Institute of Medical Technology, Hamburg University of Technology, Hamburg, 21073, Germany.
Section for Biomedical Imaging, University Medical Center Hamburg-Eppendorf, Hamburg, 20246, Germany.
Med Phys. 2019 Mar;46(3):1371-1383. doi: 10.1002/mp.13388. Epub 2019 Feb 14.
PURPOSE: Intravascular optical coherence tomography (IVOCT) is a catheter-based image modality allowing for high-resolution imaging of vessels. It is based on a fast sequential acquisition of A-scans with an axial spatial resolution in the range of 5-10 μm, that is, one order of magnitude higher than in conventional methods like intravascular ultrasound or computed tomography angiography. However, position and orientation of the catheter in patient coordinates cannot be obtained from the IVOCT measurements alone. Hence, the pose of the catheter needs to be established to correctly reconstruct the three-dimensional vessel shape. Magnetic particle imaging (MPI) is a three-dimensional tomographic, tracer-based, and radiation-free image modality providing high temporal resolution with unlimited penetration depth. Volumetric MPI images are angiographic and hence suitable to complement IVOCT as a comodality. We study simultaneous bimodal IVOCT MPI imaging with the goal of estimating the IVOCT pullback path based on the 3D MPI data. METHODS: We present a setup to study and evaluate simultaneous IVOCT and MPI image acquisition of differently shaped vessel phantoms. First, the influence of the MPI tracer concentration on the optical properties required for IVOCT is analyzed. Second, using a concentration allowing for simultaneous imaging, IVOCT and MPI image data are acquired sequentially and simultaneously. Third, the luminal centerline is established from the MPI image volumes and used to estimate the catheter pullback trajectory for IVOCT image reconstruction. The image volumes are compared to the known shape of the phantoms. RESULTS: We were able to identify a suitable MPI tracer concentration of 2.5 mmol/L with negligible influence on the IVOCT signal. The pullback trajectory estimated from MPI agrees well with the centerline of the phantoms. Its mean absolute error ranges from 0.27 to 0.28 mm and from 0.25 mm to 0.28 mm for sequential and simultaneous measurements, respectively. Likewise, reconstructing the shape of the vessel phantoms works well with mean absolute errors for the diameter ranging from 0.11 to 0.21 mm and from 0.06 to 0.14 mm for sequential and simultaneous measurements, respectively. CONCLUSIONS: Magnetic particle imaging can be used in combination with IVOCT to estimate the catheter trajectory and the vessel shape with high precision and without ionizing radiation.
目的：血管内光学相干断层扫描（IVOCT）是一种基于导管的成像方式，可实现血管的高分辨率成像。它基于快速顺序采集 A 扫描，轴向空间分辨率在 5-10μm 范围内，即比传统方法（如血管内超声或计算机断层血管造影）高一个数量级。然而，仅从 IVOCT 测量中无法获得导管在患者坐标系中的位置和方向。因此，需要建立导管的位置来正确重建三维血管形状。磁粒子成像（MPI）是一种三维层析成像、示踪剂和无辐射的成像方式，具有高时间分辨率和无限穿透深度。容积 MPI 图像是血管造影图像，因此适合作为 IVOCT 的组合模态。我们研究了同时进行双模态 IVOCT-MPI 成像，目的是基于 3D-MPI 数据来估计 IVOCT 拉回路径。
方法：我们提出了一种用于研究和评估不同形状血管模型的同时 IVOCT 和 MPI 图像采集的设置。首先，分析 MPI 示踪剂浓度对 IVOCT 所需光学特性的影响。其次，使用允许同时成像的浓度，依次和同时采集 IVOCT 和 MPI 图像数据。第三，从 MPI 图像体积中建立管腔中心线，并用于估计 IVOCT 图像重建的导管拉回轨迹。将图像体积与模型的已知形状进行比较。
结果：我们能够确定 2.5mmol/L 的合适 MPI 示踪剂浓度，对 IVOCT 信号的影响可以忽略不计。从 MPI 估计的拉回轨迹与模型的中心线吻合良好。其平均绝对误差范围分别为 0.27 至 0.28mm 和 0.25mm 至 0.28mm，分别用于顺序和同时测量。同样，重建血管模型的形状也具有良好的效果，直径的平均绝对误差范围分别为 0.11 至 0.21mm 和 0.06 至 0.14mm，分别用于顺序和同时测量。
结论：MPI 可与 IVOCT 结合使用，以高精度且无电离辐射的方式估计导管轨迹和血管形状。
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