Development of a novel vascular phantom for navigation testing in interventional MRI

Purpose Interventional MRI offers the unique capability to steer catheters by creating a magnetic field near the catheter tip. Efficacy of MR guided navigation must be tested in vitro in vascular phantoms that mimic the in vivo environment. Previous vascular phantoms have shortcomings including lack of MRI compatibility, artifact creation, non-physiologic stiffness, and high frictional resistance that limits navigation capabilities. We sought to develop a vascular phantom from poly(vinyl) alcohol cryogel (PVA-C) that overcomes these limitations and provides a tool to test our magnetically-assisted remote control (MARC) endovascular catheter. Materials and Methods Design considerations for the phantom were as follows: MRI compatible, MR relaxation times similar to body tissues, smooth lumen that mimics vessel feel during navigation, compatible with flow, range of navigational difficulty, and the ability to accommodate 6 French catheters. Phantom Box Construction: To provide physiologically relevant vessel trajectories, multiple symmetric angles (30-90°) and diameters (3/16-7/8 in.) were designed from Delrin rods connected together and placed in an acrylic box. PVA-C was poured into the phantom box and cross-linked with freeze-thaw cycles. The rods were removed leaving pathways mimicking vessel lumens. PVA-C Process: A gel was created using a process previously outlined by Surry, et al. Sevol Grade 165 PVA powder (Sekisui Specialty Chemicals America, Dallas, TX) was used to create 500 ml 10% PVA-C. Four freeze-thaw cycle were performed on the gel. Images were obtained with a 1.5 T scanner using T1 and T2-weighted images, along with quantitative T1 and T2 measurements. Results T1 and T2 relaxation times (mean ± SD) for the PVA-C were 1195 ± 36 ms and 189 ± 5 ms. Radiographic T1 and T2 images of the test phantom will be shown. Conclusion The standard deviations show acceptable ranges for homogeneity, and the T1 and T2 values are in an acceptable range for tissue. These initial steps provide the foundation for a human-scale vascular phantom that can be used for testing navigation in our MARC endovascular catheter.