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At least 577 records · Page 32Linked to original sources
PubMed2005

Liver regeneration in humans is characterized by significant changes in cellular phosphorus metabolism: assessment using proton-decoupled 31P-magnetic resonance spectroscopic imaging.

In the present study we applied proton-decoupled 31P magnetic resonance spectroscopic imaging (MRSI) to noninvasively assess liver metabolism in patients who had undergone a partial hepatectomy (PH). Proton-decoupled 31P chemical shift imaging was performed in 47 patients 2-28 days following major hepatectomy, and the results were compared with those from eight control subjects. All studies were performed on a 1.5T MR imager (General Electric, Milwaukee, WI) equipped with a stand-alone proton decoupler. A 31P-1H resonator pair was used for data acquisition, and 31P data were obtained in 34 min. Liver regeneration was characterized by increases in phosphoethanolamine (PE), and decreases in nucleoside triphosphates (NTP), glycerophosphoethanolamine (GPE), and glycerophosphocholine (GPC). These alterations were most marked 48-72 hr after hepatectomy and returned to baseline within 3 weeks. The level of PE measured by MRSI was also found to depend on the percentage of liver that was removed, while changes in levels of cellular high energy phosphates were independent of the size of liver resection. Implementation of proton-decoupling was critical for assessing individual phosphomonoester and phosphodiester components. This study demonstrates that 31P MRSI can be used to assess metabolic changes in humans during liver regeneration, and may be useful for assessing derangement of the regenerative process or guiding adjuvant chemotherapies.

Female↗
PubMed1993

Developmental differences in the use of prototype and exemplar-specific information.

This study is an attempt to clarify the nature of developmental differences in the use of prototypical features or information about specific exemplars for object categorization and to identify stimulus factors that may modulate the use of these information sources. To this end, 6-year-olds, 11-year-olds, and adults were taught to sort visual patterns into one of two overlapping categories. Immediately or 24 h following category acquisition subjects were presented with a set of transfer stimuli consisting of both old and new patterns, including the theoretical prototype. Categorization responses to these test stimuli were examined against predictions derived from the prototype and nearest-old-exemplar accounts of categorization. A significant developmental change in the process of categorization was noted. For the youngest group, only the prototype model was found to fit the test data, whereas for the older groups both models independently explained significant amounts of variance in performance. This trend was not affected by the delay between training and testing, nor by a manipulation of intracategory variability. The emergence of the specific exemplar model as a viable explanation of ill-defined categorization thus appears to be related to the developmental level attained.

Adult↗
PubMed1987

Serial acquisition of data to predict one-year mortality rate after acute myocardial infarction.

Eight hundred sixty-six patients with acute myocardial infarction (AMI) were enrolled in a prospective study to determine optimal predictors of long-term prognosis. During 12-month (mean) follow-up there were 65 cardiac deaths and 21 nonfatal repeat AMIs. Twenty-nine variables (from the history, physical examination, serum chemistries, ambulatory monitor, radionuclide ventriculogram and exercise test) were arranged into in 5 sequential groups according to the time at which results became available during hospitalization. Multivariate analysis (logistic regression) and receiver-operator characteristic curves were used to assess improvement in prediction of mortality or repeat AMI by addition of each group of variables. The first group of independent predictors included rales, left bundle branch block and symptom status at 1 month before admission. Addition of information from ambulatory monitoring or serum chemistry did not improve prediction. Radionuclide ejection fraction made a statistically significant, independent contribution to mortality prediction. Of the final group the only exercise test variable that contributed independently to prediction was whether the patients took the test. However, receiver-operator characteristic curves showed that improvement in sensitivity and specificity by addition of information from the radionuclide scan and exercise test was clinically insignificant. Our results imply that costly tests after AMI should be reserved for specific indications and not applied universally for prognosis. Although these tests were highly predictive individually, each test generally added little to preexisting prognostic information.

Follow-Up Studies↗
PubMed1993

A multiparametric data analysis showing the potential of localized proton MR spectroscopy of the brain in the metabolic characterization of neurological diseases.

We conducted an extended clinical evaluation of localized proton magnetic resonance spectroscopy (MRS) of the brain, performed on various brain diseases using short stimulated echo times. Pathologies studied were mainly multiple sclerosis, stroke, leukoaraiosis, AIDS-related leukoencephalopathies and glial tumors. Other miscellaneous pathologies were also studied. Magnetic resonance examination of the brain was conducted on a Siemens Magnetom SP63 (equipped with a 1.5 T magnet). Localized proton MRS was performed on a routine basis immediately after imaging, using the STEAM (stimulated echo acquisition mode) with a short echo time (20 ms) combined with a CHESS (chemical shift selective excitation) sequence. One or two VOI (8 ml) were examined. Data on 125 spectra were processed by principal component analysis (PCA) and conventional variance analysis. The following metabolite resonances were studied: inositol-glycine, taurine-scyllo-inositol, choline derivatives, phosphocreatine-creatine, aspartate, glutamine glutamate, N-acetylaspartate, acetate and lactate. PCA demonstrates that the different metabolic variables are independent. The analysis of groups of spectra clearly demonstrates that the metabolic profiles detected by localized MRS in various pathologies (i) differ significantly from controls, and (ii) allow a metabolic discrimination between groups of pathologies. Results of PCA are confirmed by variance analysis. Strokes are characterized by an increase in lactate concentration and leukoaraiosis by a decrease in inositol-glycine resonance. AIDS-related leukodystrophies are characterized by increases in lactate and choline concentrations. Reduction in N-acetylaspartate which is observed in most pathologies is not significant in the small lesions of white matter. Lactate has often been found in MS plaques, but no variation in the choline/phosphocreatine ratio was observed. GABA was tentatively assigned in the spectrum of a patient with epilepsy under sodium valproate treatment. This study illustrates the clinical feasibility of the technique, the value of a multiparametric data analysis in the definition of the pertinent variables characterizing the metabolic impairment, and the impact of localized proton MR spectroscopy of the brain in the assessment of cerebral suffering.

AIDS Dementia Complex↗
PubMed2004

[Digital knowledge in the coat pocket -- hand-held personal digital assistants in radiology].

The personal digital assistant (PDA) enables the independent access to large data in a pocket-sized format. The applications for hand-held computers are growing steadily and can support almost any kind of problem. An overview of the available hardware and software is provided and evaluated. Furthermore, the use of the PDA in the clinical daily routine is described. In view of the numerous software programs available in radiology, the range of software solutions for radiologists is presented. Despite the high acquisition cost, the PDA has already become the digital assistant for the radiologist. After a short time of getting used to the PDA, nobody wants to miss it at work or at home. New technical features and available software programs will continuously increase the integration of the PDA into the medical workflow in the near future.

Computers↗
PubMedDate not supplied

Sleep and the time course of motor skill learning.

Growing evidence suggests that sleep plays an important role in the process of procedural learning. Most recently, sleep has been implicated in the continued development of motor-skill learning following initial acquisition. However, the temporal evolution of motor learning before and after sleep, the effects of different training regimens, and the long-term development of motor learning across multiple nights of sleep remain unknown. Here, we report data for subjects trained and retested on a sequential finger-tapping task across multiple days. The findings demonstrate firstly that following initial training, small practice-dependent improvements are possible before, but not following the large practice-independent gains that develop across a night of sleep. Secondly, doubling the quantity of initial training does not alter the amount of subsequent sleep-dependent learning that develops overnight. Thirdly, the amount of sleep-dependent learning does not correlate with the amount of practice-dependent learning achieved during training, suggesting the existence of two discrete motor-learning processes. Finally, whereas the majority of sleep-dependent motor-skill learning develops during the first night of sleep following training, additional nights of sleep still offer continued improvements.

Adult↗
PubMed2005

Extracting data from a DICOM file.

DICOM v3.0 is a vendor-independent standard for digital medical images that describes a file format and network protocol for the exchange of images between computer systems. When simply viewing a DICOM file, it is not necessary for the user to understand the details of the entire DICOM standard. However, understanding parts of the standard is essential when DICOM files are read and processed by a user-generated program. This paper offers an overview of information a user needs to write a program for extracting the image and acquisition parameters from a DICOM file.

Computer Communication Networks↗
PubMedDate not supplied

Verb-noun double dissociation in aphasic lexical impairments: the role of word frequency and imageability.

Neurolinguistic studies have provided important evidence regarding the organization of lexical representations and the structure of underlying conceptual knowledge; in particular, it has been shown that the retrieval of verbs and nouns can be damaged selectively. Dissociated lexical damage is proof of an independent mental organization of lexical representations and/or of the underlying processes. The aim of the present study is to estimate the rate of dissociated impairments for nouns and verbs on a large sample of mild to moderate aphasic patients and to investigate the mechanisms underlying such phenomena. In addition, the authors wished to verify to what degree the impairment for nouns and verbs is related to a specific type of language disorder. A confrontation naming task for verbs and nouns was administered to 58 aphasic patients. The major lexical (word frequency and age of acquisition) and semantic variables (familiarity and imageability of the underlying concept) were considered for each noun and verb used in the task. Verbs were distinguished by major functional classes (transitive, intransitive, and ergative verbs). The data collected from this task were analyzed twice: (i) as a group study comparison of major aphasic subgroups and (ii) as a multiple single case study to evaluate the differences on the naming of verbs and nouns and the effect of the lexical semantic variables on each individual patient. The results confirm the existence of dissociated naming impairments of verbs and nouns. Selective impairment of verbs is more frequent (34%) than that of nouns (10%). In many cases, the dissociated pattern of naming impairment disappeared when the effect of the concomitant variables (word frequency and imageability) was removed, but in approximately one-fifth of the cases the noun or verb superiority was preserved. Noun superiority emerged in five of six agrammatic patients. Both the naming of verbs (n = 9) or of nouns (n = 6) could be impaired selectively in fluent aphasic patients. The results lend support to the hypothesis of an independent mental organization of nouns and verbs, but a substantial effect of imageability and word frequency suggests an interaction of the naming impairment with underlying lexical and semantic aspects.

Aphasia, Wernicke↗
PubMed1988

Use of the competing-hypotheses heuristic to reduce 'pseudodiagnosticity'.

A quasiexperimental research design involving a nonequivalent control group was used to examine the efficacy of a brief educational intervention in teaching medical students to select optimal diagnostic data consistent with the competing-hypotheses heuristic and Bayes' theorem when solving clinical problems. There was no significant difference between intervention (n = 119) and control (n = 89) groups in performance at baseline, but the intervention group performed significantly better (p less than .001) than the control group after training. The results suggest that some problem-solving skills, such as learning to use the competing-hypotheses heuristic, can be enhanced or learned independent of the acquisition of content knowledge.

Bayes Theorem↗
PubMed1998

Application of reconstruction-based scatter compensation to thallium-201 SPECT: implementations for reduced reconstructed image noise.

Scatter compensation in Tl-201 single photon emission computed tomography (SPECT) presents an interesting challenge because of the multiple emission energies and relatively large proportion of scattered photons. In this paper, we present a simulation study investigating reconstructed image noise levels arising from various implementations of iterative reconstruction-based scatter compensation (RBSC) in Tl-201 SPECT. A two-stage analysis was used to study single and multiple energy window implementations of reconstruction-based scatter compensation, and RBSC was compared to the upper limits on performance for other approaches to handling scatter. In the first stage, singular value decomposition of the system transfer matrix was used to analyze noise levels in a manner independent of the choice of reconstruction algorithm, providing results valid across a wide range of regularizations. In the second stage, the data were reconstructed using maximum-likelihood expectation-maximization, and the noise properties of the resultant images were analyzed. The best RBSC performance was obtained using multiple energy windows, one for each emission photopeak, and RBSC outperformed the upper limit on subtraction-based compensation methods. Implementing RBSC with the correct choice of energy window acquisition scheme is a promising method for performing scatter compensation for Tl-201 SPECT.

Phantoms, Imaging↗
PubMed1996

Contribution of mutations in gyrA and parC genes to fluoroquinolone resistance of mutants of Streptococcus pneumoniae obtained in vivo and in vitro.

We have analyzed by gene amplification and sequencing mutations in the quinolone resistance-determining regions of the gyrA, gyrB, and parC genes of fluoroquinolone-resistant Streptococcus pneumoniae mutants obtained during therapy or in vitro. Mutations leading to substitutions in ParC were detected in the two mutants obtained in vivo, BM4203-R (substitution of a histidine for an aspartate at position 84 [Asp-84-->His]; Staphylococcus aureus coordinates) and BM4204-R (Ser-80-->Phe), and in two mutants obtained in vitro (Ser-80-->Tyr). An additional mutant obtained in vitro, BM4205-R3, displayed a higher level of fluoroquinolone resistance and had a mutation in gyrA leading to a Ser-84-->Phe change. We could not detect any mutation in the three remaining mutants obtained in vitro. Total DNA from BM4203-R, BM4204-R, and BM4205-R3 was used to transform S. pneumoniae CP1000 by selection on fluoroquinolones. For the parC mutants, transformants with phenotypes indistinguishable from those of the donors were obtained at frequencies (5 x 10(-3) to 8 x 10(-3)) compatible with monogenic transformation. By contrast, transformants were obtained at a low frequency (4 x 10(-5)), compatible with the transformation of two independent genes, for the gyrA mutant. Resistant transformants of CP1000 were also obtained with an amplified fragment of parC from BM4203-R and BM4204-R but not with a gyrA fragment from BM4205-R3. All transformants had mutations identical to those in the donors. These data strongly suggest that ParC is the primary target for fluoroquinolones in S. pneumoniae and that BM4205-R3 is resistant to higher levels of the drugs following the acquisition of two mutations, including one in gyrA.

Amino Acid Sequence↗
PubMed1983

A comparison between 180 degrees and 360 degrees data reconstruction in single photon emission computed tomography of the liver and spleen.

Single photon emission computed tomography (SPECT) of the liver and spleen has been studied using a GE400T/STAR rotating gamma camera/computer system. We have compared section image contrast, in both phantom and patient studies, produced by 180 degrees and 360 degrees reconstructions of data from a full 360 degrees data acquisition. There is little difference in overall image quality between the two reconstruction modalities. Quantitatively, however, appropriate 180 degrees reconstructions significantly improve lesion contrast in both organs by as much as a factor of two. In all cases studied, the values of image contrast achieved when the 180 degrees arc of reconstruction was centred about the region of interest were higher than the values obtained from the 360 degrees reconstructions. These results are shown to be independent of the corrections made for photon attenuation. Clinically this technique may prove useful in clarifying the presence or absence of disease, particularly in equivocal cases where lesions have poor contrast or are small in size. An extended clinical trial of the technique is now in progress.

Adult↗
PubMed1996

Test of the acute cardiac ischemia time-insensitive predictive instrument (ACI-TIPI) for prehospital use.

STUDY OBJECTIVES: To test diagnostic performance for acute cardiac ischemia (ACI) in a manually calculated and in a computerized, ECG-calculated ACI time-insensitive predictive instrument (ACI-TIPI) in prehospital chest pain patients. METHODS: We carried out prospective inclusion and data acquisition with retrospective analysis. Over a 6-month period, 439 adult emergency medical services patients with chest pain underwent prehospital electrocardiography. Because of incomplete data, 77 cases were excluded, leaving a study sample of 362 patients. Excluded patients did not differ significantly with respect to age, sex, final diagnosis, or history of myocardial infarction, heart surgery, diabetes, or stroke. ACI-TIPI probabilities of ACI were computed on the basis of the prehospital ECGs as interpreted retrospectively and independently by two study investigators blinded to patient outcome, with a specially programmed electrocardiograph, and with a computer algorithm further modified by logistic-regression analysis. RESULTS: Diagnostic performance on the basis of receiver operating characteristic (ROC) curve areas of the ACI-TIPI was scored, by the two physician readers, .73 and .74; and by ECG, .75. Patients with low ACI-TIPI probability (0% to 9%) had no acute myocardial infarctions, a 2.3% incidence of angina, and no prehospital life-threatening events. CONCLUSION: ACI-TIPI probabilities of ACI as generated by a specially programmed electrocardiograph are comparable to those based on physician ECG interpretations and may be useful in the prehospital evaluation of chest pain.

Acute Disease↗
PubMed1997

The concept of archiving unedited and edited digital coronary angiograms.

Digital image data acquired during cardiac catheterization will soon be archived on standardized digital storage media. However, with the enormous amount of generated data, considerable time will be wasted at later reviewing or at conferences, or when performing additional quantitative studies. As a result major advantages of a digital acquisition and archiving technique will be lost. The concept of two way archiving includes an unedited (primary) digital archive as well as a (secondary) archive edited by operator guided "intelligent" data reduction (IDR). IDR is based upon the elimination of useless and redundant frame sequences (FS), documentation of coronary interventions on one representative single frame (F) and on the reduction of relevant FS and physiological data to and ECG-controlled representative cardiac cycle (CC). With a heart rate of 72/min and an acquisition rate of 12.5 F/s a documentation of each FS may be obtained with only 10 F. A redundancy-free set of 130 F of a diagnostic study as well as only 41-85 F of an interventional study will be archived on an individual 3.5" MOD or on a CD-R. Two cardiologists and two cardiosurgeons studied independently 24 IDR-edited and the corresponding unedited digital angiograms and found no significant differences in the diagnostically relevant coronary morphology and left ventricular function. IDR provides an edited digital coronary angiogram, e.g. a set of images free of redundance and without loss of relevant information. Uneditable FS can be archived in their unedited (primary) form. IDR is managed on-line by an operator interacting with the angiographer.

Angiography, Digital Subtraction↗
PubMed2002

Identification and evolution of an IS6110 low-copy-number Mycobacterium tuberculosis cluster.

A cohort of 56 patients infected with related strains of Mycobacterium tuberculosis, the S75 group, was identified in a New Jersey population-based study of all isolates with a low number of copies of the insertion element IS6110. Genotyping was combined with surveillance data to identify the S75 group and to elucidate its recent evolution. The S75 group had similar demographic and geographic characteristics. Seventeen persons (30%) were linked epidemiologically. The S75 group was segregated from other low-copy-number isolates on the basis of several independent molecular methods. This group included 3 IS6110 genotype variants: BE, H6, and C28, containing 1, 2, and 3 IS6110 insertions, respectively. IS6110 insertion site mapping and comparative sequence analysis strongly suggest a stepwise acquisition of IS6110 elements from BE to H6 to C28. S75 represents a locally produced strain cluster that has recently evolved. The combination of multiple molecular tools with traditional epidemiology provides novel insights into dissemination, local transmission, and evolution of M. tuberculosis.

DNA Transposable Elements↗
PubMed2005

Externally triggered gating of nuclear medicine acquisitions: a useful method for partitioning data.

Physiological gating in nuclear medicine image acquisition was introduced over 30 years ago to subdivide data from the beating heart into short time frames to minimize motion blurring and permit evaluation of contractile parameters. It has since been widely applied in planar gamma camera imaging, SPECT, positron tomography (PET) and anatomical modalities such as x-ray CT and MRI, mostly for cardiac or respiratory investigations. However, the gating capability of gamma cameras and PET scanners can be employed to produce multiply partitioned, statistically independent projection data that can be used in various ways such as to study the effect of varying total acquired counts or time, or administered radioactivity, on image quality and multiple observations for statistical image analyses. Externally triggered gating essentially provides 'something for nothing' as no data are lost and a 'non-gated' data set is easily synthesized post hoc, and there are few reasons for not acquiring the data in this manner (e.g., slightly longer processing time, extra disk space, etc). We present a number of examples where externally triggered gating and partitioning of image data has been useful.

Artifacts↗
PubMed1992

Computer assisted development of diagnostic expert systems. A domain-independent package (EMPTY) for acquisition and use of expert's medical knowledge.

The package EMPTY has been developed with the aim of providing a tool based on well assessed methodological principles which can support both the organisation and use of medical knowledge for diagnostic and educational purposes. EMPTY is domain-independent and results in two interactive programs: ASK guides the acquisition of medical knowledge and RUN supports medical decision-making and provides facilities for medical education. The knowledge bases developed on ASK have a standard formal structure: they include taxonomies, definitions and descriptions of diseases, clinical findings and investigations; production rules for activation and refinement of diagnostic hypotheses; frame-like profiles of diseases; and quantitative criteria for scoring the clinical evidence on the base of available data.

Computer-Assisted Instruction↗
PubMed1993

Extended temporal gradient for the retrograde and anterograde amnesia produced by ibotenate entorhinal cortex lesions in mice.

Effects of ibotenic entorhinal cortex (EC) lesions on both retrograde and anterograde amnesia in mice were assessed using two-choice discrimination tasks learned at different intervals before surgery in two eight-arm radial mazes. The results indicated that EC-lesioned mice were severely impaired in postoperative retention of discrimination problems learned 3 d or 2 weeks prior to surgery, but showed no deficit on problems learned between 4, and up to 6 weeks before surgery, as compared to sham-operated controls. When trained on a novel two-choice discrimination problem (not acquired preoperatively), experimental subjects demonstrated quite normal rates of acquisition, but were impaired in learning its reversal. Furthermore, they exhibited a faster rate of forgetting (anterograde amnesia) relative to controls over a 2-week retention interval. These results indicate that approximately 4 weeks is required before memory for a two-choice spatial discrimination problem no longer depends on the integrity of the entorhinal cortex, and suggests that, beyond this time, an EC-independent memory storage system is capable of supporting the retrieval of information. The data, together with complementary behavioral results, are discussed in the context of current theories of memory storage.

Amnesia↗