[Hybrid emission computed tomograph for brain study and its clinical applications (author's transl)].
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Blood-Brain Barrier↗
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Results for “Computers, Hybrid”
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[Electronics design for hybrid emission computed tomography "HEADTOME" (author's transl)].
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Electrons↗
Combined image interpretation of computed tomography and hybrid PET in head and neck cancer.
AIM: Evaluation of potential synergistic effects of combined image interpretation of FDG PET using a gamma camera modified for coincidence detection (hybrid PET) and computed tomography (CT) and comparison of the diagnostic accuracy of hybrid PET and dedicated PET in patients with head and neck cancer. METHODS: Forty-two patients with suspected primary or recurrent cancer were included. Twenty-four patients underwent dedicated PET in addition to attenuation-corrected hybrid PET using a one-day protocol. RESULTS: Sensitivity, specificity and accuracy for detection of primary or recurrent head and neck cancer were 74, 73, and 74% for hybrid PET, 52, 82, and 60% for CT and 77, 82, and 79% for combined reading. With the combination of CT and hybrid PET all cases of recurrent disease were detected. The largest tumour not detected was 1.7 cm in diameter. Sensitivity, specificity and accuracy for the detection of neck sides with lymph node metastases were 69, 88, and 85% for hybrid PET, 62, 88, and 84% for CT, 69, 99, and 94% for combined image interpretation. With combined interpretation four involved neck sides were missed including two cases of microscopic metastases. Hybrid PET revealed concordant results to dedicated PET in all patients with respect to the detection of primary or recurrent tumour and in 45 of 48 neck sides (94%) with the same number of false negative findings. CONCLUSION: The combination of functional information of hybrid PET and morphological information of CT by the simple approach of combined image interpretation improves the sensitivity for the detection of primary/recurrent head and neck cancer and increases the specificity of lymph node staging compared to CT alone. The accuracy of hybrid PET and dedicated PET was almost identical.
Carcinoma, Squamous Cell↗
Does computation provide a model for creativity? An epistemological perspective in neuroscience.
In 1939 Alan Turing, a major scholar in the field of mechanical computation, described a system whose computational power was beyond that of a discrete, finite state machine (Turing Machine). The composition of this system was likely the first example of what is now called an hybrid computational system. Since then, development of neural networks and brain automata has made aware that forms of computation might exist that are likely to go beyond Turing's limits. Natural systems, like the central nervous system in Mammals and man, are likely to use such a type of computation, especially to perform highly integrating activities, like feedback controls and mental creative processes. The latter are usually understood as processes that involve infinitary procedures, ending up in a complex information network, the computational maps, in which both digital, Turing-like computation and continuous, analog forms of calculus are expected to occur. Pictorial representation may be a fruitful example, mostly metaphorical, to analyze the use of this hybrid forms of computation by higher order computational maps, and the possible role of these types of computational processes in painting creativity is briefly analyzed in comparing 15th vs 16th century Renaissance Art. An open challenge for neuroscience in the 21st century is to clarify whether a hybrid neural learning network might represent a reasonable clue to scientifically interpret the theme of "creativity".
Art↗
Nonlinear cable equations for axons. II. Computations and experiments with external current electrodes.
We have investigated the steady-state potential and current distributions resulting from current injection into a close-fitting channel into which a squid axon is placed. Hybrid computer solutions of the cable equations, using the Hodgkin-Huxley equations to give the membrane current density, were in good agreement with experimental observations. A much better fit was obtained when the Hodgkin-Huxley leakage conductance was reduced fivefold.
Animals↗
A hybrid display system for computer processed scintigrams.
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Brain↗
Real-time computing platform for spiking neurons (RT-spike).
A computing platform is described for simulating arbitrary networks of spiking neurons in real time. A hybrid computing scheme is adopted that uses both software and hardware components to manage the tradeoff between flexibility and computational power; the neuron model is implemented in hardware and the network model and the learning are implemented in software. The incremental transition of the software components into hardware is supported. We focus on a spike response model (SRM) for a neuron where the synapses are modeled as input-driven conductances. The temporal dynamics of the synaptic integration process are modeled with a synaptic time constant that results in a gradual injection of charge. This type of model is computationally expensive and is not easily amenable to existing software-based event-driven approaches. As an alternative we have designed an efficient time-based computing architecture in hardware, where the different stages of the neuron model are processed in parallel. Further improvements occur by computing multiple neurons in parallel using multiple processing units. This design is tested using reconfigurable hardware and its scalability and performance evaluated. Our overall goal is to investigate biologically realistic models for the real-time control of robots operating within closed action-perception loops, and so we evaluate the performance of the system on simulating a model of the cerebellum where the emulation of the temporal dynamics of the synaptic integration process is important.
Action Potentials↗
Computer-aided real-time acquisition of physiological data: technical design and selection constraints.
For many years, physiological investigations have utilized the power and speed of analogue, digital and hybrid computers. Complex protocols often require the recording of large amounts of data in short periods, typically with simultaneous fine control of multiple experimental variables. Current systems often include data analysis in the same program which controls data acquisition. Although this is convenient from a package point of view, acquisition and analysis routines have different and sometimes conflicting purposes and requirements. This paper examines acquisition of continuous physiological signals by small dedicated computers in an attempt to separate these processes and to provide guidelines for computer selection, design and development.
Animals↗
Quantitation and mapping of integrated human papillomavirus on human metaphase chromosomes using a fluorescence microscope imaging system.
Integrated human papillomavirus type 16 (HPV-16) DNA was directly visualized on metaphase chromosomes in the two human cervical carcinoma cell lines SiHa and CaSki by fluorescence in situ hybridization with a biotinylated DNA probe (7.9 kb). The fluorescence intensities of hybridization signals from single copies and dispersed clusters of integrated HPV-16 DNA were quantified using a microscope equipped with a cooled-CCD camera that was interfaced to an image processor and host computer. Hybridization signals were localized on chromosomes using separate, registered images of 4',6-diamidino-2-phenylindole (DAPI) or propidium iodide stained metaphase chromosome spreads. In both SiHa and CaSki spreads, a single fluorescein signal was observed on one or both chromatids of chromosome 13, which was identified by simultaneous hybridization with a biotinylated centromere probe specific for chromosomes 13 and 21. Ratios of the distance from 13pter to the HPV-16 signals to the entire chromosome length were approximately 0.63 +/- 0.05 in both SiHa and CaSki cells, indicating the possibility of a common integration domain on chromosome 13. In SiHa cells, no additional signals were observed on other chromosomes. This observation, taken together with literature reports that SiHa cells contain 1 to 2 copies of the HPV-16 genome in this region of chromosome 13, suggests that each fluorescein signal on chromosome 13 represents one equivalent of the HPV-16 genome. The total integrated fluorescence intensity in isolated CaSki metaphase chromosome spreads was approximately two orders of magnitude greater than that of a single copy of HPV-16 DNA in SiHa cells, indicating an increase in HPV-16 copy number.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Technical report: Part 1. Basic requirements for designing optimal oligonucleotide probe sequences.
Although oligonucleotides can be easily synthesized and used in a variety of scientific fields, a major problem exists for each application: the difficulty of obtaining optimal oligonucleotide sequences. Oligonucleotide sequences have been described in each publication; however, little is disclosed on how to design such sequences and how specific each sequence is. This report introduces a new concept of computer hybridization simulation based on "thermodynamic hybridizability", which can overcome the problems of conventional homology analyses. Then, all the necessary components and factors for designing optimal probe sequences, such as hybridization strength, specificity, secondary structure, length of probes, probe-to-probe interaction, are discussed in detail. Also included are procedures for manipulating various types of data for selection of optimal oligonucleotides. This report provides a general guideline for optimal probe design and encourages basic and clinical scientists to enhance their research activities by using optimal oligonucleotides.
Base Sequence↗
DNA computing using single-molecule hybridization detection.
DNA computing aims at using nucleic acids for computing. Since micromolar DNA solutions can act as billions of parallel nanoprocessors, DNA computers can in theory solve optimization problems that require vast search spaces. However, the actual parallelism currently being achieved is at least a hundred million-fold lower than the number of DNA molecules used. This is due to the quantity of DNA molecules of one species that is required to produce a detectable output to the computations. In order to miniaturize the computation and considerably reduce the amount of DNA needed, we have combined DNA computing with single-molecule detection. Reliable hybridization detection was achieved at the level of single DNA molecules with fluorescence cross-correlation spectroscopy. To illustrate the use of this approach, we implemented a DNA-based computation and solved a 4-variable 4-clause instance of the computationally hard Satisfiability (SAT) problem.
Algorithms↗
Abstract and associatively based representations in human sequence learning.
We give an analysis of performance in an artificial neural network for which the claim had been made that it could learn abstract representations. Our argument is that this network is associative in nature, and cannot develop abstract representations. The network thus converges to a solution that is solely based on the statistical regularities of the training set. Inspired by human experiments that have shown that humans can engage in both associative (statistical) and abstract learning, we present a new, hybrid computational model that combines associative and more abstract, cognitive processes. To cross-validate the model we attempted to predict human behaviour in further experiments. One of these experiments reveals some evidence for the use of abstract representations, whereas the others provide evidence for associatively based performance. The predictions of the hybrid model stand in line with our empirical data.
Computer Simulation↗
Computer simulation of ciprofloxacin pharmacokinetics in patients on CAPD.
Continuous ambulatory peritoneal dialysis (CAPD) has become an accepted alternative to chronic hemodialysis in the treatment of end-stage renal disease. The method utilizes the diffusion of drugs from the blood through the peritoneal membrane to the peritoneal cavity if administered intravenously (IV) and perorally (PO) and in the opposite direction if applied intraperitoneally (IP). The present work uses an open, two-compartment pharmacokinetic model reversibly linked with the compartment representing the peritoneal cavity and an analog-hybrid computer to simulate drug levels in sampled and unsampled compartments under conditions of various routes of administration (IV, IP and sequential IV, IP and PO) and different clinical status (presence and absence of peritonitis). The drug chosen for simulation was ciprofloxacin (CIP), a new synthetic antibacterial agent of the 4-quinolone group. Eight patients were included in the study, and CIP concentrations in plasma and dialysate were obtained by HPLC analysis to assess the reliability of the model and the efficiency of the sequential dosing scheme. CIP plasma and dialysate levels were adequate for the majority of microbes causing CAPD peritonitis. The proposed regimen was efficient in 85% of cases.
Administration, Oral↗
Trend detection of pseudo-random variables using a exponentially mapped past statistical approach: an adjunct to computer assisted monitoring.
The early detection of deterioration in a patient depends on recognising trends: a capability poorly developed in monitor systems. Using exponentially mapped past (EMP) statistical variables, it has been proved that the difference between two EMP means is a function of only one variable, trend of input. Some of the signal variance appears on the difference signal, and so interpretation depends on a statistical approach based on knowledge of the normal variability of the monitored variable. The programs developed and built in a dedicated form utilise parallel hybrid computation of continuous data, but the principles are equally applicable to digital techniques with discrete data.
Computers↗
Urodynamic modeling of norfloxacin pharmacokinetics by means of computer simulation.
Urodynamic model was developed which, in conjunction with a compartmental pharmacokinetic model, was used for study of factors influencing drug concentrations in urine: urine flow rate, residual bladder urine, maximal bladder urine, stage of renal failure, and elimination kinetics of drugs. Norfloxacin (NOR) was used as a model drug, although the model haw general applicability for all urinary antiseptics. Pharmacokinetic data were obtained from a clinical study in which norfloxacin was administered orally as a single 400mg dose to four subjects with installed urine catheters. Sample of blood, bladder and catheter urine were collected and concentrations of NOR measured by a HPCL method. Modeling was performed on analog--hybrid computer EAI 580. Besides the fitting of model response to obtained in vivo data, simulations of expected clinical situations were performed in which the interplay of above mentioned factors was studied in terms of urine concentrations profiles. NOR treatment with 400mg b.i.d. secured sufficient urine concentrations in most studied cases. This approach should be applied for corresponding study of other urinary antiseptics, especially those with less favourable urinary levels.
Chromatography, High Pressure Liquid↗
Specific force field parameters determination for the hybrid ab initio QM/MM LSCF method.
The pure quantum mechanics method, called Local Self-Consistent Field (LSCF), that allows to optimize a wave function within the constraint that some predefined spinorbitals are kept frozen, is discussed. These spinorbitals can be of any shape, and their occupation numbers can be 0 or 1. Any post-Hartree-Fock method, based on the restricted or unrestricted Hartree-Fock Slater determinant, and Kohn-Sham-based DFT method are available. The LSCF method is easily applied to hybrid quantum mechanics/molecular mechanics (QM/MM) procedure where the quantum and the classical parts are covalently bonded. The complete methodology of our hybrid QM/MM scheme is detailed for studies of macromolecular systems. Not only the energy but also the gradients are derived; thus, the full geometry optimization of the whole system is feasible. We show that only specific force field parameters are needed for a correct description of the molecule, they are given for some general chemical bonds. A careful analysis of the errors induced by the use of molecular mechanics in hybrid computation show that a general procedure can be derived to obtain accurate results at low computation effort. The methodology is applied to the structure determination of the crambin protein and to Menshutkin reactions between primary amines and chloromethane.
Journal Article↗
Distribution pharmacokinetics of warfarin in the rat, a non-linear multicompartment model.
Preliminary analysis and linear two-compartment solutions of warfarin plasma concentrations recorded in the rat after intravenous bolus injections of 1, 2, 8 and 40 mg/kg of sodium warfarin revealed marked non-linearities. The half-life of total warfarin concentration in the plasma from 1-12h remained unchanged with all the doses used, but that of free warfarin was shorter with 40 mg/kg, possibly as the result of an increase in the binding of the drug to plasma proteins as the high total warfarin concentration decreased. The apparent volume of distribution generally increased with increasing dose, and differed according to the method used for its calculation. Liver warfarin data could be solved with Langmuir type saturation kinetics, but the saturation phenomena were slight in the concentration range studied. A non-linear multicompartment model was constructed, the physiological spaces of which were plasma, interstitial fluid and tissue. The binding of free warfarin to plasma proteins, interstitial fluid proteins and tissue structures was assumed to occur instantaneously, with saturable binding to plasma and interstitial fluid proteins, and a constant binding to tissues. The fluxes between the free warfarin pools of plasma and interstitial fluid as well as elimination were assumed to be linear. Following parameters were simulated simultaneously, using an analog hybrid computer: two for the above-mentioned fluxes, four for zero time drug mass distribution between plasma and interstitial fluid, and one for tissue binding. According to the best fits, warfarin is preferentially distributed into plasma, interstitial fluid and highly perfused tissues. The solution suggests that non-linearities in the pharmacokinetics of warfarin, a highly plasma protein-bound drug, first occur in plasma and interstitial fluid. Therefore, it is believed that the quantitative non-linear multicompartment approach presented in this paper might be useful in studying the kinetic behaviour of other highly plasma protein-bound drugs, too.
Animals↗
A hybrid algorithm for PET/CT image merger in hybrid scanners.
PURPOSE: To improve the PET image quality of a hybrid PET/CT scanner by merging CT borders with PET texture. PET/CT scanners provide both high-resolution CT images showing anatomical details and PET images of low-resolution physiological information about radiopharmaceutical uptake. Standard smoothing of noisy PET images may further impair PET resolution, reducing small lesion detectability. METHODS: The CT edge data and the PET texture data were merged using a modified form of an algorithm called HCT (hybrid computed tomography). In merged PET/CT images, each PET pixel value was estimated by iteratively applying a corrected 2D Taylor expansion to each of its eight neighbors. The spatial derivative term was used only near anatomical edges provided by the CT. This counts-preserving algorithm was tested on a special resolution phantom and patient data sets obtained by PET/CT acquisitions. RESULTS: The HCT algorithm provided phantom PET images with sharp borders and improved resolution (< or = 3 mm as compared to > or = 4 mm). HCT increased the signal to background contrast ratios by an average of 61% (40-89%) while maintaining noise reduction similar to the Gaussian filtering standard in PET. In the clinical PET images, HCT allowed for an improved delineation of pulmonary and pelvic lesions and an improved visualization of the brain. CONCLUSION: A new reconstruction algorithm for merging CT anatomical edge data with functional PET data has been introduced. The algorithm smooths noisy PET images while retaining sharper edges at corresponding anatomical borders, resulting in an improvement in resolution and contrast ratio.
Algorithms↗