(234i) The Phantom Generation of a Complex Nasal Geometry with Horizontal Cut for Lda Measurements

The validation of Computational Fluid Dynamic (CFD) simulations using the non-invasive flow measurement technique of Laser Doppler Anemometry (LDA) needs a model (phantom) that guarantees optical accessibility in order to result in the desired velocity vector field. The Region Of Interest (ROI) is the human nose based on a Computer Tomography (CT) dataset. Segmentation selects the relevant voxels for the breathing process (voxels with the smallest X-ray density = air) to create a 3D surface geometry [1] which is used for LDA as well as CFD.

Optical accessibility for LDA measurements is guaranteed by a transversal cut through the inferior turbinates as a part of the complex nasal structure, which is further on sealed by a glass pane to ensure appropriate airflow. Three reference points attached to the model allow aligning the LDA measurement system in a way that assures that both coordinate systems are identical.

For the investigation two models with different 3D printing systems are used: The first of which is Polyjet Connex 350 developed by Stratasys which features a spatial resolution within the range of micrometers – all cavities are filled with a support material. Second the PLA filament printer 3D20 by Dremel with a resolution of about 0.05 mm is used. The latter brings about the advantage that no support structures for the phantom are required. The defined research goal is to unveil the better suited printing system.

In order to remove the support material when using the Connex 350 created model coarse and easy accessible structures are cleared away by a water jet. However, nearly all important structures are hidden which makes a subsequent bath in an ultrasonic tank with 5% sodium hydroxide in water necessary. It should be mentioned that there is a critical point in time when fine and filigree structures begin to lose strength, requiring careful stoppage of the process in order to not harm the model.

The complete vanishing of all support material is controlled by LDA measurements of the cross-section on the inferior turbinate for both models. There is a higher velocity of about 7 m/s observed in the Polyjet model. Since flow rate is constant and velocity only depends on the crosssection, higher velocity results from still existing non-removable support material. The reason is the fulfillment of the continuity equation. Even though the 3D print with the higher resolution seems to be the preferred one, in this application the filament model is more suitable for the measurement.

The next steps are to evaluate all possible measurable regions to have good basis for the validation of CFD simulations.

[1] Newman, T. S., Yi, H., A survey of the marching cubes algorithm In: Computer Graphics, Vol. 30, Nr. 5, Oktober, p. 854-879, 2006.