Assessment of blood-brain barrier disruption using dynamic contrast-enhanced MRI. A systematic review

MRI in multiple sclerosis: an intra-individual, randomized and multicentric comparison of gadobutrol with gadoterate meglumine at 3 T

OBJECTIVES

To compare contrast effects of gadobutrol with gadoterate meglumine for brain MRI in multiple sclerosis (MS) in a multicentre, randomized, prospective, intraindividual study at 3 T.

METHODS

Institutional review board approval was obtained. Patients with known or suspected active MS lesions were included. Two identical MRIs were performed using randomized contrast agent order. Four post-contrast T1 sequences were acquired (start time points 0, 3, 6 and 9 min). If no enhancing lesion was present in first MRI, second MRI was cancelled. Quantitative (number and signal intensity of enhancing lesions) and qualitative parameters (time points of first and all lesions enhancing; subjective preference regarding contrast enhancement and lesion delineation; global preference) were evaluated blinded.

RESULTS

Seventy-four patients (male, 26; mean age, 35 years) were enrolled in three centres. In 45 patients enhancing lesions were found. Number of enhancing lesions increased over time for both contrast agents without significant difference (median 2 for both). Lesions signal intensity was significantly higher for gadobutrol (p < 0.05 at time points 3, 6 and 9 min). Subjective preference rating showed non-significant tendency in favour of gadobutrol.

CONCLUSION

Both gadobutrol and gadoterate meglumine can be used for imaging of acute inflammatory MS lesions. However, gadobutrol generates higher lesion SI.

KEY POINTS

Contrast-enhanced MRI plays a key role in the management of multiple sclerosis. Different gadolinium-based contrast agents are available. Number of visibly enhancing lesions increases over time after contrast injection. Gadobutrol and gadoterate meglumine do not differ in number of visible lesions. Gadobutrol generates higher signal intensity than gadoterate meglumine.

Optimal acquisition and modeling parameters for accurate assessment of low Ktrans blood-brain barrier permeability using dynamic contrast-enhanced MRI

PURPOSE

To determine optimal parameters for acquisition and processing of dynamic contrast-enhanced MRI (DCE-MRI) to detect small changes in near normal low blood-brain barrier (BBB) permeability.

METHODS

Using a contrast-to-noise ratio metric (K-CNR) for Ktrans precision and accuracy, the effects of kinetic model selection, scan duration, temporal resolution, signal drift, and length of baseline on the estimation of low permeability values was evaluated with simulations.

RESULTS

The Patlak model was shown to give the highest K-CNR at low Ktrans . The Ktrans transition point, above which other models yielded superior results, was highly dependent on scan duration and tissue extravascular extracellular volume fraction (ve ). The highest K-CNR for low Ktrans was obtained when Patlak model analysis was combined with long scan times (10-30 min), modest temporal resolution (<60 s/image), and long baseline scans (1-4 min). Signal drift as low as 3% was shown to affect the accuracy of Ktrans estimation with Patlak analysis.

CONCLUSION

DCE acquisition and modeling parameters are interdependent and should be optimized together for the tissue being imaged. Appropriately optimized protocols can detect even the subtlest changes in BBB integrity and may be used to probe the earliest changes in neurodegenerative diseases such as Alzheimer's disease and multiple sclerosis.

Assessment of vessel permeability by combining dynamic contrast-enhanced and arterial spin labeling MRI

The forward volumetric transfer constant (K(trans)), a physiological parameter extracted from dynamic contrast-enhanced (DCE) MRI, is weighted by vessel permeability and tissue blood flow. The permeability × surface area product per unit mass of tissue (PS) in brain tumors was estimated in this study by combining the blood flow obtained through pseudo-continuous arterial spin labeling (PCASL) and K(trans) obtained through DCE MRI. An analytical analysis and a numerical simulation were conducted to understand how errors in the flow and K(trans) estimates would propagate to the resulting PS. Fourteen pediatric patients with brain tumors were scanned on a clinical 3-T MRI scanner. PCASL perfusion imaging was performed using a three-dimensional (3D) fast-spin-echo readout module to determine blood flow. DCE imaging was performed using a 3D spoiled gradient-echo sequence, and the K(trans) map was obtained with the extended Tofts model. The numerical analysis demonstrated that the uncertainty of PS was predominantly dependent on that of K(trans) and was relatively insensitive to the flow. The average PS values of the whole tumors ranged from 0.006 to 0.217 min(-1), with a mean of 0.050 min(-1) among the patients. The mean K(trans) value was 18% lower than the PS value, with a maximum discrepancy of 25%. When the parametric maps were compared on a voxel-by-voxel basis, the discrepancies between PS and K(trans) appeared to be heterogeneous within the tumors. The PS values could be more than two-fold higher than the K(trans) values for voxels with high K(trans) levels. This study proposes a method that is easy to implement in clinical practice and has the potential to improve the quantification of the microvascular properties of brain tumors.

Disruption in the Blood-Brain Barrier: The Missing Link between Brain and Body Inflammation in Bipolar Disorder?

The blood-brain barrier (BBB) regulates the transport of micro- and macromolecules between the peripheral blood and the central nervous system (CNS) in order to maintain optimal levels of essential nutrients and neurotransmitters in the brain. In addition, the BBB plays a critical role protecting the CNS against neurotoxins. There has been growing evidence that BBB disruption is associated with brain inflammatory conditions such as Alzheimer's disease and multiple sclerosis. Considering the increasing role of inflammation and oxidative stress in the pathophysiology of bipolar disorder (BD), here we propose a novel model wherein transient or persistent disruption of BBB integrity is associated with decreased CNS protection and increased permeability of proinflammatory (e.g., cytokines, reactive oxygen species) substances from the peripheral blood into the brain. These events would trigger the activation of microglial cells and promote localized damage to oligodendrocytes and the myelin sheath, ultimately compromising myelination and the integrity of neural circuits. The potential implications for research in this area and directions for future studies are discussed.

Dynamic Contrast-Enhanced Perfusion MRI of High Grade Brain Gliomas Obtained with Arterial or Venous Waveform Input Function

BACKGROUND AND PURPOSE

The aim of this study was to evaluate the differences in dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) perfusion estimates of high-grade brain gliomas (HGG) due to the use of an input function (IF) obtained respectively from arterial (AIF) and venous (VIF) approaches by two different commercially available software applications.

METHODS

This prospective study includes 20 patients with pathologically confirmed diagnosis of high-grade gliomas. The data source was processed by using two DCE dedicated commercial packages, both based on the extended Toft model, but the first customized to obtain input function from arterial measurement and the second from sagittal sinus sampling. The quantitative parametric perfusion maps estimated from the two software packages were compared by means of a region of interest (ROI) analysis. The resulting input functions from venous and arterial data were also compared.

RESULTS

No significant difference has been found between the perfusion parameters obtained with the two different software packages (P-value < .05). The comparison of the VIFs and AIFs obtained by the two packages showed no statistical differences.

CONCLUSIONS

Direct comparison of DCE-MRI measurements with IF generated by means of arterial or venous waveform led to no statistical difference in quantitative metrics for evaluating HGG. However, additional research involving DCE-MRI acquisition protocols and post-processing would be beneficial to further substantiate the effectiveness of venous approach as the IF method compared with arterial-based IF measurement.

Molecular Imaging of Membrane Transporters' Activity in Cancer: a Picture is Worth a Thousand Tubes

Molecular imaging allows the non-invasive assessment of membrane transporter expression and function in living subjects. Such technologies have the potential to become diagnostic and prognostic tools, allowing detection, localization, and prediction of response of tumors and their metastases to therapy. Beyond tumors, imaging can also help understand the role of transporters in adverse drug effects and drug clearance. Here, we review molecular imaging technologies that monitor transporter-mediated processes. We emphasize emerging probe substrates and potential clinical applications of imaging the function of membrane transporters in cancer.

Early Blood Brain Barrier Changes in Acute Ischemic Stroke: A Sequential MRI Study

BACKGROUND AND PURPOSE

We sought to identify MRI factors associated with BBB changes at the acute stage of ischemic stroke.

METHODS

We analyzed BBB changes on admission and within 3 hours after the first scan. BBB changes was defined as the presence of leptomeningeal and parenchymal contrast enhancement on T1-weighted imaging. Tmax , CBV, and DWI lesion volume were assessed on baseline MRI. Clinical and MRI factors associated with BBB changes were assessed by univariate and multivariate logistic regressions analyses.

RESULTS

Forty-four patients were included. BBB changes on baseline MRI was observed in 2 of 44 patients (3%). BBB disruption on H3-MRI was present in 19 of 44 patients (43%). Hemodynamic status and baseline ischemic core size were not different between patients with or without BBB changes. BBB alteration on H3 MRI was strongly associated with FLAIR MRI sequence positivity, 16/19 patients (83%) P = .001.

CONCLUSION

BBB changes are exceptional during the first 3 hours after stroke onset. Delayed BBB alteration was associated with FLAIR positivity mainly reflecting vasogenic edema.

Blood-brain barrier imaging in human neuropathologies

The blood-brain barrier (BBB) is essential for normal function of the brain, and its role in many brain pathologies has been the focus of numerous studies during the last decades. Dysfunction of the BBB is not only being shown in numerous brain diseases, but animal studies have indicated that it plays a direct key role in the genesis of neurovascular dysfunction and associated neurodegeneration. As such evidence accumulates, the need for robust and clinically applicable methods for minimally invasive assessment of BBB integrity is becoming urgent. This review provides an introduction to BBB imaging methods in the clinical scenario. First, imaging modalities are reviewed, with a focus on dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). We then proceed to review image analysis methods, including quantitative and semi-quantitative methods. The advantages and limitations of each approach are discussed, and future directions and questions are highlighted.