Bimodal intravascular volumetric imaging combining OCT and MPI

Abstract

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.

In-Vitro MPI-Guided IVOCT Catheter Tracking in Real Time for Motion Artifact Compensation

“…The illustrated results of the motion artifact profiles underline the need of a catheter tracking over time. In addition to the catheter tracking in 3D [7,10,34,35], the time synchronization of the IVOCT and MPI data leads to an optimized arrangement of OCT A-scans in 3D space. The DICE metrics and stenosis lengths in Tab.…”

In-Vitro MPI-guided IVOCT catheter tracking in real time for motion artifact compensation

“…We refer to two different methods as IVOCT catheter marker tracking (MT) and input parameter (IP) based volume reconstruction, respectively. For both reconstruction methods, the inner phantom wall is segmented in the IVOCT data using a semi-automatic algorithm [34,35,45]. Especially in the narrowed phantom parts, some manual corrections are applied.…”

“…The illustrated results of the motion artifact profiles underline the need of a catheter tracking over time. In addition to the catheter tracking in 3D [7,10,34,35], the time synchronization of the IVOCT and MPI data leads to an optimized arrangement of OCT Ascans in 3D space. The DICE metrics and stenosis lengths in Table 4 emphasize the relevant errors in case of the IP method.…”

“…Catheters and guide wires are coated with magnetic markers to track their position with MPI in real time [29][30][31][32][33]. The first bimodal experiments combining IVOCT and MPI are presented in [34,35]. The 3D vessel center line can be estimated from static MPI images.…”

Magnetic particle imaging for assessment of cerebral perfusion and ischemia

“…To overcome this challenge, several systems have been developed on a preclinical scale to combine MPI with anatomical imaging modalities like MRI or CT (Franke et al, 2016, 2020; Vogel, Lother, et al, 2014; Vogel, Markert, et al, 2019; Vogel, Rückert, et al, 2014). Due to the fast imaging speed, MPI can also be combined with optical coherence tomography (OCT) to provide intravenous tracer tracking and use this information to incorporate prior knowledge for the OCT image reconstruction (Griese et al, 2019; Latus et al, 2019).…”