundary condition, either of which may vary as a function of time or temperature. This analysis extends previous work by incorporating the effects of latent heat and by including a blood perfusion rate that varies with temperature in individual tissues.

Blood Physiological Phenomena↗
PubMed1982

Quantitative low temperature optical microscopy of biological systems.

A comprehensive review is presented of low temperature optical microscopy techniques as applied to the study of freezing processes in biological systems. Emphasis is placed on analysis of physical and physiological parameters which were measured and/or controlled and the procedures for effecting such operations. Quantitative analysis of photomicrographs by digital computer processing is also discussed.

Animals↗