Biomedical subjects

A Kalisz

Publications and source records attributed to A Kalisz.

6 recordsLinked to original sources

PubMed1997

Statistical framework for ultrasonic spectral parameter imaging.

This study examines the statistics of ultrasonic spectral parameter images that are being used to evaluate tissue microstructure in several organs. The parameters are derived from sliding-window spectrum analysis of radiofrequency echo signals. Calibrated spectra are expressed in dB and analyzed with linear regression procedures to compute spectral slope, intercept and midband fit, which is directly related to integrated backscatter. Local values of each parameter are quantitatively depicted in gray-scale cross-sectional images to determine tissue type, response to therapy and physical scatterer properties. In this report, we treat the statistics of each type of parameter image for statistically homogeneous scatterers. Probability density functions are derived for each parameter, and theoretical results are compared with corresponding histograms clinically measured in homogeneous tissue segments in the liver and prostate. Excellent agreement was found between theoretical density functions and data histograms for homogeneous tissue segments. Departures from theory are observed in heterogeneous tissue segments. The results demonstrate how the statistics of each spectral parameter and integrated backscatter are related to system and analysis parameters. These results are now being used to guide the design of system and analysis parameters, to improve assays of tissue heterogeneity and to evaluate the precision of estimating features associated with effective scatterer sizes and concentrations.

Carcinoma↗

PubMed1995

Roles of hematocrit and fibrinogen in red cell aggregation determined by ultrasonic scattering properties.

Parameters of the power spectrum of backscattered echoes were applied to quantitatively evaluate red cell aggregation in vitro. Human red cell suspensions were circulated in a closed loop of tubing, and ultrasonic, radiofrequency, echo-signal data were obtained using a 10-MHz transducer. Data acquisition was performed at 30-s to 1-min intervals for 5 min after flow stoppage. Two parameters of the normalized power spectrum of the echo signals, spectral slope and Y-intercept, were computed, and estimates of two scattering properties, the scatterer size and acoustic concentration were calculated from these parameters using equations based on scattering theory. Size and acoustic concentration were observed as they changed over time after the stoppage of flow. The key findings were that hematocrit affected the rate of cell aggregation while fibrinogen controlled aggregate size and acoustic concentration.

Adult↗

PubMed1993

Ultrasonic tissue characterization of experimental venous intimal hyperplasia.

Ultrasonic tissue characterization (UTC) employing slope and Y-intercept parameters from the normalized power spectrum of backscattered echoes was employed in vivo to study compositional changes in the walls of pig jugular veins in which thrombi were experimentally induced. Light microscopy revealed these changes to be intimal hyperplasia with an early predominance of smooth muscle cells and a later mixture of smooth muscle cells and collagen deposits. UTC distinguished intimal hyperplasia from previously reported data from luminal thrombosis UTC. Furthermore, UTC was able to discriminate between early (predominantly smooth muscle cells) and older (smooth muscle cells plus collagen deposits) intimal hyperplasia. The study suggests that intimal hyperplasia in the experimental model used may be organized thrombus and that UTC may be able to follow both the development of wall changes as well as luminal changes occurring in venous thrombosis.

Animals↗

PubMed1992

Computer model of ultrasonic hyperthermia and ablation for ocular tumors using B-mode data.

Computer simulations have been conducted to examine hyperthermia and ablation for treating ocular tumors. An interactive software package has been implemented that permits relevant tissue dimensions to be determined from B-mode data. This package also permits interactive beam positioning, and it provides image displays depicting computed absorbed doses and temperature rises. Results are presented showing how hyperthermia temperature patterns are influenced by beam position, beam geometry and frequency. Images showing ablative temperature rises at various time intervals are also presented. For hyperthermia, geometric models of beam profiles showed that a non-uniform beam pattern (with a central low-intensity region) can produce more uniform heating of small ocular tumors than a beam with a uniform intensity profile. For a given tumor, the uniformity of hyperthermia temperatures was found to be a function of frequency, with 4.75 MHz providing reasonably uniform results for typical tumor heights (near 7 mm). For ablation, diffraction computations were employed to calculate beam intensity profiles; results show an initially rapid rise in temperature levels with subsequent, slower heating beyond the -3-dB limits of the focal volume. The model is now being refined, and additional phenomena, including nonlinear propagation, will be incorporated.

Body Temperature↗

PubMed1992

Computer simulations of ultrasonic heating for ocular therapy.

Computer simulations are being performed to model the temperature patterns produced during ultrasonically induced hyperthermia of ocular tumours. The software package for these simulations incorporates operator interaction and uses tissue geometry obtained from B-mode data. Previous studies used geometric approximations for the incident beams used for hyperthermia. In the current study, these beams were computed using diffraction analysis to obtain more realistic simulations of clinical exposures.

Body Temperature↗

PubMed1986

Temporal changes of acid phosphatase, arylsulphatase, beta-galactosidase and beta-N-acetyl-D-glucosaminidase activities in subcellular fractions of rat liver.

In this paper circadian changes in the liver enzyme activities of rat housed under highly standardized conditions with 12: 12 hour light-dark cycle are shown. Activities of acid phosphatase, arylsulphatase, beta-galactosidase and beta-N-acetyl-D-glucosaminidase in microsomal and lysosomal fractions and crude homogenate were estimated every 4 hr during one 24-hr period. The enzyme activities were related to 1 mg of protein, 1 mg of DNA and 1 g fresh tissue. Daily changes of enzyme activities were found. In case of activity calculated per 1 mg DNA two maxima at 0500 and at 2100 hr were observed, while activity calculated per 1 mg protein showed one maximum at 0500 hr. Activity calculated per 1 g fresh tissue showed the maximum at 0500 hr for each enzyme only in microsomal fraction. As far as acrophase table is concerned for all enzymes and fractions the acrophase occurred during the night. The obtained results are discussed in relation to lysosomal enzymes synthesis process as well as different reference values.

Acetylglucosaminidase↗