Using a highly integrated Magnetic Particle Imaging – Magnetic Resonance hybrid system, a dual-modal cardiovascular in vivo assessment in rodents under the usage of a non-toxic Resovist dosage. was performed successfully. The subject was imaged sequentially in both modality modes, whereas neither subject repositioning nor anesthesia interruption were required. Complementary datasets were acquired within a single seamless multi-modal study using ParaVison6 (Bruker BioSpin, Germany) allowing direct MRI-based MPI Field-of-View planning. After reconstructing time-resolved (TR=21.45 ms) 3D MPI images of the bolus-passage they were successfully fused with a high-resolution static 3D MRI dataset and visualized as combined 4D/3D hybrid dataset.Using alternatingly both modes of the highly integrated hybrid MPI-MRI scanner [3-4], an anesthetized rat (Lewis, 262 g body weight) was scanned (ParaVision6 software, Bruker BioSpin, Germany) sequentially: 1. Pre-injection MRI: Tri-planar low-resolution MRI scout scans (FLASH sequence) allowed matching the desired imaging region to the predefined static 3D MPI field-of-view (FOV). The 1st and 2nd order global shims were optimized for the final subject position using a FID-based algorithm including a re-adjustment of the basic frequency. Three orthogonal high spatial resolution MRI datasets (MSME, TE/TR=8.6/300 ms, matrix=128×128×9, FOV=50×50×27, BW=25 kHz, average=25, scan time=16 min,) were acquired. 2. MPI: One 20 µl bolus of undiluted Resovist (Bayer Schering Pharma AG, Germany) was administered manually into the tail vein during MPI data acquisition (ADFx,y,z=12 mT, GSFmax=2.2 T/m, BW=625 kHz, repetitions=30000). Only the bolus passage (repetition 130…350) was selected for MPI image reconstruction (ParaVision6, Kaczmarz iterative algorithm [6], background corrected raw data, AVG=1, 60 iterations, λ=8∙10-3, matrix=28×28×16, FOV=28×28×16 mm³). 3. Post-injection MRI: To reduce susceptibility artifacts caused by the iron-loaded liver, the 1st and 2nd order shims were optimized as previously described. The coronal high spatial resolution MRI scan was repeated 40 min after tracer injection. 4. Data fusion and visualization: The 3D coronal MRI pre-injection dataset and the 4D MPI dataset were fused using a globally rigid transformation (translation according to pre-determined values for x, y, and z: -2.5 mm, -1.5 mm, -1 mm) and visualized using PMOD 3.6 (PMOD Technologies Ltd, Switzerland).Fig. 1 shows the MRI-based MPI-FOV planning as overlay on 3 orthogonal high-resolution MR images. Fig. 2 depicts 3 orthogonal slices of the 3D MRI dataset (grayscale) fused with the corresponding slices (red scale) of the time-resolved 3D MPI dataset for a single point in time.This study demonstrates the system’s capability for sequential dual-modal in vivo imaging (MPI and pre/post-injection MRI) of cardiovascular dynamics in rats without the need for subject repositioning using a non-toxic dosage of Resovist as MPI-tracer. 4 high-resolution 3D MR images as well as one time-resolved 3D MPI dataset with a maximal temporal resolution of 21.45 ms/volume were acquired. MRI-based pre-injection planning of the MPI-FOV proved to be a reliable method in the described setting. The inter-modality transition duration was less than 2.5 min in each direction. A global pre-determined rigid translation of the images was used to compensate a timely stable shift of the MPI and MRI coordinate system origins. For future experiments, this offset can be avoided by adjusting the robot coordinate system to the MRI gradient iso-center prior to a new system function acquisition.All animal experiments were performed with the legal approval of the responsible Animal Ethics Committee (Regional Council of Karlsruhe, Germany; 35-9185.81/G-178/12).