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At least 667 records · Page 37Linked to original sources
PubMed2001

Decaying source method for scintillation camera resolving times.

An earlier paper by the author showed that scintillation camera systems can be described effectively using the resolving times T and tau0 of the dominant nonparalyzable and paralyzable components, that is, the detector system and the computer interface, respectively. When used with a full spectrum window, the camera has a lower nonparalyzable and an upper paralyzable operating range with normalized threshold input rate n(t)= N(t)tau(0) = ln(1 +k(T)n(t)), where kT= T/(tau)0. Correct determination of T and tau(0) requires that both r12 and r in the normalized two-source equations kT=(2/r12- 1/r) and k0=(r12/2r2)ln(2r/r12) come from the nonparalyzable (n< or =n(t)) and paralyzable (n> or =n(t)) ranges, respectively. A serious constraint of the two-source method, therefore, is that the large ratio a = n12 ln = 2 can lead to an input rate range (n,n12), which includes the threshold point n,, and in which neither T nor tau0 can be measured correctly. The decaying source method constitutes a refinement of the two-source method, which enables smaller ratios 1<a<2 to be used, and also includes the two-source method as a special case (a=2). This new method requires just two consecutive readings on a single decaying source, as opposed to three measurements on two sources of activity, for each determination of T or tau0, thus also minimizing staff exposure. The fact that only count rates and time intervals need now be recorded greatly simplifies computerization of the data acquisition and analysis activities, and the potential for real-time applications is obvious. The method enables T and tau0 to be measured accurately and with sufficient resolution to reveal possible variations with input rate. Long measurement times using a decaying source can be avoided, if required, by using a set of decaying sources simultaneously to cover different portions of the count rate range. The application of the measurement procedure in real-time and the use of the resolving times in the accurate correction of deadtime losses, also in real-time, are treated separately in another paper.

Gamma Cameras↗
PubMed1999

The VA's use of DICOM to integrate image data seamlessly into the online patient record.

The US Department of Veterans Affairs (VA) is using the Digital Imaging and Communications in Medicine (DICOM) standard to integrate image data objects from multiple systems for use across the healthcare enterprise. DICOM uses a structured representation of image data and a communication mechanism that allows the VA to easily acquire radiology images and store them directly into the online patient record. Images can then be displayed on low-cost clinician's workstations throughout the medical center. High-resolution diagnostic quality multi-monitor VistA workstations with specialized viewing software can be used for reading radiology images. Various image and study specific items from the DICOM data object are essential for the correct display of images. The VA's DICOM capabilities are now used to interface seven different commercial Picture Archiving and Communication Systems (PACS) and over twenty different radiology image acquisition modalities.

Evaluation Studies as Topic↗
PubMed2000

SPECT in the year 2000: basic principles.

OBJECTIVE: SPECT has become a routine procedure in most nuclear medicine departments. SPECT provides significant technical challenges for the nuclear medicine technologist, as compared with planar imaging, in the areas of SPECT acquisition, image reconstruction, and data processing. Many new advances in SPECT methodology are becoming available, such as iterative reconstruction, multimodality fusion, and advanced gated cardiac SPECT. SPECT imaging is demanding and requires careful attention to proper acquisition protocols, whether circular or noncircular orbits, and postprocessing is becoming more complex with the addition of iterative reconstruction and attenuation correction algorithms, among others. Understanding the principles of SPECT is essential not only to produce the highest quality scans but also to identify image artifacts. After reading this article, the nuclear medicine technologist should be able to: (a) describe the historical development and benefits of SPECT imaging; (b) state the impact of image matrix size, number of projections, and arc of rotation on final SPECT image quality; (c) discuss the trade-offs between image noise content and spatial and contrast resolution in SPECT reconstruction; (d) discuss SPECT filters and their impact on image quality; (e) explain the differences between filtered backprojection and iterative reconstruction; and (f) describe the impact of attenuation and scatter in SPECT imaging and the advantages and pitfalls of attenuation correction methods.

Humans↗
PubMed1990

Problems brought about by "reading" a sequence of pictures.

The "reading" of a sequence of narrative pictures has been studied as a specific cognitive area. Sequences of pictures were presented to children between 3 and 7 1/2 years old in either the right or wrong order. We studied four problems: the child's difficulty in seeing the same character throughout different representations, the liking-up process of several pictures into one story, the correlation between the temporal order and the spatial disposition of pictures, and the child's tendency to consider the setting of pictures as a puzzle to solve. The characteristic difficulties observed seem to be related to the double status of the picture, which is both a physical and a symbolic object. We set out to reconstruct the path taken from the initial dilemma in which a child finds herself/himself, caught between the signifier and the signified, up until the point where, all contradictions resolved, she/he definitively acquires the principles of the way in which a sequence of pictures functions. Although more or less distinct stages concerning the acquisition of different rules inherent in a sequence of pictures can be observed, the existence of transitional periods favors a continuous progression.

Attention↗
PubMed1991

Initial experience with a radiology imaging network to newborn and intensive care units.

A digital image network has been installed in the James Whitcomb Riley Hospital for Children on the Indiana University Medical Center to create a limited all digital imaging system. The system is composed of commercial components, Philips/AT&T CommView system, (Philips Medical Systems, Shelton, CT; AT&T Bell Laboratories, West Long Beach, NJ) and connects an existing Philips Computed Radiology (PCR) system to two remote workstations that reside in the intensive care unit and the newborn nursery. The purpose of the system is to display images obtained from the PCR system on the remote workstations for direct viewing by referring clinicians, and to reduce many of their visits to the radiology reading room three floors away. The design criteria includes the ability to centrally control all image management functions on the remote workstations to relieve the clinicians from any image management tasks except for recalling patient images. The principal components of the system are the Philips PCR system, the acquisition module (AM), and the PCR interface to the Data Management Module (DMM). Connected to the DMM are an Enhanced Graphics Display Workstation (EGDW), an optical disk drive, and a network gateway to an ethernet link. The ethernet network is the connection to the two Results Viewing Stations (RVS) and both RVSs are approximately 100 m from the gateway. The DMM acts as an image file server and an image archive device. The DMM manages the image data base and can load images to the EGDW and the two RVSs. The system has met the initial design specifications and can successfully capture images from the PCR and direct them to the RVSs.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer Communication Networks↗
PubMed2003

Differences in word associations to pictures and words.

Normal subjects were asked to produce the "first word that comes to mind" in response to pictures or words that differed with respect to manipulability and animacy. In separate analyses across subjects and items, normal subjects produced a significantly higher proportion of action words (that is, verbs) to pictures as compared to words, to manipulable as compared to non-manipulable stimuli and to inanimate as compared to animate stimuli. The largest proportion of action words was elicited by pictures of non-living, manipulable objects. Furthermore, associates to words matched standard word associates significantly more often than those elicited by pictures. These data suggest that pictures and words initially contact different forms of conceptual information and are consistent with an account of semantic organization that assumes that information is distributed across different domains reflecting the mode of acquisition of that knowledge.

Adult↗
PubMed1994

The development of phonological skills.

In this paper we consider the nature and consequences of the development of phonological skills in children. We begin with evidence for developmental refinements in phonological processes. These developments, in turn, affect a variety of other skills. We consider two particular examples: the relationship between the development of speech skills and verbal short-term memory and the development of children's phonological awareness. The development of phonological awareness is related to the acquisition of literacy, which, in turn, brings about further refinements in phonological skills.

Child↗
PubMed1994

Skilled expert practice: is it 'all in the mind'? A response to English's critique of Benner's novice to expert model.

In a recent critique of the work of Patricia Benner in relation to expertise, skilled intuitive grasp and the Dreyfus model of skill acquisition, English (Journal of Advanced Nursing 1993, vol. 18, pp. 387-393) uses the tenets of positivism and cognitive psychology to criticize Benner's work for lacking objectivity, validity, generalizability and predictive power. In this response to English's critique I show how he has misread, failed to read, and consequently misunderstood her work, and, equally importantly, its philosophical basis. Benner's work is developed from a philosophical foundation grounded in interpretive and Heideggerian phenomenology. This wholly different 'take' on the world and on human behaviour embodies a strong critique of those very same traditional-science worldviews which English uses to damn her work. English's critique is valuable in highlighting the ways in which Benner's work can be misrepresented and this response tries to remedy this misunderstanding by attempting to clarify the fundamental differences between phenomenological and cognitive understandings. These differences are crucial to understanding Dreyfus's and Benner's work. Here, I also attempt to correct some of English's wilder assertions regarding Benner's work. Finally, I try to show how Benner's work has empowered, enthused and challenged, rather than being 'denigrating to the majority of nurses'.

Clinical Competence↗
PubMed2003

Anticipating the correct matching response in a second-order matching-to-sample task.

A study was designed to evaluate the effects of anticipating the matching response on acquisition and transfer of a second-order matching-to-sample task. 40 college students of both sexes were assigned to different anticipation procedures that involved several verbal descriptions of the correct response, as well as others not involving explicit descriptions. All subjects were exposed to a pretest, two training blocks, two transfer test blocks, and a posttest. Anticipation procedures were evaluated during the first training block using an observational training procedure, except for 8 subjects, who were exposed to two training control procedures. Analysis showed acquisition and transfer of successful matching seems to depend on a verbal discrimination of the matching criterion exemplified by second-order stimuli. This discrimination was facilitated by prior conditions, as when subjects showed correct matching performance at pretest or was established with anticipation procedures that required explicit reading of verbal descriptions of the response choice.

Adolescent↗
PubMed2004

Quantitative assessment of percent breast density: analog versus digital acquisition.

Breast density is a moderate risk factor for breast cancer based on quantitative measurement of percent breast density from film-screen mammograms. In this study, percent breast density was determined using computer-assisted interactive thresholding software from sixty consecutive mammograms of women undergoing digital screening mammography with a prior film-screen mammogram obtained within the last two years. Observations were made regarding discrepancies in density readings. Percent breast density was significantly lower for digital mammograms (mean 32.2%) compared to analog mammograms (mean 40.3%) (p<0.0001). This was not significant for women with less than 20% breast density (range +0.3 to -2.7%), but larger differences were seen with increasing density (12.5-14.9% lower for >50% density). Differences in density readings between analog and digital mammography were largely observed to be due to better recognition of the skin line on digital mammograms resulting in inclusion of more subcutaneous fat. Difficulties with appropriate recognition of subcutaneous breast tissue and fatty tissue near the chest wall were present for both analog and digital mammography. In conclusion, percent breast density is significantly lower when the mammogram is acquired in digital format compared to film-screen, largely due to better recognition of the skin line with resultant inclusion of more subcutaneous fat. Breast cancer risk predictions based on computerized assessment of breast density may be underestimated when applied to digital mammography.

Breast Neoplasms↗
PubMed1999

Genetic analysis of the Serratia marcescens N28b O4 antigen gene cluster.

The Serratia marcescens N28b wbbL gene has been shown to complement the rfb-50 mutation of Escherichia coli K-12 derivatives, and a wbbL mutant has been shown to be impaired in O4-antigen biosynthesis (X. Rubirés, F. Saigí, N. Piqué, N. Climent, S. Merino, S. Albertí, J. M. Tomás, and M. Regué, J. Bacteriol. 179:7581-7586, 1997). We analyzed a recombinant cosmid containing the wbbL gene by subcloning and determination of O-antigen production phenotype in E. coli DH5alpha by sodium dodecyl sulfate-polyacrylamide electrophoresis and Western blot experiments with S. marcescens O4 antiserum. The results obtained showed that a recombinant plasmid (pSUB6) containing about 10 kb of DNA insert was enough to induce O4-antigen biosynthesis. The same results were obtained when an E. coli K-12 strain with a deletion of the wb cluster was used, suggesting that the O4 wb cluster is located in pSUB6. No O4 antigen was produced when plasmid pSUB6 was introduced in a wecA mutant E. coli strain, suggesting that O4-antigen production is wecA dependent. Nucleotide sequence determination of the whole insert in plasmid pSUB6 showed seven open reading frames (ORFs). On the basis of protein similarity analysis of the ORF-encoded proteins and analysis of the S. marcescens N28b wbbA insertion mutant and wzm-wzt deletion mutant, we suggest that the O4 wb cluster codes for two dTDP-rhamnose biosynthetic enzymes (RmlDC), a rhamnosyltransferase (WbbL), a two-component ATP-binding-cassette-type export system (Wzm Wzt), and a putative glycosyltransferase (WbbA). A sequence showing DNA homology to insertion element IS4 was found downstream from the last gene in the cluster (wbbA), suggesting that an IS4-like element could have been involved in the acquisition of the O4 wb cluster.

ATP-Binding Cassette Transporters↗
PubMed2002

Genetic structure and distribution of four pathogenicity islands (PAI I(536) to PAI IV(536)) of uropathogenic Escherichia coli strain 536.

For the uropathogenic Escherichia coli strain 536 (O6:K15:H31), the DNA sequences of three pathogenicity islands (PAIs) (PAI I(536) to PAI III(536)) and their flanking regions (about 270 kb) were determined to further characterize the virulence potential of this strain. PAI I(536) to PAI III(536) exhibit features typical of PAIs, such as (i) association with tRNA-encoding genes; (ii) G+C content differing from that of the host genome; (iii) flanking repeat structures; (iv) a mosaic-like structure comprising a multitude of functional, truncated, and nonfunctional putative open reading frames (ORFs) with known or unknown functions; and (v) the presence of many fragments of mobile genetic elements. PAI I(536) to PAI III(536) range between 68 and 102 kb in size. Although these islands contain several ORFs and known virulence determinants described for PAIs of other extraintestinal pathogenic E. coli (ExPEC) isolates, they also consist of as-yet-unidentified ORFs encoding putative virulence factors. The genetic structure of PAI IV(536), which represents the core element of the so-called high-pathogenicity island encoding a siderophore system initially identified in pathogenic yersiniae, was further characterized by sample sequencing. For the first time, multiple PAI sequences (PAI I(536) to PAI IV(536)) in uropathogenic E. coli were studied and their presence in several wild-type E. coli isolates was extensively investigated. The results obtained suggest that these PAIs or at least large fragments thereof are detectable in other pathogenic E. coli isolates. These results support our view that the acquisition of large DNA regions, such as PAIs, by horizontal gene transfer is an important factor for the evolution of bacterial pathogens.

Codon↗
PubMed1997

STEAM-Burst: a single-shot, multi-slice imaging sequence without rapid gradient switching.

The stimulated-echo acquisition mode-Burst sequence is a single-shot, multi-slice imaging technique that does not involve rapid gradient switching. A Burst excitation pulse train is followed by a 90 degrees hard pulse and, after a mixing time, by a 90 degrees slice-selective pulse. A read gradient refocuses a set of stimulated echoes, which can be phase-encoded to form an image. By repeating the selective pulse N times, each time with the carrier frequency offset differently, it is possible to sample N slices in a single-shot. A comparison is made of the sequence with other three-dimensional single-shot methods. Experiments implementing the technique on a 3 T whole-body imaging system and a 2 T, 31-cm bore animal imager are described. Both phantom and brain images are presented. The principal advantages of the new sequence are its speed, the absence of rapid gradient switching and corresponding freedom from artifacts, its insensitivity to static magnetic field inhomogeneities, and its low acoustic noise. The main disadvantages are the low signal-to-noise ratio of the images produced and the concomitant limitation in resolution.

Animals↗
PubMed1999

Speech and language acquisition in young children after cochlear implantation.

Auditory and speech intelligibility scores of 22 prelingually profoundly deaf children who had used cochlear implants for between 1 and 7 years in an intensive auditory/oral educational program greatly exceeded those previously obtained from similar samples of deaf children using hearing aids. Half of the children obtained language quotient scores within the average range for normal-hearing children and the majority obtained reading quotients within 80% of normal levels. Normal levels of language and reading development were associated with early implantation and open set speech perception.

Child↗
PubMed2000

Rapid genotyping of varicella-zoster virus vaccine and wild-type strains with fluorophore-labeled hybridization probes.

We developed a single-tube rapid method for the detection and differentiation of varicella-zoster virus (VZV) vaccine and wild-type strains that combines rapid-cycle PCR with wild-type-specific fluorescent probe melting profiles for product genotyping. A region including the polymorphic site in VZV open reading frame (ORF) 62 was amplified in the presence of two fluorescence-labeled hybridization probes. During the annealing step of the thermal cycling, both probes bound to their complementary sequences in the amplicon, resulting in resonance energy transfer, thus providing real-time fluorescence monitoring of PCR. Continuous acquisition of fluorescence data during a melting curve analysis at the completion of PCR revealed that loss of fluorescence occurred in a strain-specific manner as the detection probe, which was fully complementary to the wild-type VZV ORF 62 region, melted off the template. Use of this method allowed genotyping of samples within minutes after the completion of PCR, eliminating the need for post-PCR sample manipulation. In addition to reducing the time required to produce a result, this method substantially reduces the risk of contamination of the final product as well as the risk of sample tracking errors. The genotypes of 79 VZV-positive samples determined by this fluorescent resonance energy transfer (FRET) method were identical to the genotypes obtained by conventional PCR and restriction fragment length polymorphism analysis. The genotyping of VZV strains by the FRET method is a rapid and reliable method that is suitable for typing and that is also practical for use for the processing of large numbers of specimens.

Base Sequence↗
PubMedDate not supplied

Flat-panel digital radiology with amorphous selenium and active-matrix readout.

Future imaging techniques will be capable of high image quality, fast acquisition, compactness, and versatile operation. A flat-panel imager that is expected to achieve these goals is under development. It consists of a thin layer of amorphous selenium that converts x rays directly to an electric charge and a thin-film electronic circuit, or active matrix, to read out the electronic signal directly to a computer host. The advantages of amorphous selenium include high resolution and low noise without loss of signal strength. The advantages of the active matrix are real-time readout, flexible design parameters, and compactness of the readout structures. A prototype of this imager has been built and operated, and initial images (of an x-ray test bar pattern and a hand phantom) have been acquired. Although the prototype was built to test scientific principles and many possibilities for optimization remain, the images already possess the quality necessary for many radiographic procedures. A large range of current and new applications exist for this imager.

Hand↗
PubMed2005

Selection of information resources for education in medical pharmacology.

Pharmacology is the foundation science of medical pharmacotherapy. Education in medical pharmacology (EP) requires the use of information resources (IR) to meet the challenge of the continuous introduction of new drugs and new educational, didactic and pedagogical theories to enhance knowledge. Hence criteria for selecting bibliographic material for EP should be clearly outlined and implemented. In this work we present a method to select IR for EP based on systems theory and focusing on the factors determining: (a) the integration of a list of recommended IR for EP; (b) the design of the acquisition list for faculty and students work; (c) the overall organization of the resources available for its optimal use and benefit in the educational process; and (d) a general strategy for assessing the impact of the bibliographic infrastructure. The proposal is based on information from: (i) lists of recommended readings in the academic program of the Pharmacology course given at the School of Medicine of UNAM in the last 30 years; (ii) the extent of discipline development measured by two indexes derived from the contents of Goodman and Gilman's "Pharmacological Basis of Therapeutics" (G & G); (iii) the number of texts currently found in the collection of FM-UNAM which are classified in the section of Pharmacology using the Library of Congress Classification System (LCCS); and (iv) the comparison of academic versus standardized classification of pharmacology topics, such as Medical Subject Heading (MESH) and LCCS The importance of this proposal relates to its usefulness for EP and for other medical disciplines.

Books↗
PubMed2002

Visual attention to words in different languages in bilinguals: a magnetoencephalographic study.

We recorded evoked magnetic fields from bilingual subjects while they were visually presented with words. The task was to count words in a target language when most of the words were in another language and there were also nontarget deviants in a third language. Our results indicate that in a multilingual visual environment there is a different need for attention to a nontarget language depending on whether the subject is attending to words in the subject's first (L1) or second (L2) language. When words in L2 are attended to, more effort appears to be devoted to words in the nontarget language than when words in L1 are attended to. In addition, attention to the nontarget language while counting words in L2 does not seem to depend on the age of acquisition of L2.

Adolescent↗