Structural MRI of carotid artery atherosclerotic lesion burden and characterization of hemispheric cerebral blood flow before and after carotid endarterectomy

Associations Between Carotid Plaque Characteristics and Perioperative Cerebral Blood Flow Determined by Arterial Spin Labeling Imaging in Patients With Moderate-to-Severe Stenosis Undergoing Carotid Endarterectomy

Purpose

To examine the associations between carotid plaque characteristics and perioperative cerebral blood flow (CBF) by arterial spin labeling (ASL) imaging.

Materials and Methods

Patients with unilateral moderate-to-severe carotid stenosis referred for carotid endarterectomy (CEA) were recruited and underwent carotid vessel wall and brain ASL magnetic resonance imaging. The following imaging features were measured: relative CBF (rCBF = CBF_{index−hemisphere}/CBF_{contralateral−hemisphere}) in the middle cerebral artery territory; plaque burden and the presence of lipid-rich necrotic core; intraplaque hemorrhage (IPH); calcification; ulcer and fibrous-cap rupture; and the volume and maximum plaque components' area percentages. The associations between plaque characteristics and perioperative CBF were analyzed.

Results

Sixty-one patients (mean age, 66.6 ± 7.8 years; 55 males) were included. Univariate linear regression showed that rCBF_pre−CEA was associated with stenosis [β, −0.462; 95% confidence interval (CI), from −0.797 to −0.126; p = 0.008], calcification (β, 0.103; 95% CI, 0.005–0.201; p = 0.040), maximum IPH area percentage (β, −0.127; 95% CI, from −0.223 to −0.030; p = 0.012), and ulcer (β, 0.069; 95% CI, 0.025–0.113; p = 0.005); rCBF_post−CEA was associated with the IPH volume (β, −0.060; 95% CI, from −0.107 to −0.014; p = 0.013). After adjusting for the confounding factors, the associations of calcification with rCBF_pre−CEA (β, 0.099; 95% CI, from 0.004 to −0.194; p = 0.042) and IPH volume with rCBF_post−CEA (β, −0.060; 95% CI, from −0.109 to −0.011; p = 0.020) remained statistically significant, while those of rCBF_pre−CEA with maximum IPH area percentage (β, −0.089; 95% CI, from −0.188 to 0.011; p = 0.080) and ulcer (β, 0.050; 95% CI, from −0.012 to 0.112; p = 0.100) did not remain statistically significant.

Conclusion

The compositional characteristics of carotid atherosclerotic plaques, particularly IPH, were associated with perioperative CBF in patients with unilateral moderate-to-severe carotid stenosis undergoing CEA. Our findings indicated that the patients with larger carotid IPH could expect smaller improvement in CBF following CEA.

Associations between carotid atherosclerotic plaque characteristics determined by magnetic resonance imaging and improvement of cognition in patients undergoing carotid endarterectomy

BACKGROUND

To determine the predictive value of carotid plaque characteristics for the improvement of cognition in patients with moderate-to-severe carotid stenosis after carotid endarterectomy (CEA), using vessel wall magnetic resonance imaging (MRI).

METHODS

This was a prospective cohort study. Patients with unilateral, moderate-to-severe carotid stenosis referred to the Peking University Third Hospital for CEA were prospectively recruited and underwent carotid vessel wall MRI within 1 week before CEA. We performed Montreal Cognitive Assessment (MoCA) within 1 week before and 3-4 days after CEA. The morphological and compositional characteristics of carotid plaques on MRI were evaluated. Improvement of cognition was defined as >10% increase of the total MoCA score after CEA compared with baseline. Carotid plaque characteristics were compared between patients with and without cognitive improvement.

RESULTS

In total, 105 patients (91 males; mean age, 65.5±8.4 years) were included. The volume {48.0 [interquartile range (IQR), 21.0 to 91.6] vs. 16.3 (IQR, 8.1 to 53.1) mm3; P=0.005} and cumulative slice [4.0 (IQR, 3.0 to 7.0) vs. 3.0 (IQR, 2.0 to 5.0); P=0.019] of carotid calcification, and maximum percentage of calcification area [13.1% (IQR, 6.0% to 19.8%) vs. 6.2% (IQR, 3.7% to 10.8%); P=0.004] were significantly smaller in participants with cognitive improvement compared to those without. Univariate logistic regression analysis showed that volume [odds ratio (OR) =0.994; 95% confidence interval (CI): 0.989 to 1.000; P=0.043] and cumulative slice (OR =0.823; 95% CI: 0.698 to 0.970; P=0.020) of carotid calcification, and maximum percentage of calcification area (OR =0.949; 95% CI: 0.909 to 0.991; P=0.018) were significantly correlated with cognitive improvement. After adjusting for confounding factors, these associations remained statistically or marginally significant (volume: OR =0.994; 95% CI: 0.988 to 1.000; P=0.057; maximum percentage of calcification area: OR =0.937; 95% CI: 0.890 to 0.987; P=0.014; and cumulative slice: OR =0.791; 95% CI: 0.646 to 0.967; P=0.022). No significant associations were found between other plaque characteristics and cognitive improvement (all P>0.05).

CONCLUSIONS

More than half of the participants with unilateral, moderate-to-severe carotid atherosclerotic stenosis had cognitive improvement. The size of calcification might be an effective indicator of cognitive improvement after CEA.

Can 3D Pseudo-Continuous Territorial Arterial Spin Labeling Effectively Diagnose Patients With Recanalization of Unilateral Middle Cerebral Artery Stenosis?

BACKGROUND

Unilateral middle cerebral artery (MCA) stenosis, as an independent risk factor for stroke, requires an intervention operation for vessel recanalization. Accurate perfusion measurement is thus essential after the operation.

PURPOSE

To explore the feasibility of three-dimensional (3D) pseudo-continuous territorial arterial-spin-labeling (tASL) in evaluating MCA recanalization.

STUDY TYPE

Prospective and longitudinal.

SUBJECTS

Forty-seven patients with unilateral MCA stenosis or occlusion.

FIELD STRENGTH/SEQUENCE

A 3.0 T, 3D time-of-flight fast-field-echo magnetic resonance (MR) angiography sequence, spin-echo echo-planar diffusion-weighted imaging sequence, 3D fast-spin-echo pseudo-continuous ASL (pcASL) and tASL sequences.

ASSESSMENT

All patients underwent MR examination before and after MCA recanalization and scored using the National Institutes of Health Stroke Scale (NIHSS) and modified Rankin Scale (mRS) at admission and discharge. An mRS score <2 was defined as a good prognosis. 3D-pcASL and tASL cerebral blood flow (CBF) maps were obtained, and the corresponding Alberta Stroke Program Early CT Score (ASPECTS)-based scores were evaluated.

STATISTICAL TESTS

The Kolmogorov-Smirnov test, intra-class correlation coefficient, paired t-test, receiver operating characteristic (ROC) curve, and multivariable logistic regression analysis.

RESULTS

After recanalization, tASL derived absolute CBFs between the affected and contralateral sides were significantly higher than before the operation (mean: 34.3 ± 8.5 mL/100 g/min vs. 40.6 ± 9.2 mL/100 g/min, 42.6 ± 9.8 mL/100 g/min vs. 43.5 ± 9.9 mL/100 g/min, both P < 0.05). In ROC analysis, tASL provided good prognosis (area under ROC curve [AUC] = 0.829; 95% CI: 0.651-1.000, P < 0.05), while pcASL had lower prognostic value (AUC = 0.760; 95% CI: 0.574-0.946, P < 0.05). The NIHSS score before recanalization, pcASL, and tASL-based ASPECTS scores were significantly associated with good clinical outcome (P < 0.05). Multivariable analysis revealed that ASPECTS-based scores of pcASL and tASL before and after surgery were independent predictors of good clinical outcome (all P < 0.05). DATA CONCLUSION: tASL can determine hypoperfusion in the responsible vascular perfusion area and predict clinical outcome.

EVIDENCE LEVEL

4 TECHNICAL EFFICACY: Stage 2.

Associations Between Carotid Plaque Characteristics and Improvement of Cerebral Blood Perfusion in Patients With Moderate to Severe Carotid Stenosis Undergoing Carotid Endarterectomy

BACKGROUND

The relationship between plaque characteristics and their predictive value for perioperative cerebral blood flow (CBF) are unknown.

PURPOSE

To investigate the relationship between carotid plaque characteristics and perioperative CBF utilizing MRI.

STUDY TYPE

Prospective.

POPULATION

In all, 131 patients with carotid moderate-to-severe stenosis referred for carotid endarterectomy (CEA).

FIELD STRENGTH/SEQUENCE

3T, black-blood T₁ - and T₂ -weighted, 3D time-of-flight, and simultaneous noncontrast angiography intraplaque hemorrhage.

ASSESSMENT

The relative CBF (rCBF = CBF_{index-hemisphere} /CBF_{contralateral-hemisphere} ) and the CBF difference ratio (DR_CBF = [CBF_post-CEA - CBF_pre-CEA ]/CBF_pre-CEA ) in the middle cerebral artery territory were measured. The pre- and post-CEA CTP data were used as the assessment standard for CBF change. Carotid lipid-rich necrotic core (LRNC), intraplaque hemorrhage, calcification, fibrous cap rupture, maximum wall thickness, normalized wall index (NWI), and stenosis were determined.

STATISTICAL TESTS

Pearson or Spearman correlation, Mann-Whitney U-test, and linear regression.

RESULTS

Patients with LRNC had higher rCBF_pre-CEA than those without (1.0 ± 0.1 vs. 0.9 ± 0.1, P < 0.05). NWI was weakly correlated with rCBF_pre-CEA (r = -0.213, P < 0.05) and DR_CBF (r = 0.185, P < 0.05) and marginally correlated with rCBF_post-CEA (r = 0.166, P = 0.057). LRNC was weakly correlated with rCBF_pre-CEA (r = 0.179, P < 0.05). NWI was associated with rCBF_pre-CEA (β = -0.035; 95% confidence interval [CI] [-0.064, -0.006]; P < 0.05), rCBF_post-CEA (β = 0.042; 95% CI [0.002, 0.081]; P < 0.05) and DR_CBF (β = 0.105; 95% CI [0.026, 0.185]; P < 0.05). After adjusting for confounding factors, associations of NWI with rCBF_post-CEA (β = 0.059; 95% CI [0.016, 0.103]; P < 0.05) and DR_CBF (β = 0.110; 95% CI [0.021, 0.199]; P < 0.05) remained statistically significant, while the association between NWI and rCBF_pre-CEA was no longer significant (β = -0.026; 95% CI [-0.058, 0.006]; P = 0.112).The associations of LRNC with rCBF_pre-CEA (β = 0.057; 95% CI [-0.0006, 0.114]; P = 0.052) and DR_CBF (β = -0.157; 95% CI [-0.314, 0.001]; P = 0.051) were close to statistical significance. After adjusting for confounding factors, these associations were statistically significant (of LRNC vs. rCBF_pre-CEA : β = 0.060; 95% CI [0.003, 0.118]; P < 0.05; LRNC vs. DR_CBF : β = -0.205; 95% CI [-0.375, -0.036]; P < 0.05).

DATA CONCLUSION

Carotid plaque burden and components, particularly LRNC, might be effective indicators for CBF change following CEA. Level of Evidence 1 Technical Efficacy Stage 5.

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.

Effective collateral circulation may indicate improved perfusion territory restoration after carotid endarterectomy

OBJECTIVES

To investigate the relationship between the level of collateral circulation and perfusion territory normalisation after carotid endarterectomy (CEA).

METHODS

This study enrolled 22 patients with severe carotid stenosis that underwent CEA and 54 volunteers without significant carotid stenosis. All patients were scanned with ASL and t-ASL within 1 month before and 1 week after CEA. Collateral circulation was assessed on preoperative ASL images based on the presence of ATA. The postoperative flow territories were considered as back to normal if they conformed to the perfusion territory map in a healthy population. Neuropsychological tests were performed on patients before and within 7 days after surgery.

RESULTS

ATA-based collateral score assessed on preoperative ASL was significantly higher in the flow territory normalisation group (n=11, 50 %) after CEA (P < 0.0001). The MMSE (mean change=1.36±0.96) and MOCA (mean change=1.18±0.95) test scores showed a significant postoperative (7 days after CEA) improvement in the flow territory normalisation group [>mean differences+2SD among control (MMSE=1.35, MOCA=1.02)].

CONCLUSIONS

This study demonstrated that effective collateral flow in carotid stenosis patients was associated with normalisation of t-ASL perfusion territory after CEA. The perfusion territory normalisation group tends to have more cognitive improvement after CEA.

KEY POINTS

• Evaluation of collaterals before CEA is helpful for avoiding ischaemia during clamping. • There was good agreement on ATA-based ASL collateral grading. • Perfusion territories in carotid stenosis patients are altered. • Patients have better collateral circulation with perfusion territory back to normal. • MMSE and MOCA test scores improved more in the territory normalisation group.

Improvement in Cerebral and Ocular Hemodynamics Early after Carotid Endarterectomy in Patients of Severe Carotid Artery Stenosis with or without Contralateral Carotid Occlusion

Purpose. To investigate the alternation in cerebral and ocular blood flow velocity (BFV) in patients of carotid stenosis (CS) with or without contralateral carotid occlusion (CO) early after carotid endarterectomy (CEA). Patients and Methods. Nineteen patients underwent CEA for ≥50% CS. Fourteen patients had the unilateral CS, and five patients had the ipsilateral CS and the contralateral CO. Transcranial Doppler (TCD) and Color Doppler Imaging (CDI) were performed before and early after CEA. Results. In patients with unilateral CS, significant improvements in BFV were observed in anterior cerebral artery (ACA) and middle cerebral artery (MCA) on the ipsilateral side after CEA. In patients of ipsilateral CS and contralateral CO, significant improvements in BFV were observed in the ACA and MCA not only on the ipsilateral side but also on the contralateral side postoperatively. The ipsilateral ophthalmic artery (OA) retrograde flows in two patients were recovered to anterograde direction following CEA. The BFV in short posterior ciliary artery (SPCA) of the ipsilateral side significantly increased postoperatively irrespective of the presence of contralateral CO. Conclusions. CEA improved cerebral anterior circulation hemodynamics especially in patients of unilateral CS and contralateral CO, normalized the OA reverse flow, and increased the blood perfusion of SPCA.

Mapping of cerebral perfusion territories using territorial arterial spin labeling: techniques and clinical application

A knowledge of the exact cerebral perfusion territory which is supplied by any artery is of great importance in the understanding and diagnosis of cerebrovascular disease. The development and optimization of territorial arterial spin labeling (T-ASL) MRI techniques in the past two decades have made it possible to visualize and determine the cerebral perfusion territories in individual patients and, more importantly, to do so without contrast agents or otherwise invasive procedures. This review provides an overview of the development of ASL techniques that aim to visualize the general cerebral perfusion territories or the territory of a specific artery of interest. The first efforts of T-ASL with pulsed, continuous and pseudo-continuous techniques are summarized and subsequent clinical studies using T-ASL are highlighted. In the healthy population, the perfusion territories of the brain-feeding arteries are highly variable. This high variability requires special consideration in specific patient groups, such as patients with cerebrovascular disease, stroke, steno-occlusive disease of the large arteries and arteriovenous malformations. In the past, catheter angiography with selective contrast injection was the only available method to visualize the cerebral perfusion territories in vivo. Several T-ASL methods, sometimes referred to as regional perfusion imaging, are now available that can easily be combined with conventional brain MRI examinations to show the relationship between the cerebral perfusion territories, vascular anatomy and brain infarcts or other pathology. Increased availability of T-ASL techniques on clinical MRI scanners will allow radiologists and other clinicians to gain further knowledge of the relationship between vasculature and patient diagnosis and prognosis. Treatment decisions, such as surgical revascularization, may, in the near future, be guided by information provided by T-ASL MRI in close correlation with structural MRI and quantitative perfusion information.

Clinical applications of arterial spin labeling

MR arterial spin labeling is primarily applied as a neuroimaging method to measure cerebral blood flow. As this technique becomes more widely available, a basic understanding of the clinical applications is necessary for optimal utilization in the setting of patient care. This review focuses on the use of arterial spin labeling imaging for the evaluation of cerebrovascular disease, brain tumors and neuropsychiatric illness.

Applications of arterial spin labeled MRI in the brain

Perfusion provides oxygen and nutrients to tissues and is closely tied to tissue function while disorders of perfusion are major sources of medical morbidity and mortality. It has been almost two decades since the use of arterial spin labeling (ASL) for noninvasive perfusion imaging was first reported. While initial ASL magnetic resonance imaging (MRI) studies focused primarily on technological development and validation, a number of robust ASL implementations have emerged, and ASL MRI is now also available commercially on several platforms. As a result, basic science and clinical applications of ASL MRI have begun to proliferate. Although ASL MRI can be carried out in any organ, most studies to date have focused on the brain. This review covers selected research and clinical applications of ASL MRI in the brain to illustrate its potential in both neuroscience research and clinical care.

Dynamic alteration of regional cerebral blood flow during carotid compression and proof of reversibility

Background

It is difficult to non-invasively visualize changes in regional cerebral blood flow caused by manual compression of the carotid artery.

Purpose

To visualize dynamic changes in regional cerebral blood flow during and after manual compression of the carotid artery.

Material and Methods

Two healthy volunteers were recruited. Anatomic features and flow directions in the circle of Willis were evaluated with time-of-flight magnetic resonance angiography (MRA) and two-dimensional phase-contrast (2DPC) MRA, respectively. Regional cerebral blood flow was visualized with territorial arterial spin-labeling magnetic resonance imaging (TASL-MRI). TASL-MRI and 2DPC-MRA were performed in three states: at rest, during manual compression of the right carotid artery, and after decompression. In one volunteer, time-space labeling inversion pulse (Time-SLIP) MRA was performed to confirm collateral flow.

Results

During manual carotid compression, in one volunteer, the right thalamus changed to be fed only by the vertebrobasilar system, and the right basal ganglia changed to be fed by the left internal carotid artery. In the other volunteer, the right basal ganglia changed to be fed by the vertebrobasilar system. 2DPC-MRA showed that the flow direction changed in the right A1 segment of the anterior cerebral artery and the right posterior communicating artery. Perfusion patterns and flow directions recovered after decompression. Time-SLIP MRA showed pial vessels and dural collateral circulation when the right carotid artery was manually compressed.

Conclusion

Use of TASL-MRI and 2DPC-MRA was successful for non-invasive visualization of the dynamic changes in regional cerebral blood flow during and after manual carotid compression.

Arterial spin labeling measurements of cerebral perfusion territories in experimental ischemic stroke

Collateral circulation, defined as the supplementary vascular network that maintains cerebral blood flow (CBF) when the main vessels fail, constitutes one important defense mechanism of the brain against ischemic stroke. In the present study, continuous arterial spin labeling (CASL) was used to quantify CBF and obtain perfusion territory maps of the major cerebral arteries in spontaneously hypertensive rats (SHRs) and their normotensive Wistar-Kyoto (WKY) controls. Results show that both WKY and SHR have complementary, yet significantly asymmetric perfusion territories. Right or left dominances were observed in territories of the anterior (ACA), middle and posterior cerebral arteries, and the thalamic artery. Magnetic resonance angiography showed that some of the asymmetries were correlated with variations of the ACA. The leptomeningeal circulation perfusing the outer layers of the cortex was observed as well. Significant and permanent changes in perfusion territories were obtained after temporary occlusion of the right middle cerebral artery in both SHR and WKY, regardless of their particular dominance. However, animals with right dominance presented a larger volume change of the left perfusion territory (23 ± 9%) than animals with left dominance (7 ± 5%, P < 0.002). The data suggest that animals with contralesional dominance primarily safeguard local CBF values with small changes in contralesional perfusion territory, while animals with ipsilesional dominance show a reversal of dominance and a substantial increase in contralesional perfusion territory. These findings show the usefulness of CASL to probe the collateral circulation.

Distribution of cerebral blood flow in the caudate nucleus, lentiform nucleus and thalamus in patients with carotid artery stenosis

OBJECTIVE

To investigate the influence of internal carotid artery (ICA) stenosis on the distribution of blood flow to the caudate nucleus, lentiform nucleus, and thalamus.

METHODS

We studied 18 healthy control subjects, 20 patients with a unilateral asymptomatic ICA stenosis, and 15 patients with a recently symptomatic unilateral ICA stenosis. The contribution of the ICAs and the basilar artery to the perfusion of the deep brain structures was assessed by perfusion territory selective arterial spin labeling (ASL) MRI. Differences were tested with a two-tailed Fishers' exact test.

RESULTS

The caudate nucleus was predominantly supplied with blood by the ipsilateral ICA in all groups. In 4 of the 15 (27%) the symptomatic patients, the caudate nucleus partially received blood from the contralateral ICA, compared to none of the 18 healthy control subjects (p = 0.03). The lentiform nucleus and the thalamus were predominantly supplied with blood by the ipsilateral ICA and basilar artery respectively in all groups.

CONCLUSION

In patients with a symptomatic ICA stenosis, the caudate nucleus may be supplied with blood by the contralateral ICA more often than in healthy controls.

Arterial spin labeling of cerebral perfusion territories using a separate labeling coil

PURPOSE

To obtain cerebral perfusion territories of the left, the right, and the posterior circulation in humans with high signal-to-noise ratio (SNR) and robust delineation.

MATERIALS AND METHODS

Continuous arterial spin labeling (CASL) was implemented using a dedicated radio frequency (RF) coil, positioned over the neck, to label the major cerebral feeding arteries in humans. Selective labeling was achieved by flow-driven adiabatic fast passage and by tilting the longitudinal labeling gradient about the Y-axis by theta = +/- 60 degrees .

RESULTS

Mean cerebral blood flow (CBF) values in gray matter (GM) and white matter (WM) were 74 +/- 13 mL . 100 g(-1) . minute(-1) and 14 +/- 13 mL . 100 g(-1) . minute(-1), respectively (N = 14). There were no signal differences between left and right hemispheres when theta = 0 degrees (P > 0.19), indicating efficient labeling of both hemispheres. When theta = +60 degrees , the signal in GM on the left hemisphere, 0.07 +/- 0.06%, was 92% lower than on the right hemisphere, 0.85 +/- 0.30% (P < 1 x 10(-9)), while for theta = -60 degrees , the signal in the right hemisphere, 0.16 +/- 0.13%, was 82% lower than on the contralateral side, 0.89 +/- 0.22% (P < 1 x 10(-10)). Similar attenuations were obtained in WM.

CONCLUSION

Clear delineation of the left and right cerebral perfusion territories was obtained, allowing discrimination of the anterior and posterior circulation in each hemisphere.

Quantitative assessment of mixed cerebral vascular territory supply with vessel encoded arterial spin labeling MRI

BACKGROUND AND PURPOSE

Recent advances in arterial spin labeling MRI have permitted noninvasive evaluation of vascular territories. In the present study, we quantitatively assess mixing of internal carotid and basilar artery blood through cerebrovascular anastomoses using vessel-encoded arterial spin labeling and a new postprocessing method.

METHODS

Vessel-encoded arterial spin labeling was used to determine the territories of the internal carotid and basilar arteries in 14 healthy subjects and one patient with asymptomatic high-grade carotid artery stenosis before and after endarterectomy. Contributions to individual vascular territories were quantified using a voxelwise supply fraction algorithm and the results were correlated with MR angiography.

RESULTS

Vascular territories were consistent with cerebrovascular anatomy and the presence of pathology. The supply fraction method allowed quantification of mixed territorial supply arising from collateral flow and showed vascular supply changes in a patient with carotid artery stenosis after endarterectomy.

CONCLUSIONS

Vascular territories obtained with vessel-encoded arterial spin labeling correlate with cerebrovascular anatomy and allow quantitative assessment of mixed territorial supply in subjects with and without pathology.

Effect of cerebrovascular risk factors on regional cerebral blood flow

PURPOSE

To prospectively investigate which cerebrovascular risk factors are related to regional cerebral blood flow (rCBF), as measured noninvasively with arterial spin-labeling (ASL) magnetic resonance (MR) imaging, in a large group of patients with symptomatic atherosclerotic disease.

MATERIALS AND METHODS

Ethics committee approval and informed consent were obtained. One hundred thirty consecutive patients (107 men, 23 women; mean age, 58 years +/- 10 [standard deviation]) with symptomatic atherosclerotic disease were included in the study. Cerebrovascular risk factors (body mass index, carotid artery stenosis, diabetes mellitus, hyperhomocysteinemia, hyperlipidemia, hypertension, and smoking) were assessed by means of a questionnaire and physical, ultrasonographic, and laboratory examinations. The control group consisted of 10 subjects (eight men, two women; mean age, 58 years +/- 15) without symptomatic atherosclerotic disease. rCBF measurements were performed with ASL MR imaging. The effects of the individual cerebrovascular risk factors on the rCBF were assessed by using linear regression analysis.

RESULTS

Hypertension was significantly associated with higher rCBF (adjusted beta = 6.5 mL/min/100 g; 95% confidence interval: 1.4 mL/min/100 g, 11.7 mL/min/100 g). Hyperhomocysteinemia was significantly related to lower rCBF (adjusted beta = -7.4 mL/min/100 g; 95% confidence interval: -12.7 mL/min/100 g, -2.1 mL/min/100 g). No significant associations between rCBF and the other cerebrovascular risk factors were found.

CONCLUSION

In patients with symptomatic atherosclerotic disease, hypertension is related to higher rCBF and hyperhomocysteinemia is related to lower rCBF.

Measurement of cerebral perfusion territories using arterial spin labelling

The ability to assess the perfusion territories of major cerebral arteries can be a valuable asset to the diagnosis of a number of cerebrovascular diseases. Recently, several arterial spin labeling (ASL) techniques have been proposed for determining the cerebral perfusion territories of individual arteries by three different approaches: (1) using a dedicated labeling radio frequency (RF) coil; (2) applying selective inversion of spatially confined areas; (3) employing multidimensional RF pulses. Methods that use a separate labeling RF coil have high signal-to-noise ratio (SNR), low RF power deposition, and unrestricted three-dimensional coverage, but are mostly limited to separation of the left and right circulation, and do require extra hardware, which may limit their implementation in clinical systems. Alternatively, methods that utilize selective inversion have higher flexibility of implementation and higher arterial selectivity, but suffer from imaging artifacts resulting from interference between the labeling slab and the volume of interest. The goal of this review is to provide the reader with a critical survey of the different ASL approaches proposed to date for determining cerebral perfusion territories, by discussing the relative advantages and disadvantages of each technique, so as to serve as a guide for future refinement of this promising methodology.

Clinical neuroimaging using arterial spin-labeled perfusion magnetic resonance imaging

The two most common methods for measuring perfusion with MRI are based on dynamic susceptibility contrast (DSC) and arterial spin labeling (ASL). Although clinical experience to date is much more extensive with DSC perfusion MRI, ASL methods offer several advantages. The primary advantages are that completely noninvasive absolute cerebral blood flow (CBF) measurements are possible with relative insensitivity to permeability, and that multiple repeated measurements can be obtained to evaluate one or more interventions or to perform perfusion-based functional MRI. ASL perfusion and perfusion-based functional MRI methods have been applied in many clinical settings, including acute and chronic cerebrovascular disease, CNS neoplasms, epilepsy, aging and development, neurodegenerative disorders, and neuropsychiatric diseases. Recent technical advances have improved the sensitivity of ASL perfusion MRI, and increasing use is expected in the coming years. The present review focuses on ASL perfusion MRI and applications in clinical neuroimaging.

Measurement of cerebral perfusion with arterial spin labeling: Part 2. Applications

Arterial spin labeling (ASL) uses magnetic resonance imaging methods to measure cerebral blood flow (CBF) non-invasively. ASL CBF validly localizes brain function and may be especially useful for studies where the time frame of behavioral change is more than a few minutes, such as in longitudinal and treatment studies. ASL measures of cerebral perfusion are highly accurate in detecting lesion laterality in temporal lobe epilepsy, stenotic-occlusive disease, and brain tumors. Among lesioned patients, ASL CBF has excellent concurrent validity when correlated with CBF measured by Positron Emission Tomography or with dynamic susceptibility-weighted magnetic resonance. ASL CBF can predict tumor grading in vivo and can predict six-month response to the surgical treatment of brain tumors. ASL's capability to selectively and non-invasively tag flow in major vessels may refine the monitoring of treatment of cerebrovascular disease and brain tumors. Conclusions about the utility of ASL are limited by the small sample sizes of the studies currently in the literature and by the uncertainty caused by the effect of brain disease on transit times of the magnetic tag. As the method evolves, ASL techniques will likely become more widely used in clinical research and practice.

Dual vessel arterial spin labeling scheme for regional perfusion imaging

Regional perfusion imaging (RPI) based on pulsed arterial spin labeling and angulated inversion slabs has been recently proposed. The technique allows mapping of individual brain perfusion territories of the major feeding arteries and could become a valuable clinical tool for evaluation of patients with cerebrovascular diseases. Here we propose a new labeling scheme for RPI where lateral and posterior circulations are labeled simultaneously. Two scans instead of three are sufficient to obtain the same perfusion territories as in the original approach, allowing for a 33% reduction in the total RPI protocol time. Moreover, the position of the inversion slabs with respect to vascular anatomy facilitates the planning and allows potentially better labeling efficiency. The new approach was tested on seven healthy volunteers and compared to the original labeling scheme. The results showed that the same perfusion territories and regional CBF values can be obtained.