Ferumoxytol-Enhanced Myocardial T1 Tracking Using a Hybrid 2D/3D Steady-State MRI Sequence Captures Cyclic...

Measuring cyclic changes in intramyocardial blood volume (iMBV) from systole to diastole has been used as an imaging marker for assessing coronary microcirculation and detecting coronary artery disease (CAD) without the need for vasodilator stress. However, an MRI-based method for detecting cyclic iMBV dynamics does not exist. The aim of this study is to demonstrate the feasibility of using ferumoxytol-enhanced (FE) MRI to detect systolic-to-diastolic iMBV dynamics on clinical scanners enabled by a new myocardial "T1 tracking" technique. To this end, a continuous steady-state sequence was developed, combining slice/slab-selective excitation, to generate high-resolution T1-weighted images such that the myocardial signal dynamically tracks the fractional volume of blood while minimizing the influence of confounding factors such as in-flow effects, through-plane motion, and spin history. In addition to phantom studies, FE studies in swine (n = 10) were conducted to generate systolic/diastolic T1 maps from the T1-tracking data. For comparison, MOLLI T1 maps were acquired. For both the T1-tracking method and MOLLI, T1 values before/after ferumoxytol were used to calculate iMBV at end-systole (ES) and end-diastole (ED). The T1-tracking method showed a significant iMBV difference between ES and ED (ES: 6.2 ± 1.8%, ED: 7.7 ± 2.0%, p < 10^-3) as opposed to MOLLI (ES: 8.1 ± 2.9%, ED: 8.6 ± 3.1%, p = 0.4), and detected lower iMBV at ES vs. ED in all 10 studies, consistent with physiology, while MOLLI showed contradictory ES-to-ED change in 3 out of 10 studies. The proposed method showed a mean iMBV decrease of 19.1% from ED to ES, consistent with the nuclear imaging literature. In conclusion, the results show that the newly developed FE myocardial T1-tracking technique captures cyclic changes in iMBV, i.e., consistently reveals the expected drop in iMBV from diastole to systole, offering the potential to detect CAD without the need for pharmacological stress.