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.

Low Shear Stress at Baseline Predicts Expansion and Aneurysm-Related Events in Patients With Abdominal Aortic Aneurysm.

Background: Low shear stress has been implicated in abdominal aortic aneurysm (AAA) expansion and clinical events. We tested the hypothesis that low shear stress in AAA at baseline is a marker of expansion rate and future aneurysm-related events.

Methods: Patients were imaged with computed tomography angiography at baseline and followed up every 6 months >24 months with ultrasound measurements of maximum diameter.

Association between erythrocyte dynamics and vessel remodelling in developmental vascular networks.

Sprouting angiogenesis is an essential vascularization mechanism consisting of sprouting and remodelling. The remodelling phase is driven by rearrangements of endothelial cells (ECs) within the post-sprouting vascular plexus. Prior work has uncovered how ECs polarize and migrate in response to flow-induced wall shear stress (WSS).

Spatiotemporal Dynamics of Dilute Red Blood Cell Suspensions in Low-Inertia Microchannel Flow.

Microfluidic technologies are commonly used for the manipulation of red blood cell (RBC) suspensions and analyses of flow-mediated biomechanics. To enhance the performance of microfluidic devices, understanding the dynamics of the suspensions processed within is crucial. We report novel, to our knowledge, aspects of the spatiotemporal dynamics of RBC suspensions flowing through a typical microchannel at low Reynolds number.

Biomechanical Assessment Predicts Aneurysm Related Events in Patients with Abdominal Aortic Aneurysm.

Objective: To test whether aneurysm biomechanical ratio (ABR; a dimensionless ratio of wall stress and wall strength) can predict aneurysm related events.

Methods: In a prospective multicentre clinical study of 295 patients with an abdominal aortic aneurysm (AAA; diameter ≥ 40 mm), three dimensional reconstruction and computational biomechanical analyses were used to compute ABR at baseline. Participants were followed for at least two years and the primary end point was the composite of aneurysm rupture or repair.

On the optimization of low-cost FDM 3D printers for accurate replication of patient-specific abdominal aortic aneurysm geometry.

Background: There is a potential for direct model manufacturing of abdominal aortic aneurysm (AAA) using 3D printing technique for generating flexible semi-transparent prototypes. A patient-specific AAA model was manufactured using fused deposition modelling (FDM) 3D printing technology. A flexible, semi-transparent thermoplastic polyurethane (TPU), called Cheetah Water (produced by Ninjatek, USA), was used as the flexible, transparent material for model manufacture with a hydrophilic support structure 3D printed with polyvinyl alcohol (PVA).

Wall Stress and Geometry of the Thoracic Aorta in Patients With Aortic Valve Disease.

Background: Aortic valve disease increases velocity and changes the way blood enters the aorta. Over time, the biomechanical environment can cause aortic remodelling. We hypothesized that aortic geometry and wall stress would be different in patients with aortic valve disease compared with controls.

Testing a new surfactant in a widely-used blood mimic for ultrasound flow imaging.

Background: A blood-mimicking fluid developed by Ramnarine et al. has been widely used in flow phantoms for ultrasound flow imaging research, and it has also been cited by IEC 61685 as a reference for making blood-mimicking fluid.However, the surfactant material Synperonic N in this blood-mimicking fluid recipe is phased out from the European market due to environmental issues.

Exploring the Biological and Mechanical Properties of Abdominal Aortic Aneurysms Using USPIO MRI and Peak Tissue Stress: A Combined Clinical and Finite Element Study.

Inflammation detected through the uptake of ultrasmall superparamagnetic particles of iron oxide (USPIO) on magnetic resonance imaging (MRI) and finite element (FE) modelling of tissue stress both hold potential in the assessment of abdominal aortic aneurysm (AAA) rupture risk. This study aimed to examine the spatial relationship between these two biomarkers. Patients (n = 50) > 40 years with AAA maximum diameters > = 40 mm underwent USPIO-enhanced MRI and computed tomography angiogram (CTA).

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.

Fabrication of Two Flow Phantoms for Doppler Ultrasound Imaging.

Flow phantoms are widely used in studies associated with Doppler ultrasound measurements, acting as an effective experimental validation system in cardiovascular-related research and in new algorithm/instrumentation development. The development of materials that match the acoustic and mechanical properties of the vascular system is of great interest while designing flow phantoms. Although recipes that meet the flow phantom standard defined by the International Electrotechnical Commission 61685 are already available in the literature, the standard procedure for material preparations and phantom fabrications has not been well established.

Nonlinear multiscale regularisation in MR elastography: Towards fine feature mapping.

Unlabelled: Fine-featured elastograms may provide additional information of radiological interest in the context of in vivo elastography. Here a new image processing pipeline called ESP (Elastography Software Pipeline) is developed to create Magnetic Resonance Elastography (MRE) maps of viscoelastic parameters (complex modulus magnitude |G| and loss angle ϕ) that preserve fine-scale information through nonlinear, multi-scale extensions of typical MRE post-processing techniques.

Methods: A new MRE image processing pipeline was developed that incorporates wavelet-domain denoising, image-driven noise estimation, and feature detection.

Patient-specific modelling of abdominal aortic aneurysms: The influence of wall thickness on predicted clinical outcomes.

Rupture of abdominal aortic aneurysms (AAAs) is linked to aneurysm morphology. This study investigates the influence of patient-specific (PS) AAA wall thickness on predicted clinical outcomes. Eight patients under surveillance for AAAs were selected from the MA(3)RS clinical trial based on the complete absence of intraluminal thrombus.

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.

Manufacturing of microcirculation phantoms using rapid prototyping technologies.

In this paper, we describe a method for the manufacturing of a microcirculation phantom that may be used to investigate hemodynamics using optics based methods. We made an Acrylonitrile Butadiene Styrene (ABS) negative mold, manufactured in a Fused Deposition Modelling (FDM) printer, embedded it in Polydimethysilioxane (PDMS) and dissolved it from within using acetone. We successfully made an enlarged three-dimensional (3D) network of microcirculation, and tested it using red blood cell (RBC) analogues.

Assessment of Spectral Doppler for an Array-Based Preclinical Ultrasound Scanner Using a Rotating Phantom.

Velocity measurement errors were investigated for an array-based preclinical ultrasound scanner (Vevo 2100, FUJIFILM VisualSonics, Toronto, ON, Canada). Using a small-size rotating phantom made from a tissue-mimicking material, errors in pulse-wave Doppler maximum velocity measurements were observed. The extent of these errors was dependent on the Doppler angle, gate length, gate depth, gate horizontal placement and phantom velocity.

MRI using ultrasmall superparamagnetic particles of iron oxide in patients under surveillance for abdominal aortic aneurysms to predict rupture or surgical repair: MRI for abdominal aortic aneurysms to predict rupture or surgery-the MA(3)RS study.

Introduction: Population screening for abdominal aortic aneurysms (AAA) halves the associated mortality and has led to the establishment of national screening programmes. Prediction of aneurysm growth and rupture is challenging and currently relies on serial diameter measurements with ultrasound. Recently, a novel MRI-based technique using ultrasmall superparamagnetic particles of iron oxide (USPIO) has demonstrated considerable promise as a method of identifying aneurysm inflammation and expansion.

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.

Wall-less flow phantom for high-frequency ultrasound applications.

There are currently very few test objects suitable for high-frequency ultrasound scanners that can be rapidly manufactured, have appropriate acoustic characteristics and are suitably robust. Here we describe techniques for the creation of a wall-less flow phantom using a physically robust konjac and carrageenan-based tissue-mimicking material. Vessel dimensions equivalent to those of mouse and rat arteries were achieved with steady flow, with the vessel at a depth of 1.

acoustic assessment of a konjac–carrageenan tissue-mimicking material aT 5–60 MHZ.

The acoustic properties of a robust tissue-mimicking material based on konjac–carrageenan at ultrasound frequencies in the range 5–60 MHz are described. Acoustic properties were characterized using two methods: a broadband reflection substitution technique using a commercially available preclinical ultrasound scanner (Vevo 770, FUJIFILM VisualSonics, Toronto, ON, Canada), and a dedicated high-frequency ultrasound facility developed at the National Physical Laboratory (NPL, Teddington, UK), which employed a broadband through-transmission substitution technique. The mean speed of sound across the measured frequencies was found to be 1551.

BMUS guidelines for the regular quality assurance testing of ultrasound scanners by sonographers.

Quality Assurance of ultrasound systems is necessary to ensure the reliability of results and to check for deterioration in performance; a number of bodies have produced guidelines. Testing has traditionally been the responsibility of Medical Physics Departments but the important role of sonographers has been recognised and recent publications have included tests to be performed by ultrasound users. Since there are differences in approach between these publications the BMUS QA Working Party was established to provide a consistent set of guidelines specifically for sonographers.

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.