A Multilayer Monte Carlo Model for the Investigation of Optical Path and Penetration Depth at Different Perfusion States of the Colon

There is a great interest in monitoring the oxygen supply delivered to the colon. Insufficient oxygen delivery may lead to hypoxia, sepsis, multiorgan dysfunction and death. For assessing colonic perfusion, more information and understanding is required relating to the light-interaction within the colonic tissue. A multilayer Monte Carlo model of a healthy human colon has been developed to investigate the light-tissue behavior during different perfusion states within the mucosal layer of the colon. Results from a static multilayer model of optical path and reflectance at two wavelengths, 660 nm and 880 nm, through colon tissue, containing different volume fractions of blood with a fixed oxygen saturation are presented. The effect on the optical path and penetration depth with varying blood volumes within the mucosa for each wavelength has been demonstrated. The simulation indicated both wavelengths of photons penetrated similar depths, entering the muscularis layer

Development of an intraluminal intestinal photoplethysmography sensor

Intestinal ischemia is a serious medical condition and can lead to life threatening sepsis. Currently, there are no reliable techniques available for directly monitoring intestinal viability for prolonged periods of time, and intraoperatively, the majority of the surgeons still rely on subjective methods, such as visual inspection to assess viability of the intestine. The development of an intraluminal optical sensor for monitoring intestinal viability is being proposed. The sensor will continuously monitor changes in blood volume and oxygen saturation. The developed reflectance photoplethysmography/pulse oximetry sensor comprises of two emitters (red and infrared) and a photodiode. A photoplethysmography processing and data acquisition system was also utilized. The prototype sensor was evaluated in a pilot study in the buccal mucosa of 12 healthy volunteers, given the locations similarity to the intestinal mucosa and its easy accessibility. Good quality photoplethysmography signals with high signal-to-noise ratio were acquired from the buccal mucosa in all the volunteers. Preliminary blood oxygen saturation values from the intraluminal sensor were in broad agreement with the standard finger pulse oximeter probes

The effects of optical sensor-tissue separation in endocavitary photoplethysmography

Objective: Intestinal anastomotic failure that occurs mainly due to ischaemia is a serious risk in colorectal cancer patients undergoing surgery. Surgeons continue to rely on subjective methods such as visual inspection to assess intestinal viability during surgery and there are no clinical tools to directly monitor viability postoperatively. A dual-wavelength reflectance optical sensor has been developed for continuous and dynamic monitoring of intestinal viability via the intestinal lumen. Maintaining direct contact between the sensor and the inner intestinal wall can be difficult in an intraluminal design, therefore impacting on signal acquisition and quality. This paper investigates the effect of direct contact versus variable distances between the sensor and the tissue surface of the buccal mucosa as a surrogate. Approach: The in vivo study involved 20 healthy volunteers to measure the effect of optical sensor-tissue distances on the ability to acquire photoplethysmography signals and their quality. Signals were acquired from the buccal mucosa at five optical sensor-tissue distances. Main results: Distances between 0 mm (contact) to 5 mm were the most optimal, producing signals of high quality and signal-to-noise ratio, resulting in reliable estimations of the blood oxygen saturation. Distances exceeding 5 mm compromised the acquired signals, and were of poor quality, thereby unreliably estimating the blood oxygen saturation. Significance: The developed optical sensor proved to be reliable for acquiring photoplethysmography signals for cases where distances between the optical sensor-tissue may arise during the assessment of intraluminal intestinal viability

Approximated Computation of Belief Functions for Robust Design Optimization

This paper presents some ideas to reduce the computational cost of evidence-based robust design optimization. Evidence Theory crystallizes both the aleatory and epistemic uncertainties in the design parameters, providing two quantitative measures, Belief and Plausibility, of the credibility of the computed value of the design budgets. The paper proposes some techniques to compute an approximation of Belief and Plausibility at a cost that is a fraction of the one required for an accurate calculation of the two values. Some simple test cases will show how the proposed techniques scale with the dimension of the problem. Finally a simple example of spacecraft system design is presented.Comment: AIAA-2012-1932 14th AIAA Non-Deterministic Approaches Conference. 23-26 April 2012 Sheraton Waikiki, Honolulu, Hawai

Development of modelling method selection tool for health services management: from problem structuring methods to modelling and simulation methods.

BACKGROUND: There is an increasing recognition that modelling and simulation can assist in the process of designing health care policies, strategies and operations. However, the current use is limited and answers to questions such as what methods to use and when remain somewhat underdeveloped. AIM: The aim of this study is to provide a mechanism for decision makers in health services planning and management to compare a broad range of modelling and simulation methods so that they can better select and use them or better commission relevant modelling and simulation work. METHODS: This paper proposes a modelling and simulation method comparison and selection tool developed from a comprehensive literature review, the research team's extensive expertise and inputs from potential users. Twenty-eight different methods were identified, characterised by their relevance to different application areas, project life cycle stages, types of output and levels of insight, and four input resources required (time, money, knowledge and data). RESULTS: The characterisation is presented in matrix forms to allow quick comparison and selection. This paper also highlights significant knowledge gaps in the existing literature when assessing the applicability of particular approaches to health services management, where modelling and simulation skills are scarce let alone money and time. CONCLUSIONS: A modelling and simulation method comparison and selection tool is developed to assist with the selection of methods appropriate to supporting specific decision making processes. In particular it addresses the issue of which method is most appropriate to which specific health services management problem, what the user might expect to be obtained from the method, and what is required to use the method. In summary, we believe the tool adds value to the scarce existing literature on methods comparison and selection

The Effect of Prone and Supine Limb Positioning on the Radiographic Evaluation of Posterolateral Plate Fixation of the Posterior Malleolus.

AIM: To facilitate the posterolateral approach to the posterior malleolus patients are often positioned prone initially, then turned supine to complete fixation at the medial malleolus. We sought to define observed differences in the radiographic appearance of implants relative to the joint line, in prone and supine positions. METHODS: A 3.5 mm tubular plate and a 3.5 mm posterior distal tibial periarticular plate were applied sequentially to 3 individual cadaveric legs, via a posterolateral approach. The tubular plate was positioned to simulate buttress fixation and the posterolateral plate placed more distally. Each limb was secured on a custom jig and radiographs were taken on a mobile c-arm fluoroscopy machine with a calibration ball. A series of prone AP, supine PA and mortise radiographs were taken. Prone radiographs were also taken in different degrees of caudal tilt to simulate knee flexion which occurs in practice, during intraoperative positioning. Plate tip-joint line distances were measured and Mann-Whitney U tests performed. RESULTS: There was no statistically significant difference in plate tip-joint line distance when comparing equivalent prone and supine views (PA/AP or mortise). However, significant differences in apparent implant position were noted with alterations in caudal tilt. When taking a prone image, when the knee is flexed to 20 degrees, the plate tip will appear 6.5-8.5 mm more proximal than in the equivalent supine image where the knee is extended and the fluoroscopy beam is orthogonal to the anatomic axis of the tibia. CONCLUSION: Observed differences in radiographic appearance of metalwork in the prone and supine position are most likely due to knee flexion and the resulting variation in the angle of the fluoroscopy beam, rather than projectional differences between supine and prone views. Surgeons should be alert to this when analysing intraoperative images

Congenital genralized lipodystrophy in an Indian patient with a novel mutation in BSCL2 gene

peer reviewe

Computational Model Prediction and Biological Validation Using Simplified Mixed Field Exposures for the Development of a GCR Reference Field

The yield of chromosomal aberrations has been shown to increase in the lymphocytes of astronauts after long-duration missions of several months in space. Chromosome exchanges, especially translocations, are positively correlated with many cancers and are therefore a potential biomarker of cancer risk associated with radiation exposure. Although extensive studies have been carried out on the induction of chromosomal aberrations by low- and high-LET radiation in human lymphocytes, fibroblasts, and epithelial cells exposed in vitro, there is a lack of data on chromosome aberrations induced by low dose-rate chronic exposure and mixed field beams such as those expected in space. Chromosome aberration studies at NSRL will provide the biological validation needed to extend the computational models over a broader range of experimental conditions (more complicated mixed fields leading up to the galactic cosmic rays (GCR) simulator), helping to reduce uncertainties in radiation quality effects and dose-rate dependence in cancer risk models. These models can then be used to answer some of the open questions regarding requirements for a full GCR reference field, including particle type and number, energy, dose rate, and delivery order. In this study, we designed a simplified mixed field beam with a combination of proton, helium, oxygen, and iron ions with shielding or proton, helium, oxygen, and titanium without shielding. Human fibroblasts cells were irradiated with these mixed field beam as well as each single beam with acute and chronic dose rate, and chromosome aberrations (CA) were measured with 3-color fluorescent in situ hybridization (FISH) chromosome painting methods. Frequency and type of CA induced with acute dose rate and chronic dose rates with single and mixed field beam will be discussed. A computational chromosome and radiation-induced DNA damage model, BDSTRACKS (Biological Damage by Stochastic Tracks), was updated to simulate various types of CA induced by acute exposures of the mixed field beams used for the experiments. The chromosomes were simulated by a polymer random walk algorithm with restrictions to their respective domains in the nucleus [1]. The stochastic dose to the nucleus was calculated with the code RITRACKS [2]. Irradiation of a target volume by a mixed field of ions was implemented within RITRACKs, and the fields of ions can be delivered over specific periods of time, allowing the simulation of dose-rate effects. Similarly, particles of various types and energies extracted from a pre-calculated spectra of galactic cosmic rays (GCR) can be used in RITRACKS. The number and spatial location of DSBs (DNA double-strand breaks) were calculated in BDSTRACKS using the simulated chromosomes and local (voxel) dose. Assuming that DSBs led to chromosome breaks, and simulating the rejoining of damaged chromosomes occurring during repair, BDSTRACKS produces the yield of various types of chromosome aberrations as a function of time (only final yields are presented). A comparison between experimental and simulation results will be shown