Biomedical subjects

S M Powsner

Publications and source records attributed to S M Powsner.

22 records · Page 2Linked to original sources

PubMed1986

Automated production and analysis of echo contrast agents.

To develop and standardize contrast agents for use in contrast echocardiographic imaging, microbubble size, concentration, decay, and ultrasound backscatter must be known. These parameters were assessed with a scanning laser particle counter, a commercial ultrasound unit, and various sonicated intravenous solutions. The scanning laser particle counter proved to be a fast and effective means of evaluating microbubble size, concentration, and stability. In addition, sonication was found to be a reliable and reproducible technique for preparing standardized echo contrast agent solutions containing uniformly small microbubbles. The bubbles generated ranged in size from 1 to 15 micron in diameter. All solutions had mean bubble diameters less than 6 micron. The half life of solutions ranged from 44 +/- 12 seconds for Hypaque 50%, to 253 +/- 73 seconds for Iopamidol. Addition of the surfactant to dextrose 70% prolonged bubble half life from 58 +/- 12 seconds to 1018 +/- 276 seconds. Phased array two-dimensional echocardiography of sonicated microbubble solutions, and subsequent videodensitometric analysis, revealed that bubble concentration was directly proportional to echo-reflective properties, and that the solutions have significant ultrasound reflective properties in vitro at concentrations of less than 1500 bubbles/ml.

Autoanalysis↗

PubMed1986

Quantitation of echo-contrast effects.

With the recent development of sonicated microbubble echocardiographic contrast agents, it is now reasonable to attempt to quantitate actual tissue perfusion. However, this requires an understanding of the quantitative relationship between microbubble concentrations and the reflected ultrasound signal. This paper describes (1) the basic acoustic properties of sonicated microbubbles, and (2) experimental verification of this relationship, showing that the ultrasound signal actually begins to decrease at a critical concentration that may be predicted based upon bubble size. These microbubbles have acoustic properties that are essentially those of a random collection of Rayleighian scatters. Signal strength is governed primarily by the compressibility of gas, as opposed to fluid. In addition, bubble diameter is an important factor in determining signal strength (sixth power dependence). And, because the bubbles are randomly arranged, the reflected signal is not as great as might be expected, when compared to the signal reflected by a single bubble. A simple in vitro test of the acoustic analysis confirmed the critical limit for bubble concentration, the measurement of which led to a prediction for sonicated microbubble size that is within a factor of two of the published values. This acoustic analysis and confirmation, along with ongoing in vivo experimentation, promises to make possible quantitative regional perfusion measurement employing sonicated contrast agents.

Contrast Media↗

PubMedDate not supplied

Capturing the semantic relationship between clinical terms with current MeSH bibliographic coding.

This paper compares bibliographic retrieval using current MeSH (Medical Subject Headings) to bibliographic retrieval using explicitly coded semantic relationships between index terms. In a previous study, ten lists of abstracts, each list containing 20-40 papers discussing a specific pair of terms, were analyzed to identify the specific relationship(s) between those terms discussed in each paper. In the present study, we analyze how well current MeSH coding using topical subheadings and check tags, can selectively retrieve those papers discussing each semantic relationship.

Abstracting and Indexing↗

PubMedDate not supplied

Lessons learned from a pilot implementation of the UMLS information sources map.

OBJECTIVE: To explore the software design issues involved in implementing an operational information sources map (ISM) knowledge base (KB) and system of navigational tools that can help medical users access network-based information sources relevant to a biomedical question. DESIGN: A pilot biomedical ISM KB and associated client-server software (ISM/Explorer) have been developed to help students, clinicians, researchers, and staff access network-based information sources, as part of the National Library of Medicine's (NLM) multi-institutional Unified Medical Language System (UMLS) project. The system allows the user to specify and constrain a search for a biomedical question of interest. The system then returns a list of sources matching the search. At this point the user may request 1) further information about a source, 2) that the list of sources be regrouped by different criteria to allow the user to get a better overall appreciation of the set of retrieved sources as a whole, or 3) automatic connection to a source. RESULTS: The pilot system operates in client-server mode and currently contains coded information for 121 sources. It is in routine use from approximately 40 workstations at the Yale School of Medicine. The lessons that have been learned are that: 1) it is important to make access to different versions of a source as seamless as possible, 2) achieving seamless, cross-platform access to heterogeneous sources is difficult, 3) significant differences exist between coding the subject content of an electronic information resource versus that of an article or a book, 4) customizing the ISM to multiple institutions entails significant complexities, and 5) there are many design trade-offs between specifying searches and viewing sets of retrieved sources that must be taken into consideration. CONCLUSION: An ISM KB and navigational tools have been constructed. In the process, much has been learned about the complexities of development and evaluation in this new environment, which are different from those for Gopher, wide area information servers (WAIS), World-Wide-Web (WWW), and MOSAIC resources.

Abstracting and Indexing↗