PubMed · 4438445
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
G Wickman. 1974. A liquid ionization chamber with high spatial resolution.. https://doi.org/10.1088/0031-9155%2F19%2F1%2F006
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
PURPOSE: To compare the Entrance Surface Dose (ESD) for a normal patient, measured on three types of dedicated digital equipment for chest radiography: an amorphous selenium system, a CR (Computed Radiography) system, and a system for direct radiography (DR) based on an amorphous silicon active matrix (a-Si) connected to a CsI(T1) detector. MATERIALS AND METHODS: The ESD values were measured with different dosimeters placed in the air parallel to the detector plane, and at a distance equal to the thickness of a normal-build patient. The measurements were taken with the radiological parameters (Posterior-Anterior projection (PA) and Lateral projection (L)) used in diagnostic practice to obtain high-quality diagnostic radiographic images. The measurements taken with the DR equipment were repeated after the manufacturer added a 0.2 mm-thick Cu filter. The ESD values obtained by this series of measurements were reported as mean and standard deviation values (M+/-SD). RESULTS: With the PA projection, the doses measured for the different devices were the following: amorphous selenium system 0.12+/-0.06 mGy, CR system 0.3+/-0.05 mGy, DR system 0.05+/-0.02 mGy. With the L projection: amorphous selenium system 0.40+/-0.13 mGy, CR system 0.9+/-0.17 mGy, and DR system 0.21+/-0.15 mGy. CONCLUSIONS: The use of digital systems allows a significant reduction of the patient dose. In particularly the Direct Radiography system, based on a CsI/a-Si detector, administers the lowest patient dose.
When the absorbed dose conversion factor of the x-rays is looked for, generally it is being done how to measure the effective energy (keV) from the half-value layer. But, spectrum measurement is necessary to evaluate quality of x-ray precisely. So, 2.94% of the maximum differences were in the water, soft tissue, and 20.93% of the maximum differences were in search of absorbed dose conversion factor due to the half-value layer and the spectrum as a compared result by cortical bone. And, when a x-ray tube voltage rose, this difference showed a tendency of spreading out. A cause was because the rates of the photon of the higher energy than the energy measured with effective energy increased by a x-ray tube voltage's rising. The ratio of the mass energy absorption coefficient which faces air like cortical bone should be careful because an error by the absorbed dose conversion factor grows big when a absorbed dose conversion factor is measured by the big absorption medium, though it is as the difference in absorbed dose conversion factor is compared with an error by the dosimeter and there is no problem in the water, soft tissue.
This paper outlines how objective measurements of both image quality, in terms of signal-to-noise ratio, and effective dose may be used as tools to find the optimum kVp range for a digital chest radiography system. Measurements were made with Thoravision, an amorphous selenium-based digital chest X-ray system. The entrance surface dose and the effective dose to an anthropomorphic chest phantom were determined demonstrating how effective dose is related to beam quality. The image quality was measured using detective quantum efficiency, threshold contrast and a radiologist preference trial involving 100 patients. The results show that, despite the fact that the entrance surface dose decreases as the kVp increases, the effective dose, a better measure of the risk, reaches a minimum value between 90 and 110 kVp; however, the image quality decreases as the kVp increases. In this study the optimum kVp for chest radiography, using a selenium-based radiography system, is in the range 90-110 kVp. This is contrary to the 120- to 150-kVp range that is commonly used. Also, this study shows how objective measurements can be used to optimise radiographic technique without prolonged patient trials.