Fabrication of rigid and flexible refractive-index-matched flow phantoms for flow visualisation and optical flow measurements

Abstract

A method for the construction of both rigid and compliant (flexible) transparent flow phantoms of biological flow structures, suitable for PIV and other optical flow methods with refractive-index-matched working fluid is described in detail. Methods for matching the in vivo compliance and elastic wave propagation wavelength are presented. The manipulation of MRI and CT scan data through an investment casting mould is described. A method for the casting of bubble-free phantoms in silicone elastomer is given. The method is applied to fabricate flexible phantoms of the carotid artery (with and without stenosis), the carotid artery bifurcation (idealised and patient-specific) and the human upper airway (nasal cavity). The fidelity of the phantoms to the original scan data is measured, and it is shown that the cross-sectional error is less than 5% for phantoms of simple shape but up to 16% for complex cross-sectional shapes such as the nasal cavity. This error is mainly due to the application of a PVA coating to the inner mould and can be reduced by shrinking the digital model. Sixteen per cent variation in area is less than the natural patient to patient variation of the physiological geometries. The compliance of the phantom walls is controlled within physiologically realistic ranges, by choice of the wall thickness, transmural pressure and Young's modulus of the elastomer. Data for the dependence of Young's modulus on curing temperature are given for Sylgard 184. Data for the temperature dependence of density, viscosity and refractive index of the refractiveindex-matched working liquid (i.e. water-glycerol mixtures) are also presented.

A review of solid–fluid selection options for optical-based measurements in single-phase liquid, two-phase liquid–liquid and multiphase solid–liquid flows

“…Flexibility makes silicone rubbers particularly useful for compliant models of flows through flexible structures or membrane-like tissues, e.g., in RIM models for bloodflow experiments and, as a result, have been frequently employed in such systems (Duncan et al 1990;Perktold et al 1997;Bale-Glickman et al 2003;Burgmann et al 2009;Shuib et al 2010;Yousif et al 2010;Gülan et al 2012;Pielhop et al 2012;Geoghegan et al 2012;Im et al 2013;Kefayati and Poepping 2013). Sylgard 184, manufactured by Dow Corning, has been identified as a silicone rubber of particularly interest (Duncan et al 1990;Perktold et al 1997;Hopkins et al 2000;Yousif et al 2010;Shuib et al 2010;Buchmann et al 2010Buchmann et al , 2011Geoghegan et al 2012 andKefayati andPoepping 2013). Although a common choice, Hopkins et al (2000) cautioned that the effects of mixing and curing on Sylgard 184 can result in RI variations between models, and the care must, therefore, be taken in matching liquid RIs to individual models.…”

Application of a meta-analysis of aortic geometry to the generation of a compliant phantom for use in particle image velocimetry experimentation

“…The flow field may not necessarily use the same type of working fluid, however, good experimental setups will ensure that common Reynolds and Womersley numbers are used (Geoghegan et al 2012). Rapid prototyping a mould and casting silicone is an option (Biglino et al 2013;Geoghegan et al 2012). For the printing process idealised geometry can be produced from data in literature or patient-specific CT or MRI scans can be used to generate highly accurate moulds that are representative of the patient.…”

Experimental investigations of the steady flow through an idealized model of a femoral artery bypass

“…We should mention here that in conformity to [9], besides complying with the conditions imposed by ensuring geometrical similitude, the models suitable for PIV measurements must comply with two specific conditions. Thus, the material of which the model is made must be optically transparent and have a refraction index that can be easily matched to that of the working fluid.…”

“…This statement is justified if one takes into account the fact that the magnitude of WSS is proportional to the velocity gradient near the wall and that accurate measurements of the velocities close to the wall, especially when it is curved, is one of the most challenging task in PIV investigations. Some particular aspects of this kind of measurement, such as avoiding the distortion and the refraction at the walls, results in special conditions that the anastomosis models and the experimental setup should comply with [9].…”