1. ¹INSERM, U594, Functional and Metabolic Neuroimaging, Grenoble, France
2. ²Grenoble University Joseph Fourier, Grenoble, France

Correspondence: Dr H Lahrech, INSERM, U594, Functional and Metabolic Neuroimaging, CHU Albert Michallon, Pav. B BP 217, Grenoble 38043, France. E-mail: hana.lahrech@ujf-grenoble.fr

Received 24 January 2006; Revised 4 May 2006; Accepted 5 June 2006; Published online 19 July 2006.

Abstract

This paper describes a new rapid steady-state T₁ (RSST₁) method for mapping the cerebral blood volume fraction (CBVf) by magnetic resonance imaging (MRI). The principle is based on a two-compartment model of the brain (intra- and extravascular), and the effects of paramagnetic contrast agents on the intravascular longitudinal relaxation time T₁. Using appropriate parameters, an Inversion-Recovery-Fast-Low-Angle-Shot sequence acts like a low pass T₁ filter, suppressing signals from tissues with T₁TR (TR=repetition time). It was shown in vivo that, exceeding a particular contrast agent dose, the signal reaches its maximum (corresponding to the intravascular equilibrium magnetization), and is maintained for a duration related to the dose. Acquisitions during this steady state divided by an additional measure of the overall (intra- and extravascular) magnetization at thermal equilibrium provides the CBVf. Experiments were performed on healthy rats at 2.35 T using P760 (Gd³⁺—compound from Guerbet Laboratories) and Gd-DOTA. Because of its high longitudinal relaxivity, P760 is more convenient, and was used to show the feasibility of the method. The CBVf in different structures of the rat brain was compared. The average CBVf for the whole brain slice is 3.29%0.69% (n=15). The influence of transendothelial water exchange was quantified and transversal relaxation effects were found negligible in microvasculature. Finally, the sensitivity of the method to CBVf increases under hypercapnia was evaluated (1%/mm Hg PaCO₂), demonstrating its potential for longitudinal studies and functional MRI. Clinical applications are feasible since equivalent results were obtained with Gd-DOTA.