Toxicity and possible synergistic effects of ultrasound.
Explore the source record for details and available documents.
Humans↗
Biomedical subjects
P L Carson
Publications and source records attributed to P L Carson.
Sonographic identification of lung maturation in the fetal lamb.
Ultrasound evaluation of fetal lung development in utero could be a noninvasive method for frequent monitoring of the state of pulmonary maturity and predicting when parturition could occur with minimum or no risk of respiratory distress syndrome of the newborn. In cases of high-risk obstetric management in premature labor, this ability may be a particularly useful tool. To pursue this possibility, the lungs and livers of 13 living fetal lambs were successfully imaged with a modified clinical B-scanner under carefully controlled conditions; physiologic function tests on the excised lungs determined the state of pulmonary maturity. In eight cases, maturity or immaturity was correctly identified by sonographic criteria. The results wer ambiguous in four cases. One case of immature lung was incorrectly identified as mature. The trends established in these animal studies appear promising and with refinement may form the basis for sonographic assessment of fetal lung maturity in a clinical setting.
Animals↗
Absolute kilovoltage calibration of a diagnostic x-ray generator.
A method for absolute calibration of diagnostic x-ray generators is presented and discussed. The method employs a Ge(Li) detector and relies on the direct observation of the onset of fluorescence radiation from scattering foils placed in the primary beam.
Filtration↗
Intensity distribution, modulation transfer function, and the effective dimension of a line-focus x-ray focal spot.
The radiant intensity along the anode-cathode dimension of a line-focus x-ray focal spot tends to peak at the center and decrease gradually to zero at the edges. In recognition of this varying intensity, the ICRU has recommended that the anode-cathode dimension of the focal spot be reported as 0.7 times the dimension measured with a pinhole camera. In this paper more objective correction factors are developed. These correction factors are based upon comparison of calculated MTFs of focal spots with Gaussian and cosine intensity distributions with the MTF for focal spots with a uniform intensity distribution.
Radiography↗
Imaging soft tissue through bone with ultrasound transmission tomography by reconstruction.
A phantom consisting of a 2.5-cm-diameter aluminum rod, a balloon filled with castor oil, and a ballon filled with a phenylated silicone fluid was imaged in water with ultrasound transmission tomography by reconstruction (UTTR). This phantom was chosen for investigation of the feasibility of detecting small changes in the ultrasound velocity and ultrasound attenuation coefficient of soft tissues in planes containing bones. Attenuation images of a transverse section of a leg of lamb were obtained as well. Opposed transmitting and receiving transducers were scanned on either side of the imaged object, just as an x-ray tube and detector are scanned in the pencil beam geometry employed with the first x-ray computerized axial tomographic system. More than adequate signal was transmitted through the aluminum rod and the bone to obtain reconstructions; but, in these crude images, there were numerous artifacts which maintain the uncertainty regarding the future utility of this promising technique. Although velocity imaging should not be as sensitive to reflection and refraction as attenuation imaging, a very narrow ultrasound beam must be employed to obtain reasonable resolution in velocity imaging.
Models, Structural↗
Computational analysis and dosimetric evaluation of a commercial irregular-fields computer program.
The proper evaluation of the accuracy of a new computer program for radiation-therapy dosimetry requires consideration of both the mathematical algorithm used in the program and the performance required in clinical applications. As an example, our evaluation of the irregular-fields dosimetry program currently marketed by SHM for their Rad-8 system is described. The evaluation begins with an explanation of the mathematical computation described. The evaluation begins with an explanation of the mathematical computation method, with emphasis on the points where the calculation differs from previous methods. Next, the procedure for setting up the beam data file is discussed. Finally, a step-by-step procedure is described in which calculated doses are compared with measured doses, using a Varian Clinac-4 with lead flattening filter, and the limits within which a +/- 5% accuracy is attainable are estimated. Some sources of error and areas for possible improvements are mentioned.
Computers↗
Thermal conductivity and diffusivity of neuroblastoma tumor.
In the application of hyperthermia to cancer management, it would be useful to know the temperature/tim profile of heated tissues, including the tumor and surrounding normal structures. To obtain this information, knowledge of thermal conductivity and diffusivity of the tissues is required. The thermal conductivity of neuroblastoma was determined by a transient technique to be 89% of the thermal conductivity of water at 25 degrees, 37 degrees, and 44 degrees C. From the latter measurements, the thermal diffusivity of neuroblastoma cells was estimated as 93% of the thermal diffusivity for water. Further, in this study of neuroblastoma cells, the water content was measured as 87.4 g/100 ml of cells, a rather high value not atypical of tumor cells. From literature values of density, specific heat, and thermal conductivity, values for the thermal diffusivity of a variety of normal tissues were estimated. The thermal diffusivity values of normal tissues and neuroblastoma cells exhibit an excellent correlation with water content.
Animals↗
Assessment of errors in intensity measurements of pulse echo ultrasound using miniature hydrophones.
Total transmitted power and intensity distributions from diagnostic ultrasound systems have been measured with a radiation force balance and with a miniature hydrophone and instrumentation available in many medical centers. In assessing the accuracy of absolute intensity and power determinations from measurements of acoustic pressure with a hydrophone, ultrasonic power was computed from hydrophone measurements. This power value was compared with the power determined by a radiation force technique. On five pulse echo ultrasound systems, the ratio of the power measured with a radiation force balance to the power determined with the hydrophone varied from 0.25 to 5.5. These differences are attributed mainly to the known large variations in hydrophone response as a function of frequency, and possible time, since several other possible sources of error were evaluated and estimated to have a reasonably small net effect of 25%. The errors evaluated were those dealing primarily with measurement procedures.
Ultrasonics↗
Median and spatial low-pass filtering in ultrasonic computed tomography.
To reduce noise- and reconstruction-related artifacts in ultrasound computed tomography, the use of combined median and Hamming-weighted spatial low-pass filtering is evaluated. The evaluation of the reconstruction filters uses both computer-generated projections of a known object with the least mean-square error criterion as well as a more subjective evaluation of conventional ultrasonic attenuation and speed of sound images.
Breast↗
Automated analysis of multiple performance characteristics in magnetic resonance imaging systems.
As with other digital imaging systems in heavy medical use, it is desirable with magnetic resonance imaging (MRI) to obtain extensive, rigorous system performance measures from a small set of images of one or two relatively simple test objects. Digital analysis of the parallel square rod (PSR) test object introduces digital image system self-evaluation to MRI and extends automated image evaluation to include rigorous measures throughout the imaging volume rather than just average measures over the image. Precise comparisons with theory and between systems can be performed as well as quality control and corrections for nonuniformities. The PSR test object consists of an 18 X 18 X 36 cm rectangular acrylic container enclosing 60 parallel square acrylic rods running the entire length. The inter-rod space is filled with a liquid or gel that produces strong, tissuelike signals in MRI and high contrast relative to the rods for computed tomography (CT). For profiles of slice thickness and separation, the rods are tilted in the test object to intersect the image plane at a 45 degree angle when the test object sides are parallel and perpendicular to the image plane. The test object itself is rotated 6-12 degrees about its major axis so that the sides of the rods make a small angle to the rows and columns of pixels. This allows digital sampling at finer spacing than the pixels for determination of edge response functions.(ABSTRACT TRUNCATED AT 250 WORDS)
Humans↗
Hardware design of an ultrasound CT scanner.
Explore the source record for details and available documents.
Computers↗