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Biomedical subjects

J W Strohbehn

Publications and source records attributed to J W Strohbehn.

At least 37 records · Page 2Linked to original sources
PubMed1986

Two-dimensional ultrasonic variation in myocardium throughout the cardiac cycle.

This study was performed to investigate the two-dimensional unprocessed radiofrequency (rf) ultrasonic backscatter from myocardium throughout the cardiac cycle. Eleven mongrel dogs underwent left lateral thoracotomy and had two-dimensional echocardiographic studies performed using a 5 MHz transducer. Regions of interest, selected to encompass a portion of the myocardium, were transported at 33 ms intervals to a host computer and disc. Results show a reproducible cyclic variation in backscatter power throughout the cardiac cycle for the anterior wall. The backscatter power was highest during diastolic relaxation and lowest during systolic contraction. The average change was 4.5 dB.

Animals↗
PubMed1986

Interstitial hyperthermia and iridium brachytherapy in treatment of malignant glioma. A phase I clinical trial.

An oncolytic effect of hyperthermia in the 42 degrees to 43 degrees C range has been previously demonstrated in cell culture and animal models. To apply this modality clinically, an interstitial microwave antenna array system has been developed for the delivery of controlled hyperthermia to an intracranial tumor volume, and a Phase I clinical trial involving six patients with malignant gliomas was undertaken. The protocol to study technical feasibility and patient tolerance combined interstitial iridium-192 irradiation and interstitial hyperthermia with 60-minute hyperthermia sessions immediately before and after brachytherapy. After-loading catheters suitable for both treatment modalities were implanted using a computerized tomography-assisted technique. Thermometry data confirmed the ability of a microwave antenna system to achieve reliable temperature distributions, and reasonable patient tolerance was documented.

Adult↗
PubMed1986

A frameless stereotaxic integration of computerized tomographic imaging and the operating microscope.

A computer-based system has been developed for the integration and display of computerized tomography (CT) image data in the operating microscope in the correct perspective without requiring a stereotaxic frame. Spatial registration of the CT image data is accomplished by determination of the position of the operating microscope as its focal point is brought to each of three CT-imaged fiducial markers on the scalp. Monitoring of subsequent microscope positions allows appropriate reformatting of CT data into a common coordinate system. The position of the freely moveable microscope is determined by a non-imaging ultrasonic range-finder consisting of three spark gaps attached to the microscope and three microphones on a rigid support in the operating room. Measurement of the acoustic impulse transit times from the spark gaps to the microphones enables calculation of those distances and unique determination of the microscope position. The CT data are reformatted into a plane and orientation corresponding to the microscope's focal plane or to a deeper parallel plane if required. This reformatted information is then projected into the optics of the operating microscope using a miniature cathode ray tube and a beam splitter. The operating surgeon sees the CT information (such as a tumor boundary) superimposed upon the operating field in proper position, orientation, and scale.

Evaluation Studies as Topic↗
PubMed1985

Comparative theoretical performance for two types of regional hyperthermia systems.

Regional hyperthermia systems have drawn attention because of their potential for depositing power noninvasively in deep-seated tumors. Two such systems that have received clinical attention because of their ability to deposit significant amounts of power in tissue are magnetic induction devices and annular phased array applicators. In this paper, theoretical calculations for the specific absorption rate (SAR) and the resulting temperature distributions for these systems are compared. The finite element method is used in the formulation of both the electromagnetic and thermal boundary value problems. Six detailed patient models based on CT-scan data from the pelvic, visceral, and thoracic regions are generated to simulate a variety of tumor locations. In general, the annular phased array deposited more power within the tumor and produced better temperature distributions than the magnetic induction device. However, the ratio of the maximum power absorbed by the tumor to the maximum power absorbed in normal tissue does not appear to be high enough for either device to heat significant portions of perfused tumors to therapeutic temperatures under a wide range of physiological conditions. The results contained herein should aid the physician in comparative treatment planning with existing regional hyperthermia systems.

Electromagnetic Fields↗
PubMed1985

Intraoperative interstitial microwave-induced hyperthermia and brachytherapy.

Intra-operative placement of 11-gauge nylon catheters into deep-seated unresectable tumors for interstitial brachytherapy permits localized heating of tumors (hyperthermia) using microwave (915 MHz) antennas which are inserted into these catheters. Four preliminary cases are described where epithelial tumors at various sites were implanted with an antenna array and heated for 1 hour, both before and after the iridium-192 brachytherapy. Temperatures were monitored in catheters required for the appropriate radiation dosimetry but not required for the interstitial microwave antenna array hyperthermia (IMAAH) system. Additional thermometry was obtained using nonperturbed fiberoptic thermometry probes inserted into the catheters' housing antennas. No significant complications, such as bleeding or infection, were observed. This approach to cancer therapy is shown to be feasible and it produces controlled, localized hyperthermia, with temperatures of 50 degrees C or more in tumors. This technique may offer a therapeutic option for pelvic, intra-abdominal and head and neck tumors.

Adult↗
PubMed1985

Laser scanning phase modulation microscope.

We describe the concept and first implementation of an innovative new instrument for quantitative light microscopy. Currently, it provides selective imaging of optical path differences due to birefringence; with further development, it is also possible to selectively image several optical properties, including refractive path differences, optical rotation, and linear and circular dichroism, all with diffraction-limited resolution. An image consists of a 512 X 512 element array, with each pixel displaying one of 256 grey levels, linearly proportional to the specific optical property being observed. Additionally, conventional brightfield and polarized light microscopy are available, with the accompanying advantages of laser scanning and digital image processing. The microscope consists of three subsystems, representing three distinct technologies. The laser scanning subsystem moves a focused microspot across the specimen; the output of a photodetector is an electric signal corresponding to a scanned image. The image display subsystem digitizes this signal and displays it as an image on a video monitor. When used in conjunction with a phase modulation feedback loop, the image formed is of the specimen's birefringent retardation or other selected optical property. The digitized images are also available for computer enhancement.

Animals↗
PubMed1984

Theoretical temperature profiles for concentric coil induction heating devices in a two-dimensional, axi-asymmetric, inhomogeneous patient model.

In this paper we report on theoretical calculations for the temperature distributions produced by an rf magnetic induction device that is placed concentrically about the long axis of the patient. A two-dimensional, axi-asymmetric, inhomogeneous patient model was used in conjunction with a numerical moment method for calculating the electric fields in the tissues of the model and a numerical finite element method for calculating the resulting temperature distributions. The electric fields and the absorbed power per unit volume of tissue were calculated for both a thorax and viscera model, each of which included a tumor volume. The absorbed power values were input into the bioheat transfer equation and the temperature distributions were calculated for a wide range of blood flow rates. Based on the steady-state and transient results, our computer simulations predict poor therapeutic temperature profiles for tumors embedded deeply in the thorax and viscera. This heating technique appears to produce significant therapeutic volumes in superficial tumors located not greater than 7 cm in depth. These theoretical calculations should aid the clinician in the evaluation of induction heating devices for their effectiveness in heating deep-seated and superficial tumors.

Humans↗
PubMed1984

Calculation of absorbed power in tissue for various hyperthermia devices.

Recently, there has been increased interest in the use of hyperthermia (temperatures, 42 to 45 degrees) as an adjuvant modality to radiation therapy or chemotherapy for the treatment of cancer. This paper discusses the use of the finite element method as a technique for calculating the power deposited per unit volume of tissue for two regional-type hyperthermia devices. The two types of devices investigated are inductive concentric coils and annular phased arrays. The mathematical basis for the finite element method and its advantages when dealing with problems involving irregular boundaries and nonhomogeneous tissue are reviewed. Specific examples are shown for the calculations of the electromagnetic fields and the resulting absorbed power density. Furthermore, it is shown how the basic finite element formulation for the electromagnetic problem can be extended to solving the temperature distribution problem. Temperature distributions for both types of devices are illustrated. Finally, the limitations of the finite element method are reviewed, and possible implications of the specific results for the efficacy of regional devices are raised.

Body Temperature↗
PubMed1984

Theoretical temperature distributions produced by an annular phased array-type system in CT-based patient models.

Theoretical calculations for the specific absorption rate (SAR) and the resulting temperature distributions produced by an annular phased array (APA)-type system are made. The finite element numerical method is used in the formulation of both the electromagnetic (EM) and thermal boundary value problems. A number of detailed two-dimensional patient models based on CT-scan data from the pelvic, visceral, and thoracic regions are generated to simulate a variety of tumor locations and surrounding normal tissues. The SAR values from the EM solution are put into the bioheat transfer equation, and steady-state temperature distributions are calculated for a wide range of blood flow rates. Based on our theoretical modeling, the APA shows no preferential heating of superficial over deep-seated tumors. However, in most cases for all three regions of the human trunk only fair thermal profiles (therapeutic area near 60%) are obtained in tumors with little or no blood flow and poor temperature patterns (therapeutic area less than 50%) are found in tumors with moderate to high perfusion rates. These theoretical calculations should aid the clinician in the evaluation of the effectiveness of APA-type devices in heating tumors located in the trunk region.

Humans↗
PubMed1983

Temperature distributions from interstitial rf electrode hyperthermia systems: theoretical predictions.

In recent years, there has been increased interest in the use of hyperthermia as an adjuvant modality to radiation and chemotherapy in the treatment of cancer. One of the more promising techniques is the application of an rf voltage to an array of electrodes inserted directly into the tumor. The electrodes are usually small, hollow stainless steel needles that are inserted as the first step in a brachytherapy procedure. By applying a voltage between the needles, an rf current is induced in the tissue, resulting in joule heating. In this paper, we calculate numerically the temperature distributions for an array of such needles. In our model we assume a two-dimensional problem, i.e. infinitely long needles, and a homogeneous medium. Blood flow effects are included in the calculation. The results show that for low blood perfusion rates, e.g., on the order of 3 ml/100 gm X min, very smooth temperature distributions result, and the electrodes can be spaced fairly far apart. However, for blood flow rates on the order of 20 ml/100 gm X min the temperature distributions are not smooth, and there are hot spots around the electrodes and cool regions between them. However, if the electrodes are spaced about 1 cm apart and the voltages are adjusted to optimize the temperature distribution then reasonably good results should be achievable. The equation is solved using a finite difference technique. By applying the superpostion principle, we are able to introduce a procedure which substantially reduces the amount of core storage required and results in reasonably efficient run times on a moderate size mini-computer.

Brachytherapy↗
PubMed1983

Interstitial hyperthermia in combination with brachytherapy.

Flexible coaxial cables were modified to serve as microwave antennas operating at a frequency of 915 MHz. These antennas were inserted into nylon afterloading tubes that had been implanted in tumors using conventional interstitial implantation techniques for iridium-192 seed brachytherapy. The tumor volume was heated to 42-45 degrees C within 15 minutes and heating was continued for a total of 1 hour per treatment. Immediately following a conventional brachytherapy dose and removal of the iridium seeds the tumors were heated again in a second treatment. This interstitial technique for delivering local hyperthermia should be compatible with most brachytherapy methods. The technique has proved so far to be practical and without complications. Temperature distributions obtained in tissue phantoms and a patient are described.

Brachytherapy↗