Self-navigated low-rank MRI for MPIO-labeled immune cell imaging of the heart.

Super-paramagnetic iron oxide (SPIO) particles can magnetically label immune cells in circulation; the accumulation of labeled cells can then be detected by magnetic resonance imaging (MRI). This has enormous potential for imaging inflammatory responses in the heart, but it has been difficult to do in vivo using conventional free-breathing, ungated cardiac imaging. Subspace imaging with temporal navigation and sparse sampling of (k, t)-space has previously been used to accelerate several cardiac imaging applications, conventionally alternating between acquiring navigator data and sparse data every other TR. Here we describe a more efficient self-navigated pulse sequence to acquire both navigator and sparse (k, t)-space data in the space of a single TR, doubling imaging speed to approach 100 frames per second (fps). We show the feasibility of using the resulting method to assess myocardial inflammation in a pre-clinical rodent ischemic reperfusion injury (IRI) model using micron-sized paramagnetic iron oxide (MPIO) particles to label immune cells in situ.