Initial simulated FFR investigation using flow measurements in patient-specific 3D printed coronary phantoms

Abstract

Purpose Accurate patient-specific phantoms for device testing or endovascular treatment planning can be 3D printed. We expand the applicability of this approach for cardiovascular disease, in particular, for CT-geometry derived benchtop measurements of Fractional Flow Reserve, the reference standard for determination of significant individual coronary artery atherosclerotic lesions. Materials and Methods Coronary CT Angiography (CTA) images during a single heartbeat were acquired with a 320×0.5mm detector row scanner (Toshiba Aquilion ONE). These coronary CTA images were used to create 4 patient-specific cardiovascular models with various grades of stenosis: severe, <75% (n=1); moderate, 50–70% (n=1); and mild, <50% (n=2). DICOM volumetric images were segmented using a 3D workstation (Vitrea, Vital Images); the output was used to generate STL files (using AutoDesk Meshmixer), and further processed to create 3D printable geometries for flow experiments. Multi-material printed models (Stratasys Connex3) were connected to a programmable pulsatile pump, and the pressure was measured proximal and distal to the stenosis using pressure transducers. Compliance chambers were used before and after the model to modulate the pressure wave. A flow sensor was used to ensure flow rates within physiological reported values. Results 3D model based FFR measurements correlated well with stenosis severity. FFR measurements for each stenosis grade were: 0.8 severe, 0.7 moderate and 0.88 mild. Conclusions 3D printed models of patient-specific coronary arteries allows for accurate benchtop diagnosis of FFR. This approach can be used as a future diagnostic tool or for testing CT image-based FFR methods.

Initial evaluation of three-dimensionally printed patient-specific coronary phantoms for CT-FFR software validation

“…Previous conference proceedings from this study have shown the significant impact of distal resistance on the measured FFR values. 25 Simulation of the capillary bed effect on flow is not possible with the current 3D printing technologies; while 3D printing resolution would allow creation of very fine structures, removal of support material would be very challenging. Hence, distal resistance can be simulated within reasonable ranges by controlling the diameter of the outflow tubes with mechanical clamps for each coronary artery.…”

“…25 These two flow controls were adjusted in conjunction until pressure within the aorta reached a minimum of 80 mmHg to ensure physiological accuracy. 22,25,26 Previous in vitro studies using idealized 3D printed coronary phantoms have indicated a dependence on FFR with increasing aortic pressure, making this adjustment in the 3D printed phantoms a necessary step toward replicating physiological conditions. 16 Figure 4(a) shows the setup of the phantoms within the flow loop and Fig.…”

3D printed cardiovascular patient specific phantoms used for clinical validation of a CT-derived FFR diagnostic software

“…FFR measures blood flow conditions by invasively navigating a pressure wire through the artery and reading out a ratio of the pressure both proximal and distal to the stenosis. 3,4 This method allows for lesions of intermediate stenosis to be better analyzed with regards to hemodynamics. Typically, a threshold FFR ratio of 0.8 determines whether or not a stent will be used to treat the stenosis.…”

“…Geometry extension and inclusion of pathologies such as atherosclerotic plaques or surrounding anatomical structures gives rise to 3D printed models in which flow measurements can be accurately tested 4 . This study leverages 3D printing to build patient specific phantoms that closely mimic the arterial wall mechanics as a validation tool for a diagnostic software.…”

“…5 For each patient we 3D printed a phantom 2–9 which was used in a benchtop simulation where flow conditions were measured with high accuracy using flow and pressure sensors. 4 …”