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

Abstract

We developed three-dimensionally (3D) printed patient-specific coronary phantoms that are capable of sustaining physiological flow and pressure conditions. We assessed the accuracy of these phantoms from coronary CT acquisition, benchtop experimentation, and CT-FFR software. Five patients with coronary artery disease underwent 320-detector row coronary CT angiography (CCTA) (Aquilion ONE, Canon Medical Systems) and a catheter lab procedure to measure fractional flow reserve (FFR). The aortic root and three main coronary arteries were segmented (Vitrea, Vital Images) and 3D printed (Eden 260V, Stratasys). Phantoms were connected into a pulsatile flow loop, which replicated physiological flow and pressure gradients. Contrast was introduced and the phantoms were scanned using the same CT scanner model and CCTA protocol as used for the patients. Image data from the phantoms were input to a CT-FFR research software (Canon Medical Systems) and compared to those derived from the clinical data, along with comparisons between image measurements and benchtop FFR results. Phantom diameter measurements were within 1 mm on average compared to patient measurements. Patient and phantom CT-FFR results had an absolute mean difference of 4.34% and Pearson correlation of 0.95. We have demonstrated the capabilities of 3D printed patient-specific phantoms in a diagnostic software.

Keywords: CT-FFR; blood flow simulations; coronary CT angiography; coronary phantoms; patient specific 3D printed phantoms.

Figures

Fig. 1

Five key steps in phantom design process, starting with CT angiography images from the patient, segmentation of the desired geometry, simplifying and smoothing of vasculature, designing a support for the vasculature and appending it, then finally 3D printing the phantom.

Fig. 2

Waveform used with the CompuFlow 1000 programmable pulsatile pump.

Fig. 3

Overview of key components of flow loop for experimentation. Blue arrows represent the direction of flow.

Fig. 4

Benchtop setup of 3D printed patient-specific phantoms. (a) Phantoms in established flow loop with programmable pulsatile pump with pressure sensors attached and (b) phantom, outlined in red, in Aquilion ONE scanner for CCTA scans.

Fig. 5

CCTA images for case #3. Patient (a) CCTA of LCX and (b) phantom CCTA images of LCX.

Fig. 6

(a) Segmented patient and (b) phantom CCTA images in Mimics Research, centerline shown in red. In the phantoms, only the main arteries (LAD, LCX, and RCA) were maintained. Measurement of tortuosity in (c) patient and (d) phantom.

Fig. 7

CT-FFR software utilized for this research, patient data. Viewing imported images from 70% to 99% R-R and selecting the phase with the least amount of motion as the target phase (top image). Generation of centerline and contours (bottom left image). CT-FFR measurement with user control for distal measurement location indicated (bottom right image).

Fig. 8

Comparison of all measurements between patient and phantom images, (a) minimum diameter, (b) maximum diameter, (c) best fit diameter, (d) cross-sectional area, and (e) tortuosity. A line of unity is included in all graphs to show the ideal comparison.

Fig. 9

Comparison of all CT-FFR results for both the phantom and the patient.