The Characterization of Ozone Exposures in Rural West Virginia and Virginia

Ozone (O3) is suspected of being the most significant air pollutant affecting vegetation in the United States. Ozone concentrations measured at Bearden Knob and Parsons, located in a remote forested region of northcentral West Virginia, were characterized and compared with exposures experienced at other sites in the region. From 1988 to 1992, 1988 was one of the highest O3 exposure years in the region, while 1992 was the lowest. At almost all sites in 1992, few hourly average concentrations were > or = 0.10 ppm, while in 1988 several sites had more than 100 hourly average concentrations > or = 0.10 ppm. These instances occurred at both high- and low-elevation sites. In 1992, the high-elevation Bearden Knob site experienced a flat-type diurnal pattern, while the nearby low-elevation Parsons site experienced a changing diurnal pattern, indicative of scavenging. Using several indices, O3 exposures at Parsons were less than those at Bearden Knob. Evaluation of hourly averaged data for all sites in the region from 1988 to 1992 showed that Horton Station experienced the highest W126 O3 exposures. Horton Station is a high-elevation site in the mountains of southwestern Virginia. Square-wave exposures have been used under artificial conditions in vegetation experiments. If square-wave exposures are observed under ambient conditions, then the vegetation data collected under artificial conditions may be relevant for predictive purposes. Square-wave exposures were characterized for two high-elevation sites. In 1992, Horton Station experienced 25 episodes for which the hourly average concentrations remained near 0.05 ppm for eight hours or longer; there were 18 episodes for which the hourly average concentrations remained near 0.06 ppm, and three episodes for which the concentrations remained near 0.07 ppm. Bearden Knob experienced 31 episodes of eight hours or longer for hourly average concentrations near 0.05 ppm, 13 episodes at or near 0.06 ppm, and three episodes at or near 0.07 ppm. Until experiments are performed to determine the relative importance of hourly average concentrations above 0.03 ppm for assessing vegetation effects, using single-parameter exposure indices to predict effects may produce inconsistent results.

The creation and characterisation of a National Compound Collection: the Royal Society of Chemistry pilot

We present a summary of the National Compound Collection (NCC) pilot; which harvested chemical structure data from 746 publicly-available PhD theses to create an enhanced database of diverse and interesting (largely organic) molecular entities. The database comprised ∼75 000 structure entries, of which 70% were new to ChemSpider at the time of upload. The dataset was evaluated for structural uniqueness by twelve external drug discovery groups from the pharmaceutical, biotech, academic and not-for-profit sectors. These partners generated data reported here comparing the NCC pilot with their in-house compound collections. The proportion of NCC structures considered to be useful for drug discovery ranged from 5-80% depending on the strictness of the filters used; most interestingly from a drug discovery standpoint ∼13k NCC compounds (18% of the NCC) passed the filters and were of good diversity. These compounds are quite different from those that are already present in the screening collections but not so different that they are no longer considered to be drug-like. In general, the drug discovery teams would consider these compounds to be high value molecules for inclusion in their screening collections. This pilot addressed the potential value of unpublished data and explored the practicalities of large-scale data extraction, to inform both retrospective and prospective extraction of chemical data from theses.

The vascular Ca2+-sensing receptor regulates blood vessel tone and blood pressure

The extracellular calcium-sensing receptor CaSR is expressed in blood vessels where its role is not completely understood. In this study, we tested the hypothesis that the CaSR expressed in vascular smooth muscle cells (VSMC) is directly involved in regulation of blood pressure and blood vessel tone. Mice with targeted CaSR gene ablation from vascular smooth muscle cells (VSMC) were generated by breeding exon 7 LoxP-CaSR mice with animals in which Cre recombinase is driven by a SM22α promoter (SM22α-Cre). Wire myography performed on Cre-negative [wild-type (WT)] and Cre-positive (SM22α)CaSR(Δflox/Δflox) [knockout (KO)] mice showed an endothelium-independent reduction in aorta and mesenteric artery contractility of KO compared with WT mice in response to KCl and to phenylephrine. Increasing extracellular calcium ion (Ca(2+)) concentrations (1-5 mM) evoked contraction in WT but only relaxation in KO aortas. Accordingly, diastolic and mean arterial blood pressures of KO animals were significantly reduced compared with WT, as measured by both tail cuff and radiotelemetry. This hypotension was mostly pronounced during the animals' active phase and was not rescued by either nitric oxide-synthase inhibition with nitro-l-arginine methyl ester or by a high-salt-supplemented diet. KO animals also exhibited cardiac remodeling, bradycardia, and reduced spontaneous activity in isolated hearts and cardiomyocyte-like cells. Our findings demonstrate a role for CaSR in the cardiovascular system and suggest that physiologically relevant changes in extracellular Ca(2+) concentrations could contribute to setting blood vessel tone levels and heart rate by directly acting on the cardiovascular CaSR.

Widespread phenotypic and genetic divergence along altitudinal gradients in animals

Altitudinal gradients offer valuable study systems to investigate how adaptive genetic diversity is distributed within and between natural populations and which factors promote or prevent adaptive differentiation. The environmental clines along altitudinal gradients tend to be steep relative to the dispersal distance of many organisms, providing an opportunity to study the joint effects of divergent natural selection and gene flow. Temperature is one variable showing consistent altitudinal changes, and altitudinal gradients can therefore provide spatial surrogates for some of the changes anticipated under climate change. Here, we investigate the extent and patterns of adaptive divergence in animal populations along altitudinal gradients by surveying the literature for (i) studies on phenotypic variation assessed under common garden or reciprocal transplant designs and (ii) studies looking for signatures of divergent selection at the molecular level. Phenotypic data show that significant between-population differences are common and taxonomically widespread, involving traits such as mass, wing size, tolerance to thermal extremes and melanization. Several lines of evidence suggest that some of the observed differences are adaptively relevant, but rigorous tests of local adaptation or the link between specific phenotypes and fitness are sorely lacking. Evidence for a role of altitudinal adaptation also exists for a number of candidate genes, most prominently haemoglobin, and for anonymous molecular markers. Novel genomic approaches may provide valuable tools for studying adaptive diversity, also in species that are not amenable to experimentation.

Identification of benzofurano[3,2-d]pyrimidin-2-ones, a new series of HIV-1 nucleotide-competing reverse transcriptase inhibitors

Screening of our sample collection led to the identification of a set of benzofurano[3,2-d]pyrimidine-2-one hits acting as nucleotide-competing HIV-1 reverse transcriptase inhibitiors (NcRTI). Significant improvement in antiviral potency was achieved when substituents were introduced at positions N1, C4, C7 and C8 on the benzofuranopyrimidone scaffold. The series was optimized from low micromolar enzymatic activity against HIV-1 RT and no antiviral activity to low nanomolar antiviral potency. Further profiling of inhibitor 30 showed promising overall in vitro properties and also demonstrated that its potency was maintained against viruses resistant to the other major classes of HIV-1 RT inhibitors.

Nucleotide competing reverse transcriptase inhibitors: discovery of a series of non-basic benzofurano[3,2-d]pyrimidin-2-one derived inhibitors

A HTS screen led to the identification of a benzofurano[3,2-d]pyrimidin-2-one core structure which upon further optimization resulted in 1 as a potent HIV-1 nucleotide competing reverse transcriptase inhibitor (NcRTI). Investigation of the SAR at N-1 allowed significant improvements in potency and when combined with the incorporation of heterocycles at C-8 resulted in potent analogues not requiring a basic amine to achieve antiviral activity. Additional modifications at N-1 resulted in 33 which demonstrated excellent antiviral potency and improved physicochemical properties.

Confidence estimation methods for neural networks: a practical comparison

Feedforward neural networks, particularly multilayer perceptrons, are widely used in regression and classification tasks. A reliable and practical measure of prediction confidence is essential. In this work three alternative approaches to prediction confidence estimation are presented and compared. The three methods are the maximum likelihood, approximate Bayesian, and the bootstrap technique. We consider prediction uncertainty owing to both data noise and model parameter misspecification. The methods are tested on a number of controlled artificial problems and a real, industrial regression application, the prediction of paper "curl". Confidence estimation performance is assessed by calculating the mean and standard deviation of the prediction interval coverage probability. We show that treating data noise variance as a function of the inputs is appropriate for the curl prediction task. Moreover, we show that the mean coverage probability can only gauge confidence estimation performance as an average over the input space, i.e., global performance and that the standard deviation of the coverage is unreliable as a measure of local performance. The approximate Bayesian approach is found to perform better in terms of global performance.

Enhanced MLP performance and fault tolerance resulting from synaptic weight noise during training

We analyze the effects of analog noise on the synaptic arithmetic during multilayer perceptron training, by expanding the cost function to include noise-mediated terms. Predictions are made in the light of these calculations that suggest that fault tolerance, training quality and training trajectory should be improved by such noise-injection. Extensive simulation experiments on two distinct classification problems substantiate the claims. The results appear to be perfectly general for all training schemes where weights are adjusted incrementally, and have wide-ranging implications for all applications, particularly those involving "inaccurate" analog neural VLSI.

Discovery of a series of imidazopyrazine small molecule inhibitors of the kinase MAPKAPK5, that show activity using in vitro and in vivo models of rheumatoid arthritis

MAPKAPK5 has been proposed to play a role in regulation of matrix metalloprotease expression and so to be a potential target for intervention in rheumatoid arthritis. We present here the identification of a series of compounds against this target which are effective in both biochemical and cell assays. The expansion of the series is described, along with early SAR and pharmacokinetics for some representative compounds.

HTS promiscuity analyses for accelerating decision making

Frequent hitters are compounds that are detected as a "hit" in multiple high-throughput screening (HTS) assays. Such behavior is specific (e.g., target family related) or unspecific (e.g., reactive compounds) or can result from a combination of such behaviors. Detecting such hits while predicting the underlying reason behind their promiscuous behavior is desirable because it provides valuable information not only about the compounds themselves but also about the assay methodology and target classes at hand. This information can also greatly reduce cost and time during HTS hit profiling. The present study exemplifies how to mine large HTS data repositories, such as the one at Boehringer Ingelheim, to identify frequent hitters, gain further insights into the causes of promiscuous behavior, and generate models for predicting promiscuous compounds. Applications of this approach are demonstrated using two recent large-scale HTS assays. The authors believe this analysis and its concrete applications are valuable tools for streamlining and accelerating decision-making processes during the course of hit discovery.

Current parallel chemistry principles and practice: application to the discovery of biologically active molecules

This article describes the use of parallel chemistry techniques for drug discovery, based on publications from January 2006 to December 2008. Chemical libraries that yielded active compounds across a range of biological targets are presented, together with synthetic details when appropriate. Background information for the biological targets involved and any SAR that could be discerned within members of a library series also is discussed. New technological developments, as applied to library design and synthesis and, more generally, in the discovery of biologically active entities, are highlighted. In addition, the likely future directions for parallel chemistry in its ability to impact upon drug discovery are also presented.

The design of potent and selective inhibitors of DPP-4: optimization of ADME properties by amide replacements

For a series of beta-homophenylalanine based inhibitors of dipeptidyl peptidase IV ADME properties were improved by the incorporation of amide replacements. These efforts led to a novel series of potent and selective inhibitors of DPP-4 that exhibit an attractive pharmacokinetic profile and show excellent efficacy in an animal model of diabetes.

Discovery of beta-homophenylalanine based pyrrolidin-2-ylmethyl amides and sulfonamides as highly potent and selective inhibitors of dipeptidyl peptidase IV

Modifications of DPP-4 inhibitor 5, that was discovered by structure based design, are described and structure-activity relationships discussed. With analogue 7k one of the most potent non-covalent inhibitors of DPP-4 reported to date (IC(50)=0.38nM) was discovered. X-ray structure of inhibitor 7k bound to DPP-4 revealed a hydrogen bonding interaction with Q553. First successful efforts in balancing overall properties, as demonstrated by improved metabolic stability, highlight the potential of this series.

Minimizing risk using prediction uncertainty in neural network estimation fusion and its application to papermaking

The paper presents Bayesian information fusion theory in the context of neural-network model combination. It shows how confidence measures can be combined with individual model estimates to minimize risk through the fusion process. The theory is illustrated through application to the real task of quality prediction in the papermaking industry. Prediction uncertainty estimates are calculated using approximate Bayesian learning. These are incorporated into model combination as confidence measures. Cost functions in the fusion center are used to control the influence of the confidence measures and improve the performance of the resultant committee.

Prediction uncertainty of environmental change effects on temperate European biodiversity

Observed patterns of species richness at landscape scale (gamma diversity) cannot always be attributed to a specific set of explanatory variables, but rather different alternative explanatory statistical models of similar quality may exist. Therefore predictions of the effects of environmental change (such as in climate or land cover) on biodiversity may differ considerably, depending on the chosen set of explanatory variables. Here we use multimodel prediction to evaluate effects of climate, land-use intensity and landscape structure on species richness in each of seven groups of organisms (plants, birds, spiders, wild bees, ground beetles, true bugs and hoverflies) in temperate Europe. We contrast this approach with traditional best-model predictions, which we show, using cross-validation, to have inferior prediction accuracy. Multimodel inference changed the importance of some environmental variables in comparison with the best model, and accordingly gave deviating predictions for environmental change effects. Overall, prediction uncertainty for the multimodel approach was only slightly higher than that of the best model, and absolute changes in predicted species richness were also comparable. Richness predictions varied generally more for the impact of climate change than for land-use change at the coarse scale of our study. Overall, our study indicates that the uncertainty introduced to environmental change predictions through uncertainty in model selection both qualitatively and quantitatively affects species richness projections.

Food-poisoning and commercial air travel

With the introduction of budget airlines and greater competitiveness amongst all airlines, air travel has now become an extremely popular form of travel, presenting its own unique set of risks from food poisoning. Foodborne illness associated with air travel is quite uncommon in the modern era. However, when it occurs, it may have serious implications for passengers and when crew are affected, has the potential to threaten safety. Quality, safe, in-flight catering relies on high standards of food preparation and storage; this applies at the airport kitchens (or at subcontractors' facilities), on the aircraft and in the transportation vehicles which carry the food from the ground source to the aircraft. This is especially challenging in certain countries. Several foodborne outbreaks have been recorded by the airline industry as a result of a number of different failures of these systems. These have provided an opportunity to learn from past mistakes and current practice has, therefore, reached such a standard so as to minimise risk of failures of this kind. This review examines: (i) the origin of food safety in modern commercial aviation; (ii) outbreaks which have occurred previously relating to aviation travel; (iii) the microbiological quality of food and water on board commercial aircraft; and (iv) how Hazard Analysis Critical Control Points may be employed to maintain food safety in aviation travel.

Phylogeography of the high alpine plant Senecio halleri (Asteraceae) in the European Alps: in situ glacial survival with postglacial stepwise dispersal into peripheral areas

Whether alpine plant species survived Pleistocene glaciations in situ on high alpine nunatak mountains is still under debate. To test this hypothesis, Senecio halleri, a high alpine and endemic species with a narrow distribution range in the European Alps, was chosen as a model organism. Polymerase chain reaction-restriction fragment length polymorphisms of chloroplast DNA (cpDNA PCR-RFLPs) were used in a phylogeographic analysis of 14 populations of S. halleri, covering its total distribution area. The results of haplotype diversity and distribution gave evidence of in situ glacial survival on siliceous central-alpine nunatak mountains in two areas, southwest and northeast of the Aosta valley. According to the absence of genetic differentiation between these two nunatak areas (based on amova), nested clade analysis implied a history of preglacial gene flow, in situ survival and extinction of intermediate populations during glaciation and postglacial stepwise recolonization of peripheral and intermediate areas.

Expediting drug discovery: recent advances in fast medicinal chemistry--optimization of hits and leads

This article reviews the literature from January 2004 to January 2006 relating to the use of parallel chemistry compound libraries in drug discovery. Examples of libraries that have yielded active compounds across a range of biological targets are presented, together with synthetic details where relevant. The background of the biological target, and any structure-activity relationship that can be discerned from members of a library series, are also commented upon. A brief discussion of new technological developments in library design and synthesis, and likely future directions for parallel chemistry in the context of drug discovery, is also presented.

Cadaver validation of intensity-based ultrasound to CT registration

A method is presented for the rigid registration of tracked B-mode ultrasound images to a CT volume of a femur and pelvis. This registration can allow tracked surgical instruments to be aligned with the CT image or an associated preoperative plan. Our method is fully automatic and requires no manual segmentation of either the ultrasound images or the CT volume. The parameter which is directly related to the speed of sound through tissue has also been included in the registration optimisation process. Experiments have been carried out on six cadaveric femurs and three cadaveric pelves. Registration results were compared with a "gold standard" registration acquired using bone implanted fiducial markers. Results show the registration method to be accurate, on average, to 1.6 mm root-mean-square target registration error.

The impact of parallel chemistry in drug discovery

With the application of parallel synthesis of single compounds to drug-discovery efforts, improvements in the efficiency of synthesis are possible. However, for improvements to occur in effective drug design - a critical requirement to increase productivity in the modern pharmaceutical industry - the implementation of in silico design hypotheses that incorporate comprehensive information on a target, including considerations of absorption, distribution, metabolism and excretion, is also necessary. Concomitantly, the use of automated methods of synthesis and purification is also required to improve drug design. Combining all of these elements allows the possibility to uncover unique insights into a biological target quickly and to therefore accelerate the rate of drug discovery.

The reversed binding of β-phenethylamine inhibitors of DPP-IV: X-ray structures and properties of novel fragment and elaborated inhibitors

The co-crystal structure of beta-phenethylamine fragment inhibitor 5 bound to DPP-IV revealed that the phenyl ring occupied the proline pocket of the enzyme. This finding provided the basis for a general hypothesis of a reverse binding mode for beta-phenethylamine-based DPP-IV inhibitors. Novel inhibitor design concepts that obviate substrate-like structure-activity relationships (SAR) were thereby enabled, and novel, potent inhibitors were discovered.

Case Study Part 1: How to calculate appropriate deterministic long-term toxicity to exposure ratios (TERs) for birds and mammals

In the European Union, first-tier assessment of the long-term risk to birds and mammals from pesticides is based on calculation of a deterministic long-term toxicity/exposure ratio (TER(lt)). The ratio is developed from generic herbivores and insectivores and applied to all species. This paper describes two case studies that implement proposed improvements to the way long-term risk is assessed. These refined methods require calculation of a TER for each of five identified phases of reproduction (phase-specific TERs) and use of adjusted No Observed Effect Levels (NOELs) to incorporate variation in species sensitivity to pesticides. They also involve progressive refinement of the exposure estimate so that it applies to particular species, rather than generic indicators, and relates spraying date to onset of reproduction. The effect of using these new methods on the assessment of risk is described. Each refinement did not necessarily alter the calculated TER value in a way that was either predictable or consistent across both case studies. However, use of adjusted NOELs always reduced TERs, and relating spraying date to onset of reproduction increased most phase-specific TERs. The case studies suggested that the current first-tier TER(lt )assessment may underestimate risk in some circumstances and that phase-specific assessments can help identify appropriate risk-reduction measures. The way in which deterministic phase-specific assessments can currently be implemented to enhance first-tier assessment is outlined.

Case Study Part 2: Probabilistic modelling of long-term effects of pesticides on individual breeding success in birds and mammals

Long term exposure of skylarks to a fictitious insecticide and of wood mice to a fictitious fungicide were modelled probabilistically in a Monte Carlo simulation. Within the same simulation the consequences of exposure to pesticides on reproductive success were modelled using the toxicity-exposure-linking rules developed by R.S. Bennet et al. (2005) and the interspecies extrapolation factors suggested by R. Luttik et al. (2005). We built models to reflect a range of scenarios and as a result were able to show how exposure to pesticide might alter the number of individuals engaged in any given phase of the breeding cycle at any given time and predict the numbers of new adults at the season's end.

Image-guided navigation in oral and maxillofacial surgery

Image-guided surgery is the logical extension of imaging as it integrates previously acquired radiological or nuclear medicine images with the operative field. In conventional image-guided surgery, a surgeon uses a surgical instrument or a pointer to establish correspondence between features in the preoperative images and the surgical scene. This is not ideal because the surgeon has to look away from the operative field to view the data. Augmented reality guidance systems offer a solution to this problem but are limited by deformation of soft tissues. Real-time intraoperative imaging offers a potential solution but is currently only experimental. The additional precision and confidence that this technology provides make it a useful tool, and recent advances in image-guided surgery offer new opportunities in the field of oral and maxillofacial surgery. Here, we review the development, current technologies, and applications of image-guided surgery and illustrate them with two case reports.

Tissue deformation and shape models in image-guided interventions: a discussion paper

This paper promotes the concept of active models in image-guided interventions. We outline the limitations of the rigid body assumption in image-guided interventions and describe how intraoperative imaging provides a rich source of information on spatial location of anatomical structures and therapy devices, allowing a preoperative plan to be updated during an intervention. Soft tissue deformation and variation from an atlas to a particular individual can both be determined using non-rigid registration. Established methods using free-form deformations have a very large number of degrees of freedom. Three examples of deformable models--motion models, biomechanical models and statistical shape models--are used to illustrate how prior information can be used to restrict the number of degrees of freedom of the registration algorithm and thus provide active models for image-guided interventions. We provide preliminary results from applications for each type of model.

Wound induced defences in plants and their consequences for patterns of insect grazing

Three scales of wound-induced chemical responses in plants are identified: (1) highly localised chemical changes associated with disruption of cell compartmentation; (2) changes induced in cells surrounding the damaged area, forming a kind of halo around the damage, and (3) more widely-dispersed changes which may affect an entire organ, branch or plant. A brief review of the literature reveals that such chemical responses are very widespread in plants, and many of the substances formed are known to affect adversely the growth, development, or reproduction of insects. It is argued that wound-induced changes in plant chemistry represent for insects a powerful selective pressure for the dispersal of grazing. Levels and patterns of invertebrate grazing in a range of herbaceous and deciduous woody plants sampled at the end of the growing seasons were examined. Leaves of many species exhibited a strikingly evident over-dispersion of grazing initiations, and in some cases the arrangement of holes appeared close to regularity. The pattern of damage between leaves was, in most cases, heavily biased towards a large proportion of leaves receiving a low level of grazing. These highly dispersed patterns of grazing damage are consistent with the hypothesis that wound-induced responses play an important role in determining patterns of insect feeding. They have important implications for the expected levels of insect exploitation of host plants and for the advantages to the plant of distributing grazing damage evenly through the canopy.

Synthesis of (±)-Secosyrin 1 and a Formal Synthesis of (−)-Secosyrin 1

[reaction: see text] A short synthesis of (+/-)-secosyrin 1 is presented that starts from an electron-deficient furan; reductive alkylation under Birch conditions gives rapid access to the natural product skeleton. Two aspects of stereoselectivity are explored, the first being directed dihydroxylation of a homoallylic alcohol. Second, the facial selectivity obtained during reduction of a highly substituted cyclic ketone was examined. Finally, our synthesis was rendered enantioselective by the reduction of a furan bearing a chiral auxiliary.

Purification strategies for combinatorial and parallel chemistry

This review surveys the methods developed for the purification of intermediates and final compounds originating from parallel and combinatorial chemistry. Included will be reviews of polymer-assisted purification, liquid-phase combinatorial chemistry, fluorous synthesis, liquid-liquid and solid-phase extraction, reverse-phase HPLC and supercritical fluid chromatography. A critique of each method is given, highlighting the methodologies strengths and weaknesses.

Solid-phase compound library synthesis in drug design and development

This article is a subjective review of the literature between December 2000 and January 2002 related to the solid-phase synthesis of compound libraries for drug discovery and development. Examples of libraries yielding active compounds across a range of biological targets are presented, together with synthetic details where this is deemed of sufficient note. Background to the biological target and any structure-activity relationship, which can be discerned within members of a library series, is also discussed. A brief overview of new developments in solid-phase technology that is likely to impact upon drug discovery is also included.

Level-crossing statistics of the horizontal wind speed in the planetary surface boundary layer

The probability density of the times for which the horizontal wind remains above or below a given threshold speed is of some interest in the fields of renewable energy generation and pollutant dispersal. However there appear to be no analytic or conceptual models which account for the observed power law form of the distribution of these episode lengths over a range of over three decades, from a few tens of seconds to a day or more. We reanalyze high resolution wind data and demonstrate the fractal character of the point process generated by the wind speed level crossings. We simulate the fluctuating wind speed by a Markov process which approximates the characteristics of the real (non-Markovian) wind and successfully generates a power law distribution of episode lengths. However, fundamental questions concerning the physical basis for this behavior and the connection between the properties of a continuous-time stochastic process and the fractal statistics of the point process generated by its level crossings remain unanswered. (c) 2001 American Institute of Physics.

Stereo augmented reality in the surgical microscope

We present an augmented reality system that allows surgeons to view features from preoperative radiological images accurately overlaid in stereo in the optical path of a surgical microscope. The purpose of the system is to show the surgeon structures beneath the viewed surface in the correct 3-D position. The technical challenges are registration, tracking, calibration and visualisation. For patient registration, or alignment to preoperative images, we use bone-implanted markers and a dental splint is used for patient tracking. Both microscope and patient are tracked by an optical localiser. Calibration uses an accurately manufactured object with high contrast circular markers which are identified automatically. All ten camera parameters are modelled as a bivariate polynomial function of zoom and focus. The overall system has a theoretical overlay accuracy of better than 1 mm. Implementations of the system have been tested on seven patients. Recent measurements in the operating room conformed to our accuracy predictions. For visualisation the system has been implemented on a graphics workstation to enable high frame rates with a variety of rendering schemes. Several issues of 3-D depth perception remain unsolved, but early results suggest that perception of structures in the correct 3-D position beneath the viewed surface is possible.

Design and evaluation of a system for microscope-assisted guided interventions (MAGI)

The problem of providing surgical navigation using image overlays on the operative scene can be split into four main tasks--calibration of the optical system; registration of preoperative images to the patient; system and patient tracking, and display using a suitable visualization scheme. To achieve a convincing result in the magnified microscope view a very high alignment accuracy is required. We have simulated an entire image overlay system to establish the most significant sources of error and improved each of the stages involved. The microscope calibration process has been automated. We have introduced bone-implanted markers for registration and incorporated a locking acrylic dental stent (LADS) for patient tracking. The LADS can also provide a less-invasive registration device with mean target error of 0.7 mm in volunteer experiments. These improvements have significantly increased the alignment accuracy of our overlays. Phantom accuracy is 0.3-0.5 mm and clinical overlay errors were 0.5-1.0 mm on the bone fiducials and 0.5-4 mm on target structures. We have improved the graphical representation of the stereo overlays. The resulting system provides three-dimensional surgical navigation for microscope-assisted guided interventions (MAGI).

A system for microscope-assisted guided interventions

We present a system for surgical navigation using stereo overlays in the operating microscope aligned to the operative scene. This augmented reality system provides 3D information about nearby structures and offers a significant advancement over pointer-based guidance, which provides only the location of one point and requires the surgeon to look away from the operative scene. With a previous version of this system, we demonstrated feasibility, but it became clear that to achieve convincing guidance through the magnified microscope view, a very high alignment accuracy was required. We have made progress with several aspects of the system, including automated calibration, error simulation, bone-implanted fiducials and a dental attachment for tracking. We have performed experiments to establish the visual display parameters required to perceive overlaid structures beneath the operative surface. Easy perception of real and virtual structures with the correct transparency has been demonstrated in a laboratory and through the microscope. The result is a system with a predicted accuracy of 0.9 mm and phantom errors of 0.5 mm. In clinical practice errors are 0.5-1.5 mm, rising to 2-4 mm when brain deformation occurs.

Locking acrylic resin dental stent for image-guided surgery

This article presents a procedure for fabricating a locking acrylic resin dental stent for use in image-guided base-of-skull surgery and neurosurgery. The stent offers advantages over conventional bone screw-anchored systems to surgeons and patients. In view of the increasing use of image guidance in base-of-skull surgery and neurosurgery, prosthodontists will meet a growing demand for this type of device in the future.

A study of early stopping and model selection applied to the papermaking industry

This paper addresses the issues of neural network model development and maintenance in the context of a complex task taken from the papermaking industry. In particular, it describes a comparison study of early stopping techniques and model selection, both to optimise neural network models for generalisation performance. The results presented here show that early stopping via use of a Bayesian model evidence measure is a viable way of optimising performance while also making maximum use of all the data. In addition, they show that ten-fold cross-validation performs well as a model selector and as an estimator of prediction accuracy. These results are important in that they show how neural network models may be optimally trained and selected for highly complex industrial tasks where the data are noisy and limited in number.

Applications of combinatorial chemistry to drug design and development

This article is a subjective review of the literature from 1998 to April 1999 describing combinatorial chemistry as applied to drug discovery. The first two sections cover proteinase inhibition and small molecule lead discovery for other target classes. The final section describes those combinatorial chemistry-related technologies we think most likely to impact on drug discovery in the future.

A three-component deformation model for image-guided surgery

In image-guided surgery it is necessary to align preoperative image data with the patient. The rigid-body approximation is usually applied, but is often not valid due to tissue deformation. Non-rigid deformation algorithms have been applied to related, but not identical problems, such as atlas matching and surgery simulation. In image-guided surgery we have the additional information that the deformation is constrained by the physical properties of the different tissues. The most important properties that must be incorporated are the rigidity of bone, the unconstrained nature of fluid regions and the relatively smooth deformation of soft tissue. Hence, we have developed a simplified model of tissue deformation based on a three-component system. Rigid regions are constrained by the rigid-body transformation and fluid regions are unconstrained. A number of energy models for deformable tissues have been compared. The model can be deformed using intraoperative data, in this case landmarks, using a technique similar to active contours. A novel strategy to avoid folding in the transformation is described. Our method was applied to MRI and CT data from a neurosurgery patient with epilepsy. Although the current implementation is only two dimensional, the initial results are promising. As the algorithm must ultimately run in or near 'real-time' an improved implementation of the energy minimization is underway. This paper presents the problem of tissue deformation, which has received little attention in the literature and outlines the framework we have developed for tackling this difficult subject.

Toward optimally distributed computation

This article introduces the concept of optimally distributed computation in feedforward neural networks via regularization of weight saliency. By constraining the relative importance of the parameters, computation can be distributed thinly and evenly throughout the network. We propose that this will have beneficial effects on fault-tolerance performance and generalization ability in large network architectures. These theoretical predictions are verified by simulation experiments on two problems: one artificial and the other a real-world task. In summary, this article presents regularization terms for distributing neural computation optimally.