Agreement of novel hemodynamic imaging parameters for the acute and chronic stages of ischemic stroke: a matched-pair cohort study

Hemodynamic Failure Staging With Blood Oxygenation Level-Dependent Cerebrovascular Reactivity and Acetazolamide-Challenged (15O-)H2O-Positron Emission Tomography Across Individual Cerebrovascular Territories

BACKGROUND

Staging of hemodynamic failure (HF) in symptomatic patients with cerebrovascular steno-occlusive disease is required to assess the risk of ischemic stroke. Since the gold standard positron emission tomography-based perfusion reserve is unsuitable as a routine clinical imaging tool, blood oxygenation level-dependent cerebrovascular reactivity (BOLD-CVR) with CO2 is a promising surrogate imaging approach. We investigated the accuracy of standardized BOLD-CVR to classify the extent of HF.

METHODS AND RESULTS

Patients with symptomatic unilateral cerebrovascular steno-occlusive disease, who underwent both an acetazolamide challenge (15O-)H2O-positron emission tomography and BOLD-CVR examination, were included. HF staging of vascular territories was assessed using qualitative inspection of the positron emission tomography perfusion reserve images. The optimum BOLD-CVR cutoff points between HF stages 0-1-2 were determined by comparing the quantitative BOLD-CVR data to the qualitative (15O-)H2O-positron emission tomography classification using the 3-dimensional accuracy index to the randomly assigned training and test data sets with the following determination of a single cutoff for clinical application. In the 2-case scenario, classifying data points as HF 0 or 1-2 and HF 0-1 or 2, BOLD-CVR showed an accuracy of >0.7 for all vascular territories for HF 1 and HF 2 cutoff points. In particular, the middle cerebral artery territory had an accuracy of 0.79 for HF 1 and 0.83 for HF 2, whereas the anterior cerebral artery had an accuracy of 0.78 for HF 1 and 0.82 for HF 2.

CONCLUSIONS

Standardized and clinically accessible BOLD-CVR examinations harbor sufficient data to provide specific cerebrovascular reactivity cutoff points for HF staging across individual vascular territories in symptomatic patients with unilateral cerebrovascular steno-occlusive disease.

Hemodynamic imaging parameters in brain metastases patients - Agreement between multi-delay ASL and hypercapnic BOLD

Arterial spin labeling (ASL) MRI is a routine clinical imaging technique that provides quantitative cerebral blood flow (CBF) information. A related technique is blood oxygenation level-dependent (BOLD) MRI during hypercapnia, which can assess cerebrovascular reactivity (CVR). ASL is weighted towards arteries, whereas BOLD is weighted towards veins. Their associated parameters in heterogeneous tissue types or under different hemodynamic conditions remains unclear. Baseline multi-delay ASL MRI and BOLD MRI during hypercapnia were performed in fourteen patients with brain metastases. In the ROI analysis, the CBF and CVR values were positively correlated in regions showing sufficient reserve capacity (i.e. non-steal regions, rrm = 0.792). Additionally, longer hemodynamic lag times were related to lower baseline CBF (rrm = -0.822) and longer arterial arrival time (AAT; rrm = 0.712). In contrast, in regions exhibiting vascular steal an inverse relationship was found with higher baseline CBF related to more negative CVR (rrm = -0.273). These associations were confirmed in voxelwise analyses. The relationship between CBF, AAT and CVR measures seems to be dependent on the vascular status of the underlying tissue. Healthy tissue relationships do not hold in tissues experiencing impaired or exhausted autoregulation. CVR metrics can possibly identify at-risk areas before perfusion deficiencies become visible on ASL MRI, specifically within vascular steal regions.

More pronounced hemodynamic alterations in patients with brain arteriovenous malformation–associated epilepsy

OBJECTIVE

Epileptic seizures in patients with brain arteriovenous malformations (bAVMs) may be caused by hemodynamic alterations due to the complex angioarchitecture of bAVMs. In particular, an arterial steal phenomenon and venous outflow disruption may play an etiological role in seizure development but remain challenging to demonstrate quantitatively. Blood oxygenation level–dependent (BOLD) cerebrovascular reactivity (CVR) imaging is an emerging technique that can measure both arterial steal phenomenon (as a paradoxical BOLD signal decrease during a vasodilatory stimulus) and impaired perinidal BOLD-CVR (which has been found in the presence of venous congestion on conventional angiography in bAVM patients with epilepsy). By applying this innovative BOLD-CVR technique, the aim is to better study CVR patterns and their correlation with morphological features on conventional angiography in patients with bAVM with and without epilepsy.

METHODS

Twenty-two patients with unruptured and previously untreated bAVMs (8 with and 14 without epilepsy) were included in this case-control study. Quantitative CVR measurements were derived from BOLD functional MRI volumes using a novel standardized and precise hypercapnic stimulus (i.e., % BOLD/mm Hg CO2). In addition, 22 matched healthy controls underwent an identical BOLD-CVR study. Evaluation of venous congestion was performed on conventional angiography for all patients with bAVM.

RESULTS

Patients with bAVM-associated epilepsy showed impaired whole-brain BOLD-CVR compared to those in the nonepilepsy group, even after correction for AVM volume and AVM grade (epilepsy vs nonepilepsy group: 0.17 ± 0.07 vs 0.25 ± 0.07, p = 0.04). A BOLD-CVR–derived arterial steal phenomenon was observed in 2 patients with epilepsy (25%). Venous congestion was noted in 3 patients with epilepsy (38%) and in 1 patient without epilepsy (7%; p = 0.08).

CONCLUSIONS

These data suggest that whole-brain CVR impairment, and more pronounced hemodynamic alterations (i.e., arterial steal phenomenon and venous outflow restriction), may be more present in patients with bAVM-associated epilepsy. The association of impaired BOLD-CVR and bAVM-associated epilepsy will need further investigation in a larger patient cohort.