Evaluation of cross-beam vector Doppler ultrasound systems for accurate 3-D velocity measurements

Vector Doppler ultrasound (VDUS) systems offer the potential for improved accuracy in mapping of complex flow parameters, such as recirculation, turbulence, and shear stress which are probable risk factors leading to vascular disease and stroke. Cross-beam VDUS systems were evaluated for velocity accuracy to optimize the number of receivers for the inter-beam angle, wall filter, system orientation, and complexity of flow seen in a stenosed carotid artery. Preliminary results for velocity estimation show promise for validation of numerical results. © 2012 IEEE.published_or_final_versio

Rapid prototyping compliant arterial phantoms for <it>in</it>-<it>vitro</it> studies and device testing

<p>Abstract</p> <p>Background</p> <p>Compliant vascular phantoms are desirable for <it>in</it>-<it>vitro</it> patient-specific experiments and device testing. TangoPlus FullCure 930® is a commercially available rubber-like material that can be used for PolyJet rapid prototyping. This work aims to gather preliminary data on the distensibility of this material, in order to assess the feasibility of its use in the context of experimental cardiovascular modelling.</p> <p>Methods</p> <p>The descending aorta anatomy of a volunteer was modelled in 3D from cardiovascular magnetic resonance (CMR) images and rapid prototyped using TangoPlus. The model was printed with a range of increasing wall thicknesses (0.6, 0.7, 0.8, 1.0 and 1.5 mm), keeping the lumen of the vessel constant. Models were also printed in both vertical and horizontal orientations, thus resulting in a total of ten specimens. Compliance tests were performed by monitoring pressure variations while gradually increasing and decreasing internal volume. Knowledge of distensibility was thus derived and then implemented with CMR data to test two applications. Firstly, a patient-specific compliant model of hypoplastic aorta suitable for connection in a mock circulatory loop for <it>in</it>-<it>vitro</it> tests was manufactured. Secondly, the right ventricular outflow tract (RVOT) of a patient necessitating pulmonary valve replacement was printed in order to physically test device insertion and assess patient’s suitability for percutaneous pulmonary valve intervention.</p> <p>Results</p> <p>The distensibility of the material was identified in a range from 6.5 × 10^-3 mmHg^-1 for the 0.6 mm case, to 3.0 × 10^-3 mmHg^-1 for the 1.5 mm case. The models printed in the vertical orientation were always more compliant than their horizontal counterpart. Rapid prototyping of a compliant hypoplastic aorta and of a RVOT anatomical model were both feasible. Device insertion in the RVOT model was successful.</p> <p>Conclusion</p> <p>Values of distensibility, compared with literature data, show that TangoPlus is suitable for manufacturing arterial phantoms, with the added benefit of being compatible with PolyJet printing, thus guaranteeing representative anatomical finishing, and quick and inexpensive fabrication. The appealing possibility of printing models of non-uniform wall thickness, resembling more closely certain physiological scenarios, can also be explored. However, this material appears to be too stiff for modelling the more compliant systemic venous system.</p

Characterisation of Elastic and Acoustic Properties of an Agar-Based Tissue Mimicking Material

As a first step towards an acoustic localisation device for coronary stenosis to provide a non-invasive means of diagnosing arterial disease, measurements are reported for an agar-based tissue mimicking material (TMM) of the shear wave propagation velocity, attenuation and viscoelastic constants, together with one dimensional quasi-static elastic moduli and Poisson’s ratio. Phase velocity and attenuation coefficients, determined by generating and detecting shear waves piezo-electrically in the range 300 Hz–2 kHz, were 3.2–7.5 ms−1 and 320 dBm−1. Quasi-static Young’s modulus, shear modulus and Poisson’s ratio, obtained by compressive or shear loading of cylindrical specimens were 150–160 kPa; 54–56 kPa and 0.37–0.44. The dynamic Young’s and shear moduli, derived from fitting viscoelastic internal variables by an iterative statistical inverse solver to freely oscillating specimens were 230 and 33 kPa and the corresponding relaxation times, 0.046 and 0.036 s. The results were self-consistent, repeatable and provide baseline data required for the computational modelling of wave propagation in a phantom