On the measurement of absolute cerebral blood volume (CBV) using vascular‐space‐occupancy (VASO) MRI

Abstract

Recently, a vascular-space-occupancy (VASO) MRI technique was developed for quantitative assessment of cerebral blood volume (CBV). This method uses the T 1 -shortening effect of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) with imaging parameters chosen that null the precontrast blood magnetization but allow the postcontrast blood magnetization to recover to equilibrium. A key advantage of VASO CBV estimation is that it provides a straightforward procedure for converting MR signals to absolute physiologic values. However, as with other T 1 -based steady-state approaches, several important factors need to be considered that influence the accuracy of CBV values obtained with VASO MRI. Here, the transverse relaxation (T 2 /T* 2 ) effect in VASO MRI was investigated using multiecho spin-echo and gradient-echo experiments, resulting in underestimation of CBV by 14.9% ؎ 1.1% and 16.0% ؎ 2.5% for spin echo (TE ‫؍‬ 10 ms) and gradient echo (TE ‫؍‬ 6 ms), respectively. In addition, the influence of contrast agent clearance was studied by acquiring multiple postcontrast VASO images at 2.2-min intervals, which showed that the concentration of Gd-DTPA in the first 14 min (single dose) was sufficient for the blood magnetization to fully recover to equilibrium. Finally, the effect of vascular Gd-DTPA leakage was assessed for scalp tissue, and signal extrapolation as a function of postinjection time was demonstrated to be useful in minimizing the associ- Quantitative measurement of cerebral blood volume (CBV, defined as ml blood in 100 ml brain) is useful for advancing our understanding of brain physiology and pathophysiology (1,2). It has been reported that many brain disorders, including stroke (1,3,4) and Alzheimer's disease (5)(6)(7)(8), are associated with abnormal CBV. Compared to cerebral blood flow (CBF), CBV has been less extensively studied, but it was recently shown to be particularly sensitive to brain tumor grade (9), and it may be a useful marker for angiogenesis and synaptogenesis (10,11). In addition, CBV is an important parameter for quantitative functional MRI (fMRI) and investigation of the blood oxygenation level-dependent (BOLD) signal mechanism (12)(13)(14).We recently developed a vascular-space-occupancy (VASO) MRI technique for quantitative assessment of CBV. This technique uses the T 1 -shortening effect of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) and is based on pre/post image subtraction, in which the imaging parameters are chosen such that the precontrast blood signal is zero and the postcontrast blood signal corresponds to equilibrium magnetization (15). VASO MRI has several potential advantages in comparison to the dynamic susceptibility contrast (DSC) MRI (16 -18) method: It does not require the arterial input function (AIF). It does not use single-shot EPI acquisition, and thus the image distortion is minimal and higher resolution is feasible. In contrast to other T 1 -based steady-state methods (19 -22), VASO MRI does not need a whole blood voxel for signal referenc...

Optimization and Reliability of Multiple Postlabeling Delay Pseudo-Continuous Arterial Spin Labeling during Rest and Stimulus-Induced Functional Task Activation

“…Sequences that account for this variability in arterial arrival time (AAT) can be used to improve the reliability of ASL; thereby supporting its use to image more complex conditions where cerebral perfusion may be undermined by a particular pathology. 21 Recent work supports this by showing that: (1) it is possible to account for heterogeneity in AAT by incorporating multiple PLDs; 22,23 (2) acquisition of multiple PLDs improves the accuracy of CBF quantification by facilitating the removal of the macrovascular component of the ASL signal. 24 At present, no study has assessed the within-and betweensession reproducibility of multi-PLD pCASL.…”

Validation of VASO cerebral blood volume measurement with positron emission tomography

“…1). The post-contrast image acquisition started 6.5 min after the injection to allow the contrast agent to be fully mixed in the systemic blood (4). The Gd-DTPA contrast agent (Omniscan™, GE Healthcare Inc., Princeton, NJ) was administered intravenously by an MRI power injector (MEDRAD, Pittsburgh, PA) with a standard dosage (0.1 mmol/kg) and injection rate (5 ml/s).…”

“…We have recently developed a Vascular-Space-Occupancy (VASO) MRI technique to quantify CBV (1,3,4). This technique uses an MR contrast agent, gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA), to differentiate tissue and vessel spaces, and is based on pre/post-contrast signal differences to calculate CBV.…”

Simulation-based comparison of two approaches frequently used for dynamic contrast-enhanced MRI

“…Additionally, novel models are rarely implemented in the commercial analysing software. As a consequence, many investigations, especially clinical studies, have been published using Approach 1 [20][21][22][23][24][25][26][27][28][29] or Approach 2 [30][31][32][33][34][35][36][37][38][39] in the recent past. Therefore, we intended to compare these two frequently used approaches with regard to: (1) the influence of differences in modelling the AIF [Approach 1 assumes a rapid-bolus injection of the contrast agent (CA), Approach 2 a short-time constant-rate infusion] and (2) the dependency of the estimated model parameters on the underlying physiological parameters.…”