17th International Symposium on Application of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, July 07 – 10, 2014

4.4.2

Endoscopic PIV and holography applied to the study of opaque vessels mechanics

L. Arévalo1, V. Palero1*, J. Lobera2, N. Andrés1, M P. Arroyo1

1: Dept. of Applied Physics, I3A-University of Zaragoza, Zaragoza, Spain 2: Centro Universitario de la Defensa de Zaragoza, Zaragoza, Spain

* correspondent author: palero@unizar.es

Keywords: Endoscopy, PIV, Digital Holography, Vascular Systems

In this work endoscopy and traditional fluid and solid mechanics measurement techniques have been combined for the study of opaque vessels characteristics. We propose the combination of well known measurement techniques such as high speed PIV and digital holography to obtain both fluid mechanics (flow velocity field) and solid mechanics (wall deformation) information in a model of a vessel using commercial endoscopes. We are going to explore different possibilities. A priori, the simplest technique to be implemented with endoscopes is PIV: the flow velocity can be obtained using PIV illumination and endoscopic image recording. Even more, one or two endoscopes can be set in a stereoscopic configuration, to measure the velocity inside an opaque vessel. Digital holography can be implemented combining endoscopic illumination and imaging. The reconstructed phase should provide information on the wall deformation while the reconstructed intensity should allow calculating the velocity field.

Endoscopic high speed PIV To combine PIV and endoscopy, an artroscope was used as the imaging system in a high speed PIV set-up. The central plane of the vein was illuminated with a laser sheet and the artroscope formed its image on a high speed camera sensor. The high speed system consists of a two-cavity New Wave Pegasus laser (λ = 527 nm, energy per pulse = 10 mJ at 1000 Hz), each cavity with maximum repetition rate of 10000 Hz. A Photron Fastcam SA2 camera was used for recording 12 bits PIV images at 1000 frames/s, (∆T= 1 ms). The camera sensor has 2048×2048 pixels (10mm pixel size). Images were recorded with�θ = 90º, where the image corresponds to a regular PIV image (vein longitudinal section) and with� θ = 40º. Figure 1a shows the image provided by the endoscope for� θ = 90º, where a small section of the vein is imaged (image magnification, M=1.14). The velocity vector map was obtained with the software Davis 7.2 from LaVision and can be observed in figure 1b. The vector color represents the velocity magnitude. The velocity field shows the typical parabolic profile corresponding to a viscous liquid moving along a pipe.

a) b) Fig. 1 a) PIV image recorded with the artroscope at 90º; b) Velocity vector map.

Figure 2a shows the vein image and the displacement vector map in pixels for� θ = 40º, where the perspective distortion can be appreciated. The image magnification is not constant, and changes along the image. In order to obtain the displacement and velocity in mm, the image has to be corrected as in stereoscopic PIV. Figure 2b shows the corrected image and displacement field.

a) b) Fig. 2 a) PIV image recorded with the artroscope at 40º. The displacement field in pixels is overlapped; b) Corrected image and velocity vector map.

Endoscopic digital holography Different experiments have been carried out combining

digital holography with endoscopy. Both the flow velocity and the vessel wall deformation have been analyzed using different endoscopes and vessel models, showing that endoscopic digital holography is a very promising technique.

Acknowledgments: Authors thank Spanish Ministerio de

Ciencia e Innovación and European Commission FEDER program (project DPI2010-20746-C03-03) and Gobierno de Aragón (Laser Optical Technology - T63- research group) for financial support.

References

Palero VR, Lobera J, Arroyo MP (2010) Three-component velocity field measurement in confined liquid flows with high-speed digital image plane holography, Exp Fluids 49:471-483. Arévalo L, Palero V, Lobera J, Arroyo MP (2012) Endoscopic digital holography for measuring flows in opaque vessels, Proc. SPIE 8413, Speckle 2012: V International Conference on Speckle Metrology, 84131B, doi:10.1117/12.977946 Arévalo L, Roche E, Palero V, Martínez MA, Arroyo MP (2013) PIV and digital holography for measuring blood flows and vessel wall dynamics Proc. SPIE 8785, 8th Iberoamerican Optics Meeting and 11th Latin American Meeting on Optics, Lasers, and Applications, 8785CY; doi:10.1117/12.2026222