To assess differences in flow through patient-specific total cavo-pulmonary connection (TCPC) models made with three different three-dimensional (3D) printing techniques using four-dimensional, flow-sensitive magnetic resonance imaging (4D flow MRI).The use of 3D printing to create patient-specific models is becoming more widely adopted, including complex congenital heart disease(1), as the technology becomes more ubiquitous and less expensive. There are now a variety of 3D printing techniques commercially available, including stereolithography (SLA), selective laser sintering (SLS), and fused deposition modeling (FDM). There are substantial differences between each of these technologies with respect to their printing resolution, material properties, and costs. The impact of different printing resolutions and material properties on quantitative 4D flow MRI measurements in TCPC are unknown. In this study, we compared in vitro 4D flow MRI measurements in three different models to determine if there are any significant differences between these methods.

Patient specific models: Three physical models of TCPC were created using 3D printing according to an IRB-approved and HIPAA-compliant protocol. The TCPC was segmented from images acquired as part of a clinical cardiac MRI study in MIMICs (Materialise, Leuven, Belgium). The segmented TCPC volume was saved in STL format and printed using either an SLS (DTM Sinterstation 2500CI ATC) or FDM (Makerbot Replicator) 3D printer (Figure 1). Two FDM models were printed and one was imaged as is with residual support material within the lumen of the model and one model treated with acetone to remove the support material and smooth the internal surfaces.

In vitro MRI: Polyethylene tubing was attached to the inlets and outlets of the TCPC and then connected to a perfusion pump (Stockert SIII Heart-Lung Machine). MRI was performed on a clinical 3T scanner (GE Discovery MR 750, Waukesha, WI) with a 32-channel phase array body coil. 4D flow MRI was performed with a 5-pt radial-undersampled technique (PC-VIPR with following parameters: FOV = 32 x 32 x 32 cm3, TR/TE = 5.5/2.3 ms, α = 15°, Venc = 150 cm/s, projection number ≈ 22000, 16 reconstructed cardiac time frames, scan time: 5 minutes 15 seconds. Each TCPC model was imaged separately secured in a saline bath as water was pumped through the TCPC models at four different flow rates (1, 2, 3, and 4 L/min), resulting in 12 4D flow MRI data sets.

Analysis: The 4D flow MRI data was segmented and quantified in Ensight (CEI, Inc., Apex, NC) (Figure 1). Flow (L/min) in the inferior vena cava (Fontan), superior vena cava (Glenn), left pulmonary artery (LPA), and right pulmonary artery (RPA) were quantified at each flow rate. Differences in flow in each of the regions of interest between the different models were calculated at each flow rate.

4D flow MRI data was successfully acquired at each flow rate in all three models. No significant differences in net flow measurements were observed (Figure 2). Differences in flow through the Fontan, Glenn, LPA, and RPA are summarized in the plots in Figures 3-5. Differences in net flow measured with 4D flow MRI in the different models ranged from -0.04 to 0.04 L/min. Although net flow was not significantly different between the different models, it is feasible that more complex hemodynamic parameters such as wall shear stress, pressure distributions, and energy dissipation could reveal more significant differences.The fact that measured flow rates through the Fontan, Glenn, LPA, and RPA of these three different 3D printed models were not different implies that creating patient specific models for future in vitro studies can be conducted using readily available and relatively inexpensive 3D printing technology. Future studies are required to determine if more complex hemodynamic parameters such as wall shear stress, pressure distributions, and energy dissipation reveal more significant differences between these additive manufacturing techniques.