  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 to 10 {\mu}m, i.e., 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 co-modality. We study
simultaneous bimodal IVOCT MPI imaging with the goal of estimating the IVOCT
pullback path based on the 3D MPI data. We present a setup to study and
evaluate simultaneous IVOCT and MPI image acquisition of differently shaped
vessel phantoms. First, the infuence 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 is
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. 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. (...)
