Sixty-four-section CT cerebral perfusion evaluation in patients with carotid artery stenosis before and after stenting with a cerebral protection device

Choice of imaging to evaluate carotid stenosis and guide management

Carotid artery disease is a cause of ischemic stroke and is associated with cognitive decline. Besides the evaluation of the degree of stenosis, it is also crucial to assess the morphology of the atherosclerotic plaque, for a prompt and accurate diagnosis, and to make the best decision for the patient. On top of noninvasive duplex ultrasound (DUS) and invasive digital subtraction angiography (DSA), compute tomography angiography (CTA) and magnetic resonance angiography (MRA) are often used effectively as noninvasive imaging tools to study carotid stenoses. This review describes the fundamental characteristics of carotid artery plaques, and how they can be best evaluated with currently available imaging methods.

Neurocognitive Changes After Carotid Revascularization According to Perfusion Parameters: A Meta-analysis of Current Literature

BACKGROUND

Although the clinical outcomes continue to be scrutinized, there are a few data summarizing the changes in perfusion parameters in postoperative patients. The objective was to undertake a systematic literature review and perform a meta-analysis to assess the effects of cerebral perfusion changes in cognitive and functional status.

METHODS

A systematic search was conducted in July 2018 identifying articles comparing perfusion parameter changes before and after carotid revascularization in patients with carotid artery stenosis. Combined overall effect sizes were calculated using random-effects models.

RESULTS

The literature search identified 1031 unique articles eligible for analysis. Sixteen studies including 755 patients were identified. The studies were different for many methodological factors, for example, sample size, type of patients, statistical measure, type of test, timing of assessment, and so on. There were no differences in cerebral blood volume (CBV), cerebral metabolic rate of oxygen (CMRO₂), and relative cerebral blood volume (rCBV) between preintervention and postintervention, but there was a significant increase of cerebral blood flow (CBF) (95% confidence interval [CI] standardized mean difference [Std. MD] : -0.83 [-1.27, -0.40]; P = 0.0002; I² = 68%) and relative cerebral blood flow (rCBF) (95% CI Std. MD: -0.72 [-1.61, -0.27]; P < 0.0001; I² = 48%) after operation. In addition, the perfusion of mean transit time (MTT) (95% CI Std. MD: 1.26 [0.62, 1.90]; P = 0.0001; I² = 84%), oxygen extraction fraction (OEF) (95% CI Std. MD: 0.78 [0.24, 1.33]; P = 0.005; I² = 0%), time to peak (TTP) (95% CI Std. MD: 0.46 [0.16, 0.77]; P = 0.003; I² = 47%), and relative mean transit time (rMTT) (95% CI Std. MD: 0.41 [0.33, 0.50]; P < 0.00001; I² = 67%) was higher before than after operation.

CONCLUSIONS

The increase in changes in CBF and rCBF and the decrease in MTT, OEF, TTP, and rMTT after operation may indicate the improvement of cognition in the short term. Intraoperative perfusion parameters could be an important adjuvant monitoring method in neurocognitive changes after carotid revascularization.

Multiple blood flow measurements before and after carotid artery stenting via phase-contrast magnetic resonance imaging: An observational study

After carotid artery stenting, the procurement of information about blood flow redistribution among brain-feeding arteries and its time trend is essential to understanding a patient’s physiological background and to determine their care regimen. Cerebral blood flow has been measured twice following carotid artery stenting in few previous studies, with some discrepancies in the results. The purpose of this study was to measure cerebral blood flow at multiple time points after carotid artery stenting, and to elucidate the time trend of cerebral blood flow and redistribution among arteries. Blood flow rates in 11 subjects were measured preoperatively, at one day, one week, and about three months, respectively after carotid artery stenting by using phase-contrast magnetic resonance imaging. The target vessels were the bilateral internal carotid arteries, the basilar artery, and the bilateral middle cerebral arteries. Lumen was semi-automatically defined using an algorithm utilizing pulsatility. The results showed that blood flow rates in the stented internal carotid artery and the ipsilateral middle cerebral artery increased following carotid artery stenting. Blood flow rates in the contralateral internal carotid artery and the basilar artery gradually declined, and they were lower than the preoperative values at three months after stenting. The sum of blood flow rates of the bilateral internal carotid arteries and the basilar artery increased after carotid artery stenting, and then decreased over the next three months. There was no significant change in the blood flow rate in the contralateral middle cerebral artery. From these results, it was concluded that redistribution among the bilateral internal carotid arteries and the basilar artery occurs after carotid artery stenting, and that it takes months thereafter to reach another equilibrium.

Carotid Artery Stenting and Blood-Brain Barrier Permeability in Subjects with Chronic Carotid Artery Stenosis

Failure of the blood-brain barrier (BBB) is a critical event in the development and progression of diseases such as acute ischemic stroke, chronic ischemia or small vessels disease that affect the central nervous system. It is not known whether BBB breakdown in subjects with chronic carotid artery stenosis can be restrained with postoperative recovery of cerebral perfusion. The aim of the study was to assess the short-term effect of internal carotid artery stenting on basic perfusion parameters and permeability surface area-product (PS) in such a population. Forty subjects (23 males) with stenosis of >70% within a single internal carotid artery and neurological symptoms who underwent a carotid artery stenting procedure were investigated. Differences in the following computed tomography perfusion (CTP) parameters were compared before and after surgery: global cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), time to peak (TTP) and PS. PS acquired by CTP is used to measure the permeability of the BBB to contrast material. In all baseline cases, the CBF and CBV values were low, while MTT and TTP were high on both the ipsi- and contralateral sides compared to reference values. PS was approximately twice the normal value. CBF was higher (+6.14%), while MTT was lower (−9.34%) on the contralateral than on the ipsilateral side. All perfusion parameters improved after stenting on both the ipsilateral (CBF +22.66%; CBV +18.98%; MTT −16.09%, TTP −7.62%) and contralateral (CBF +22.27%, CBV +19.72%, MTT −14.65%, TTP −7.46%) sides. PS decreased by almost half: ipsilateral −48.11%, contralateral −45.19%. The decline in BBB permeability was symmetrical on the ipsi- and contralateral sides to the stenosis. Augmented BBB permeability can be controlled by surgical intervention in humans.

Intracranial Blood Flow Changes in Patients with High-Grade Severe Carotid Artery Stenosis After Stenting

OBJECTIVE

We investigated whether the cerebral hemodynamic changes of pre- and poststenting in patients with severe carotid stenosis differ by stenosis grades.

METHODS

We prospectively recruited patients who underwent carotid artery stenting (CAS) after acute ischemic stroke from June 2014 to December 2015. We compared the mean relative cerebral blood flow (rCBF) changes (measured by whole-brain computed tomography perfusion) pre- and poststenting in patients with high-grade severe stenosis (HGSS) (90%-99%) versus patients with low-grade severe stenosis (LGSS) (70%-89%).

RESULTS

Among 24 patients included in the study (mean age, 66.2 ± 7.2 years; 91.7% men), 62.5% (15/24) were in the HGSS group and 37.5% (9/24) were in the LGSS group. In the HGSS group, rCBF increased in territories of the anterior cerebral artery (P = 0.021), middle cerebral artery (P < 0.001), posterior cerebral artery (P = 0.001), and basil ganglia (P = 0.003) after stenting. Of the patients with HGSS, 53.3% (8/15) had collateral flow through anterior communicating artery (AcomA) prestenting. After stenting, all the AcomA collaterals in HGSS reverted to normal (P = 0.002).

CONCLUSIONS

The improvement of brain perfusion combined with the normalization of collateral flow through the circle of Willis after CAS was observed only in patients with HGSS.

Role of Extracranial Carotid Duplex and Computed Tomography Perfusion Scanning in Evaluating Perfusion Status of Pericarotid Stenting

Carotid stenting is an effective treatment of choice in terms of treating ischemic stroke patients with concomitant carotid stenosis. Though computed tomography perfusion scan has been recognized as a standard tool to monitor/follow up this group of patients, not everyone could endure due to underlying medical illness. In contrast, carotid duplex is a noninvasive assessment tool and could track patient clinical condition in real time. In this study we found that “resistance index” of the carotid ultrasound could detect flow changes before and after the stenting procedure, thus having great capacity to replace the role of computed tomography perfusion exam.

Brain perfusion evaluated by perfusion-weighted magnetic resonance imaging before and after stenting internal carotid artery stenosis in asymptomatic and symptomatic patients

PURPOSE

To evaluate the brain perfusion with MRI perfusion weighted imaging (PWI) before and after ICA stenting in asymptomatic and symptomatic patients.

MATERIALS AND METHODS

PWI was performed 3-21 days before and 3 days after ICA stenting in 31 asymptomatic patients with ICA >70% stenosis - Group I, and in 14 symptomatic patients with ICA >50% stenosis - Group II. PWI was evaluated qualitatively and quantitatively in 5 cerebral territories with: mean transit time (MTT), cerebral blood volume (CBV) and cerebral blood flow (CBF). Mean values of perfusion parameters were measured before and after stenting ΔMTT, ΔCBV, ΔCBF were calculated as subtraction of after-treatment values from those before treatment.

RESULTS

In qualitative evaluation after ICA stenting perfusion was normalized in 21 patients (80.8%) in Group I and in 8 patients (80%) in Group II. In quantitative estimation MTT decreased significantly after CAS on stented side vs. non-stented side in all examined patients regardless of the group, p<0.05. MTT decreased more in Group II than in Group I in all territories (p<0.05) with the exception of temporal lobe. CBV and CBF have shown insignificant differences.

Loss of labelling efficiency caused by carotid stent in pseudocontinuous arterial spin labelling perfusion study

AIM

To elucidate the cause of cerebral hypoperfusion on the stent placement side after carotid artery stent placement (CAS) measured by pseudocontinuous arterial spin labelling (PCASL) perfusion imaging.

MATERIALS AND METHODS

Consecutive patients with symptomatic internal carotid artery stenosis receiving CAS were included in the study. Cerebral blood flow (CBF) was measured by PCASL perfusion imaging at 3 T magnetic resonance imaging (MRI) the day before and 3 days after the procedure. Changes in cerebral haemodynamics after CAS were assessed.

RESULTS

Twenty-two patients were included; 17 patients had increased or stationary CBF after CAS and five patients had significantly reduced CBF on the stenting side after CAS whereas CBF increased on the contralateral side. High stent position was noticed in the five patients. After labelling plane adjustment to avoid labelling on the stent, no more cerebral hypoperfusion was noticed.

CONCLUSION

When using PCASL perfusion imaging to monitor post-stenting CBF, the stent may cause an artefact that leads to a low CBF in the territory of the stented vessel. Routinely adding a fast T2 star gradient-echo echo-planar-imaging covering the upper neck region before PCASL perfusion imaging to identify the stent position and avoid the stent-related artefact is recommended.

Haemodynamic alterations in cerebral blood vessels after carotid artery revascularisation: quantitative analysis using 2D phase-contrast MRI

OBJECTIVES

This study was conducted to evaluate the effect of revascularisation, whether revascularisation improves total cerebral blood flow volume (FVTCBF), and how cerebral veins would respond to altered FVTCBF.

METHODS

The 39 carotid artery stenoses in 37 patients who underwent revascularisation including 32 stentings and 7 endarterectomies were included in this prospective study. From the two-dimensional phase-contrast (2D-PC) MRI acquired before and after revascularisation, the flow volumes (FVs) of the arteries and veins were compared using paired t-test. The relationships between these parameters were correlated using Pearson's correlation coefficient.

RESULTS

The mean FV in the treated carotid artery (proportion of treated artery among total FV) increased from 162.06 ml/min (25.80 %) to 267.71 ml/min (37.21 %; P < 0.001). Revascularisation increased the FVTCBF of patients from 638.66 ml/min to 716.72 ml/min (P < 0.001). The FV of the internal jugular veins, superior sagittal and straight sinuses (FVSS + SSS), and transverse sinuses increased after revascularisation (P < 0.05). Positive relationships were shown between the FVTCBF and the FVSS + SSS (r = 0.584-0.741, P < 0.001).

CONCLUSIONS

Revascularisation improves the FVTCBF by increasing the FV in the treated carotid artery. The venous drainages are closely linked to FVTCBF. 2D-PC-MRI is a feasible method for evaluating comprehensively the haemodynamic improvement after revascularisation.

KEY POINTS

• Revascularisation may be beneficial in ischaemic strokes due to carotid artery stenosis. • Revascularisation of the affected artery increases total cerebral blood flow volume ( FV TCBF). • Cerebral venous drainage, closely linked to FV TCBF, is also improved. • Two-dimensional phase-contrast MRI can comprehensively assess these haemodynamic improvements after carotid revascularisation.

Near-infrared transillumination back scattering sounding--new method to assess brain microcirculation in patients with chronic carotid artery stenosis

Purpose

The purpose of the study was to assess the responses of pial artery pulsation (cc-TQ) and subarachnoid width (sas-TQ) to acetazolamide challenge in patients with chronic carotid artery stenosis and relate these responses to changes in peak systolic velocity (PSV), cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT) and time to peak response (TTP).

Methods

Fifteen patients with carotid artery stenosis ≥90% on the ipsilateral side and <50% on the contralateral side were enrolled into the study. PSV was assessed using colour-coded duplex sonography, CBF, CBV, MTT and TTP with perfusion computed tomography, cc-TQ and sas-TQ with near-infrared transillumination/backscattering sounding (NIR-T/BSS).

Results

Based on the ipsilateral/contralateral cc-TQ ratio after acetazolamide challenge two groups of patients were distinguished: the first group with a ratio ≥1 and the second with a ratio <1. In the second group increases in CBF and CBV after the acetazolamide test were significantly higher in both hemispheres (ipsilateral: +33.0%±8.1% vs. +15.3%±4.4% and +26.3%±6.6% vs. +14.3%±5.1%; contralateral: +26.8%±7.0% vs. +17.6%±5.6% and +20.0%±7.3% vs. +10.0%±3.7%, respectively), cc-TQ was significantly higher only on the ipsilateral side (+37.3%±9.3% vs. +26.6%±8.6%) and the decrease in sas-TQ was less pronounced on the ipsilateral side (−0.7%±1.5% vs. −10.2%±1.5%), in comparison with the first group. The changes in sas-TQ following the acetazolamide test were consistent with the changes in TTP.

Conclusions

The ipsilateral/contralateral cc-TQ ratio following acetazolamide challenge may be used to distinguish patient groups characterized by different haemodynamic parameters. Further research on a larger group of patients is warranted.

Evaluating quantitative approaches to dynamic susceptibility contrast MRI among carotid endarterectomy patients

PURPOSE

To evaluate two dynamic susceptibility contrast (DSC) quantification methods in symptomatic carotid artery disease patients undergoing carotid endarterectomy (CEA) surgery by comparing methods directly and assessing the reliability of each method in the hemisphere contralateral to surgery.

MATERIALS AND METHODS

Absolute cerebral blood flow (CBF) and volume (CBV) was calculated in putamen and sensorimotor gray matter of 17 patients using two methods: 1) The Bookend method that scales relative DSC images to CBV values calculated from the ratio of pre- and postcontrast T1-weighted images, and 2) the Tail-scaling method that uses the ratio of area under the tails of the venous and arterial concentration time-courses to scale the DSC images.

RESULTS

There was a positive correlation between the methods with significant correlation post-CEA (P < 0.035). Intersession correlation was greater when using the Tail-scaling method contralateral to surgery (P < 0.004).

CONCLUSION

We have demonstrated correlation between methods that is significant after surgery and have found that the Tail-scaling method produces better test-retest reliability than our implementation of the Bookend method. Results from this study suggest that DSC has the potential to measure hemodynamic changes after endarterectomy and future work is required to establish clinical value.

Validation of frontal near-infrared spectroscopy as noninvasive bedside monitoring for regional cerebral blood flow in brain-injured patients

OBJECT

Near-infrared spectroscopy (NIRS) offers noninvasive bedside measurement of direct regional cerebral arteriovenous (mixed) brain oxygenation. To validate the accuracy of this monitoring technique, the authors analyzed the statistical correlation of NIRS and CT perfusion with respect to regional cerebral blood flow (CBF) measurements.

METHODS

The authors retrospectively reviewed all cases in which NIRS measurements were obtained at a single, academic neurointensive care unit from February 2008 to June 2011 in which CT perfusion was performed at the same time as NIRS data was collected. Regions of interest were obtained 2.5 cm below the NIRS bifrontal scalp probe on CT perfusion with an average volume between 2 and 4 ml, with mean CBF values used for purposes of analysis. Linear regression analysis was performed for NIRS and CBF values.

RESULTS

The study included 8 patients (2 men, 6 women), 6 of whom suffered subarachnoid hemorrhage, 1 ischemic stroke, and 1 intracerebral hemorrhage and brain edema. Mean CBF measured by CT perfusion was 61 ml/100 g/min for the left side and 60 ml/100 g/min for the right side, while mean NIRS values were 75 on the right and 74 on the left. Linear regression analysis demonstrated a statistically significant probability value (p<0.0001) comparing NIRS frontal oximetry and CT perfusion-obtained CBF values.

CONCLUSIONS

The authors demonstrated a linear correlation for frontal NIRS cerebral oxygenation measurements compared with regional CBF on CT perfusion imaging. Thus, frontal NIRS cerebral oxygenation measurement may serve as a useful, noninvasive, bedside intensive care unit monitoring tool to assess brain oxygenation in a direct manner.

Short- and long-term hemodynamic and clinical effects of carotid artery stenting

BACKGROUND AND PURPOSE

Stenosis of the carotid artery may cause reduced hemodynamic and neural function that may be ameliorated with CAS. The goal of this study was to evaluate short- and long-term hemodynamic and clinical effects after CAS.

MATERIALS AND METHODS

Hemodynamic parameters were acquired by PCT within 1 week before CAS and at 1 week and 1 year (10-13 months) after CAS. In ACA territory, MCA territory, PCA territory, basal ganglia, anterior and posterior CWS and IWS, the rCBF, rCBV, and rMTT were determined in 20 patients with unilateral carotid artery stenosis who underwent CAS. MR and noncontrast CT were performed within 1 week before CAS. Noncontrast CT and carotid arteriography were performed immediately after CAS. Carotid arteriography was performed 1 year after CAS. MRS was performed in 3 measurements. The variance analysis was performed to determine whether there were significant differences among the 3 measurements.

RESULTS

No significant differences were found among rCBV in any territory (P > .05). In the non-PCA territories, rMTT decreased and rCBF increased at 1 week after CAS (P < .01), but there was no significant difference between 1-week and 1-year effects (P > .05). For MR spectroscopy, no significant differences were found between 1 week after CAS and pretreatment (P > .05); the 1-year scores improved significantly (P < .01).

CONCLUSIONS

The long-term hemodynamic and clinical results after treatment validated that CAS is a durable procedure. The 1-week hemodynamic effects can predict long-term effects.

Imaging in endovascular therapy: our future

The endovascular therapist now has many modern imaging techniques available to plan and execute treatment, whereas in the past vascular surgeons relied mostly on clinical examination and arteriography. Advances in computer technology have enabled fast acquisition and processing of the large amounts of digital data essential to capture the dynamic information from fast-flowing blood at high resolution. Functional imaging has begun to play a role in predicting stability of progressive vascular disease and the need for and risks of intervention. Computing power now affords the interventionist the ability to handle imaging data in powerful 3-dimensional programs and electronically "in-lay" a variety of devices to plan complex endovascular procedures from the familiar platform of a laptop. In four major clinical areas, carotid intervention, peripheral intervention, endoluminal grafting, and cardiac imaging, we review the latest advances and changes with an eye toward how we should best be using imaging in our patients undergoing endovascular treatment...now and into the future.