The authors show that the intrinsic ultrasonic attenuation of a gallstone is an important factor in determining the degree of shadowing. B scans in vivo and in vitro demonstrated that stones with higher attenuation also show the most shadowing. In addition, attenuation can be correlated with physical structure: more highly attenuating stones tend to have the largest percentage of crystalline material, a larger average crystal size, and a more rigid structure. The authors recommend that higher-frequency transducers be used where possible if nonshadowing structures are seen in the gallbladder.
Extrafocal radiation was investigated using four different rotating-anode radiographic units currently employed in a pediatric hospital. It was found to exhibit significant penetration, with an effective energy only slightly lower than that of the primary radiation. The percentage of extrafocal relative to focal radiation in pediatric procedures involving rare-earth screens ranged from 2 to 15%. The ratio of extrafocal to focal radiation tended to increase with increasing kVp, mA, and field size but was independent of focal spot size. Since extrafocal radiation may extend significantly outside of the primary collimated field, radiosensitive organs such as the gonads, thyroid, and eyes which are assumed to be shielded may actually receive as much as 25 mR per radiograph.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.