Walled vessel-mimicking phantom for ultrasound imaging using 3D printing with a water-soluble filament: design principle, fluid-structure interaction (FSI) simulation, and experimental validation

Abstract

The geometry and stiffness of a vessel are pertinent to blood dynamics and vessel wall mechanical behavior and may alter in diseased conditions. Ultrasound-based ultrafast Doppler (uDoppler) imaging and shear wave imaging (SWI) techniques have been extensively exploited for the assessment of vascular hemodynamics and mechanics. Their performance is conventionally validated on vessel-mimicking phantoms (VMPs) prior to their clinical use. Compared with commercial ones, customized VMPs are favored for research use because of their wider range of material properties, more complex lumen geometries, or wall structures. Fused deposition modeling (FDM) 3D printing technique with plastic filaments is a promising method for making VMPs with a complex vessel lumen. However, it may require a toxic solvent or a long dissolution time currently. In this paper, we present a safe, efficient and geometrically flexible method where FDM 3D printing with a water-soluble polyvinyl alcohol (PVA) filament is exploited to fabricate a walled three-branch VMP (VMP-I). As a key step in fabrication, to avoid dissolution of the PVA-printed vessel core by the solution of the tissue-mimicking material, paraffin wax was used for isolation. Paraffin wax is easy to coat (i.e. without any special equipment), of satisfactory thickness (∼0.1 mm), chemically stable, and easy to remove after fabrication, thus making the proposed method practicable for ultrasound imaging studies. VMP-I was examined by B-mode imaging and power Doppler imaging (PDI) to verify complete dissolution of PVA-printed vessel core in its lumen, confirming good fabrication quality. The flow velocities in VMP-I were estimated by uDoppler imaging with a −0.8% difference, and the shear wave propagation speeds for the same phantom were estimated by SWI with a −6.03% difference when compared with fluid-structure interaction (FSI) simulation results. A wall-less VMP of a scaled and simplified coronary arterial network (VMP-II) was additionally fabricated and examined to test the capability of the proposed method for a complex lumen geometry. The proposed fabrication method for customized VMPs is foreseen to facilitate the development of ultrasound imaging techniques for blood vessels.

Tissue mimicking materials for imaging and therapy phantoms: a review

“…The 3D printed models were embedded in 6% gelatin and imaged using pulsed wave imaging (Cloonan et al 2014). Vessel mimicking phantoms have also been constructed by 3D printing water-soluble PVA filament vessel cores which were coated in paraffin wax before being encased in PVAc (Dong et al 2020). The vessel core was then be dissolved after the PVAc had undergone the appropriate FT cycles to create a walled vessel-mimicking phantom.…”

Patient-Specific Polyvinyl Alcohol Phantom Fabrication with Ultrasound and X-Ray Contrast for Brain Tumor Surgery Planning

“…If this step is missed and hot PVA-c is added to the molds, it can cause the molds to melt or distort. It is also crucial that once the glass spheres are added (steps 5.1.2 – 5.1.4), the PVA-c is not left to sit for more than around 10 minutes; if left for a prolonged period of time, the glass spheres will settle to the bottom, and the resulting phantom will have inhomogeneous ultrasound contrast 29 . Once the glass spheres are added, the PVA-c must be added directly into the molds and placed into the freezer.…”

3D‐printed, patient‐specific intracranial aneurysm models: From clinical data to flow experiments with endovascular devices

“…Moreover, the additional coating can change the vessel's diameter (thickness of the wax layer ≈ 0.1 mm), which can become crucial for vessels with a diameter <2 mm (e.g., an increase in the diameter of 10%). 15 The second concept solely utilizes 3D printing. Here, (tube-like) models of the vasculature are created digitally and printed directly.…”

“…Moreover, toxic solvents such as chloroform 10 are often required to remove the inner core. It is possible to print a water‐soluble core, 14,15 although an additional wax coating is needed to prevent the vessel core from dissolving prematurely. Moreover, the additional coating can change the vessel's diameter (thickness of the wax layer ≈ 0.1 mm), which can become crucial for vessels with a diameter <2 mm (e.g., an increase in the diameter of 10%) 15 …”