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PubMed1991

Halfscan: clinical applications in MR imaging.

A series of phantom experiments was performed to evaluate the effects of half-Fourier scanning, also known as Halfscan, on signal-to-noise and in-plane resolution. Resolution was not demonstrably effected with the available phantoms and signal-to-noise was seen to vary as the square root of time independent of the implementation of Halfscan. Evaluation of the Halfscan technique was made using data from 240 patients. The technique was found to "salvage" examination in an estimated 70% of uncooperative patients where motion artifact or other patient concerns would have precluded clinically useful studies. Halfscan was also combined with other techniques such as increased number of signal acquisitions, prolonged repetition times and three-dimensional Fourier transform technique.

Artifacts↗
PubMed2001

[Multi-slice spiral CT of the abdomen in oncological patients: influence of table support and detector configuration on image quality and radiation exposure].

PURPOSE: To evaluate the image quality and radiation exposure of different spiral CT scanning parameters for routine staging examination of the abdomen in oncologic patients using a multi-slice CT scanner. METHODS/MATERIALS: Examination of 40 patients in 4 groups on a multi-slice CT scanner (Somatom VolumeZoom, Siemens AG, Forchheim). Functional detector width (4 x 2.5, 4 x 5 mm) and pitch (table feed in relation to collimated slice width) were varied (3 and 5). Tube voltage (120 kV), effective tube current (160 mAs), slice-thickness (6 mm), increment (4 mm), kernel (B 30), and contrast injection parameters were kept constant. Axial images were assessed by three radiologists regarding delineation of anatomic structures, artifacts, and overall image quality. RESULTS: Significantly reduced image quality especially due to artifacts was observed using a 5 mm detector configuration with a pitch of 5 (scan time 9 sec). Image quality was rated best for a 2.5 mm detector configuration with a pitch of 3 and a scan time of 28 sec. The effective dose was independent of the pitch. However, the mean effective dose was 9% higher using the smaller detector configuration (9.9 mSv vs 10.9 mSv). CONCLUSIONS: For routine staging CT of the abdomen use of a 4 x 2.5 mm detector configuration with a pitch between 3 and 5 is recommended. A 4 x 5 mm detector configuration using overlapping data acquisition can also be recommended, but additional thin slice reformations are not possible.

Abdominal Neoplasms↗
PubMed2000

Pathogenic significance of methicillin resistance for patients with Staphylococcus aureus bacteremia.

To assess whether methicillin resistance is a microbial characteristic associated with deleterious clinical outcome, we performed a cohort study on 908 consecutive episodes of Staphylococcus aureus bacteremia and a case-control study involving 163 pairs of patients matched for preexisting comorbidities, prognosis of the underlying disease, length of hospitalization, and age. Of 908 bacteremic episodes, 225 (24.8%) were due to methicillin-resistant S. aureus (MRSA). Multivariate analysis did not reveal that methicillin resistance was an independent predictor for mortality when shock, source of bacteremia, presence of an ultimately or rapidly fatal underlying disease, acquisition of the infection in an intensive care unit (ICU), inappropriate empirical therapy, female sex, and age were taken into account. Nonetheless, methicillin resistance was an independent predictor for shock. The case-control study could not confirm that shock was linked to MRSA when prior antimicrobial therapy, inappropriate treatment, ICU residence, and female sex were considered. Our data suggest that cohort studies tend to magnify the relationship of MRSA with clinical markers of microbial pathogenicity and that this effect is a shortcoming of these kind of studies that is caused by inadequate control for underlying diseases.

Adult↗
PubMed2003

Population-based study of the epidemiology of and the risk factors for invasive Staphylococcus aureus infections.

A population-based active-surveillance study of the Calgary Health Region (population, 929,656) was conducted from May 1999 to April 2000, to define the epidemiology of invasive Staphylococcus aureus (ISA) infections. The annual incidence was 28.4 cases/100,000 population; 46% were classified as nosocomial. Infection was most common in people at the extremes of the age spectrum and in males. Several conditions were associated with acquisition of ISA infection, and the highest risk was observed in persons undergoing hemodialysis or peritoneal dialysis and in persons infected with human immunodeficiency virus. Forty-six patients (19%) died. Significant independent risk factors for mortality included positive blood-culture result, respiratory focus, empirical antibiotic therapy, and older age. A higher systolic blood pressure at presentation was associated with reduced case-fatality rate. ISA infections are common, with several definable groups of patients at increased risk for acquisition and death from these infections. This study provides important data on the burden of ISA disease and identifies risk groups that may potentially benefit from preventive efforts.

Adolescent↗
PubMed2006

Rapid polarizing field cycling in magnetic resonance imaging.

We describe the electronics for controlling the independently pulsed polarizing coil in a prepolarized magnetic resonance imaging (PMRI) system and demonstrate performance with free induction decay measurements and in vivo imaging experiments. A PMRI scanner retains all the benefits of acquiring MRI data at low field, but with the higher signal of the polarizing field. Rapidly and efficiently ramping the polarizing coil without disturbing the data acquisition is one of the major challenges of PMRI. With our modular hardware design, we successfully ramp the 0.4-T polarizing coil of a wrist-sized PMRI scanner at up to 100 T/s without causing image artifacts or otherwise degrading data acquisition.

Computer-Aided Design↗
PubMed1994

On the evolution of protamines in bony fish: alternatives to the "retroviral horizontal transmission" hypothesis.

Fish protamines are highly specialized molecules which are responsible for chromatin condensation during the last stages of spermatogenesis (spermiogenesis). However, not all fish contain protamines in their sperm nuclei; rather, there seems to be a random distribution of protamines within this group. The origin of this sporadic presence of protamines in the sperm and its significance have not yet been precisely determined. In this paper we have conducted an exhaustive survey of the literature available on the different types of nuclear protein composition of the sperm of teleost fish in order to try to correlate these data with what is presently known about the taxonomy of this group. The results of this analysis have allowed us to make the following observations. The divergence between protamines and histones has occurred several times during the evolution of the bony fish. However, the relative frequency of this divergence is almost negligible during the differentiation of genera and species (intrafamily variation) and is very small during the differentiation of families (interfamily variation). Nevertheless, the divergence is very noticeable among the different orders. It is therefore possible to conclude from all this that the sporadic distribution of protamines in bony fish is not a random event as initially believed. Furthermore, such a heterogeneous distribution of protamines cannot be easily accounted for by a mechanism of horizontal retroviral transmission through repeated and independent acquisition of a protamine gene as has been recently proposed (Jankowski, Stater, Dixon (1986) J Mol Evol 23:1-10). Rather, it could possibly be explained by a repeated and independent loss of the expression of the protamine gene (or loss of the gene itself) which mainly occurred during the diversification of the orders of this group.

Amino Acid Sequence↗
PubMed2005

Four-dimensional fetal echocardiography with spatiotemporal image correlation (STIC): a systematic study of standard cardiac views assessed by different observers.

OBJECTIVE: To test the agreement between observers and reproducibility of a technique to display standard cardiac views of the left and right ventricular outflow tracts from four-dimensional volume datasets acquired with Spatiotemporal Image Correlation (STIC). METHODS: A technique was developed to obtain dynamic multiplanar images of the left ventricular outflow tract (LVOT) and right ventricular outflow tract (RVOT) from volume datasets acquired with STIC. Volume datasets were acquired from fetuses with normal cardiac anatomy. Twenty volume datasets of satisfactory quality were pre-selected by one investigator. The data was randomly assigned for a blinded review by two independent observers with previous experience in fetal echocardiography. Only one volume dataset was used for each fetus. After a training session, the observers obtained standardized cardiac views of the LVOT and RVOT, which were scored on a scale of 1 to 5, based on diagnostic value and image quality (1=unacceptable, 2=marginal, 3=acceptable, 4=good, and 5=excellent). Median scores and interquartile range, as well as inter- and intraobserver agreement were calculated for each view. RESULTS: The mean menstrual age at the time of volume acquisition was 25.5+/-4.5 weeks. Median scores (interquartile range) for LVOT images, obtained by the first and second observers, were 3.5 (2.25-5.00) and 4 (3.00-5.00), respectively. The median scores (interquartile range) for RVOT images obtained by the first and second observers were 3 (3.00-5.00) and 3 (2.00-4.00), respectively. The interobserver intraclass correlation coefficient for the LVOT was 0.693 (95% CI 0.380-0.822), and 0.696 (95% CI 0.382-0.866) for the RVOT. For the intraobserver agreement analysis, observer 1 gave higher scores to the LVOT the second time the volumes were analyzed [LVOT: 3.50 (2.25-5.00) vs. 5.00 (4.00-5.00, p=0.008)]. CONCLUSION: STIC can be reproducibly used to evaluate fetal cardiac outflow tracts by independent examiners. Slightly better image quality rating scores during the intraobserver variability trial suggests the presence of a learning curve for the manipulation and analysis of volume data obtained by STIC.

Double-Blind Method↗
PubMed2003

Analysis of the tuning and operation of reflection resonator EPR spectrometers.

This paper investigates basic characteristics of the electron paramagnetic resonance (EPR) signal obtained from spectrometers employing reflection resonators. General equations are presented which reveal the phase and amplitude dependence on instrumental parameters of both components of the continuous wave (CW) EPR signal (absorption and dispersion). New phase vector diagrams derived from these general equations are presented for the analysis of the EPR response. The dependence of the phase and absolute value of the CW EPR signal on the local oscillator (LO) phase and on resonator offset and coupling is presented and analyzed. The EPR spectrometer tuning procedures for both balanced and unbalanced heterodyne receivers are analyzed in detail using the new phase diagrams. Extraneous signals at the RF input of the microwave receiver (resulting from circulator leakage and reflections in the resonator transmission line) have been taken into account and analyzed. It is shown that a final tuning condition that corresponds to an extremum of the receiver output as a function of the resonator frequency is necessary and sufficient for the acquisition of pure absorption signal. This condition is universal: it applies to all spectrometer configurations in all frequency ranges. High Frequency EPR spectrometer (130 GHz) data are used to generate experimental phase diagrams that illustrate the theoretical concepts presented in the paper. Conditions are presented under which the absorption signal can be measured with complete suppression of the dispersion, independent of the mutual frequency offset between the microwave source and the EPR sample resonator. Equations describing the approximate relationship between changes of the resonator properties (Q-factor and frequency) and paramagnetic susceptibility are derived and analyzed.

Journal Article↗
PubMed1985

Visually induced adaptive changes in primate saccadic oculomotor control signals.

Saccades are the rapid eye movements used to change visual fixation. Normal saccades end abruptly with very little postsaccadic ocular drift, but acute ocular motor deficits can cause the eyes to drift appreciably after a saccade. Previous studies in both patients and monkeys with peripheral ocular motor deficits have demonstrated that the brain can suppress such postsaccadic drifts. Ocular drift might be suppressed in response to visual and/or proprioceptive feedback of position and/or velocity errors. This study attempts to characterize the adaptive mechanism for suppression of postsaccadic drift. The responses of seven rhesus monkeys were studied to postsaccadic retinal slip induced by horizontal exponential movements of a full-field stimulus. After several hours of saccade-related retinal image slip, the eye movements of the monkeys developed a zero-latency, compensatory postsaccadic ocular drift. This ocular drift was still evident in the dark, although smaller (typically 15% of the amplitude of the antecedent saccade, up to a maximum drift of 8 degrees). Retinal slip alone, without a net displacement of the image, was sufficient to elicit these adaptive changes, and compensation for leftward and rightward saccades was independent. It took several days to complete adaptation, but recovery (in the light) was much quicker. The decay of this adaptation in darkness was very slow; after 3 days the ocular drift was reduced by less than 50%. The time constants of single exponential curve fits to adaptation time courses of data from five animals were 35 h for acquisition, 4 h for recovery, and at least 40 h for decay in darkness. Descriptions of the central innervation for a saccade are usually simplified to only two components: a pulse and a step. It has been hypothesized that suppression of pathological postsaccadic drift is achieved by adjusting the ratio of the pulse to the step of innervation (19, 26). However, we show that the time constant of the ocular drift is influenced by the time constant of the adapting stimulus, which cannot be explained by the simple pulse-step model of saccadic innervation. A more realistic representation of the saccadic innervation has three components: a pulse, an exponential slide, and a step. Normal saccades were accurately simulated by a fourth-order, linear model of the ocular motor plant driven by such a pulse-slide-step combination. Saccades made after prolonged exposure to optically induced retinal image slip could also be simulated by properly adjusting the slide and step components.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Ocular↗
PubMed1990

Timing of data acquisition determines image quality in femoropopliteal phase-sensitive MR angiography.

To study the effects of timing of data acquisition on quality of femoropopliteal magnetic resonance (MR) angiograms, the authors studied 16 healthy men, mean age 34.3 +/- 6 years, by color Doppler imaging and by phase-sensitive (PS) MR angiography. PS MR imaging was performed at 1.5T using a flow adjustable gradient (FLAG) pulse sequence. The images were graded in a blinded fashion by two independent observers. Of 16 MR angiograms consisting of 141 angiographic images (AI), 45 (31.9%) were diagnostic. At least 1 diagnostic AI was obtained in each subject, and 38 (84.4%) of the diagnostic images were acquired within the first 120 milli-seconds (ms) of the systolic flow pulse. The highest yield of diagnostic images (90.9%) was obtained in the interval of thirty to sixty ms before the peak flow velocity. In healthy man diagnostic PS MR angiography requires triggering to the femoropopliteal systolic flow pulse. The highest yield of diagnostic images is acquired during the flow pulse acceleration.

Adult↗
PubMed1987

Reactions to blindness: a four-year follow-up study.

A previously studied group of newly blind adults was followed up after four years. There was only a slight increase in the acquisition of blind skills, while there was a surprising continuing pervasiveness of depression and poor health. A number of variables from the original study and from the follow-up data predicted outcome measures. Significant predictors of depression and distress were poor health, being married, being nonProtestant in this predominantly Protestant London population, and lacking ability to be more independent. Higher social class and an absence of a family history of blindness predicted greater distress. Earlier acceptance of blindness, early learning of blind skills, and better preillness adjustment predicted better coping and greater use of blind skills at follow-up. The extent of the depression and poor health are discussed, and recommendations are made for caregivers.

Adaptation, Psychological↗
PubMed1999

Mitochondria connects the antigen receptor to effector caspases during B cell receptor-induced apoptosis in normal human B cells.

We have previously reported that CD40 stimulation sensitizes human memory B cells to undergo apoptosis upon subsequent B cell receptor (BCR) ligation. We have proposed that activation stimuli connect the BCR to an apoptotic pathway in mature B cells and that BCR-induced apoptosis of activated B cells could serve a similar function as activation-induced cell death in the mature T cell compartment. Although it has been reported that caspases are activated during this process, the early molecular events that link the Ag receptor to these apoptosis effectors are largely unknown. In this study, we report that acquisition of susceptibility to BCR-induced apoptosis requires entry of memory B cells into the S phase of the cell cycle. We also show that transduction of the death signal via the BCR sequentially proceeds through a caspase-independent and a caspase-dependent phase, which take place upstream and downstream of the mitochondria, respectively. Furthermore, our data indicate that the BCR-induced alterations of the mitochondrial functions are involved in activation of the caspase cascade. We have found both caspases-3 and -9, but not caspase-8, to be involved in the BCR apoptotic pathway, thus supporting the notion that initiation of the caspase cascade could be under the control of the caspase-9/Apaf-1/cytochrome c multimolecular complex. Altogether, our findings establish the mitochondria as the connection point through which the Ag receptor can trigger the executioners of apoptotic cell death in mature B lymphocytes.

Apoptosis↗
PubMedDate not supplied

Detection of gastrointestinal and abdominal infections by 99mTc-ciprofloxacin.

BACKGROUND/AIMS: The aim of the study is detection and evaluation of the abdominal and gastrointestinal infective foci using 99mTc-ciprofloxacin (Laboratory for radioactive isotopes, Vinca). METHODOLOGY: In total 21 patients with clinical suspicion on abdominal or gastrointestinal infection were investigated. In all the patients, planar liver/spleen scintigraphy was performed. Ciprofloxacin chloride (3.5 mg) was mixed with 555 MBq of 99mTc in 3 mL of physiological solution and incubated for 20 min. After slow i.v. injection in a cubital vein, dynamic acquisition (1 f/min) was performed during the first 60 min in the position of interest, followed by static acquisition (500,000 imp) anterior and posterior view, abdomen and pelvis after 1 h and 4 h in all patients. When necessary, additional scintigrams were acquired after 24 h. In all the patients with negative or equivocal findings of planar scintigraphy, emission computerized tomography (SPECT) was performed (60 positions, 6 degrees). Interpretation was made by three independent observers. Additional data were provided using clinical findings, ultrasonography, computed tomography and magnetic resonance imaging, laboratory analyses, and surgical or microbiological confirmation of infection. RESULTS: There were eleven true-positive findings, seven true negative, two were false negative while one was false positive due to intestinal obstruction. Sensitivity was 79%, specificity 91%, positive predictive value 92%, negative predictive value 77%, accuracy 84%. CONCLUSIONS: According to our results, scintigraphy with radiolabeled ciprofloxacin is a useful method for detection and assessment of exact localization of abdominal and gastrointestinal infections.

Abdomen↗
PubMed2006

Acquisition of autonomy skills in adolescents with myelomeningocele.

This study describes ages of acquisition (AOA) of typical adolescent autonomy skills in a regional cohort of individuals with myelomeningocele (MM), aged 12 to 18 years, with a mean age of 14 years 11 months (SD 2y 5mo). Prospectively collected data over 10 years were analyzed. Regression analysis, using Generalized Estimation Equation, provided 50th centile and 75th centile AOA for each skill. One hundred and fifty-eight participants (90 males, 68 females) attended 378 annual patient visits. Patient contacts were equally distributed across age and physical severity groupings. Twenty-four percent of participants had functional lesion levels at or above L2, and 38% between L3-L5, 38% at S1 or below. Eighty-four percent had shunted hydrocephalus, 24% were independent in ambulation, and 69% achieved toileting independence before adolescence. AOA for autonomy skills were delayed by 25 to 30% when compared with typically developing adolescents. Differences in cognitive ability explained the variance in median ages for skill acquisition (p=0.01) more than physical lesion level. Participants acquired community skills at a median age of 16 years 6 months. Twelve percent of 18-year-olds drove cars (9% with supervision, 3% independently), regardless of physical lesion severity. We conclude that adolescents with MM acquire the majority of autonomy skills 2 to 5 years later than their typically developing peers. This study establishes AOA timelines for autonomy skills in adolescents with MM.

Adolescent↗
PubMed2006

Target volume definition for 18F-FDG PET-positive lymph nodes in radiotherapy of patients with non-small cell lung cancer.

PURPOSE: FDG PET is increasingly used in radiotherapy planning. Recently, we demonstrated substantial differences in target volumes when applying different methods of FDG-based contouring in primary lung tumours (Nestle et al., J Nucl Med 2005;46:1342-8). This paper focusses on FDG-positive mediastinal lymph nodes (LN(PET)). METHODS: In our institution, 51 NSCLC patients who were candidates for radiotherapy prospectively underwent staging FDG PET followed by a thoracic PET scan in the treatment position and a planning CT. Eleven of them had 32 distinguishable non-confluent mediastinal or hilar nodal FDG accumulations (LN(PET)). For these, sets of gross tumour volumes (GTVs) were generated at both acquisition times by four different PET-based contouring methods (visual: GTV(vis); 40% SUVmax: GTV40; SUV=2.5: GTV2.5; target/background (T/B) algorithm: GTV(bg)). RESULTS: All differences concerning GTV sizes were within the range of the resolution of the PET system. The detectability and technical delineability of the GTVs were significantly better in the late scans (e.g. p = 0.02 for diagnostic application of SUVmax = 2.5; p = 0.0001 for technical delineability by GTV2.5; p = 0.003 by GTV40), favouring the GTV(bg) method owing to satisfactory overall applicability and independence of GTVs from acquisition time. Compared with CT, the majority of PET-based GTVs were larger, probably owing to resolution effects, with a possible influence of lesion movements. CONCLUSION: For nodal GTVs, different methods of contouring did not lead to clinically relevant differences in volumes. However, there were significant differences in technical delineability, especially after early acquisition. Overall, our data favour a late acquisition of FDG PET scans for radiotherapy planning, and the use of a T/B algorithm for GTV contouring.

Algorithms↗
PubMed1985

A computerized low-shear pendulum viscoelastometer, stress-relaxation, shear creep, and dynamic elastic moduli measurements of soft biogels.

A computerized low-shear pendulum viscoelastometer that is well suited for measurements of the viscoelastic properties of soft biogels is described. The instrument has three modes of operation: (i) measurement of dynamic elastic moduli, (ii) stress relaxation, and (iii) shear creep-creep recovery. The main mechanical parts of the instrument include a specimen cuvette and a pendulum with a thin metal plate extending into the specimen cuvette. The cuvette and pendulum can undergo independent angular movements relative to a horizontal axis located about 12 cm above the specimen cuvette. The absolute angular position of the cuvette is under on-line computer control through a stepping motor driven micrometer. The angular position of the pendulum relative to the cuvette is measured using an inductive position detector. The necessary software for automatic operation, data acquisition and processing has been developed for all the three modes of operation. The instrument is well suited for measurements of dynamic elastic moduli in the range 0.02-150 dyn/cm2. Calibration data obtained using 100% ethanol are presented. The instrument suitability for measurements of stress relaxation and shear creep-creep recovery is illustrated by presenting the results of such measurements on a 5.5-mg/ml erythrocyte spectrin gel in isotonic solution.

Biophysical Phenomena↗
PubMedDate not supplied

An enhanced role for the recirculating lymphocyte in the neonatal immune system.

Lymphocytes continually recirculate between the blood and the tissues via the lymph independent of antigen. A great deal is known regarding both the physiology and the molecular mechanisms responsible for the process in adults. However, relatively little is known regarding the development of the recirculating lymphocyte pool in very young animals or fetuses. We have directly measured the recirculation of lymphocyte subsets in antigen-inexperienced newborn animals, and found extensive recirculation of T cells through both intestinal and subcutaneous lymph nodes. Apparent selective migration of recirculating lymphocytes could be attributed to subset-specific migration of gammadelta-T cells through subcutaneous lymph nodes. This clearly demonstrates that the preference for gammadelta-T cells to recirculate through SCLN is lineage specific, and independent of the presence of antigen. Most surprising was the observation that the recirculating lymphocyte pool was proportionately larger in neonatal animals than in adults, which correlated with the histological appearance of newborn lymph nodes. This data strongly suggests that development of the recirculating lymphocyte pool is inversely correlated with antigen exposure, and decreases in size with age and the acquisition of immunological memory.

Animals↗
PubMed2005

Evolutionary optimization of radial basis function classifiers for data mining applications.

In many data mining applications that address classification problems, feature and model selection are considered as key tasks. That is, appropriate input features of the classifier must be selected from a given (and often large) set of possible features and structure parameters of the classifier must be adapted with respect to these features and a given data set. This paper describes an evolutionary algorithm (EA) that performs feature and model selection simultaneously for radial basis function (RBF) classifiers. In order to reduce the optimization effort, various techniques are integrated that accelerate and improve the EA significantly: hybrid training of RBF networks, lazy evaluation, consideration of soft constraints by means of penalty terms, and temperature-based adaptive control of the EA. The feasibility and the benefits of the approach are demonstrated by means of four data mining problems: intrusion detection in computer networks, biometric signature verification, customer acquisition with direct marketing methods, and optimization of chemical production processes. It is shown that, compared to earlier EA-based RBF optimization techniques, the runtime is reduced by up to 99% while error rates are lowered by up to 86%, depending on the application. The algorithm is independent of specific applications so that many ideas and solutions can be transferred to other classifier paradigms.

Algorithms↗