Microvessel density estimation in the human brain by means of dynamic contrast‐enhanced echo‐planar imaging

Animal studies have shown that in vivo estimates of microvessel density in the brain may be obtained from an MRI‐measurable index ( Q ) provided that a sufficiently high dose of an intravascular paramagnetic contrast agent is employed. Q is determined from the shifts in the transverse relaxation rates induced by the contrast agent, and a high dose is required for the validity of analytic expressions relating Q to the microvessel density. However, the steady‐state imaging techniques used in these prior investigations are not appropriate for humans, as the required contrast agent dose is too large. Here results of a pilot study with three subjects are reported. The results suggest that reliable Q measurements can be performed in the human brain at 1.5 T by using an interleaved spin‐echo (SE)/gradient‐echo (GE) echo‐planar imaging (EPI) sequence and a bolus injection of a triple dose of Gd‐DTPA. Lower‐ and upper‐bound estimates for the microvessel density were derived from the Q ‐values, and were found to be in reasonable accord with previously cited values determined by histology. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.