Mapping Cyclic Change of Regional Myocardial Blood Volume Using Steady-State Susceptibility Effect of Iron Oxide Nanoparticles

Purpose: To demonstrate an in vivo magnetic resonance imaging (MRI) technique that maps the cyclic change of regional myocardial blood volume (MBV) during the cardiac cycle. Materials and Methods: The method is based on the dominant T₂* shortening effect of iron oxide nanoparticle-induced magnetic susceptibility perturbation in myocardium in the steady state. The technique was demonstrated in vivo with normal mouse hearts at 9.4 T. The regional MBV maps in left ventricular myocardium were computed from the steady-state pre- and post-monocrystalline iron oxide nanoparticle (MION) gradient echo (GE) cine images. Cyclic changes of MBV in normal mice were analyzed quantitatively in different transmural and angular locations. Results: High-resolution MBV maps at various cardiac points were obtained. The study showed a general regional MBV decrease from end-diastole (ED) to end-systole (ES). Percentage reductions were 18.2 ± 6.6%, P < 0.03 in the lateral wall and 24.7 ± 3.1%, P < 0.0002 in the interventricular septum. The heterogeneous characteristics of MBV transmural distribution were also reported. Conclusion: The steady-state susceptibility effect of intravascular superparamagnetic contrast agent (CA) can be used to map the cyclic change of regional MBV. This imaging approach is relatively simple and may provide a new perspective for functional assessment of the microvasculature in myocardium.