Earley, Christopher J.

AbstractIron Dextran is a widely used iron oxide compound to treat iron‐deficiency anemia patients in the clinic. Similar to other iron oxide compounds such as Ferumoxytol, it can also be used off‐label as an intravascular magnetic resonance imaging (MRI) contrast agent due to its strong iron‐induced T2 and T2* shortening effects. In this study, we seek to evaluate the feasibility of using Iron Dextran enhanced multi‐echo susceptibility weighted imaging (SWI) MRI at 7T to image arterial and venous blood vessels in the human brain. Phantom experiments were performed to measure the r2* relaxivity for Iron Dextran in blood, based on which the SWI sequence was optimized. Pre‐ and post‐infusion MR images were acquired in human subjects from which maps of arteries and veins were extracted. The post‐contrast SWI images showed enhanced susceptibility difference between blood and the surrounding tissue in both arteries and veins. Our results showed that the proposed Iron Dextran enhanced multi‐echo SWI approach allowed the visualization of blood vessels with diameters down to ~100 μm, including small blood vessels supplying and draining small brain structures such as the hippocampus. We conclude that Iron Dextran can be an alternative iron‐based MRI contrast agent for blood vessel imaging in the human brain.

AbstractPurposeThe inflow‐based vascular‐space‐occupancy (iVASO) MRI was originally developed in a single‐slice mode to measure arterial cerebral blood volume (CBVa). When vascular crushers are applied in iVASO, the signals can be sensitized predominantly to small pial arteries and arterioles. The purpose of this study is to perform a systematic optimization and evaluation of a 3D iVASO sequence on both 3 T and 7 T for the quantification of CBVa values in the human brain.MethodsThree sets of experiments were performed in three separate cohorts. (1) 3D iVASO MRI protocols were compared to single‐slice iVASO, and the reproducibility of whole‐brain 3D iVASO MRI was evaluated. (2) The effects from different vascular crushers in iVASO were assessed. (3) 3D iVASO MRI results were evaluated in arterial and venous blood vessels identified using ultrasmall‐superparamagnetic‐iron‐oxides–enhanced MRI to validate its arterial origin.Results3D iVASO scans showed signal‐to‐noise ratio (SNR) and CBVa measures consistent with single‐slice iVASO with reasonable intrasubject reproducibility. Among the iVASO scans performed with different vascular crushers, the whole‐brain 3D iVASO scan with a motion‐sensitized‐driven‐equilibrium preparation with two binomial refocusing pulses and an effective TE of 50 ms showed the best suppression of macrovascular signals, with a relatively low specific absorption rate. When no vascular crusher was applied, the CBVa maps from 3D iVASO scans showed large CBVa values in arterial vessels but well‐suppressed signals in venous vessels.ConclusionA whole‐brain 3D iVASO MRI scan was optimized for CBVa measurement in the human brain. When only microvascular signals are desired, a motion‐sensitized‐driven‐equilibrium–based vascular crusher with binomial refocusing pulses can be applied in 3D iVASO.