Determination of lateral pharyngeal wall motion during connected speech by use of pulsed ultrasound.

Variations in the position of a point on the lateral pharyngeal wall relative to the external neck wall can be monitored by time-motion display of pulsed ultrasound. Such a portrayal is used to evaluate the lateral pharyngeal wall motion in normal and pathologic speakers during connected discourse.

Miniature radiation dosimeter for in vivo radiation measurements.

We have made initial characterization measurements on a miniature radiation dosimeter which can be used for in vivo radiation measurements. It consists of a radiation sensing field effect transistor (RADFET) mounted in a 0.8 mm OD plastic catheter. The RADFET acts as a dosimeter by storing trapped charge proportional to absorbed dose. The stored charge signal can be differentiated to give dose rate. We report on the techniques for mounting, a circuit for dose readout, drift of the readings, linearity of response, temperature and angular dependence, and unpowered operation of the device.

Trends and utilization of nuclear medicine in the United States: 1972-1982.

In the decade 1972-1982, in vivo nuclear medicine procedures in the United States increased from 3.3 million to about 7.5 million per annum. This growth has been the result of a markedly increased frequency in some types of examinations; particularly bone, liver, lung, and cardiovascular imaging. The only type of imaging in which a decrease in frequency has been observed has been in radionuclide brain imaging. Examination of these trends illustrates the difficulty in forecasting, even over time periods as short as 5 years. Competing tests have largely replaced radionuclide imaging in some areas; although in other areas, such as cardiac nuclear medicine, competing technologies appear to have been additive in terms of the frequency of examinations. Comparison with recent data from other countries indicates that the frequency of nuclear medicine procedures in the United States is probably the highest in the world.

Some effects of method on the measured conspicuity of chest lesions.

Both the magnitude and the precision of the conspicuity of a series of solitary chest nodules depends on the number and spacing of the measurement points. Observer accuracy in detecting 1.0 cm and 1.5 cm psuedo chest lesions does not correlate well with conspicuity.

Perception of simulated lung lesions.

Two series of test radiographs were produced, each containing a single nodular lesion. Each series was identical except that the lesions were spatially shifted with respect to adjacent structures, resulting in matched pairs of chest radiographs simulating a stereoscopic examination. Observation of each set singly and in pairs (non-stereoscopically) demonstrated a marked improvement in observer performance when the shifted pairs were viewed side-by-side.

Observer Performance as a function of viewing distance.

The performance of observers in detecting solitary lung nodules of 1.0 and 1.5 cm diameter has been measured for viewing distances of 46, 91, 183, and 470 cm. The data indicate that observer accuracy for detection of 1.5-cm nodules as measured by the area under the ROC curves is essentially unchanged for the three closest viewing distances and falls of by about 30% at the largest viewing distance. Observer performance for detection of 1.0 cm nodules, however, improves as the viewing distance is increased from 46 to 91 cm and then decreases at larger viewing distances.

Directed versus free search for nodules in chest radiographs.

Nodule detection in chest radiographs was compared under free-search and directed-search conditions. In directed search, the observer was told which quadrant of the chest to examine. Each of five observers read a test series of 96 radiographs seven times. Results were analyzed in terms of signal detection theory. NOdule detection was found to be significantly more accurate in directed search than in free search. The results were compared with those of previous experiments which found no such effect or an opposite effect. The present results do not support a previously hypothesized preattentive visual mechanism with better detection capabilities than focused visual attention.

Current status of DT targets for cancer therapy.

The current status of DT targets for cancer therapy is reviewed with regard to beam composition and energy as well as target configuration, lifetime, and neutron output. The advantages and shortcomings of the various target designs are discussed. It is concluded that several approaches can provide the necessary dose rate and target lifetime for clinical therapy purposes.

Accuracy of a two-sensor sonic digitizer.

Digitizing devices are typically used in radiotherapy computer treatment planning for entering patient anatomy, the locations of internal radioactive source, and the outlines of irregularly shaped external beams. The errors encountered in the use of a large-area two-sensor sonic digitizer for computer input have been studied. Conversion of data from triangular to Cartesian coordinates makes the precision of the digitizer nonuniform over the sensitive area. The response of each senor has been measured and found to be a nonlinear function of distance. The assumption of linearity in computing the triangular distances from the sensor readings produces errors in the computed distances of up to 0.8%. An alternative method of computing the distances using a fitted cubic function reduces the errors to less than 0.1%. For a test pattern, the maximum position error was reduced from 0.5 to 0.1 cm.

Radiation dose and image quality of double-loaded cassettes.

Some U.S. hospitals double-load x-ray cassettes for certain procedures. Loading two films in the same cassette for portable emergency room (ER), intensive care unit (ICU), or operating room radiographs provides both the referring clinicians and the radiologists with immediate images. Our study demonstrates a cost increase of 15%, an increase in air kerma for a chest x ray from 0.12 to 0.35 mGy (12-35 mrad), slight differences in optical density, image contrast, and spatial resolution under double-loading conditions. Our study shows that double loading cassettes may improve patient care by economically expediting the communication of radiographic findings. The decision to double load portable ICU or ER cassettes must be based on a balance of factors.

CT scanner selection and specification for radiation therapy.

The underlying considerations necessary for selecting a CT scanner for radiation therapy treatment planning are analyzed and discussed. To obtain best value for funds expended it is desirable to compare CT scanner mechanical characteristics, data quality, and data handling capabilities. Specifications can be written to ensure prompt delivery of a unit containing all essential features without adding to the cost or complexity of the unit.

Computer interface for a linear accelerator.

A computer interface for the Clinac-18 linear accelerator has been developed, using a standard CAMAC interface plus buffer amplifiers to isolate the CAMAC from the accelerator electronics. Buffer amplifiers are employed because direct connection of the CAMAC system to the accelerator was found to affect accelerator operation. The total interface accommodates the four gantry position analog signals and thirteen digital signals describing all available treatment options. The interface also allows the computer to inhibit beam operation.

Computer-based collection of mammographic exposure data for quality assurance and dosimetry.

PURPOSE: There is potentially more to quality assurance in mammography than the MQSA mandated tests. In this paper we describe a method of capturing individual mammogram technical parameters and the creation of new measures. These include the numbers of images required for each screening examination by technologist, median compression by technologist, and the radiation dose of the examination to the general population of patients. METHOD/MATERIALS: With this method we describe a semiautomated method of the collection of technical data from mammography exposures. The data that are automatically created by the mammography unit are saved on a computer for later analysis. The method was used on 2738 consecutive screening mammography examinations and 13 621 exposures from one machine. Data were obtained from November 1998 through December 1999. RESULTS: Using standard methods, the mean glandular dose (MGD) per exposure was 2.62 mGy (SD 1.2). The mean dose per bilateral screening examination was 6.53 mGy (SD 3.07), the median dose was 6.11 mGy, and the dose range was 1.13-34.23 mGy. Rhodium filtration was used for 18% of the exposures. The average and median breast thickness was 4.9 cm. The ACR phantom MGD for this machine was 2.44 mGy at 25 kVp, and 1.97 mGy at 26 kVp. The mean number of exposures for a bilateral mammogram was 4.9, and varied by a technologist from 4.7 to 5.2. The mean compression pressure varied by technologist from 13 to 30 lbs (58-134 N). CONCLUSIONS: The mean dose per mammogram is slightly greater than the ACR phantom dose at 25 kVp. Almost five exposures were necessary for a standard bilateral examination, and this varied by technologist. The compression used also varied by technologist. The semiautomated collection of technical data can aid in maintaining an effective mammography QA program.

Dosimetry of pion therapy beams.

Cellular, animal, and human radiobiology studies are in progress at the Los Alamos Meson Physics Facility as part of a joint University of New Mexico and Los Alamos Scientific Laboratory pion therapy project. To support these activities, dosimetry has been performed on many different pion beam configurations. The effect of both static and dynamic momentum spreaders and of collimators on beam profiles, depth-dose distributions, and peak-to-plateau ratios have been studied. The absorbed dose is obtained by the application of Bragg-Gray cavity theory to ionization chamber measurements. Calculations have been made for the effective W values and average mass-stopping-power ratios needed for the Bragg-Gray equation. Kerma corrections are applied to transform the dose from the chamber wall to dose in muscle.

The effect of geometric errors in the reconstruction of iridium-192 seed implants.

In the treatment of tumors using interstitial implants of radioactive seeds, the accuracy of computed dose distributions depends upon the accuracy with which the three-dimensional source geometries are reconstructed from radiographs of the implants. The effect of geometric reconstruction errors in iridium-192 seed implants were studied, using tumor dose as the measure. Tumor dose was defined as the average dose around the periphery of the treatment volume. Three ideal mathematical implants and five actual patient implants were used. The implants were distorted by randomly moving a specified number of seeds a specified distance. Tumor doses were directly calculated for the ideal implants. For the actual implants, isodose distributions were plotted and were read by a radiotherapist. For both types of implants, percentage errors in the tumor doses were calculated for the distorted reconstructions relative to the correct reconstructions. It was found that the tumor dose was accurate to within 5% if all the seeds were reconstructed to within 0.5 cm of their actual positions. Furthermore, up to 5% of the seeds could be mismatched between films, or otherwise incorrectly reconstructed, with position errors as large as 20 cm, and not change the tumor dose by more than 5%.

Measurement of the effect of inhomogeneities and compensating bolus in clinical pion beams.

Measurement of the effects of Telfon and air inhomogeneities on the ionization distributions of clinical negative-pion beams have been made at the Los Alamos Meson Physics Facility. Inhomogeneity location and pion-beam energy vary the effect of multiple coulomb scattering on the dose distribution lying in the penumbra of the inhomogeneity. CH2 bolus adequately corrects for the effects of these inhomogeneities. Bolus misalignment less than 0.5 cm does not seem critical because of large multiple coulomb scattering of the pion beam. However, this and secondary particles emitted from pion stars prevent the pion beam from being precisely shaped with sharp edges, as demonstrated by measurements under a patient bolus.

Factors affecting perception of pulmonary lesions.

The authors review some of the factors that influence the perception of pulmonary lesions: the observer and his environment, the film or other image-recording and display media, the lesion and its qualities, and the technique or modality of examination used.

Evaluation of a continuously variable collimator for 14 MeV neutrons.

This paper presents an evaluation of a continuously variable collimator for 14 MeV neutrons. Beam profiles measured in air and a phantom are used to demonstrate the relative importance of patient scatter and collimator throat scatter as they limit the performance characteristics of the collimator. The collimator consists basically of two sets of jaws each composed of 30 cm of steel followed by 20 cm of polyethylene. A solution is presented for the asymmetry in vertical and horizontal collimating characteristics resulting from the use of thick collimators. Beam profiles obtained with the collimator are comparable to published values for a fixed field 14 MeV neutron collimator.

Performance of a gas target neutron source for radiotherapy.

The performance of a compact and efficient neutron generator, using the 3H(d, n) reaction and a gas target, is reported. The target is formed in a windowless, differentially pumped vessel pressurised to 7.5 Torr. An extended source of 15 MeV neutrons is produced when the target is bombarded by a 10 mA beam of 210 keV deuterons. Measurements are reported of the neutron energy spectra, neutron and gamma-ray dose rates, target lifetime and tritium handling. The neutron flux distribution of the extended target was measured and compared with the predictions of a simple beam-gas interaction model. The measured neutron source strength is 1.7 +/- 0.4 X 10(12) neutrons per second. The source output is limited by target beam current, not target power considerations.

Experimentally determined tissue air ratios and scatter air ratios for collimated beams of 14 mev neutrons.

Tissue air ratios (TAR) and scatter air ratios (SAR) for collimated beams of 14 MeV neutrons were determined from depth dose curves measured in air and water using a tissue equivalent proportional counter. Central axis depth dose data were obtained as a function of field size and depth in a water phantom for an SSD or 125 cm. The collimator was composed of steel and polyethylene and was continuously variable from a 3 times 3 cm to a 20 times 20 cm field size at 125 cm SSD. The field scans for this collimator were flat within plus or minus 2 per cent over 80 per cent of the field dimension in air and were reduced to 20 per cent of the central axis dose at 1-2 field radii in air. Relative depth dose data in air and phantom were measured with an accuracy of plus or minus 2 per cent and were used for the TAR and SAR calculations. The resulting scatter air ratios for 14 MeV neutrons have roughly the same characteristics as 60-Co SAR, but are 60 per cent larger at maximum build-up and reach that maximum at about 60 per cent of the peak depth for 60-Co for all field sizes. The effects of collimator throat scatter on the central axis depth dose characteristics of this particular collimator design are discussed in detail using the measured tissue and scatter air ratios.