Measurement of microvascular cerebral blood volume changes over the cardiac cycle with ferumoxytol-enhanced T2 * MRI. 
This feasibility study investigates the non-invasive measurement of microvascular cerebral blood volume (BV) changes over the cardiac cycle using cardiac-gated, ferumoxytol-enhanced T 2 ∗ MRI.  Institutional review board approval was obtained and all subjects provided written informed consent.  Cardiac gated MR scans were prospectively acquired on a 3.0T scanner in 22 healthy subjects using T 2 ∗ -weighted sequences with 2D-EPI and 3D spiral trajectories.  Images were collected before and after the intravenous administration of 2 doses of ferumoxytol (1 mg FE/kg and 4 mg FE/kg).  Cardiac cycle-induced R 2 ∗ (1/ T 2 ∗ ) changes (Δ R 2 ∗ ) and BV changes (ΔBV) throughout the cardiac cycle in gray matter (GM) and white matter (WM) were quantified and differences assessed using ANOVA followed by post hoc analysis.  Δ R 2 ∗ was found to increase in a dose-dependent fashion.  A significantly larger increase was observed in GM compared to WM in both 2D and 3D acquisitions (P < 0.050).  In addition, Δ R 2 ∗ increased significantly (P < 0.001) post versus pre-contrast injection in GM in both T 2 ∗ MRI acquisitions.  Mean GM Δ R 2 ∗ derived from 2D-EPI images was 0.14 ± 0.06 s-1 pre-contrast and 0.33 ± 0.13 s-1 after 5 mg FE/kg.  In WM, Δ R 2 ∗ was 0.19 ± 0.06 s-1 pre-contrast, and 0.23 ± 0.06 s-1 after 5 mg FE/kg.  The fractional changes in BV throughout the cardiac cycle were 0.031 ± 0.019% in GM and 0.011 ± 0.008% in WM (P < 0.001) after 5 mg FE/kg.  Cardiac-gated, ferumoxytol-enhanced T 2 ∗ MRI enables characterization of microvascular BV changes throughout the cardiac cycle in GM and WM tissue of healthy subjects.