Modelling skeletal muscle fibre orientation arrangement

Skeletal muscle tissues have complex geometries. In addition, the complex fibre orientation arrangement makes it quite difficult to create an accurate finite element muscle model. There are many possible ways to specify the complex fibre orientations in a finite element model, for example defining a local element coordinate system. In this paper, an alternative method using ABAQUS, which is combination of the finite element method and the non-uniform rational B-spline solid representation, is proposed to calculate the initial fibre orientations. The initial direction of each muscle fibre is specified as the tangent direction of the NURBS curve which the fibre lies on, and the directions of the deformed fibres are calculated from the initial fibre directions, the deformation gradients and the fibre stretch ratios. Several examples are presented to demonstrate the ability of the proposed method. Results show that the proposed method is able to characterise both the muscle complex fibre orientation arrangement and its complex mechanical response.

Avian nest success, mammalian nest predator abundance, and invertebrate prey availability in a fragmented landscape

Avian nest success is largely determined by predation, but factors affecting the abundance of potential nest predators are rarely studied. We used an information–theoretic approach to assess relative support for models including invertebrate biomass, mammalian nest predator abundance, and percent cover at nests as explanatory variables for nest success of Ovenbirds ( Seiurus aurocapilla (L., 1766)) and Wood Thrush ( Hylocichla mustelina (J.F. Gmelin, 1789)). We ranked models including local vegetation characteristics and landscape composition at two spatial scales (100 and 2000 m) as explanatory variables for the abundance of mammalian nest predator groups and for prey biomass. The nest success of Ovenbirds was best explained by a positive association with percent cover by forbs and seedlings, whereas a positive relationship with prey biomass best explained the nest success of Wood Thrush. Most mammal genera were associated with landscape composition within 100 m of the study sites, and most were positively associated with housing density. Prey biomass was best explained by a positive association with less intensive agriculture within 2000 m. Implementing silvicultural techniques that preserve important habitat features within fragmented forests, limiting housing density within 100 m, and increasing the amount of less intensive agriculture within 2000 m of forest fragments may improve nest success for forest songbirds.

A visco-hyperelastic model for skeletal muscle tissue under high strain rates

In this paper, a visco-hyperelastic skeletal muscle model is developed. The constitutive relation is based on the definition of a Helmholtz free energy function. It is assumed that the Helmholtz energy can be decomposed into volumetric and isochoric parts; furthermore, the isochoric energy can be decoupled into hyperelastic and viscous parts. The model developed involves 14 material parameters and its performance is evaluated by comparing the finite element simulation results with the published experimental studies on the New Zealand white rabbit tibialis anterior muscle. Results show that this model is able to describe the visco-hyperelastic behaviour of both passive and active skeletal muscle tissues under high strain rates (10/s and 25/s).

The PREM score: a graphical tool for predicting survival in very preterm births

OBJECTIVE

To develop a tool for predicting survival to term in babies born more than 8 weeks early using only information available at or before birth.

DESIGN

1456 non-malformed very preterm babies of 22-31 weeks' gestation born in 2000-3 in the north of England and 3382 births of 23-31 weeks born in 2000-4 in Trent.

OUTCOME

Survival to term, predicted from information available at birth, and at the onset of labour or delivery.

METHOD

Development of a logistic regression model (the prematurity risk evaluation measure or PREM score) based on gestation, birth weight for gestation and base deficit from umbilical cord blood.

RESULTS

Gestation was by far the most powerful predictor of survival to term, and as few as 5 extra days can double the chance of survival. Weight for gestation also had a powerful but non-linear effect on survival, with weight between the median and 85th centile predicting the highest survival. Using this information survival can be predicted almost as accurately before birth as after, although base deficit further improves the prediction. A simple graph is described that shows how the two main variables gestation and weight for gestation interact to predict the chance of survival.

CONCLUSION

The PREM score can be used to predict the chance of survival at or before birth almost as accurately as existing measures influenced by post-delivery condition, to balance risk at entry into a controlled trial and to adjust for differences in "case mix" when assessing the quality of perinatal care.

Study of the scan uniformity from an i-CAT cone beam computed tomography dental imaging system

OBJECTIVES

As part of an ongoing programme to improve diagnosis and treatment planning relevant to implant placement, orthodontic treatment and dentomaxillofacial surgery, a study has been made of the spatial accuracy and density response of an i-CAT, a cone beam CT (CBCT) dental imaging system supplied by Imaging Sciences International Inc.

METHODS

Custom-made phantoms using acrylic sheet and water were used for measurements on spatial accuracy, density response and noise. The measurements were made over a period of several months on a clinical machine rather than on a machine dedicated to research.

RESULTS

Measurements on a precision grid showed the spatial accuracy to be universally within the tolerance of +/-1 pixel. The density response and the noise in the data were found to depend strongly on the mass in the slice being scanned.

CONCLUSIONS

The density response was subject to two effects. The first effect changes the whole slice uniformly and linearly depends on the total mass in the slice. The second effect exists when there is mass outside the field of view, dubbed the "exo-mass" effect. This effect lowers the measured CT number rapidly at the scan edge furthest from the exo-mass and raises it on the adjacent edge. The noise also depended quasi-linearly on the mass in the slice. Some general performance rules were drafted to describe these effects and a preliminary correction algorithm was constructed.

A three-dimensional look for facial differences between males and females in a British-Caucasian sample aged 151/2 years old

BACKGROUND

Optical surface scanning accurately records the three-dimension (3D) shape of the face non-invasively. Many software programs have been developed to process and analyze the 3D data, enabling the clinicians to create average templates for groups of subjects to provide a comparison of facial shape.

OBJECTIVE

Differences in facial morphology of males and females were identified using a laser scan imaging technology.

SUBJECTS AND METHODS

This study was undertaken on 380 British-Caucasian children aged 15 and a half year old, recruited from the Avon Longitudinal Study of Parents and Children (ALSPAC). 3D facial images were obtained for each individual using two high resolution Konica/Minolta laser scanners. The scan quality was assessed and any unsuitable scans were excluded from the study. Average facial templates were created for males and females, and a registration technique was used to superimpose the facial shells of males and females so that facial differences can be quantified.

RESULTS

Thirty unsuitable scans were excluded from the study. The final sample consisted of 350 subjects (166 females, 184 males). Females tend to have more prominent eyes and cheeks in relation to males with a maximum difference of 2.4 mm. Males tend to have more prominent noses and mouths with a maximum difference of 2.7 mm. About 31% of the facial shells match exactly (no difference), mainly in the forehead and chin regions of the face.

CONCLUSIONS

Differences in facial morphology can be accurately quantified and visualized using 3D imaging technology. This method of facial assessment can be recommended and applied for future research studies to assess facial soft tissue changes because of growth or healthcare intervention.

Weight change in the term baby in the first 2 weeks of life

BACKGROUND

Midwives once used serial weighing to highlight lactation problems, but this is now discouraged for the fear of undermining maternal confidence.

AIM

To explore weight changes in healthy newborn term babies, to gain information to aid interpretation of such measurements and to construct a centile chart for those exclusively breastfed during the first 2 weeks.

METHOD

Two hundred ninety-nine mothers weighed their baby daily using the same electronic scales. In 46 cases, three or more consecutive measurements were omitted leaving 253 series to evaluate, of which 111 were exclusively breastfed.

RESULTS

Breastfed babies lost a mean 6.4% of birthweight (95% CI: 5.5-7.3%) before starting to gain, and 54% took more than 8 days to regain birthweight. Artificially fed babies lost less (3.7%, 95% CI: 2.7-4.7%), but 39% had not regained their birthweight by 8 days. Once birthweight was regained, average gain was about 1% of birthweight per day in both breast- and artificially-fed babies. Measurements less than 5 days apart predicted average weight gain poorly.

CONCLUSIONS

Feeding problems should be considered if weight is not increasing by 6 days, but some healthy babies take 17 days to regain their birthweight.

A randomised controlled trial of clinical outreach education to rationalise antibiotic prescribing for acute dental pain in the primary care setting

OBJECTIVE

To assess the effect of educational outreach visits on antibiotic prescribing for acute dental pain in primary care.

STUDY DESIGN

RCT.

SETTING

General dental practices in four health authority areas in Wales.

SUBJECTS AND METHODS

General dental practitioners were recruited to the study and randomly allocated to one of the three study groups (control group, guideline group or intervention group). Following the intervention, practitioners completed a standardised questionnaire for each patient that presented with acute dental pain.

INTERVENTIONS

The control group received no intervention. The guideline group received educational material by post. The intervention group received educational material by post and an academic detailing visit by a trained pharmacist. The educational material included evidence-based guidelines on prescribing for acute dental pain and patient information leaflets.

MAIN OUTCOME MEASURES

The number of antibiotic prescriptions issued to patients presenting with dental pain and the number of 'inappropriate' antibiotic prescriptions. Antibiotics were considered to be inappropriate if the patient did not have symptoms indicative of spreading infection.

RESULTS

A total of 1,497 completed questionnaires were received from 23, 20 and 27 general dental practitioners in the control, guideline and intervention group respectively. Patients in the intervention group received significantly fewer antibiotic prescriptions than patients in the control group (OR (95% CI) 0.63 (0.41, 0.95)) and significantly fewer inappropriate antibiotic prescriptions (OR (95% CI) 0.33 (0.21, 0.54)). However, antibiotic and inappropriate antibiotic prescribing were not significantly different in the guideline group compared to the control group (OR (95% CI) 0.83 (0.55, 1.21) and OR (95% CI) 0.82 (0.53, 1.29) respectively).

CONCLUSIONS

Strategies based upon educational outreach visits may be successfully employed to rationalise antibiotic prescribing by dental practitioners.

[Not Available]

The ICON (Index of Complexity, Outcome and Need) is a new index based on the consensus opinion of 97 European and American orthodontists. It records orthodontics treatment need on the basis of 5 components i.e. crossbite, upper arch crowding/spacing, buccal segment antero-posterior relationship and anterior vertical relationship. This index can be used in epidemiological studies and by public services and third party co-payment for the determination of those patients who may be eligible for public funding or reimbursement of fees.

Facial templates: a new perspective in three dimensions

PURPOSE

This paper describes the use of adult facial template in gender-specific facial analysis.

SUBJECTS AND METHODS

Eighty adults, mean age 24.5, were selected for the study. Laser-scanned images of the subjects were obtained under a reproducible and controlled environment with two Minolta Vivid 900 (Osaka, Japan) optical laser-scanning devices assembled as a stereo-pair. A set of left and right scanned images was taken for each subject and each scan took an average of 2.5 s. These scanned images were processed and merged to form a composite three-dimensional soft tissue reproduction of the subjects using commercially available reverse modelling software. The differences in facial morphology were measured using shell deviation colour maps. The facial template was used to compare differences between males vs. females groups and two subjects with facial disproportions.

RESULTS

The difference between the male and female facial templates was 1.28 +/- 1.02 mm. The areas of greatest deviation were at the nasal, zygomatic area and lower jaw line. The results of the surface deviation maps between the templates and subjects with facial disproportion showed that the results could be applied for orthodontic diagnosis.

CONCLUSIONS

The construction of the adult facial templates provides an interesting perspective into measuring changes in groups of patients and also acts as a useful template for the comparison of skeletal disproportion.