A mobile calcified spontaneously amputated ovary.
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Abdomen, Acute↗
Biomedical subjects
P D Lester
Publications and source records attributed to P D Lester.
Magnetic resonance imaging of an orbital varix with CT and ultrasound correlation.
A case of orbital varix demonstrated with computed tomography, ultrasound, and magnetic resonance imaging is reported. The clinical and radiographic findings are discussed.
Child↗
Computer-assisted design of surface coils used in magnetic resonance imaging. III. The design and construction of two long twin axial antennae for imaging of the whole human spine.
Two modified folded dipole MRI surface coils were designed, constructed and tested. These antenna which are long twin axial lines use the effective distributive capacitance resulting from the distance between two longitudinal elements to provide tuning. The principal advantage of this type of antenna is the ability to image longer objects such as vertebrae, spinal cord, and longer portions of the extremities. This type of antenna shows less localized high intensity in the image due to a more evenly distributed current pickup from the sample. The coils were designed by calculating theoretical magnetic field distribution for the twin axial coils. These were obtained by integrating the Biot-Savart equation. This gave excellent agreement with an MR image of a di-electrically uniform phantom. As antennae of this sort are nonlinear in response, giving rise to an image intensity nonuniformity, computer software for the MR image was developed to correct the image intensity profile over the experimental volume. The software significantly improved the image quality by reducing the saturated intensity of the region near the antenna, thereby revealing detailed structure of the tissue being imaged.
Equipment Design↗
Absolute kVp calibration using characteristic x-ray yields.
A spectrometer with a high-resolution room-temperature silicon detector was used to obtain spectra including characteristic x-ray peaks produced after fluoroscopic beams were incident on W, Pb, and Th absorbers. Characteristic x-ray yield points were obtained from spectra taken at several generator kVp settings which produced x rays with energy above the K-shell absorption edge for each element. A line drawn through the yield points when projected to zero yield served to locate the console setting corresponding to the actual K-absorption edge energy for each absorber. The technique is useful for precision measurement of generator kVp and absolute calibration of indirect kVp measuring devices under operational conditions.
Biophysical Phenomena↗
Field-focusing hyperthermia and magnetic resonance imaging (MRI) with a grounded probe and a commercial MRI scanner.
A method for performing magnetic resonance imaging (MRI) and producing field-focusing hyperthermia sequentially in phantoms and rat tissues with a grounded hyperthermic probe and a commercial MRI scanner was demonstrated. In the treatment mode the MRI scanner was used as a radiofrequency (RF) power source, and an invasive, electrically grounded, tuned probe was used to produce hyperthermia in phantoms via induced eddy current convergence. Temperature increases of 4.5 degrees C/5 minutes in a dielectrically uniform phantom and 5.0 degrees C/6 minutes in the peritoneum of a rat were measured in the vicinity (3-5 mm) of the grounded probe with the transmitter of the MRI scanner working at 2 per cent duty cycle. The advantage of this combined diagnostic and therapeutic approach is that the position of the hyperthermic probe can be monitored before each treatment, with observation of the tumor during and after treatment, if desired. In addition, the total cost is significantly less than that of both an MRI scanner and an RF hyperthermia treatment system.
Animals↗