A New Magnetic Resonance Imaging Method for Mapping the Cerebral Blood Volume Fraction: The Rapid Steady-State T₁ Method

Abstract

This paper describes a new rapid steady-state T 1 (RSST 1 ) method for mapping the cerebral blood volume fraction (CBVf) by magnetic resonance imaging (MRI). The principle is based on a twocompartment model of the brain (intra-and extravascular), and the effects of paramagnetic contrast agents on the intravascular longitudinal relaxation time T 1 . Using appropriate parameters, an Inversion-Recovery-Fast-Low-Angle-Shot sequence acts like a low pass T 1 filter, suppressing signals from tissues with T 1 bTR (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 (Gd 3 + -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%60.69% (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 PaCO 2 ), demonstrating its potential for longitudinal studies and functional MRI. Clinical applications are feasible since equivalent results were obtained with Gd-DOTA.

Cerebral Blood Volume Quantification in a C6 Tumor Model Using Gadolinium per (3,6-Anhydro) α-Cyclodextrin as a New Magnetic Resonance Imaging Preclinical Contrast Agent

“…However, the ROIs placed in vascular structures revealed similar maximal values (70%) as obtained with other CAs (Perles-Barbacaru and Lahrech, 2007). A value of 100% is never attained because of partial volume and transversal relaxation effects.…”

“…The rapid steady-state T 1 (RSST 1 ) method for mapping the CBVf was used (Perles-Barbacaru and Lahrech, 2007). After CA injection, the method allowed for the suppression of the extravascular signal (characterized by a T 1 Z1 sec) and the selective visualization of the intravascular signal, which was proportional to the equilibrium magnetization of the intravascular water protons and consequent to the CBV (as long as T 1 rTI (inversion time)/5).…”

How Stereological Analysis of Vascular Morphology Can Quantify the Blood Volume Fraction as a Marker for Tumor Vasculature: Comparison with Magnetic Resonance Imaging

“…In malignant brain tumors, the vascular endothelium is often permeable to low-molecular-weight CAs, such as Gd-DOTA, precluding BVf quantification. In our previous study (Lahrech et al, 2008), we used the RSST 1 technique (Perles-Barbacaru and Lahrech, 2007) with Gd-ACX, providing evidence for the vascular confinement of this new CA in a C6 rat brain tumor model enabling the quantification of the tumor BVf. In this study, we measured the tumor BVf in the same animals by MRI with Gd-ACX and by vascular morphometric analysis combined with a stereological technique.…”

“…Uncertainties also exist with the MRI technique: Although with the RSST 1 -MRI technique only the intravascular water should contribute to the signal, the water exchange (Perles-Barbacaru and Lahrech, 2007) probably extends the origin of the acquired signal to the vessel wall or beyond.…”

“…A homogeneous radio frequency (RF) saddle coil was used for emission, and a surface coil for reception. BVf maps were obtained in a coronal plane through the largest extension of the tumor with a spatial resolution of 0.75 Â 0.75 Â 2 mm 3 (Lahrech et al, 2008) using the RSST 1 -MRI method (Perles-Barbacaru and Lahrech, 2007). During MRI examination, each rat underwent two CA injections: Gd-ACX (administered at a dose of 0.05 mmol/kg in terms of gadolinium) was the CA under investigation and has been found to remain confined to the blood pool even in the tumor tissue, allowing quantification of tumor BVf in this tumor model (Lahrech et al, 2008).…”