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PubMed2002

Note on formulation of the enhanced scattering- (transmittance-) matrix approach.

The enhanced transmittance matrix approach developed by Moharam et al. [J. Opt. Soc. Am. A 12, 1077 (1995)] is reformulated in a concise and illuminating form in terms of scattering (reflection and transmission) matrices directly. Two equivalent recursive formulations, corresponding to their full- and partial-solution approaches, are presented and extended to allow simultaneous determination of both reflected and transmitted amplitudes. The relationships between these formulations and the S-matrix algorithm, together with their relative efficiencies and usefulness, are ascertained and compared by means of compact formulas featuring parallel algebraic structures. It is made evident that given the eigenmode solutions, the enhanced approach is the most direct and efficient way for deducing global scattering matrices.

Journal Article↗

PubMed2005

Enhancement of blood vessel visualization in 3D time-of-flight MR angiography utilizing surface array coil.

Array coils play an important role in improving the signal-to-noise ratio (SNR) and achieving parallel imaging; however, one disadvantage of array coils is the nonuniformity of their sensitivity. We propose a simple algorithm to enhance blood vessel visualization in 3D-TOF-MRA (three-dimensional time-of-flight magnetic resonance angiography) utilizing this surface array sensitivity, and we apply it to the MRA data of normal volunteers. We have verified that visualization of peripheral vessels has been remarkably improved.

Adult↗

PubMed2000

Parallel cone bipolar pathways to a ganglion cell use different rates and amplitudes of quantal excitation.

The cone signal reaches the cat's On-beta (X) ganglion cell via several parallel circuits (bipolar cell types b1, b2, and b3). These circuits might convey different regions of the cone's temporal bandwidth. To test this, I presented a step of light that elicited a transient depolarization followed by a sustained depolarization. The contribution of bipolar cells to these response components was isolated by blocking action potentials with tetrodotoxin and by blocking inhibitory synaptic potentials with bicuculline and strychnine. Stationary fluctuation analysis of the sustained depolarization gave the rate of quantal bombardment: approximately 5100 quanta sec(-1) for small central cells and approximately 45,000 quanta sec(-1) for large peripheral cells. Normalizing these rates for the vastly different numbers of bipolar synapses (150-370 per small cell vs 2000 per large cell), quantal rate was constant across the retina, approximately 22 quanta synapse(-1) sec(-1). Nonstationary fluctuation analysis gave the mean quantal EPSP amplitude: approximately 240 microV for the transient depolarization and 30 microV for the sustained depolarization. The b1 bipolar cell is known from noise analysis of the On-alpha ganglion cell to have a near-maximal sustained release of only approximately two quanta synapse(-1) sec(-1). This implies that the other bipolar types (b2 and b3) contribute many more quanta to the sustained depolarization (>/=46 synapse(-1) sec(-1)). Type b1 probably contributes large quanta to the transient depolarization. Thus, bipolar cell types b1 and b2/b3 apparently constitute parallel circuits that convey, respectively, high and low frequencies.

Algorithms↗

PubMed2002

Evaluation of rapid assays for screening and confirming HIV-1 infection in Ethiopia.

To evaluate a simple and rapid testing strategy to diagnose HIV infection in Ethiopia, we subjected a panel of 688 sera with known HIV serologic status (confirmed by ELISA/WB or double ELISA) to 3 rapid assays: Determine HIV-1/2, Capillus HIV-1/2 and Serocard HIV. Samples were obtained from participants in a cohort study on HIV-infection (72%), from tuberculosis patients (18%) and from participants in surveillance studies among police recruits and commercial sex workers (10%). The panel consisted of 249 HIV-1 positive samples, of which 68 were HIV-1 subtype C and 1 HIV-1 subtype A, and 439 HIV-1 negative samples. Determine and Capillus were 100% sensitive and 99.8% specific, Serocard was 100% sensitive and specific. On retrospective evaluation, both parallel (samples tested simultaneously by two rapid assays) and serial (samples tested by two consecutive rapid assays) testing algorithms were 100% sensitive and specific when compared to ELISA/WB or double ELISA testing strategy. In conclusion rapid assays have high sensitivity and specificity. HIV serodiagnosis based on rapid assays may therefore be a valuable alternative in voluntary counselling and testing centres and in facilities where sophisticated laboratories are not available.

AIDS Serodiagnosis↗

PubMed1997

[Quality assurance of inpatient care--exemplified by surgery].

Internal quality assurance is natural for hospital physicians. External quality control is undertaken in cooperation with medical societies and sponsors-partly on voluntary basis. Despite considerable efforts in optimizing treatment procedures by classification of injuries and tumor stages, algorithms and tightly scheduled practical medical training, further control mechanisms are demanded; the economic drive is evident. In parallel to the introduction of quality control for services with a case-based flat rate, an interstructural result quality is desired. Hospital certification procedures are no longer utopian. The physician's duty for continuing medical education, which is set down in the professional code, has to be proven. The development of guidelines by scientific societies may help but is in need of a corrective. The medical chambers may play a particular role in this connection. Even if mechanisms of quality assurance differ, it is in the patient's interest that there must be no difference between ambulant and hospital care.

Cost Control↗

PubMedDate not supplied

Cone-beam SPECT with a tilted detector.

In this article we report on the TOMOCONIC project for cerebral SPECT using cone-beam collimators. First, we describe our experimental set-up. The cone-beam collimator improves both spatial resolution and sensitivity. We tilt the detector to center the focal point rotation plane on the region to reconstruct. Then, to minimize cone-beam artefacts, we use the Grangeat algorithm for image reconstruction. We describe here how it can be generated to this tilted acquisition geometry. Finally, we present our first experimental results and a comparison with parallel-beam SPECT. The improvement ratio on transverse spatial resolution is 1.5. We conclude with our first clinical images.

Algorithms↗

PubMed2003

Clinical brain MR imaging prescriptions in Talairach space: technologist- and computer-driven methods.

BACKGROUND AND PURPOSE: Variability in patient head positioning may yield substantial interstudy image variance in the clinical setting. We describe and test three-step technologist and computer-automated algorithms designed to image the brain in a standard reference system and reduce variance. METHODS: Triple oblique axial images obtained parallel to the Talairach anterior commissure (AC)-posterior commissure (PC) plane were reviewed in a prospective analysis of 126 consecutive patients. Requisite roll, yaw, and pitch correction, as three authors determined independently and subsequently by consensus, were compared with the technologists' actual graphical prescriptions and those generated by a novel computer automated three-step (CATS) program. Automated pitch determinations generated with Statistical Parametric Mapping '99 (SPM'99) were also compared. RESULTS: Requisite pitch correction (15.2 degrees +/- 10.2 degrees ) far exceeded that for roll (-0.6 degrees +/- 3.7 degrees ) and yaw (-0.9 degrees +/- 4.7 degrees ) in terms of magnitude and variance (P <.001). Technologist and computer-generated prescriptions substantially reduced interpatient image variance with regard to roll (3.4 degrees and 3.9 degrees vs 13.5 degrees ), yaw (0.6 degrees and 2.5 degrees vs 22.3 degrees ), and pitch (28.6 degrees, 18.5 degrees with CATS, and 59.3 degrees with SPM'99 vs 104 degrees ). CATS performed worse than the technologists in yaw prescription, and it was equivalent in roll and pitch prescriptions. Talairach prescriptions better approximated standard CT canthomeatal angulations (9 degrees vs 24 degrees ) and provided more efficient brain coverage than that of routine axial imaging. CONCLUSION: Brain MR prescriptions corrected for direct roll, yaw, and Talairach AC-PC pitch can be readily achieved by trained technologists or automated computer algorithms. This ability will substantially reduce interpatient variance, allow better approximation of standard CT angulation, and yield more efficient brain coverage than that of routine clinical axial imaging.

Adolescent↗

PubMed1987

Rapid three-dimensional treatment planning: I. Ray-tracing approach to primary component dose calculations.

Algorithms for fully three-dimensional divergent-beam radiotherapy treatment planning have been developed to achieve very high sampling of dose in heterogeneous (inhomogeneous density) tissue throughout an arbitrarily oriented patient volume, in clinically acceptable times of calculation. Dose is calculated at points along numerous rays which sample each beam. To display the dose distribution, the calculated dose values for each beam are interpolated onto rectilinear grids of (arbitrary) parallel planes, scaled for beam weight and finally merged with the weighted dose contributions of other beams. In this paper we describe and demonstrate the algorithm for the primary component of the three-dimensional photon dose distribution delivered to a patient.

Clinical Trials as Topic↗

PubMed2006

From 2D PET to 3D PET: issues of data representation and image reconstruction.

Positron emission tomography (PET), intrinsically a 3D imaging technique, was for a long time exclusively operated in 2D mode, using septa to shield the detectors from photons emitted obliquely to the detector planes. However, the use of septa results in a considerable loss of sensitivity. From the late 1980s, significant efforts have been made to develop a methodology for the acquisition and reconstruction of 3D PET data. This paper focuses on the differences between data acquisition in 2D and 3D mode, especially in terms of data set sizes and representation. Although the real time data acquisition aspect in 3D has been mostly solved in modern PET scanner systems, there still remain questions on how to represent and how to make best use of the information contained in the acquired data sets. Data representation methods, such as list-mode and matrix-based methods, possibly with additional compression, will be discussed. Moving from 2D to 3D PET has major implications on the way these data are reconstructed to images. Two fundamentally different approaches exist, the analytical one and the iterative one. Both, at different expenses, can be extended to directly handle 3D data sets. Either way the computational burden increases heavily compared to 2D reconstruction. One possibility to benefit from the increased sensitivity in 3D PET while sticking to high-performance 2D reconstruction algorithms is to rebin 3D into 2D data sets. The value of data rebinning will be explored. An ever increasing computing power and the concept of distributed or parallel computing have made direct 3D reconstruction feasible. Following a short review of reconstruction methods and their extensions to 3D, we focus on numerical aspects that improve reconstruction performance, which is especially important in solving large equation systems in 3D iterative reconstruction. Finally exemplary results are shown to review the properties of the discussed algorithms. This paper concludes with an overview on future trends in data representation and reconstruction.

Humans↗

PubMedDate not supplied

A new algorithm of brain volume contours segmentation.

This paper explores brain CT slices segmentation technique and some related problems, including contours segmentation algorithms, edge detector, algorithm evaluation and experimental results. This article describes a method for contour-baed segmentation of anatomical structures in 3D medical data sets. With this method, the user manually traces one or more 2D contours of an anatomical structure of interest on parallel planes arbitrarily cutting the data set. The experimental results show the segmentation based on 3D brain volume and 2D CT slices. The main creative contributions in this paper are: (1) contours segmentation algorithm; (2) edge detector; (3) algorithm evaluation.

Algorithms↗

PubMed2004

Integration of fuzzy logic and structure tensor towards mammogram contrast enhancement.

In this paper, we describe a combined approach with fuzzy logic and structure tensor towards improved enhancement of possible MCs (microcalcifications) in digital mammograms. The proposed contrast enhancement algorithm has two operational components. One is structure tensor operator and the other is fuzzy enhancement operator, both of which are arranged in parallel to process the input digital mammograms. While the structure tensor operator processes the digital mammograms and produces a corresponding eigen-image to highlight the region-of-interests, the fuzzy enhancement operator fuzzifies the mammogram via the maximum fuzzy entropy principle in fuzzy domain. As a result, the local fuzzy contrast can be extracted and modified adaptively in accordance with the information provided by the eigen-image, and those non-MCs regions are suppressed by being taken as noise. After that, the mammogram is transformed back to the pixel domain and the enhanced mammogram is constructed. Extensive experimental results show that our proposed algorithm outperforms the existing benchmark in terms of cost figures across the whole range of true positive fractions (TPF).

Algorithms↗

PubMed2005

Multi-criterion optimization for heel-toe running.

This paper presents an optimization procedure for multi-criterion analysis essential in many biomechanical studies. The optimization is illustrated with a heel-toe running analysis wherein the rate of load and the passive load on support leg are minimized concurrently. The goal of multi-criterion optimization is achieved by incorporating the criterion of Pareto optimality in the genetic algorithm. The proposed procedure can replace the popular weighted-sum approach for problems with multiple objectives. The selection of a final design from the Pareto optimum points (non-dominated designs) can be determined, based on the min-max objective deviation criterion. Nevertheless, a different decision can be made in the final selection without incurring recalculations. The scheme is readily adoptable for parallel computing, which deserves further study to reduce the execution time in a complex biomechanical analysis.

Algorithms↗

PubMed2005

Magic number silicon dioxide-based clusters: laser ablation-mass spectrometric and density functional theory studies.

The magic number silica clusters [(SiO(2))(n)O(2)H(3)](-) with n = 4 and 8 have been observed in the XeCl excimer laser (308 nm) ablation of various porous siliceous materials. The structural origin of the magic number clusters has been studied by the density functional theoretical calculation at the B3LYP/6-31G** level, with a genetic algorithm as a supplementary tool for global structure searching. The DFT results of the first magic number cluster are parallel to the corresponding Hartree-Fock results previously reported with only small differences in the structural parameters. Theoretical calculation predicts that the first magic number cluster (SiO(2))(4)O(2)H(4) and its anion [(SiO(2))(4)O(2)H(3)](-) will most probably take pseudotetrahedral cage-like structures. To study the structural properties of the second magic number cluster, geometries of the bare cluster (SiO(2))(8), the neutral complex cluster (SiO(2))(8)O(2)H(4), and the anionic cluster [(SiO(2))(8)O(2)H(3)](-) are fully optimized at the B3LYP/6-31G** level, and the corresponding vibrational frequencies are calculated. The DFT calculations predict that the ground state of the bare silica octamer (SiO(2))(8) has a linear chain structure, whereas the second magic number complex cluster (SiO(2))(8)O(2)H(4) and its anion [(SiO(2))(8)O(2)H(3)](-) are most probably a mixture of cubic cage-like structural isomers with an O atom inside the cage and several quasi-bicage isomers with high intercage interactions. The stabilization of these structures can also be attributed to the active participation of the group of atoms 2O and 4H (3H for the anion) in chemical bonding during cluster formation. Our theoretical calculation gives preliminary structural interpretation of the presence of the first and second magic number clusters and the absence of higher magic numbers.

Journal Article↗

PubMed1996

A key by which the toad's visual system gets access to the domain of prey.

Searching for principles that allow toads to distinguish between prey and nonprey, we wondered how the toad's prey-catching activity measured as R differs in response to changes in significant configurational stimulus features. Elongated shapes moving worm-like in the direction of their longer axes are preferred prey dummies; but a toad is not a worm detector, and a worm is not the unique prey-catching releaser. Considering the frequency distributions of R values, we show that the release of prey catching is in a specific manner sensitive to the relation between the extensions of an object parallel (xl1) and perpendicular (xl2) to its direction of movement. It is the xl1 and xl2 features-relating algorithm that provides the key (instruction) by which the toad's visual system gets access to the domain of potential prey in terms of configurational cues. This, within behaviorally relevant limits, largely invariant algorithm also holds for segmented stimuli. Further investigations show that this principle of object discrimination is not due to experimental procedures but emerges as a species-common property, of which different toad species take advantage in a species-specific manner. Neurobiological correlates are discussed.

Animals↗

PubMed2005

Tailored utilization of acquired k-space points for GRAPPA reconstruction.

The generalized auto-calibrating partially parallel acquisition (GRAPPA) is an auto-calibrating parallel imaging technique which incorporates multiple blocks of data to derive the missing signals. In the original GRAPPA reconstruction algorithm only the data points in phase encoding direction are incorporated to reconstruct missing points in k-space. It has been recognized that this scheme can be extended so that data points in readout direction are also utilized and the points are selected based on a k-space locality criterion. In this study, an automatic subset selection strategy is proposed which can provide a tailored selection of source points for reconstruction. This novel approach extracts a subset of signal points corresponding to the most linearly independent base vectors in the coefficient matrix of fit, effectively preventing incorporating redundant signals which only bring noise into reconstruction with little contribution to the exactness of fit. Also, subset selection in this way has a regularization effect since the vectors corresponding to the smallest singular values are eliminated and consequently the condition of the reconstruction is improved. Phantom and in vivo MRI experiments demonstrate that this subset selection strategy can effectively improve SNR and reduce residual artifacts for GRAPPA reconstruction.

Algorithms↗

PubMed1994

Conductance catheter measurements of left ventricular volume in the intact dog: parallel conductance is independent of left ventricular size.

OBJECTIVE: It has recently been suggested that conductance catheter parallel conductance (alpha Vc) is a function of left ventricular volume. To confirm this, alpha Vc was measured in this study over a wide range of steady state volumes. In addition, conductance derived volumes were compared to those obtained by radionuclide angiography to determine if the conductance catheter can be used to measure absolute left ventricular volume accurately in the intact dog heart. METHODS: Seven dogs were anaesthetised and instrumented with left ventricular conductance and pressure tip catheters, a flow through rho cuvette to continually measure blood resistance, a thermodilution catheter, and a venous catheter for volume infusion/withdrawal. Conductance and angiographic data were acquired at 8(SD 1) variably loaded states. Parallel conductance was measured twice at each state using a saline dilution technique and a new non-linear algorithm that allows variability in the observations of both maximum and minimum conductance volumes. RESULTS: The mean value of alpha Vc was 89.1(18.0) ml (71.8 to 111.3 ml) with a mean within-animal coefficient of variation of 7.3(3.4)%. Multiple linear regression using dummy variables to account for the large interanimal variability did not reveal any relationship between alpha Vc and either maximum or minimum left ventricular volume. Furthermore, no difference was found when alpha Vc values measured at the lowest and highest loading levels in each dog were compared. Linear regression showed good agreement between conductance and radionuclide derived end diastolic volumes (slope = 0.94, R = 0.9, p < 0.001). CONCLUSIONS: While alpha Vc varies between animals, it remains constant within any given animal over a broad range of left ventricular volumes. Thus the conductance catheter can provide reliable absolute left ventricular volume measurements under steady state conditions.

Animals↗

PubMed2000

A double-blind, placebo-controlled study of Adderall and methylphenidate in the treatment of attention-deficit/hyperactivity disorder.

OBJECTIVE: While Adderall has been available for the treatment of attention-deficit/hyperactivity disorder (ADHD) for several years, there are few controlled studies comparing it to methylphenidate. METHOD: Fifty-eight children with ADHD (mean age 8.1 +/- 1.4 years) were randomly assigned to receive placebo, methylphenidate, or Adderall in a double-blind, parallel-group design for 3 weeks. Dosage was adjusted at the end of weeks 1 and 2 via an algorithm based on teacher and parent ratings. Final doses were 12.5 +/- 4.1 mg/day for Adderall and 25.2 +/- 13.1 mg/day for methylphenidate. Teacher and parent ratings, as well as the psychiatrist's Clinical Global Impression (CGI), were the final outcome measures at the end of week 3. RESULTS: Both medications were superior to placebo at reducing inattentive and oppositional symptoms in the classroom and on the CGI. Adderall produced significantly more improvements on teacher ratings and the CGI than methylphenidate, although the algorithm may have limited dosing in the methylphenidate group. Seventy percent of children in the Adderall group were given medication once a day, compared with 15% of the subjects receiving methylphenidate. CONCLUSIONS: Adderall compared favorably to methylphenidate, and the behavioral effects of Adderall appear to persist longer than those of methylphenidate after individual doses.

Algorithms↗

PubMedDate not supplied

Distributed shared memory for roaming large volumes.

We present a cluster-based volume rendering system for roaming very large volumes. This system allows to move a gigabyte-sized probe inside a total volume of several tens or hundreds of gigabytes in real-time. While the size of the probe is limited by the total amount of texture memory on the cluster, the size of the total data set has no theoretical limit. The cluster is used as a distributed graphics processing unit that both aggregates graphics power and graphics memory. A hardware-accelerated volume renderer runs in parallel on the cluster nodes and the final image compositing is implemented using a pipelined sort-last rendering algorithm. Meanwhile, volume bricking and volume paging allow efficient data caching. On each rendering node, a distributed hierarchical cache system implements a global software-based distributed shared memory on the cluster. In case of a cache miss, this system first checks page residency on the other cluster nodes instead of directly accessing local disks. Using two Gigabit Ethernet network interfaces per node, we accelerate data fetching by a factor of 4 compared to directly accessing local disks. The system also implements asynchronous disk access and texture loading, which makes it possible to overlap data loading, volume slicing and rendering for optimal volume roaming.

Computer Graphics↗