Development of a patient-specific modular vascular phantom with clinically relevant mechanical properties. Academic Year:

Transcription

1 Development of a patient-specific modular vascular phantom with clinically relevant mechanical properties Student: Supervisor: Co-Supervisor: Prof. Elena De Momi Dr. Helge Wurdemann Academic Year:

2 Cardiovascular Diseases Introduction Average life expectancy reached 80.5 years in 2013 (OECD, 2015) 15% of population aged over 65 years in 2010 expected to grow up to 27% in 2050 Cardiovascular diseases remain the main cause of mortality in OECD countries They represent the highest share of inpatient expenditure in hospitals The global cardiovascular market is projected to grow with a Compound Annual Grow Rate of 6.6% (Grandviewresearch, 2016) Need of new devices able to reduce hospitalization costs and patient recovery time 15% Aged over 65 $33bn Cardiovascular device market value in % Up to 80.5 y.o. 18% of hospital inpatient expenditure in 2015 of deaths in

3 Device validation procedure Introduction Discovery + Ideation Researchers test the prototypes in controlled laboratory settings refining it aiming at reducing risk of harm in people In vivo In vitro Invention + Prototyping Clinical Trials x They are usually expensive x They require ethical approval x Animal-specific conditions Complete animal anatomy Can be cost-efficient Do not require ethical approval Controllable and repeatable x Usually simplified models Product on market Need for human-like in vitro models which can be able to mimic patientspecific conditions and are physiologically shaped (Sulaiman et al., 2008) 3

4 Vascular phantoms: a review Introduction Use: In-vitro device testing Particle Image Velocimetry (PIV) Training and rehearsal purposes Manufacturing: Rigid or flexible materials Idealised or patient-specific morphologies 3D Printing or traditional processes Aortic Rigid Flexible arch patient-specific and phantom descending of aortic tortuous aorta arch 3D aneurysm printed with for endovascular HeartPrint stenting procedure Flex repair and used for testing a Intravascular surgery simulation (Sulaiman Ultrasound (Peerin et al., Catheter 2008) al., (Poorten 2016). et al., 2016). 4

5 Aim and objectives Objectives Development of a vascular phantom environment according to Kbasnytsia et al., 2016 Patient specific data Good transparency Cost-effective MR Compatibility Human-like distensibility Hard-wearing materials The phantom will be used at UCL for early-stage test of a new 2-DOFs catheter 5

6 The workflow 3D Reconstruction Phantom design Material evaluation Validation protocols 6

7 3D Reconstruction Methods Imaging High quality Compute Tomography (CT) angiography: Contrast agent allows highlighting of the blood vessels. 3D Reconstruction Refining Segmentation and 3D reconstruction (3D Slicer): ROI selection and cropping Segmentation 3D model generation STL mesh refining (Meshmixer, Autodesk): Undesired features removal 7

8 Materials Methods Materials TangoPlus FLX 930 (Shore 27A), Stratasys Ecoflex 00-30, Smooth-on Ecoflex 00-50, Smooth-on Dragon skin 00-30, Smooth-on Specimen preparation Tensile tests 3D Printable material using Polyjet technology, it needs support material Rubber-like silicones relying on traditional manufacturing procedures Material modelling Ogden Ogden Ogden Neo-Hookean Order i Coefficients Dragonskin µ i α i D i Eco-Flex µ i α i D i E E Eco-Flex µ i α i D i E E TangoPlus D 1 C 10 C UCL Internal Standards Cardiovascular Eng. Lab 8

9 Simulation-I Methods Geometry Hollow-tube model Cylindrical sector r α r = 13.4 [mm] α = 20 Variable thickness t ϵ (0.5; 5) [mm] t Materials TangoPlus FLX 930 [Neo-Hookean] Ecoflex [Ogden 2 nd order] Ecoflex [Ogden 2 nd order] Dragon skin [Ogden 3 rd order] P(1)= MPa= 80 mmhg; Boundary Conditions Load Longitudinal Displacement and Rotation Circumferential Displacement and Rotation Pressure on the internal surface P(2)= MPa = 120 mmhg 9

10 Simulation-II Methods Displacement Compliance= 2 [ If left to atmospheric pressure, all the materials experience too large deformations that would lead to non physiological conditions A constrained configuration must be adopted for the phantom where its displacement can be controlled also acting on the environment surrounding it 10

11 Manufacturing-I: The phantom Methods EcoFlex has been adopted to create the phantom with a human-like thickness of 2 mm Casting process Internal core External Mould +2 mm Editing Slicing Printing (PVA) Editing Splitting 11

12 Manufacturing-II: The hosting system Methods Valves Compliance chamber Silicone phantom ½ BSP Connections Connection Watertight acrylic box Floating in water 12

13 Validation protocols-i Methods Non-pulsatile validation Setup: Syringe pump Pressure sensor Procedure: Distensibility measure varying the level of water in the compliance chamber D= [ ] Compliance module 13

14 Results I Results Results of the non-pulsatile validation where the range of achievable compliance has been investigated. (Baeck) Compliance module Std [1/mmHg] [10-5 ] The achievable compliance has very high repeatability Increasing the size of the chamber higher values could be reached 14

15 Validation protocols-ii Methods Pulsatile validation HFR Camera Lumped resistance Compliance Systemic resistance Setup: Vivitro Pulse Duplicator HFR (50 fps) camera Catheter tip pressure sensor Throttle valve for lumped resistance Connection With Aortic aortic valve valve Chessboard for plane detection Ventricle Atrium Mitral valve 15 Procedure 10 cycles with 70 bpm H.R. 9 configurations Tracking algorithm for vessel deformation

16 Results II Results Results of the pulsatile validation for each configuration 16

17 Results II Results Resistance Pressure waveform for each configuration Compliance 17

18 Validation protocols-iii Methods MR Setup: 3T MR Scan Procedure: MR scans of the phantom were performed in an inflated (120 mmhg) and in a deflated condition (0 mmhg) 18

19 Results III Results MRI results of the phantom scan 1 st scan 2 nd scan Chemical shift artefacts can be attenuated with Fluid Attenuated Inversion Recovery (FLAIR) 19

20 Conclusion & Future work Discussion Future work Human like distensibility MR Compatibility Further advance this model to cover the entire morphology of the aorta in a modular manner. Include pathological conditions such as aneurysms and dissections. Other materials could be investigated as transparency might allow PIV studies. Patient specific data Thank you! Hard-wearing materials Cost-effective Good transparency 20