Nonlinear Harmonic Distortion of Complementary Golay Codes.

Recent advances in electronics miniaturization have led to the development of low-power, low-cost, point-of-care ultrasound scanners. Low-cost systems employing simple bi-level pulse generation devices need only utilize binary phase modulated coded excitations to significantly improve sensitivity; however the performance of complementary codes in the presence of nonlinear harmonic distortion has not been thoroughly investigated. Through simulation, it was found that nonlinear propagation media with little attenuative properties can significantly deteriorate the Peak Sidelobe Level (PSL) performance of complementary Golay coded pulse compression, resulting in PSL levels of -62 dB using nonlinear acoustics theory contrasted with -198 dB in the linear case. Simulations of 96 complementary pairs revealed that some pairs are more robust to sidelobe degradation from nonlinear harmonic distortion than others, up to a maximum PSL difference of 17 dB between the best and worst performing codes. It is recommended that users consider the effects of nonlinear harmonic distortion when implementing binary phase modulated complementary Golay coded excitations.

Validity and reliability of metrics for translation of regional anaesthesia performance from cadavers to patients.

BACKGROUND: Our goal is to develop metrics that quantify the translation of performance from cadavers to patients. Our primary objective was to develop steps and error checklists from a Delphi questionnaire. Our second objective was to show that our test scores were valid and reliable. METHODS: Sixteen UK experts identified 15 steps conducive to good performance and 15 errors to be avoided during interscalene block on the soft-embalmed cadaver and patients. Thereafter, six experts and six novices were trained, and then tested. Training consisted of psychometric assessment, an anatomy tutorial, volunteer scanning, and ultrasound-guided needle insertion on a pork phantom and on a soft-embalmed cadaver. For testing, participants conducted a single interscalene block on a dedicated soft-embalmed cadaver whilst wearing eye tracking glasses. RESULTS: We developed a 15-step checklist and a 15-error checklist. The internal consistency of our steps measures were 0.83 (95% confidence interval [CI]: 0.78-0.89) and 0.90 (95% CI: 0.87-0.93) for our error measures. The experts completed more steps (mean difference: 3.2 [95% CI: 1.5-4.8]; P<0.001), had less errors (mean difference: 4.9 [95% CI: 3.5-6.3]; P<0.001), had better global rating scores (mean difference: 6.8 [95% CI: 3.6-10.0]; P<0.001), and more eye-gaze fixations (median of differences: 128 [95% CI: 0-288]; P=0.048). Fixation count correlated negatively with steps (r=-0.60; P=0.04) and with errors (r=0.64; P=0.03). CONCLUSIONS: Our tests to quantify ultrasound-guided interscalene nerve block training and performance were valid and reliable.

Enhanced Antibacterial and Antiadhesive Activities of Silver-PTFE Nanocomposite Coating for Urinary Catheters.

Catheter-associated urinary tract infection (CAUTI) presents a significant health problem worldwide and is associated with increased morbidity and mortality. Herein, a silver-polytetrafluoroethylene (Ag-PTFE) nanocomposite coating for catheters was developed via a facile wet chemistry method. Benefiting from the synergistic effect of Ag and PTFE, the as-prepared Ag-PTFE-coated catheter exhibited enhanced antibacterial and antiadhesive activities against two CAUTI-associated strains: E. coli WT F1693 and S. aureus F1557. Compared to the uncoated commercial silicone catheters and the Ag-coated catheters, the Ag-PTFE-coated catheters were able to reduce bacterial adhesion by up to 60.3% and 55.2%, respectively. The Ag-PTFE-coated catheters also exhibited strong antibiofilm activity, reducing biofilm coverage by up to 97.4% compared with the commercial silicone catheters. In an in vitro bladder model, the Ag-PTFE-coated catheter displayed excellent anti-infection efficacy against bacteriuria, extending the lifetime of silicone catheters from a mean of 6 days to over 40 days. The Ag-PTFE coating also showed good biocompatibility with fibroblast cells in culture, making it a prospective strategy to overcome current challenges in CAUTI.

Investigation of Ultrasound-Measured Flow Velocity, Flow Rate and Wall Shear Rate in Radial and Ulnar Arteries Using Simulation.

Parameters of blood flow measured by ultrasound in radial and ulnar arteries, such as flow velocity, flow rate and wall shear rate, are widely used in clinical practice and clinical research. Investigation of these measurements is useful for evaluating accuracy and providing knowledge of error sources. A method for simulating the spectral Doppler ultrasound measurement process was developed with computational fluid dynamics providing flow-field data. Specific scanning factors were adjusted to investigate their influence on estimation of the maximum velocity waveform, and flow rate and wall shear rate were derived using the Womersley equation. The overestimation in maximum velocity increases greatly (peak systolic from about 10% to 30%, time-averaged from about 30% to 50%) when the beam-vessel angle is changed from 30° to 70°. The Womersley equation was able to estimate flow rate in both arteries with less than 3% error, but performed better in the radial artery (2.3% overestimation) than the ulnar artery (15.4% underestimation) in estimating wall shear rate. It is concluded that measurements of flow parameters in the radial and ulnar arteries with clinical ultrasound scanners are prone to clinically significant errors.

A study of the effect of clinical washing decontamination process on corrosion resistance of Martensitic Stainless Steel 420.

Corrosion of surgical instruments provides a seat for contamination and prevents proper sterilisation, placing both patients and medical staff at risk of infection. Corrosion can also compromise the structural integrity of instruments and lead to mechanical failure in use. It is essential to understand the various factors affecting corrosion resistance of surgical instruments and how it can be minimised.This paper investigates the effect on corrosion resistance from the clinical washing decontamination (WD) process, specifically by studying the changes in surface roughness and Cr/Fe ratio. Results indicate that the WD process provides a positive effect on smooth polished samples, while a lesser positive effect was observed on rough reflection reduced samples.

Investigation of Ultrasound-Measured Flow Rate and Wall Shear Rate in Wrist Arteries Using Flow Phantoms.

The aim of this study was to evaluate the errors in measurement of volumetric flow rate and wall shear rate measured in radial and ulnar arteries using a commercial ultrasound scanning system. The Womersley equations were used to estimate the flow rate and wall shear rate waveforms, based on the measured vessel diameter and centerline velocity waveform. In the experiments, each variable (vessel depth, diameter, flow rate, beam-vessel angle and different waveform) in the phantom was investigated in turn, and its value was varied within a normal range while others were fixed at their typical values. The outcomes revealed that flow rate and wall shear rate were overestimated in all cases, from around 13% to nearly 50%. It is concluded that measurements of flow rate and wall shear rate in radial and ulnar arteries with a clinical ultrasound scanner are vulnerable to overestimation.

Quantitative assessment of Thiel soft-embalmed human cadavers using shear wave elastography.

INTRODUCTION: Thiel soft-embalmed human cadavers are increasingly being used as a model to train surgeons and anesthetists because they look and feel like patients. However, there is a need to validate quantitatively the tissue properties of this model. Thus, the main objective of this study was to measure the elasticity of tissue in the Thiel soft-embalmed cadaver, using results in the literature for human volunteers for comparison. MATERIALS AND METHODS: Two independent ultrasound-trained operators measured the elasticity (Youngs modulus), E, of the thyroid, parotid and submandibular glands, the gastrocnemius and masseter muscles and the supraspinatus tendon in six Thiel soft-embalmed human cadavers using quantitative shear wave elastography. Each measurement was repeated 10 times. The elasticity values of Thiel soft-embalmed human cadavers were compared with human values reported in the literature. The relationship between elasticity and gender, age at death and number of days after embalming was also investigated. RESULTS: Elasticity data for the cadavers displayed similar patterns as in the literature for human volunteers. The results show a positive correlation between Young's modulus (YM) and time after embalming, but no correlation with cadaver age at death or gender. CONCLUSIONS: The stiffness of the Thiel embalmed soft cadaver was validated against historical human data, confirming the life-like quality of the cadavers. Our results indicate that shear wave elastography is a promising tool to evaluate the stiffness of Thiel embalmed soft cadavers.

Comparison of vortical structures induced by arteriovenous grafts using vector Doppler ultrasound.

Arteriovenous prosthetic grafts are used in hemodialysis. Stenosis in the venous anastomosis is the main cause of occlusion and the role of local hemodynamics in this is considered significant. A new spiral graft design has been proposed to stabilize the flow phenomena in the host vein. Cross-flow vortical structures in the outflow of this graft were compared with those from a control device. Both grafts were integrated in identical in-house ultrasound-compatible flow phantoms with realistic surgical configurations. Constant flow rates were applied. In-plane 2-D velocity and vorticity mapping was developed using a vector Doppler technique. One or two vortices were detected for the spiral graft and two to four for the control, along with reduced stagnation points for the former. The in-plane peak velocity and circulation were calculated and found to be greater for the spiral device, implying increased in-plane mixing, which is believed to inhibit thrombosis and neo-intimal hyperplasia.

Elastic properties of Thiel-embalmed human ankle tendon and ligament.

Thiel embalming is recommended as an alternative to formalin-based embalming because it preserves tissue elasticity, color, and flexibility in the long term, with low infection and toxicity risk. The degree to which Thiel embalming preserves elasticity has so far been assessed mainly by subjective scoring, with little quantitative verification. The aim of this study is to quantify the effect of Thiel embalming on the elastic properties of human ankle tendons and ligament. Biomechanical tensile tests were carried out on six Thiel-embalmed samples each of the peroneus longus, peroneus brevis, and calcaneal tendons, and the calcaneofibular ligament, with strain rates of 0.25%s(-1), 2%s(-1), and 8%s(-1). The stress-strain relationship was calculated from the force-extension response with cross-sectional area and gauge length. Young's modulus was determined from the stress-strain curve. The results showed that the tendon and ligament elasticity were lower after Thiel embalming than the literature values for fresh nonembalmed tendons and ligament. The biomechanical tensile test showed that the measured elasticity of Thiel-embalmed tendons and ligaments increased with the strain rate. The Thiel embalming method is useful for preserving human ankle tendons and ligaments for anatomy and surgery teaching and research, but users need to be aware of its softening effects. The method retains the mechanical strain rate effect on tendons and ligament.

Secondary flow in peripheral vascular prosthetic grafts using vector Doppler imaging.

Prosthetic grafts are used for the treatment of peripheral arterial disease. Re-stenosis in the distal anastomosis of these grafts is a common reason for graft occlusion. The role of local hemodynamics in development of neo-intimal hyperplasia is well known. A new graft design has been proposed for the induction of optimized spiral flow in the host vessel. The secondary flow motions induced by this graft were compared with those of a control device. Both types of grafts were connected with vessel mimic and positioned in ultrasound flow phantoms with identical geometry. Constant flow rates were applied. Data collected in the cross-sectional view distal from the graft outflow and dual-beam vector Doppler was applied to create 2-D velocity maps. A single-spiral flow pattern was found for the flow-modified graft, and double or triple spirals for the control graft. In-plane maximum velocity was greater for the flow-modified graft than for the control device.

Echogenic regional anaesthesia needles: a comparison study in Thiel cadavers.

Ultrasound guidance is now the standard procedure for regional nerve block in anesthesiology. However, ultrasonic visualisation of needle manipulation and guidance within tissues remains a problem. Two new echogenic needles (Pajunk and Braun) have been introduced to anesthesiology clinical practice but evaluation has been restricted to preserved animal tissue. In this study, the visibility of both echogenic needles was compared with a standard nonechogenic needle in a Thiel cadaver model. A total of 144 intramuscular injections were made in the upper arm in-plane and out-of-plane to the ultrasound beam at four angles (30°, 45°, 60° and 75°). The visibility of the needle was assessed by two independent, blinded observers using a 5-point Likert ordinal scale. Weighted κ for interobserver agreement was 0.77 (95% confidence interval [CI]: 0.68-0.86). The Pajunk echogenic needle was more visible than the Braun standard needle in-plane (p = 0.04), and the Braun standard and Braun echogenic needles out-of-plane (p = 0.02). Independent predictors of visibility using logistic regression were needle (p < 0.001) and plane of insertion (p = 0.08), receiver operator characteristic (ROC) area under the curve 0.90. In conclusion, the Pajunk echogenic needle offers the best visibility for ultrasound-guided regional anesthesia.

The development of therapeutic ultrasound with assistance of robotic manipulator.

High Intensity Focused Ultrasound (HIFU) is finding increasing application and acceptance as a non-invasive approach to the treatment of targeted malignancy. Despite the wealth of research and interest in HIFU, there are still a number of issues that need to be overcome to extend its clinical applications. These relate to the accuracy of placing the HIFU beam, the ability to visualize the target volume, and the understanding of the beam interaction with tissue. In this paper, the output characteristics of a single element HIFU transducer have been investigated with the assistance of a six-axis modified industrial robot. It is shown in the experimental results that clearly defined thermal or mechanical damage can be produced by changing the parameters of the HIFU. The nature and patterns of damage produced by pre-programmed treatment are now being investigated in tissue.