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Biomedical subjects

M F Iskander

Publications and source records attributed to M F Iskander.

11 recordsLinked to original sources
PubMed1997

Synthesis of acyclo-C-nucleosides: 2-(alditol-1-yl)-5-methylthio- and -5-benzylthio-1,3,4-thiadiazoles.

Condensation of S-methylhydrazinecarbodithioate or S-benzylhydrazinecarbodithioate with aldopentoses or aldohexoses gave the corresponding aldehydo-sugar S-methylhydrazonecarbodithioates of S-benzylhydrazonecarbodithioates. Oxidative cyclization of these hydrazones with bromine in acetic acid gave the corresponding 2-(alditol-1-yl)-5-alkylthio-1,3,4-thiadiazoles. Acetylation of the latter gave the corresponding per-O-acetyl derivatives which were also obtained by one-pot preparation by treatment of the hydrazones with bromine and sodium acetate in acetic acid followed by acetic anhydride. Some of the prepared compounds were tested for antimicrobial activity against Escherichia coli, Bacillus subtilis, Staphylococcus aureus and Candida albicans. While hydrazones showed significant activity against these organisms, the thiadiazoles were devoid of antimicrobial activity.

Anti-Bacterial Agents↗
PubMed1993

Calculations of heating patterns of an array of microwave interstitial antennas.

In this paper, the heating (temperature) distribution patterns of an array of uniformly and step-insulated interstitial antennas located in inhomogeneous tissue and cancerous regions of the human body are calculated. Specifically, the bioheat equation, which takes into account various heat exchange mechanisms such as blood flow rate, heat conduction, and metabolic heat generation, was solved using the finite difference method, while the electromagnetic power absorbed (SAR) in the tissue region heated using an array of interstitial antennas was determined using the finite-difference time-domain (FDTD) method. Numerical results showing the validation of the developed computer program are presented, and the effect of varying parameters such as the blood flow rate on the resulting heating rate and patterns are examined. Possible clinical implementation of the developed temperature distribution-EM power deposition pattern computer code in treatment planning is described.

Absorption↗
PubMed1990

Evaluation and optimization of the electromagnetic performance of interstitial antennas for hyperthermia.

Effective and realistic evaluation of the performance of interstitial antennas for microwave hyperthermia involves: (a) calculations of the radiation characteristics of these antennas, including those of multi-section designs, and (b) the development of 3-dimensional models of tumors and the computation of the power deposition patterns in these tumors due to their irradiation by an array of interstitial antennas. In this paper, we address both of these issues. Specifically, we developed numerical models for calculating the radiation characteristics of multi-section insulated antennas, and we utilized a 3-dimensional model based on a volume integral equation formulation for calculating the power deposition pattern in tumors. Numerical results were verified by comparing them with experimental data available in the literature. New numerical data are presented to illustrate the advantages of multi-section designs over uniformly-insulated interstitial antennas and to show the feasibility of using amplitude and phase steering capabilities to control the power deposition patterns of an interstitial antenna array. The role of each section in a multi-section antenna design in guiding versus radiating the electromagnetic energy and hence in controlling the power deposition pattern of multi-section antennas is also described.

Equipment Design↗
PubMed1989

Design optimization of interstitial antennas.

To improve the performance of interstitial antennas for microwave hyperthermia, parameters such as the uniformity of the heating pattern, the depth of penetration, and the impedance matching properties must be optimized. We examined analytically and experimentally the radiation characteristics of multisection insulated antennas in conductive tissue. The effects of varying the diameters and lengths of the center conductors in the various sections of the antenna and the diameter and type of the insulation on the electromagnetic power deposition pattern and input impedance characteristics were examined. A new approximate numerical model which calculates the current distribution and the radiation characteristics of multisection insulated antennas was developed. The numerical predictions were verified in a qualitative way experimentally by mapping the various near- and far-field components of these antennas. Based on the obtained results, design tradeoffs are identified and quantified, and guidelines for optimum designs are specified. In particular, it is shown that an insulation-to-center-conductor diameter ratio between 1.5 to 2.0 is optimum for a uniform Teflon insulation, and that a multisection arrangement with the thinnest insulation near the antenna tip has superior performance compared with the uniform insulation or other multisection designs.

Electric Conductivity↗
PubMed1989

Three-dimensional electromagnetic power deposition in tumors using interstitial antenna arrays.

Interstitial arrays of insulated antennas have shown promise for microwave hyperthermia treatment of deep-seated tumors. Available analytical techniques for predicting the electromagnetic (EM) power deposition of these antennas have been limited to the case of a homogeneous conductive medium surrounding the array. Since tumors and host tissue may differ in their electrical characteristics, it is necessary to consider the impact of this variation in electrical properties and the geometry of the tumor in the calculation of the EM field distribution and power deposition pattern when modeling interstitial antennas. In this paper a three-dimensional model of a tumor of arbitrary shape subjected to the fields of an interstitial antenna array is developed to predict the EM power deposition in an inhomogeneous tumor-tissue medium. The volume integral equation for the imbedded tumor is developed and solved by method of moments. The incident fields are calculated based on the available formulation of interstitial antennas in homogeneous media. The accuracy of the developed computer code was checked by comparing the results from the volume integral approach with the Mie solution for the special case of spherical tumors. Good comparison was obtained for tumors with properties approximately 25 percent different from those of the surrounding tissue. Comparisons of results from models of antenna arrays with and without imbedded tumors show significant differences in their predictions of the EM power deposition in the tumor. Hyperthermia protocols generally specify uniform temperature distribution within the tumor. The developed inhomogeneous model was used to examine the feasibility of controlling the uniformity of the power deposition pattern in large tumors by adjusting the amplitude or relative phase between the array elements. Results are presented to show that a phase lead of +90 degrees or relative amplitude of 4.0 on one antenna in a square array of four antennas could be used to shift the power deposition pattern to sequentially heat outer portions of a 2 cm diameter tumor, thereby achieving a more uniform time-averaged temperature distribution in the tumor.

Electromagnetic Phenomena↗
PubMed1984

Numerical calculations of the temperature distribution in realistic cross sections of the human body.

Numerical calculations of the temperature distribution in detailed cross sections of the human body are presented. The solution procedure uses a finite-difference representation of the bioheat transfer equation, and thus it routinely considers the various heat exchange mechanisms including the blood flow rate, heat conduction and the metabolic heat generation. The new feature of the presented solution, however, is related to the utilization of the detailed electromagnetic power deposition patterns obtained numerically using the method of moment. In the present calculations, therefore, the temperature distribution is based on a realistic description of the various tissue distributions in the cross section of the human body and the radiation characteristics of the electromagnetic source. The obtained results clearly showed a significant dependence of the temperature distribution on the values of the blood flow rates used in the modeling. Present efforts which include the use of the developed computer program in the planning of the hyperthermia treatments, as well as its use as a study tool for investigating the effect of the variation of the various radiation and thermal parameters on the desired temperature distributions, are described.

Body Temperature↗
PubMed1983

Microwave methods of measuring changes in lung water.

Two microwave methods for measuring changes in lung water content have been investigated. The first is based on measuring changes in the phase of an active microwave signal transmitted through the thorax, while the other is based on measuring the natural microwave radiation emitted by the body with a radiometer. The feasibility of using the active microwave method is investigated by making measurements on phantoms, on anesthetized dogs with induced pulmonary edema, and on isolated dog lungs. The obtained results clearly illustrated that the method is sensitive enough to measure small changes in lung water content. In the radiometer method, on the other hand, both calculations and preliminary measurements in phantoms indicate that the natural microwave emission changes with lung water content and that conventional radiometry systems should be able to detect as little as three to four percent change in lung water content. Initial results from both methods, therefore, indicate the soundness of the basic ideas and justify further development of these methods for clinical use.

Adult↗
PubMed1982

Postresonance electromagnetic absorption by man and animals.

A surface integral equation (SIE) method is used to calculate the specific absorption rate (SAR) in spherically capped cylindrical models irradiated by an axially incident electromagnetic plane wave (K polarization) in a frequency range for which calculations previously have not been available (80-400 MHz for man models). In the SIE method, the electromagnetic (EM) field relations are formulated in terms of electric and magnetic currents on the surface of the model. The average SAR is calculated from the far scattered EM fields by means of the forward scattering theorem. SAR data calculated by the SIE method agree with data calculated by the extended boundary condition method (EBCM) for frequencies up to 80 MHz (the upper frequency limit of the EBCM) for man models. For rat models exposed to 1-3 GHz radiation, reasonable agreement was also obtained with the limited experimental data available.

Animals↗
PubMed1982

Two-dimensional technique to calculate the EM power deposition pattern in the human body.

A numerical procedure to calculate the electromagnetic (EM) power deposition in two-dimensional models of cross sections in the human body is described. The procedure involves obtaining X-ray images of cross sections of specific areas with computer axial tomographic scans and then solving the EM boundary value problem by using the method of moments. The formulation thus takes into account not only the spatial distribution of the different tissue types, but also the radiation characteristics of the typical EM source. Numerical results are given to illustrate the accuracy of the developed procedure. Special emphasis is placed on characterizing and analyzing the EM power deposition patterns obtained using the annular phased array system recently developed by BSD Medical Corporation for hyperthermia treatments.

Computers↗