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PubMed2006

A model of flow-through pore formation in methacrylate ester-based monolithic columns.

The main factors affecting the porosity of methacrylate-ester based monolithic columns were investigated. We prepared 23 monolithic capillary columns with porosity controlled by varying the proportions of butyl methacrylate and ethylene dimethacrylate monomers and of 1,4-butanediol and 1-propanol as the porogen solvent in the polymerization mixtures by thermally initiated in-situ polymerization in fused-silica capillaries. Using mixture design software, we systematically varied the composition of the polymerisation mixtures to find significant factors affecting flow-through pore formation. Multivariate analysis of the experimental data obtained for the fabricated columns yielded a model for prediction of the flow-through porosity in monolithic beds as a function of the composition of the polymerization mixture used to prepare polymethacrylate monolithic capillary columns. The mean error of prediction was lower than 8% for eight columns prepared independently of the original set of 15 columns used to derive the flow-through model. The flow-through porosity increases with increasing concentration of the binary porogen solvent mixture, the concentration of 1,4-butanediol being the main factor enhancing flow-through pore formation. On the other hand, increasing concentrations of the hydrophobic monomer butyl methacrylate and increasing concentrations of 1-propanol have a negative effect on flow-through pore formation. The capillary columns prepared with a high proportion of flow-through pores and a minimum amount of mesopores can be used for fast gradient separations of both low-molecular weight compounds and biopolymers.

Journal Article↗

PubMedDate not supplied

Development of new methodologies for the mass spectrometry study of bioorganic macromolecules.

In recent years, mass spectrometry has been increasingly used for the analysis of various macromolecules of biological, biomedical, and biochemical interest. This increase has been made possible by two key developments: the advent of electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) sources. The two new techniques produce a significant increase in mass range and in sensitivity that led to the development of new applications and of new analyzer designs, software, and robotics. This review, apart from the description of the status of mass spectrometry in the analysis of bioorganic macromolecules, is mainly devoted to the illustration of the more recent promising techniques and on their possible future evolution.

Macromolecular Substances↗

PubMed2005

Standardization of power Doppler quantification of blood flow in the human fetus using the aorta and inferior vena cava.

OBJECTIVE: This study aimed to test the applicability to the fetus of mathematical techniques developed to standardize power Doppler indices of adult regional perfusion. METHOD: Fetal power Doppler imaging was performed on 14 fetuses (25-37 weeks' gestation) using a standardized parasagittal plane, examining renal and aortic blood flow, and additionally inferior vena caval (IVC) flow in one fetus. Images were stored and transferred for off-line computer analysis using purpose-designed software. We first tested the need for techniques to remove the effects of red blood cell clumping on power Doppler amplitude, then performed further analyses to: (1) investigate cardiac cycle effects on aortic amplitude; (2) determine the spatial consistency of, and influence of angle of insonation on, maximal pixel value; (3) quantify temporal consistency; and (4) compare peak pixel values in the fetal aorta and IVC. RESULTS: No rouleaux effect on the vascular profile was detectable, in contrast to that identified in the adult. Within each fetus a consistent value was seen in the center of the aorta corresponding to 100% vascular amplitude, which was unaltered by the phase of the cardiac cycle, with a coefficient of variation of 28.9% at 89 degrees and 6.5% at 73 degrees . This value was constant in the aorta and IVC. CONCLUSION: Fetal blood does not appear to form rouleaux to any significant degree, so there is no artificially elevated maximal value for power Doppler amplitude as seen in the adult. We propose that the value representing 100% amplitude may be consistently measured in the center of large fetal vessels such as the aorta, allowing the direct measurement of fractional moving blood volumes in the human fetus.

Adult↗

PubMed1999

Eating patterns in French subjects studied by the "weekly food diary" method.

The "weekly food diary" was translated and adapted for use by French subjects. This validated method requires subjects to record every food and drink intake over 1 week, with several descriptors of the physical, psychological and social circumstances. Ten male [age 23. 6+/-2.3 years, body mass index (BMI) 20.7+/-0.6] and 16 female (age 23.3+/-0.6 years, BMI 20+/-0.6) students completed four weekly diaries over 1 year, one per season. Data were processed using a specially designed software. Breakfast was important, (about 400 kcalories). Lunch and dinner were almost equal in energy content but alcohol was consumed mainly with dinner. Meal size correlated positively with premeal hunger, number of people present, duration of premeal interval and time of day. Postmeal satiety correlated positively with meal size, aftermeal stomach content, and negatively with time of day, postmeal hunger and duration of sleep the preceding night. These observations allow hypotheses to be developed about mechanisms of intake in a French population and cross-cultural comparisons to be made.

Adult↗

PubMed1993

Monitoring free-text data using medical language processing.

In this paper, we describe a software system for automated monitoring of free-text data in a medical information system that we call RadTRAC (Radiology Text Report Analyzer and Classifier). RadTRAC uses a medical language processing tool and rules derived from statistical analysis of a database to process free-text chest X-ray (CXR) reports and identify reports that describe new or expanding neoplasms for the purpose of monitoring the follow-up of these patients. To evaluate the RadTRAC system, we examined a set of 470 consecutive radiology reports at the Veterans Administration Medical Center, Palo Alto, CA. We compared RadTRAC classification of CXR reports with retrospective expert classification of the reports and with clinical classification from CXR films as recorded in a logbook while the films were being read. The RadTRAC system had a sensitivity of 90% and a specificity of 82% using the logbook as the gold standard. This was similar to the performance of expert radiologists (sensitivity, 92%; specificity, 90%). We then reviewed the charts, appointment schedule, and subsequent X-ray reports of cases either in the logbook or that were identified by RadTRAC as needing follow-up. Two cases in the logbook could have potentially benefited from an automatic monitoring system to ensure follow-up. RadTRAC identified six confirmed new tumors or new metastatic lesions that were not in the logbook. Six other cases were identified by the RadTRAC system with suspicious X-ray findings that had either no follow-up or no further mention of the X-ray lesion in medical records. This suggests that a reminder system based on the RadTRAC technology would be potentially useful.

Abstracting and Indexing↗

PubMed1997

Visualization-based analysis of multiparameter models using environment for N-dimensional model analysis.

We present a methodology, based on N-dimensional computer visualization, for analyzing multiparameter models. This approach originally consisted of three steps: behavior analysis, sensitivity analysis, identifiability analysis. We have now developed a new way of calculating sensitivity based on the statistical measure of the coefficient of variation. Furthermore, we extended the methodology through the addition of an extra step, visual regression. Visual regression allows the user to visualize the process of actual parameter identification and presents a combined, empirical view of the first three steps in a single image. Next we applied this methodology to pulmonary capillary-transport models. Finally, we implemented the model analysis process as a stand-alone program. EN-DIMAN, the resulting software, allows researchers to carry out model analysis in a graphical user interface (GUI)-based environment.

Algorithms↗

PubMed1994

Straw thermal stabilizer for embryo cryopreservation.

Embryo cryopreservation procedures have been highly developed to support in vitro fertilization techniques, but the clinical results have not met initial expectations. Many variables influence the outcome of the embryo cryopreservation procedure. Exposure to classical freezing media does not affect further embryo development. Therefore, the first crucial step seems to be embryo thermal behavior during the freezing/thawing procedure. With the aim of avoiding thermal oscillations to the embryos due to liquid nitrogen injection into the freezing chamber, we have developed a straw thermal stabilizer (STS) cryopreservation accessory that when adapted to a programmable biological freezer offers a more exact control of the straws temperature and also a greater reproducibility of the freezing process. The STS incorporates a seeding mechanism controlled by specially designed software. For the biological assays, 2-cell mouse embryos were cooled until seeding at -7 degrees C or frozen to -120 degrees C using 1.5 M 1,2-propanediol and 0.1 M sucrose. As control groups, embryos were either untreated or were exposed to cryoprotectants, developing to blastocyst at rates of 90.8 and 88.4%, respectively. The embryos cooled until seedling or subjected to the complete freezing procedure developed into blastocysts at rates of 95.7 and 82.8%, respectively, disregarding the effect of the cryoprotectant exposure. These results show a substantial improvement in cryopreservation with no loss in embryo development due to the seeding procedure.

Animals↗

PubMed1993

Comparison of a phospholipid-based protein-free surfactant and a natural bovine surfactant (SURVANTA) during pressure and volume-controlled ventilation in an improved rabbit fetus model.

During pressure- or volume-controlled ventilation different surfactant preparations were compared in an improved rabbit fetus model. Based on a self-designed software program, this model enables on-line registration of lung mechanics and heart rate in up to ten fetuses. Using a commercially available bovine lung surfactant (SURVANTA) as standard, we compared animals treated with a protein-free surfactant preparation containing only phospholipids, PL (dipalmitoylphosphatidylcholine:palmitoyloleoylphosphatidylglycerol++ +, DPPC:POPG 70:30) plus palmitic acid (PA) with an untreated ventilated control group. During pressure-controlled ventilation the insufflation pressure (IP) was decreased and increased stepwise with and without positive end-expiratory pressure (PEEP). SURVANTA was significantly more potent than PL plus PA and both differed significantly from the untreated controls. With additional PEEP the differences between SURVANTA and PL+PA disappeared but the differences to the controls were still present. We found that, with additional PEEP, active natural surfactants lead to ECG-irregularities, which indicates that PEEP influences pulmonary and cardiovascular function and compromises the benefits of surfactant therapy. Also during volume-controlled ventilation SURVANTA was superior to PL+PA and the untreated controls. In order to raise the level of activity of pure PL mixtures to that of natural bovine surfactants, we suggest that a surface active protein (probably SP-C) must be added to such mixtures.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1991

Trans-fissural or trans-sulcal approach versus combined stereotactic-microsurgical approach.

The combined stereotactic-microsurgical approach has been used mainly to allow the removal of small subcortical lesions, determining their location and the route to be followed. In our experience, this approach has been most useful in 5 cases of small paraventricular AVMs and another 6 small deep-seated tumoural lesions. Since the availability of MRI, we have systematically applied Yasargil's proposal to perform dissection of the cisterns or sulci to reach a lesion with minimal or no injury to normal neuroanatomy. Assisted by Computer Aided Design software, we can superimpose the MR images with those provided by conventional or digital angiography (mainly the venous phase). MRI allows us to select a route or pathway through a sulcus, and angiography helps us in locating it on the brain surface. We have applied this technique systematically during the past year, and can report 20 cases (1 AVM, 12 tumoural lesions, 1 abscess and 6 haematomas). This trans-fissural or trans-sulcal approach has allowed us resection with minimal surgical damage, after a prompt and precise location. We think that both methods are not mutually exclusive, although the trans-sulcal approach is more adequate because of less discomfort for the patient, the smaller cerebral parenchyma injury and greater anatomofunctional information for the surgeon.

Astrocytoma↗

PubMed1986

An automated technique for analysis of current transitions in multilevel single-channel recordings.

Detailed kinetic studies of ion channel gating are best carried out using the patch-clamp technique which permits the measurement of the ionic current through individual channels. Typical patch-clamp recordings show the current signal, in the form of a sequence of rectangular pulses (analogous to a random telegraph signal), riding on slow baseline drift, partially obscured by high-frequency noise and distorted by filtering. In order to analyze such recordings, we have developed a set of interactive Pascal programs based on a feature-detection algorithm capable of identifying current transitions in multiple-channel recordings in the presence of substantial levels of noise and drift. Software operation is largely automated but includes provisions for examination and correction of the output. The software was optimized and systematically evaluated using simulated data with variable amounts of noise and drift. Results indicate that satisfactory performance is obtained for signal-to-noise ratio as low as four even with uncommonly large baseline drift. Steady-state processing speeds varied from 1,000 to 4,000 samples per second depending on data complexity.

Automation↗

PubMed1990

Experience with gated cardiac software phantoms for quality control of applications programmes.

Ten gated cardiac software phantoms, representing normal and abnormal clinical conditions, were transferred to 9 different computer systems and tested with 11 cardiac programmes. Problems of inappropriate data format were encountered when analysing the phantoms on other systems. The global left ventricular ejection fraction (LVEF) values resulting from the different programmes were compared. Significant programme differences were found, the programmes falling generally into two groups. Few LVEF outlier values were identified. Full functional assessment of cardiac phantoms requires a set of different views which together form the phantom. Application of software phantoms for programme assessment and training requires prudence and attention to the acquired data format, frame time, and gating method for the appropriate use of phantoms.

Computer Simulation↗

PubMed1990

Structured spreadsheet modeling in medical decision making and research.

The construction, evaluation, implementation, and use of models representing various algorithms, strategies, methods, theories etc. based on the analysis of great amounts of data are necessary in both Medical Research and Decision Making (MR/DM). Performing such tasks manually is not only time consuming and tedious, but also very error-prone. The appearance of a computer with its ability to store and process information has opened an opportunity to facilitate enormously and improve activities. However, the effective use of computers is limited by difficulties accompanying noncomputer specialists like doctors, nurses, and other medical staff in learning and using conventional programming languages, tools, and techniques. In this paper we present Structured Spreadsheet Modeling as a possible solution, and show that it is applicable in the MR/DM field on a concrete basis.

Adolescent↗

PubMed1995

LabVIEW: a software system for data acquisition, data analysis, and instrument control.

Computer-based data acquisition systems play an important role in clinical monitoring and in the development of new monitoring tools. LabVIEW (National Instruments, Austin, TX) is a data acquisition and programming environment that allows flexible acquisition and processing of analog and digital data. The main feature that distinguishes LabVIEW from other data acquisition programs is its highly modular graphical programming language, "G," and a large library of mathematical and statistical functions. The advantage of graphical programming is that the code is flexible, reusable, and self-documenting. Subroutines can be saved in a library and reused without modification in other programs. This dramatically reduces development time and enables researchers to develop or modify their own programs. LabVIEW uses a large amount of processing power and computer memory, thus requiring a powerful computer. A large-screen monitor is desirable when developing larger applications. LabVIEW is excellently suited for testing new monitoring paradigms, analysis algorithms, or user interfaces. The typical LabVIEW user is the researcher who wants to develop a new monitoring technique, a set of new (derived) variables by integrating signals from several existing patient monitors, closed-loop control of a physiological variable, or a physiological simulator.

Analog-Digital Conversion↗

PubMed1995

Computer assisted data analysis in intensive care: the ICDEV project--development of a scientific database system for intensive care (Intensive Care Data Evaluation Project).

INTRODUCTION: Patient Data Management Systems (PDMS) for ICUs collect, present and store clinical data. Various intentions make analysis of those digitally stored data desirable, such as quality control or scientific purposes. The aim of the Intensive Care Data Evaluation project (ICDEV), was to provide a database tool for the analysis of data recorded at various ICUs at the University Clinics of Vienna. SETTINGS: General Hospital of Vienna, with two different PDMSs used: CareVue 9000 (Hewlett Packard, Andover, USA) at two ICUs (one medical ICU and one neonatal ICU) and PICIS Chart+ (PICIS, Paris, France) at one Cardiothoracic ICU. CONCEPT AND METHODS: Clinically oriented analysis of the data collected in a PDMS at an ICU was the beginning of the development. After defining the database structure we established a client-server based database system under Microsoft Windows NI and developed a user friendly data quering application using Microsoft Visual C++ and Visual Basic; RESULTS: ICDEV was successfully installed at three different ICUs, adjustment to the different PDMS configurations were done within a few days. The database structure developed by us enables a powerful query concept representing an 'EXPERT QUESTION COMPILER' which may help to answer almost any clinical questions. Several program modules facilitate queries at the patient, group and unit level. Results from ICDEV-queries are automatically transferred to Microsoft Excel for display (in form of configurable tables and graphs) and further processing. CONCLUSIONS: The ICDEV concept is configurable for adjustment to different intensive care information systems and can be used to support computerized quality control. However, as long as there exists no sufficient artifact recognition or data validation software for automatically recorded patient data, the reliability of these data and their usage for computer assisted quality control remain unclear and should be further studied.

Austria↗

PubMed1999

Thermal distribution of radio-frequency inductive hyperthermia using an inductive aperture-type applicator: evaluation of the effect of tumour size and depth.

A new radio-frequency (RF) inductive hyperthermia device using an inductive aperture-type applicator (IATA) is proposed. This paper reports the evaluation of the heating characteristics of the IATA using a computer simulation and clinical thermal parameters obtained during treatment of superficial and subsurface-seated tumours. The configuration of the IATA is a one-turn square column-like coil whose bottom plate is set to face the heating target. The IATA has advantages over RF capacitive-type heating, such as: generating less heat in the subcutaneous fat layer; less convergency of electric line of force at the edge of the applicator; and no physical contact with the target lesion. The induced magnetic fields and electrical currents within the heating substance are simulated using computer-assisted design software for electro-magnetic analysis. A total of 40 superficial and subsurface tumours are treated with the IATA. Invasive thermometry is performed continuously for 110 sessions using multi-sensor probes of an optical thermometer. Thermal parameters (Tmax, Tmin, Tave) are assessed based on the tumour size and depth. The treated tumours are categorised into three groups according to tumour depth: group 1 (< 3 cm, n = 28), group 2 (3-5 cm, n = 35) and group 3 (> 5 cm, n = 47). The computer simulation shows that induced electrical currents run without convergency, parallel to the surface of the heating material. All thermal parameters of group 3 are significantly higher than those of group 1 and 2 (p < 0.05), indicating that the larger lesions tend to abtain a higher temperature distribution. In conclusion, RF inductive hyperthermia using the IATA results in effective temperature distributions in superficial and subsurface tumours, with large tumours being most effectively heated.

Aged↗

PubMed2005

A quantitative computed tomography assessment of brain weight, volume, and specific gravity in severe head trauma.

BACKGROUND: Computed tomography DICOM images analysis allows a quantitative measurement of organ weight, volume and specific gravity in humans. METHODS: The brain weight, volume and specific gravity of 15 traumatic brain-injury patients (3+/-2 days after trauma) were computed using a specially designed software (BrainView). Data were compared with those obtained from 15 healthy subjects paired for age and overall intracranial volume. RESULTS: Hemisphere weight were 91 g higher in patients than in controls (1167+/-101 vs 1076+/-112 g; p<0.05). Specific gravity of hemispheres (1.0367+/-0.0017 vs 1.0335+/-0.0012 g/ml; p<0.001), brainstem (1.0302+/-0.0016 vs 1.0277+/-0.0015 g/ml; p<0.001) and cerebellum (1.0396+/-0.0020 vs 1.0375+/-0.0015 g/ml; p<0.05) was significantly higher in traumatic brain injury (TBI) patients than in controls (all p<0.0001 without interaction). This increase in specific gravity was evenly distributed between the hemispheres, the brainstem and the cerebellum, and the grey and white matter. It was more pronounced in the rostral than in the caudal areas of the hemispheres. It was independent of the volume of brain contusion, of the mechanism of head injury, of natremia and of initial Glasgow coma score. CONCLUSION: Human TBI patients present a diffuse increase in specific gravity. This observation is in sharp opposition with the data derived from the experimental literature.

Adolescent↗

PubMed2000

Regional distribution of gas and tissue in acute respiratory distress syndrome. III. Consequences for the effects of positive end-expiratory pressure. CT Scan ARDS Study Group. Adult Respiratory Distress Syndrome.

OBJECTIVE: To determine whether differences in lung morphology assessed by computed tomography (CT) affect the response to positive end-expiratory pressure (PEEP). DESIGN: Prospective study over a 53-month period. SETTING: Fourteen-bed surgical intensive care unit of a university hospital. PATIENTS AND PARTICIPANTS: Seventy-one consecutive patients with early adult respiratory distress syndrome (ARDS). MEASUREMENTS AND RESULTS: Fast spiral thoracic CT was performed at zero end-expiratory pressure (ZEEP) and after implementation of PEEP 10 cmH2O. Hemodynamic and respiratory parameters were measured in both conditions. PEEP-induced overdistension and alveolar recruitment were quantified by specifically designed software (Lungview). Overdistension occurred only in the upper lobes and was significantly correlated with the volume of lung, characterized by a CT attenuation ranging between -900 and -800 HU in ZEEP conditions. Cardiorespiratory effects of PEEP were similar in patients with primary and secondary ARDS. PEEP-induced alveolar recruitment of the lower lobes was significantly correlated with their lung volume (gas + tissue) at functional residual capacity. PEEP-induced alveolar recruitment was greater in the lower lobes with "inflammatory atelectasis" than in the lower lobes with "mechanical atelectasis." Lung morphology as assessed by CT markedly influenced the effects of PEEP: in patients with diffuse CT attenuations PEEP induced a marked alveolar recruitment without overdistension, whereas in patients with lobar CT attenuations PEEP induced a mild alveolar recruitment associated with overdistension of previously aerated lung areas. These results can be explained by the uneven distribution of regional compliance characterizing patients with lobar CT attenuations (compliant upper lobes and stiff lower lobes) contrasting with a more even distribution of regional compliances observed in patients with diffuse CT attenuations. CONCLUSIONS: In patients with ARDS, the cardiorespiratory effects of PEEP are affected by lung morphology rather than by the cause of the lung injury (primary versus secondary ARDS). The regional distribution of the loss of aeration and the type of atelectasis -- "mechanical" with a massive loss of lung volume, or "inflammatory" with a preservation of lung volume-- characterizing the lower lobes are the main determinants of the cardiorespiratory effects of PEEP.

Analysis of Variance↗

PubMed2000

Volume measurement of cerebral arteriovenous malformations from angiography.

We designed software for measuring the volume of cerebral arteriovenous malformations from angiography and validated it against prescription volumes in radiosurgery. We aimed to create a model for the risk for complications as a function of volume, based on established outcome prediction models for Gamma Knife radiosurgery, but without the need for dose planning. We created an application for computing the volume of cerebral arteriovenous malformations from the intersection of two X-ray cones in stereotactic space. Volume measurements were compared with prescription volumes from dose planning, in phantoms and in patients treated with Gamma Knife radiosurgery for cerebral arteriovenous malformations. Previous studies of 1128 treated patients were used to calculate the risk for complication as a function of the nidus volume. In 63 patients volumes measured with either method correlated, R2 = 0.85. Volume as measured with the intersecting cone model (ICM) correlated with predicted Gamma Knife radiosurgery complication rate, R2 = 0.84. The ICM can thus be used for measurement of AVM volumes less than 10 cm3 from angiography. Outcome models from Gamma Knife radiosurgery may be applied, but with reduced exactness. Standardised AVM volume measurement is valuable for comparing outcome and for quantification of volume reduction after therapy, notably embolisation. Thus the optimal management plan may be selected in conjunction with diagnostic or therapeutic angiography.

Cerebral Angiography↗