Intraoperative +/- external beam irradiation.
Explore the source record for details and available documents.
Bile Duct Neoplasms↗
Biomedical subjects
E C McCullough
Publications and source records attributed to E C McCullough.
CT-number variability in thoracic geometry.
The use of absolute CT numbers for in vivo tissue characterization is compromised by a number of technical and geometrical factors. A phantom simulating thoracic geometry and containing intrapulmonary "features" was scanned on three CT scanners allowing for assessment of CT-number variations with a wide number of scanning and geometric parameters. It was found that, with thoracic geometry, the absolute CT numbers of intrapulmonary features (e.g., solitary pulmonary nodules) can vary significantly due to a number of CT scanning parameters, such as geometry, CT scanner used, and/or time. Such variations must be taken into account when establishing criteria for characterizing tissue types using CT numbers. However, results show that variations in quantitative behavior with reasonable changes in patient geometry do not preclude meaningful characterization of solitary lung nodules (using CT-number averages) using CT scans for the three CT scanners studied, providing CT-number threshold data are derived from the same model scanner and operating conditions. The use of CT-number patterns within high-density intrapulmonary pathology (e.g., solitary pulmonary nodules) is compromised by the fact that high CT-number patterns were found to be a function of the reconstruction filter used and object size as well as being influenced by details of the surrounding medium.
Humans↗
X-ray transmission CT scanner survey, January 1982.
Explore the source record for details and available documents.
Tomography, X-Ray Computed↗
A measurement of doses to the neck for mantle field treatment of lymphomas with cobalt-60, 4-, and 10-MV photon beams.
Dose distributions within the neck, resulting from equally weighted, parallel, opposed mantle fields, were measured using thermoluminescence dosimetry in using thermoluminescence dosimetry in an anthropomorphic phantom. Results show the similarity and adequacy of the neck dose distribution using photon beams from cobalt 60, a 4-MV linear accelerator with an external filter, and a 10-MV linear accelerator. For equal mid-plane doses, the 4-MV beam without external flattening resulted in superficial dose rates to the lateral neck approximately 10%-15% higher than the other three beams studied.
Cobalt Radioisotopes↗
The unreliability of CT numbers as absolute values.
The use of CT numbers as absolute values was examined by scanning a standard phantom on five CT scanners under a variety of conditions simulating those encountered in routine body CT scanning. The results show that: (1) There are significant differences in absolute CT numbers between most scanners (only one scanner produced CT numbers that were equal to zero for water); (2) There are significant differences in absolute CT numbers between two scanners of the same manufacturer and model that were examined; (3) There is a significant difference in CT numbers in a single phantom scan, dependent on location in the scan, and the format of this variability is not constant from one scanner to another; and (4) There may be a significant difference in absolute CT numbers depending on various physical factors (e.g., kilovoltage, phantom orientation in scan aperture, and position of the phantom in the scan aperture). The findings suggest that there is a wide range of CT numbers observed for a given tissue type as a result of scanner performance alone, and that if absolute CT numbers are to be used for diagnosis the user must document that these machine-related variations are less than the differences thought to be significant.
Technology, Radiologic↗
Nuclear magnetic resonance imaging.
Nuclear magnetic resonance scanning provides the potential for measurement of new properties of tissue which may permit better pathologic differentiation. NMR will be less affected by bone, and so neurologic studies in which bone artifacts are a problem in CT may be facilitated. Direct sagittal and coronal imaging are possible. As far as we know, the biologic hazards are expected to be minimal but cannot be definitely ruled out at this time. At present, the relaxation times that are most frequently measured are such that clinically acceptable spatial resolution (2 to 3mm) requires scan times on the order of two minutes or more. Whether chemical cross-sections that are acceptable to clinical demands can be obtained remains to be demonstrated.
Electromagnetic Fields↗
Fact or artifact: an analysis of artifact in high-resolution computed tomographic scanning of the sella.
Computed tomography (CT) artifacts within the sella turcica, associated with the bones of the skull base, were identified and examined by use of a human skull phantom immersed in water. These artifacts were identified in 63% of 27 clinical high-resolution CT scans performed on patients with suspected sellar or parasellar pathology. Intrasellar artifacts may be minimized or eliminated by careful choice of scanning plane. Identification and elimination of intrasellar CT artifacts are necessary for accurate interpretation of sellar image.
Adult↗
Dynamic sequential scanning with table incrementation.
Dynamic sequential scanning with table incrementation is a method of rapid computed tomographic head scanning in which a complete 10-section scan can be made in 2 minutes 40 seconds or less. Although some measurable and visible loss of low-contrast resolution occurs, there is no loss of high-contrast resolution. Monthly throughput of patients has been increased by about 30% since this technique was instituted.
Brain↗
Performance evaluation of computerized treatment planning systems for radiotherapy: external photon beams.
Explore the source record for details and available documents.
Computers↗
Signal variance in computed tomography: the square root of N syndrome.
Explore the source record for details and available documents.
Tomography, X-Ray Computed↗
The selection, acceptance testing, and quality control of radiotherapy treatment simulators.
The critical aspects of selection, acceptance testing, and quality control of a radiotherapy treatment simulator are discussed. The selection of a simulator involves consideration of: (a) motions and readouts, (b) safety features, (c) x-ray and imaging systems, and (d) mechanical tolerances (including guarantees). When considering motions, it is important to ascertain the extent of each motion, motorization and speed, control location, and the location accuracy, and type of scale. Important questions in x-ray system selection concern (a) x-ray generator ratings and phase, and (b) details of the x-ray tube and image intensification system.
Humans↗
The Z2.94 "rule".
Explore the source record for details and available documents.
Biophysical Phenomena↗
Anthropomorphic phantoms for computed tomography scanner performance evaluation.
Phantom simulating materials and geometries encountered in computed tomography of the head and body have been constructed. They permit the quantitative study of artifactual behavior as well as low contrast detectability and spatial resolution of a computed tomography (CT) scanner. These phantoms may be useful in comparative evaluation of CT performance and in quality control programs.
Head↗
Patient dosage in computed tomography.
The maximum surface dosage in most clinical CT scans seems to range from 2-10 rads/study but much larger dose per study values seem possible with both rotate-translate and rotary geometry designs. The CT scanner type in itself does not significantly reduce doses. Secondary radiation dose values were measured for critical organs and indicate that dosage from secondary radiations may be reduced significantly by external shielding. Dose values in the vicinity of most CT scanners are typically 1-2 mrad/scan at 1 meter at the parameters of a typical clinical scan.
Female↗
Potentials of computed tomography in radiation therapy treatment planning.
CT can provide detailed 3-dimensional representation of diseased and dose-limiting structures; it detects lung metastases and may be of use in follow-up studies. The potential use of the electron density cross section may be limited by (a) the small number of planning situations where inhomogeneity corrections are truly useful, (b) the lack of sensitivity of certain correction schemes (e.g., megavoltage photons), (c) the inherent inaccuracy of certain correction schemes, (d) the inaccuracy of in vivo determinations of electron density and (e) the narrow range of electron densities observed in most soft tissues of the body.
Follow-Up Studies↗
Radiation protection requirements for a whole-body CT scanner.
Exposure values for a whole-body CT scanner, obtained from a room protection survey covering one month (119 patients), are reported. It was found that weekly exposures could be expected to be in the range of 350-750 mR/week for a daily load of 12 patients. The h.v.l. of gypsum board, lead, and plate glass at this radiation level was 1.8, 0.020, and 1.3 cm, respectively. The authors suggest that plate glass is not the method of choice for shielding a high-volume body scanner installation unless a large enough lead glass window is not available or cannot be installed in time to meet construction deadlines.
Radiation Dosage↗
The use of CT scanners in megavoltage photon-beam therapy planning.
Several problems related to the true value of quantitative information from CT scanners in improving estimates of photon-beam isodose distribution remain unanswered. The authors conclude that two widely used correction factors provide satisfactory isodose corrections behind heterogeneities of simple geometry. Lateral perturbations were found to be small for megavoltage photon beams, indicating that complex computational schemes are uncalled for. It appears doubtful that the use of CT information in megavoltage photon-beam isodose curve generation requires (a) larger computers than those currently available either in existing therapy planning systems or on the scanner itself or (b) direct access to the CT numbers.
Radiotherapy Dosage↗
Factors affecting the use of quantitative information from a CT scanner.
Computed tomography can be used quantitatively in a variety of ways in both diagnosis and therapy. However, the successful use of CT numbers depends on the appreciation of several features of CT scanning, including the diagnostic viewer. It is also possible to employ the quantitative output of a CT scanner to improve the accuracy of isodase curve computations for photon (or electron) beam radiotherapy. A quality-control program is mandatory for anyone wishing to use CT numbers for this purpose.
Technology, Radiologic↗