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


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 refractive-index-matched working liquid (i.e. water–glycerol mixtures) are also presented.

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  1. The viscosity of water/glycerol is obtained using a HAAKE Viscometers Rotovisco© RV20 concentric cylinder viscometer.

  2. STL is a widely used file format for rapid prototyping and computer-aided design. It describes the unstructured triangulated surface by the unit normal and vertices of the triangles.

  3. Dow Corning SYLGARD® 184 Silicone Elastomer data sheet.

  4. Temperatures obtained with a Maxim DS19121G Thermochron® iButton® that has an accuracy of ±1°C and a resolution of 0.5°C.



Womersley number


Uniaxial strain

εθ :

Hoop strain


Propagation wavelength




Uniaxial stress


Kinematic viscosity


Angular frequency of the oscillation

A :

Cross-sectional area

B :

Dispersion coefficient


Computer-aided design


Carotid artery


Common carotid artery


Computational fluid dynamics


X-ray computed tomography

c 0 :

Propagation wave speed

d :


D :


E :

Young’s modulus


External carotid artery

F :



Fluid–structure interaction

h :

Wall thickness


Internal carotid artery

L, L 0 :

Vessel length


Laser doppler anemometry


Laser doppler velocimetry


Magnetic resonance imaging


Particle image velocimetry

N :

Index of refraction

P :



Polyvinyl acetate

Q :

Inlet flow rate

R :


Re :

Reynolds Number


Standard deviation

St :

Strouhal number



T :

Time period


Time of flight

U m :

Time-averaged mean inlet velocity


Wall shear stress


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We are grateful to Prof. Olaf Diegel of AUT for his advice and assistance in producing the 3D-printed cores, and to Mr Graeme Harris and the staff of the Department Of Mechanical Engineering workshop for technical support. NB and PHG carried out their parts of the work under UC Doctoral Scholarships, and CJS under an Enterprise scholarship supported by Fisher and Paykel Healthcare.

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Correspondence to M. Jermy.

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Geoghegan, P.H., Buchmann, N.A., Spence, C.J.T. et al. Fabrication of rigid and flexible refractive-index-matched flow phantoms for flow visualisation and optical flow measurements. Exp Fluids 52, 1331–1347 (2012).

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  • Particle Image Velocimetry
  • Nasal Cavity
  • Digital Model
  • Silicone Elastomer
  • Medical Imaging Data