Carotid Artery Stenosis: Intraindividual Correlations of 3D Time-of-Flight MR Angiography, Contrast-enhanced MR Angiography, Conventional DSA, and Rotational Angiography for Detection and Grading

ACR Appropriateness Criteria® Cerebrovascular Diseases-Stroke and Stroke-Related Conditions

Cerebrovascular disease encompasses a vast array of conditions. The imaging recommendations for stroke-related conditions involving noninflammatory steno-occlusive arterial and venous cerebrovascular disease including carotid stenosis, carotid dissection, intracranial large vessel occlusion, and cerebral venous sinus thrombosis are encompassed by this document. Additional imaging recommendations regarding complications of these conditions including intraparenchymal hemorrhage and completed ischemic strokes are also discussed. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Diagnostic accuracy of DSA in carotid artery stenosis: a comparison between stenosis measured on carotid endarterectomy specimens and DSA in 644 cases

BACKGROUND AND PURPOSE

DSA (digital subtraction angiography) is the gold standard for measuring carotid artery stenosis (CS). Yet, the correlation between DSA and stenosis is not well documented.

MATERIAL AND METHODS

We compared CS as measured by DSA to carotid artery specimens obtained from carotid endarterectomy surgery. Patients were divided into three groups according to NASCET criteria (North American Symptomatic Carotid Endarterectomy Trial): stenosis of 30-49% (mild), stenosis of 50-69% (moderate), and stenosis of 70-99% (severe).

RESULTS

This prospective cohort study involved 644 patients. The mean stenosis in the mild stenosis group (n = 128 patients) was 54% ECST (European Carotid Surgery Trial), 40% NASCET, and 72% ESs (endarterectomy specimens). The mean absolute difference between ECST and NASCET was 14%. The mean stenosis in the moderate stenosis group (n = 347 patients) was 66% ECST, 60% NASCET, and 77% ES. The mean absolute difference between ECST and NASCET was 6%. The mean stenosis in the severe group (n = 169 patients) was 80% ECST, 76% NASCET, and 79% ES. No significant correlation coefficients were found between DSA and ES methods. In the mild group, the CC was 0.16 (ESCT) and 0.13 (NASCET); in the moderate group, the CC was 0.05 (ESCT) and 0.01 (NASCET); and in the severe group, the CC was 0.23 (ESCT) and 0.10 (NASCET). For all groups combined, CC was 0.22 for the ECST and 0.20 for the NASCET method.

CONCLUSION

The relationship between DSA and ES methods to measure CS is almost random. This lack of a relationship between the DSA and ES techniques questions the validity of current DSA-based guidelines.

MRI and MR angiography evaluation of pulsatile tinnitus: A focused, physiology-based protocol

BACKGROUND AND PURPOSE

Pulsatile tinnitus (PT) is the subjective sensation of a pulse-synchronous sound, most often due to a cerebrovascular etiology. PT can severely impact quality of life and may indicate a life-threatening process, yet a timely and accurate diagnosis can often lead to effective treatment. Clinical assessment with a history and physical examination can often suggest a diagnosis for PT, but is rarely definitive. Therefore, PT should be evaluated with a comprehensive and targeted radiographic imaging protocol. MR imaging provides a safe and effective means to evaluate PT. Specific MR sequences may be used to highlight different elements of cerebrovascular anatomy and physiology. However, routine MR evaluation of PT must comply with economic and practical constraints, while effectively capturing both common and rarer, life-threatening etiologies of PT.

METHODS

In this state-of-the-art review, we describe our institutional MR protocol for evaluating PT.

RESULTS

This protocol includes the following dedicated sequences: time-of-flight magnetic resonance angiography; arterial spin labeling; spoiled gradient recalled acquisition in the steady state; time-resolved imaging of contrast kinetics; diffusion weighted imaging, and 3-dimensional fluid-attenuated inversion recovery.

CONCLUSIONS

We describe the physiologic and clinical rationale for including each MR sequence in a comprehensive PT imaging protocol, and detail the role of MR within the broader evaluation of PT, from clinical presentation to treatment.

Non-contrast mDixon MR angiography of the neck: Comparison with time-of-flight MR angiography in normal subjects

We investigated the feasibility of non-contrast three-dimensional modified Dixon (mDixon) magnetic resonance angiography (MRA) to evaluate the carotid artery.We studied 30 normal patients who underwent non-contrast mDixon and conventional time-of-flight (TOF) MRA of the neck with a clinical 3T MR scanner. Carotid artery signal-to-noise ratio (SNR) and contrast-to-noise ratio were compared between mDixon-MRA and TOF-MRA. Two readers independently evaluated vessel sharpness, image contrast, and overall image quality using a 4-point scale.SNR was significantly higher on mDixon-MRA than TOF-MRA (P < .01). There was no significant difference in contrast-to-noise ratio. The visual score for vessel sharpness was significantly higher on mDixon-MRA than TOF-MRA (P < .01), whereas the score for contrast was significantly higher on TOF-MRA (P < .01).Although non-contrast three-dimensional mDixon-MRA showed lower visual contrast than conventional TOF-MRA, it provided images with significantly higher SNR and better vessel sharpness than TOF-MRA.

Application of MAGnetic resonance imaging compilation in acute ischemic stroke

BACKGROUND

Synthetic magnetic resonance imaging (MRI) MAGnetic resonance imaging compilation (MAGiC) is a new MRI technology. Conventional T1, T2, T2-fluid-attenuated inversion recovery (FLAIR) contrast images, quantitative images of T1 and T2 mapping, and MAGiC phase sensitive inversion recovery (PSIR) Vessel cerebrovascular images can be obtained simultaneously through post-processing at the same time after completing a scan. In recent years, studies have reported that MAGiC can be applied to patients with acute ischemic stroke. We hypothesized that the synthetic MRI vascular screening scheme can evaluate the degree of cerebral artery stenosis in patients with acute ischemic stroke.

AIM

To explore the application value of vascular images obtained by synthetic MRI in diagnosing acute ischemic stroke.

METHODS

A total of 64 patients with acute ischemic stroke were selected and examined by MRI in the current retrospective cohort study. The scanning sequences included traditional T1, T2, and T2-FLAIR, three-dimensional time-of-flight magnetic resonance angiography (3D TOF MRA), diffusion-weighted imaging (DWI), and synthetic MRI. Conventional contrast images (T1, T2, and T2-FLAIR) and intracranial vessel images (MAGiC PSIR Vessel] were automatically reconstructed using synthetic MRI raw data. The contrast-to-noise ratio (CNR) values of traditional T1, T2, and T2-FLAIR images and MAGiC reconstructed T1, T2, and T2-FLAIR images in DWI diffusion restriction areas were measured and compared. MAGiC PSIR Vessel and TOF MRA images were used to measure and calculate the stenosis degree of bilateral middle cerebral artery stenosis areas. The consistency of MAGiC PSIR Vessel and TOF MRA in displaying the degree of vascular stenosis with computed tomography angiography (CTA) was compared.

RESULTS

Among the 64 patients with acute ischemic stroke, 79 vascular stenosis areas showed that the correlation between MAGiC PSIR Vessel and CTA (r = 0.90, P < 0.01) was higher than that between TOF MRA and CTA (r = 0.84, P < 0.01). With a degree of vascular stenosis > 50% assessed by CTA as a reference, the area under the receiver operating characteristic (ROC) curve of MAGiC PSIR Vessel [area under the curve (AUC) = 0.906, P < 0.01] was higher than that of TOF MRA (AUC = 0.790, P < 0.01). Among the 64 patients with acute ischemic stroke, 39 were scanned for traditional T1, T2, and T2-FLAIR images and MAGiC images simultaneously, and CNR values in DWI diffusion restriction areas were measured, which were: Traditional T2 = 21.2, traditional T1 = -6.7, and traditional T2-FLAIR = 11.9; and MAGiC T2 = 7.1, MAGiC T1 = -3.9, and MAGiC T2-FLAIR = 4.5.

CONCLUSION

The synthetic MRI vascular screening scheme for patients with acute ischemic stroke can accurately evaluate the degree of bilateral middle cerebral artery stenosis, which is of great significance to early thrombolytic interventional therapy and improving patients’ quality of life.

Vascular emergencies in neuro-ophthalmology

The cerebral vascularization is assured by the 2 internal carotids and 2 vertebral arteries, and the Willis circle.

Carotid artery obstruction is the most common abnormality associated with ocular ischemic syndrome. Obstruction may be due to atheromatous plaque, external compression, arteritis, or dissection of the artery. An atheromatous lesion of the carotid artery is the most frequent lesion responsible for ocular ischemic syndrome. The signs and symptoms of ocular ischemic syndrome are associated with severe hypoperfusion of the eye. Inflammatory lesions of the carotid artery are responsible for decreased flow in the carotid system. Other vascular emergencies are carotid artery dissection, Horton arteritis, aneurysms and carotid-cavernous fistula.

The most common ocular signs and symptoms are transient monocular blindness, persistent monocular blindness, ocular ischemia, Claude Bernard Horner syndrome and oculomotor palsies.

The carotid pathology can be a life-threatening pathology and it is important to recognize all these signs and symptoms. A multi-specialty approach will prevent misdiagnosis and lead to a better patient management.

Abbreviations: OIS = ocular ischemic syndrome, TMB = transient monocular blindness, TIA = transient ischemic attack, ESR = erythrocyte sedimentation rate, CRP = C reactive protein, NVE = neovascularization elsewhere in the retina, NVD = neovascularization on the disc, AION A = anterior ischemic arteritic optic neuropathy, CBH = Claude Bernard Horner syndrome, MRI = magnetic resonance imaging

Overcoming calcium blooming and improving the quantification accuracy of percent area luminal stenosis by material decomposition of multi-energy computed tomography datasets

Purpose: Conventional stenosis quantification from single-energy computed tomography (SECT) images relies on segmentation of lumen boundaries, which suffers from partial volume averaging and calcium blooming effects. We present and evaluate a method for quantifying percent area stenosis using multienergy CT (MECT) images. Approach: We utilize material decomposition of MECT images to measure stenosis based on the ratio of iodine mass between vessel locations with and without a stenosis, thereby eliminating the requirement for segmentation of iodinated lumen. The method was first assessed using simulated MECT images created with different spatial resolutions. To experimentally assess this method, four phantoms with different stenosis severity (30% to 51%), vessel diameters (5.5 to 14 mm), and calcification densities (700 to 1100    mgHA / cc ) were fabricated. Conventional SECT images were acquired using a commercial CT system and were analyzed with commercial software. MECT images were acquired using a commercial dual-energy CT (DECT) system and also from a research photon-counting detector CT (PCD-CT) system. Three-material-decomposition was performed on MECT data, and iodine density maps were used to quantify stenosis. Clinical radiation doses were used for all data acquisitions. Results: Computer simulation verified that this method reduced partial volume and blooming effects, resulting in consistent stenosis measurements. Phantom experiments showed accurate and reproducible stenosis measurements from MECT images. For DECT and two-threshold PCD-CT images, the estimation errors were 4.0% to 7.0%, 2.0% to 9.0%, 10.0% to 18.0%, and - 1.0 % to - 5.0 % (ground truth: 51%, 51%, 51%, and 30%). For four-threshold PCD-CT images, the errors were 1.0% to 3.0%, 4.0% to 6.0%, - 1.0 % to 9.0%, and 0.0% to 6.0%. Errors using SECT were much larger, ranging from 4.4% to 46%, and were especially worse in the presence of dense calcifications. Conclusions: The proposed approach was shown to be insensitive to acquisition parameters, demonstrating the potential to improve the accuracy and precision of stenosis measurements in clinical practice.

Multiple reader comparison of 2D TOF, 3D TOF, and CEMRA in screening of the carotid bifurcations: Time to reconsider routine contrast use?

Background and purpose

MR contrast-enhanced techniques are undergoing increased scrutiny since the FDA applied a warning for gadolinium-based MR contrast agents due to gadolinium deposition within multiple organ systems. While CE-MRA provides excellent image quality, is it required in a screening carotid study? This study compares 2D TOF and 3D TOF MRA vs. CE-MRA in defining carotid stenosis in a large clinical patient population, and with multiple readers with varying experience.

Materials and methods

200 consecutive patients had their carotid bifurcations evaluated with 2D TOF, 3D TOF and CE-MRA sequences by 6 board-certified neuroradiologists. Stenosis and quality of examinations were defined for each study. Inter-rater reliability was assessed using two-way random effects intraclass correlation coefficients. Intra-reader reliability was computed via weighted Cohen’s κ. Weighted Cohen’s κ were also computed to assess agreement in stenosis ratings between enhanced images and unenhanced images.

Results

Agreement between unenhanced and enhanced ratings was substantial with a pooled weighted κ of 0.733 (0.628–0.811). For 5 of the 6 readers, the combination of unenhanced 2D TOF and 3D TOF showed better agreement with contrast-enhanced than either 2D TOF or 3D TOF alone. Intra-reader reliability was substantial.

Conclusions

The combination of 2D TOF and 3D TOF MRA showed substantial agreement with CE-MRA regarding degree of carotid stenosis in this large outpatient population across multiple readers of varying experience. Given the scrutiny that GBCA are undergoing due to concerns regarding CNS and soft tissue deposition, it seems prudent to reserve CE-MRA for cases which are not satisfactorily answered by the nonenhanced study or other noninvasive examinations.

Clinical evaluation of subtracted pointwise encoding time reduction with radial acquisition-based magnetic resonance angiography compared to 3D time-of-flight magnetic resonance angiography for improved flow dephasing at 3 Tesla

OBJECTIVE

Flow dephasing artifacts within intracranial internal carotid artery (ICA) have been problematic for 3D time-of-flight magnetic resonance angiography (3D-TOF-MRA). This study aimed to evaluate pointwise encoding time reduction with radial acquisition subtraction-based MR angiography (PETRA-MRA) for decreasing flow dephasing artifacts compared to 3D-TOF-MRA in intracranial segments of ICA at 3 T.

METHODS

Sixty healthy participants and seven patients with intracranial ICA aneurysms were enrolled to undergo 3D-TOF-MRA and PETRA-MRA. Two radiologists each evaluated the image quality of healthy participants using a 4-point scale (1: the best and 4: the worst). Quantitative analysis of the extent of homogeneity in signal intensity within the ICA and intracranial aneurysms was conducted using a parameter d: the higher the d value, the greater the signal homogeneity. Wilcoxon signed rank test, Chi-square test and the weighted kappa (κ) statistic were used for statistical analyses.

RESULTS

The image quality of PETRA-MRA with an overall score of 1.35 ± 0.53 was significantly better than that obtained with 3D-TOF-MRA, with an overall score of 3.50 ± 0.62 (Z = -9.56, p < 0.001). The parameter d of PETRA-MRA was higher than that of 3D-TOF-MRA for both 60 healthy participants (0.97 ± 0.05, 0.87 ± 0.11; z = -13.21, p < 0.001) and 7 patients with intracranial aneurysms (0.81 ± 0.18, 0.74 ± 0.16; z = -2.37, p = 0.018).

CONCLUSION

Compared with conventional 3D-TOF-MRA, PETRA-MRA remarkably improved the image quality with reduced flow dephasing artifacts in segments of intracranial ICA.

Delivering the diluted contrast agent with saline via a spiral flow tube improves arterial enhancement for contrast enhancement of magnetic resonance angiography of the neck: A retrospective study

A contrast agent can be pushed by a saline solution more effectively through a spiral flow tube than through a conventional T-shaped tube in contrast-enhanced magnetic resonance angiography (CEMRA). To compare the degree of contrast enhancement and signal stability in the carotid artery by using CEMRA between a spiral flow tube and a T-shaped tube.A total of 100 patients were analyzed in this retrospective study. The first 50 patients underwent CEMRA of the carotid artery with the T-shaped tube, while the last 50 patients used the spiral flow tube. Gadoterate meglumine was diluted with saline to make a total volume of 20 mL. Injection was performed with a bolus rate of 2.5 mL/s for 8 seconds. Five regions of interest (ROIs) were placed on the contrast-enhanced area in each carotid artery and the signal intensity (SI) in the ROI was used for the analysis. The ROIs on the brain stem were also placed and the average SI in this ROI was used as a reference signal. The enhancement of the artery (Eartery) was calculated as a normalized signal using the following equation: Eartery = SI in the ROI of the carotid bifurcation/SI in the ROI of the brain stem. Signal homogeneity in the contrast-enhanced area (SHenhance) was assessed by calculating the coefficient of variation from the SI in the 5 ROIs. The value of SHenhance and Eartery between the data obtained from the spiral flow tube and the T-shaped tube were compared. P-values <.05 were considered significant.We found a significant difference in SHenhance between the data obtained from the spiral flow tube (0.20 ± 0.060) and the T-shaped tube (0.24 ± 0.056) (P = .001). The Eartery values significantly increased by 15% (spiral flow tube, median 14.1 with interquartile range [IQR] 11.8-15.4 vs T-shaped tube, median 12.3 IQR 11.3-14.0, P = .02) using the spiral flow tube.These findings suggest that, by using the Spiral flow tube, the homogeneity of the contrast-enhanced signal intensity in the carotid artery was significantly improved without decreasing the signal intensity in CEMRA.

The role of multislice computerized tomography angiography in assessing postoperative vascular complications in liver transplant patients

Background/aim

Vascular complications can be detected in liver transplant patients. Digital subtraction angiography has served as the gold standard to make this diagnosis; however, due to its invasive nature, ultrasonography is used for the preliminary evaluation. The purpose of this study was to evaluate the role of multislice computerized tomography angiography (MSCTA) in the detection of vascular complications of symptomatic and asymptomatic liver transplant patients and to compare the results with Doppler ultrasound (Doppler US) findings.

Materials and methods

Fifty-three liver transplant patients (6 symptomatic, 47 asymptomatic) underwent Doppler US examination followed by an MSCTA. The findings in each modality were interpreted in a blinded fashion and then compared.

Results

MSCTA detected 15 abnormalities, none of which were detected by Doppler US. There were hepatic and splenic artery aneurysms (n = 4) and various stenoses (n = 4), infrarenal aortic anastomosis (n = 4), vena cava inferior thrombosis (n = 1), arteriovenous malformation (n = 1), and esophageal varices (n = 1).

Conclusion

MSCTA detected more lesions and we believe that it should be considered as a road map for Doppler US follow-ups as well as a routine screening modality for early detection of vascular complications in symptomatic and asymptomatic liver transplantation patients that may be missed by Doppler US.

Improved carotid lumen delineation on non-contrast MR angiography using SNAP (Simultaneous Non-Contrast Angiography and Intraplaque Hemorrhage) imaging

PURPOSE

Simultaneous Non-Contrast Angiography and Intraplaque Hemorrhage (SNAP) was developed for improved imaging of intraplaque hemorrhage (IPH). Its signal polarity also allows for non-contrast time-of-flight MR angiography (TOF). This study sought to compare SNAP and TOF in delineating carotid lumen using contrast-enhanced MRA (CE-MRA) as the reference standard.

MATERIALS AND METHODS

Two hundred and eighty-nine matched slices from 15 arteries among 11 subjects (9 males and 2 females, mean age of 72.1 ± 8.6 years) with luminal stenosis on CE-MRA were studied. Cross-sectional slices centered around the carotid bifurcation were matched between the three MRA techniques (SNAP, TOF, and CE-MRA) and classified as slices with or without plaque (focal wall thickness ≥ 1.5 mm) by additional black-blood vessel wall MRI. Lumen area was measured using a Sobel gradient map for TOF and CE-MRA (magnitude images) and a polarity map for SNAP. Agreement between techniques for measuring lumen area and percent stenosis was evaluated using intraclass correlation coefficient (ICC) and paired t-test.

RESULTS

Among the 289 matched slices, SNAP showed a higher agreement with CE-MRA than TOF for measuring lumen area (ICC: 0.93 vs. 0.83; p = 0.03). Agreement with CE-MRA was high for both SNAP and TOF in slices without plaque (ICC: 0.91 vs. 0.89; p > 0.05) but favored SNAP over TOF in slices with plaque (ICC: 0.93 vs. 0.80; p = 0.02).

CONCLUSION

SNAP, assisted by signal polarity information, demonstrated a higher agreement with CE-MRA in delineating carotid lumen compared to TOF, particularly in slices with plaque where flow conditions may be more complex.

Evaluation of four injection profiles for uniform contrast-enhanced signal intensity profiles in MR angiography

BACKGROUND

Gadolinium concentration variation during acquisition of contrast-enhanced MR angiography (CE-MRA) may lead to artifacts.

PURPOSE

To compare signal intensity (SI) profiles of four different contrast agent injection strategies during CE-MRA with the goal of minimizing SI variation during acquisition.

STUDY TYPE

Prospective.

SUBJECTS

Forty subjects randomized to receive one of four injection profiles of gadobenate dimeglumine (0.1 mmol/kg), either undiluted (0.5 M) or diluted to 40 ml total volume. Tested profiles: 1) nondiluted single-phase ("standard" NS; 1.6 ml/s), 2) diluted single-phase (DS; 1.6 ml/s), 3) diluted biphasic (DB; 9 ml @ 3.3 ml/s, 29 ml @ 1.4 ml/s), 4) patient-tailored protocol using linear prediction (DT).

FIELD STRENGTH/SEQUENCE

Time-resolved SI measured at 3T with spoiled gradient echo sequences having analogous parameters to those of CE-MRA.

ASSESSMENT

Plateau arrival time, rise time, duration, peak and tail SI, plateau quality (sum of squared residuals; SSR), average SI for each injection type derived were used.

STATISTICAL TEST

Two-tailed t-test.

RESULTS

Peak SI, arrival, and rise times were not significantly different between groups, excepting peak SI DB slightly > DS (P = 0.042). Duration of NS vs. the diluted groups was significantly shorter (all P < 0.0001), and DS duration was significantly shorter than that of DT and DB (NS 11.4 ± 3.5 vs. DS 22.9 ± 4.3, DB 25.4 ± 2.3, DT 28.3 ± 4.1 sec). Quality (SSR) of the 20-second plateau was significantly better for DS, DB, DT as compared with NS (all P < 0.001).

DATA CONCLUSION

Three different strategies to power-inject diluted gadobenate dimeglumine targeting a 20-second plateau produced SI profiles with longer duration, more consistent plateau, and no significant loss in peak SI. Such injection profiles may provide more uniform SI during CE-MRA, potentially reducing blurring artifacts.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:1808-1816.

Ultrasound assessment of carotid arteries: Current concepts, methodologies, diagnostic criteria, and technological advancements

Following cardiac disease and cancer, stroke continues to be the third leading cause of death and disability due to chronic disease in the developed world. Appropriate screening tools are integral to early detection and prevention of major cardiovascular events. In a carotid artery, the presence of increased intima-media thickness, plaque, or stenosis is associated with increased risk of a transient ischemic attack or a stroke. Carotid artery ultrasound remains a long-standing and reliable tool in the current armamentarium of diagnostic modalities used to assess vascular morbidity at an early stage. The procedure has, over the last two decades, undergone considerable upgrades in technology, approach, and utility. This review examines in detail the current state and usage of this integrally important means of extracranial cerebrovascular assessment.

Comparison of extracranial artery stenosis and cerebral blood flow, assessed by quantitative magnetic resonance, using digital subtraction angiography as the reference standard

Extracranial arteriosclerosis usually indicates a high risk of ischemic stroke. In the past, a clinical decision following diagnosis was dependent on the percentage of vessel stenosis determined by an invasive technique. We aimed to develop a quantitative magnetic resonance (QMR) technique to evaluate artery structure and cerebral hemodynamics noninvasively.QMR and digital subtraction angiography (DSA) were performed in 67 patients with suspected cerebral vascular disease at our hospital. Accuracy, sensitivity, positive predictive values (PPVs), negative predictive values (NPVs), and Pearson correlation coefficient of QMR were calculated and compared for the detection and measurement of vascular stenoses using DSA as a gold standard. For patients with unilateral artery stenosis, quantitative cerebral blood flow (CBF) was measured by QMR in ipsilateral and contralateral hemispheres.Among 67 subjects (male 54, female 12), 201 stenoses were detected by QMR and DSA. QMR measuring the degree of stenosis and lesion length was in good correlation with the results obtained by DSA (r = 0.845, 0.721, respectively). As for artery stenosis, PPV and NPV of QMR were 89.55% and 95.71%, respectively. As for severe stenosis, sensitivity and specificity of QMR were 82.3% and 86.0% with DSA as a reference. For subjects with unilateral carotid stenosis, CBF in basal ganglia decreased significantly (P < 0.001) compared with the contralateral one in symptomatic and asymptomatic groups. For subjects with moderate stenosis (50-79%), CBF of temporal and basal ganglia was decreased compared with the contralateral ganglia. However, CBF in subjects with severe stenosis or occlusion in the basal ganglia was mildly elevated compared with the contralateral ganglia (P < 0.001).In our study, a good correlation was found between QMR and DSA when measuring artery stenosis and CBF. QMR may become an important method for measuring artery stenosis and cerebral hemodynamics in the future.

Artefacts at a glance: differentiating features of artefactual stenosis from true stenosis at the genu of the petrous internal carotid artery on TOF MRA

AIM

To investigate the distinguishing features of artefactual stenosis from true stenosis at the genu of the petrous internal carotid artery (ICA) on time of flight (TOF) magnetic resonance angiography (MRA).

MATERIALS AND METHODS

Both TOF MRA and digital subtraction angiography (DSA) were performed in 65 patients with 74 vessels who demonstrated artefactual stenosis in 43 patients with 50 vessels and true stenosis in 22 patients with 24 vessels. The following findings of the signal loss were compared between the two groups: (1) margin, (2) darkness, (3) the presence of bilaterality, (4) the presence of tandem arterial stenosis, (5) the location of the epicentre, and (6) length.

RESULTS

In five out of the six evaluated items, statistically significant differences were present between the two groups (p<0.00 in all five items). Artefactual stenosis more frequently showed signal loss with ill-defined margins (47/50), less darkness compared to the background darkness (46/50), the absence of tandem arterial stenosis (35/50), epicentre at the genu (34/50), and shorter length (2.57 ± 0.68 mm). No significant difference was noted in the presence of bilaterality of signal loss between the two groups (p=0.706).

CONCLUSION

Several MRA features can be useful for suggesting artefactual stenosis rather than true stenosis at the genu of the petrous ICA on TOF MRA.

Multimodality Imaging of Carotid Stenosis

Four diagnostic modalities are used to image the following internal carotid artery: digital subtraction angiography (DSA), duplex ultrasound (DUS), computed tomography angiography (CTA), and magnetic resonance angiography (MRA). The aim of this article is to describe the potentials of these techniques and to discuss their advantages and disadvantages. Invasive DSA is still considered the gold standard and is an indivisible part of the carotid stenting procedure. DUS is an inexpensive but operator-dependent tool with limited visibility of the carotid artery course. Conversely, CTA and MRA allow assessment of the carotid artery from the aortic arch to intracranial parts. The disadvantages of CTA are radiation and iodine contrast medium administration. MRA is without radiation but contrast-enhanced MRA is more accurate than noncontrast MRA. The choice of methods depends on the clinical indications and the availability of methods in individual centers. However, the general approach to patient with suspected carotid artery stenosis is to first perform DUS and then other noninvasive methods such as CTA, MRA, or transcranial Doppler US.

Computed Tomography Angiography of Carotid Arteries and Vertebrobasilar System: A Simulation Study for Radiation Dose Reduction

Computed tomography angiography (CTA) of carotid arteries and vertebrobasilar system is a standardized procedure with excellent image quality, but radiation exposure remains a matter of concern. The aim of this study is to examine to what extent radiation dose can be lowered in relation to a standard protocol by simulating examinations with lower tube currents applying a dedicated software.Lower tube current was simulated by a dedicated noise insertion and reconstruction software (ReconCT). In a phantom study, true scans were performed with different dose protocols and compared to the results of simulated dose reductions of the same degree, respectively. In a patient study, 30 CTAs of supra-aortic vessels were reconstructed at a level of 100%, 75%, 50%, and 25% of the initial dose. Objective and subjective image analyses were performed.No significant noise differences between true scans and simulated scans of mimicked contrasted vessels were found. In the patient study, the quality scores of the 4 dose groups differed statistically significant; this difference vanished for the comparison of the 100% and 75% datasets after dichotomization into the categories of diagnostic and nondiagnostic image quality (P = .50).This study suggests an easy-to-implement method of simulating CTAs of carotid arteries and vertebrobasilar system with lower tube current for dose reduction by artificially adding noise to the original raw data. Lowering the radiation dose in a moderate extent to 75% of the original dose levels does not significantly alter the diagnostic image quality.

Optimal MRI sequence for identifying occlusion location in acute stroke: which value of time-resolved contrast-enhanced MRA?

BACKGROUND AND PURPOSE

Identifying occlusion location is crucial for determining the optimal therapeutic strategy during the acute phase of ischemic stroke. The purpose of this study was to assess the diagnostic efficacy of MR imaging, including conventional sequences plus time-resolved contrast-enhanced MRA in comparison with DSA for identifying arterial occlusion location.

MATERIALS AND METHODS

Thirty-two patients with 34 occlusion levels referred for thrombectomy during acute cerebral stroke events were consecutively included from August 2010 to December 2012. Before thrombectomy, we performed 3T MR imaging, including conventional 3D-TOF and gradient-echo T2 sequences, along with time-resolved contrast-enhanced MRA of the extra- and intracranial arteries. The 3D-TOF, gradient-echo T2, and time-resolved contrast-enhanced MRA results were consensually assessed by 2 neuroradiologists and compared with prethrombectomy DSA results in terms of occlusion location. The Wilcoxon test was used for statistical analysis to compare MR imaging sequences with DSA, and the κ coefficient was used to determine intermodality agreement.

RESULTS

The occlusion level on the 3D-TOF and gradient-echo T2 images differed significantly from that of DSA (P < .001 and P = .002, respectively), while no significant difference was observed between DSA and time-resolved contrast-enhanced MRA (P = .125). κ coefficients for intermodality agreement with DSA (95% CI, percentage agreement) were 0.43 (0.3%-0.6; 62%), 0.32 (0.2%-0.5; 56%), and 0.81 (0.6%-1.0; 88%) for 3D-TOF, gradient-echo T2, and time-resolved contrast-enhanced MRA, respectively.

CONCLUSIONS

The time-resolved contrast-enhanced MRA sequence proved reliable for identifying occlusion location in acute stroke with performance superior to that of 3D-TOF and gradient-echo T2 sequences.

Highly undersampled contrast-enhanced MRA with iterative reconstruction: Integration in a clinical setting

PURPOSE

To integrate, optimize, and evaluate a three-dimensional (3D) contrast-enhanced sparse MRA technique with iterative reconstruction on a standard clinical MR system.

METHODS

Data were acquired using a highly undersampled Cartesian spiral phyllotaxis sampling pattern and reconstructed directly on the MR system with an iterative SENSE technique. Undersampling, regularization, and number of iterations of the reconstruction were optimized and validated based on phantom experiments and patient data. Sparse MRA of the whole head (field of view: 265 × 232 × 179 mm(3) ) was investigated in 10 patient examinations.

RESULTS

High-quality images with 30-fold undersampling, resulting in 0.7 mm isotropic resolution within 10 s acquisition, were obtained. After optimization of the regularization factor and of the number of iterations of the reconstruction, it was possible to reconstruct images with excellent quality within six minutes per 3D volume. Initial results of sparse contrast-enhanced MRA (CEMRA) in 10 patients demonstrated high-quality whole-head first-pass MRA for both the arterial and venous contrast phases.

CONCLUSION

While sparse MRI techniques have not yet reached clinical routine, this study demonstrates the technical feasibility of high-quality sparse CEMRA of the whole head in a clinical setting. Sparse CEMRA has the potential to become a viable alternative where conventional CEMRA is too slow or does not provide sufficient spatial resolution.

Impact of 3D Rotational Angiography on Liver Embolization Procedures: Review of Technique and Applications

In the last years, the interest into interventional applications of C-arm cone-beam CT (CBCT) progressively raised, widening its clinical application from the original field of interventional neuroradiology to the field of peripheral procedures. Liver embolization procedures, due to their complexity and potential treatment-related life-threatening complications, represent one of the main clinical applications of this novel angiographic technique. CBCT has been demonstrated to render procedures safer and technically easier, and to predict outcome as well as to avoid major complications in different treatment scenarios (trans-arterial embolization, trans-arterial chemoembolization, selective internal radiation therapy, percutaneous portal vein embolization). This review summarizes all technical, dosimetric and procedural aspects of CBCT techniques, underlying all its potential clinical advantages in the field of liver embolization procedures. Moreover, the paper provides all the instructions to obtain the best diagnostic performance out of this novel angiographic technique.

Whole body magnetic resonance angiography and computed tomography angiography in the vascular mapping of head and neck: an intraindividual comparison

Introduction

The aim of the study was to compare the detectability of neck vessels with contrast enhanced magnetic resonance angiography (MRA) in the setting of a whole-body MRA and multislice computed tomography angiography (CTA) for preoperative vascular mapping of head and neck.

Methods

In 20 patients MRA was performed prior to microvascular reconstruction of the mandible with osteomyocutaneous flaps. CTA of the neck served as the method of reference.

1.5 T contrast enhanced magnetic resonance angiograms were acquired to visualize the vascular structures of the neck in the setting of a whole-body MRA examination. 64-slice spiral computed tomography was performed with a dual-phase protocol, using the arterial phase images for 3D CTA reconstruction. Maximum intensity projection was employed to visualize MRA and CTA data. To retrieve differences in the detectability of vessel branches between MRA and CTA, a McNemar test was performed.

Results

All angiograms were of diagnostic quality. There were no statistically significant differences between MRA and CTA for the detection of branches of the external carotid artery that are relevant host vessels for microsurgery (p = 0.118). CTA was superior to MRA if all the external carotid artery branches were included (p < 0.001).

Conclusions

MRA is a reliable alternative to CTA in vascular mapping of the cervical vasculature for planning of microvascular reconstruction of the mandible. In the setting of whole-body MRA it could serve as a radiation free one-stop-shop tool for preoperative assessment of the arterial system, potentially covering both, the donor and host site in one single examination.

Carotid Artery Stenosis: Comparison of 3D Time-of-Flight MR Angiography and Contrast-Enhanced MR Angiography at 3T

Purpose. The aim of this study was to assess the correlation of 3D time-of-flight MR angiography (TOF MRA) and contrast-enhanced MR angiography (CEMRA) for carotid artery stenosis evaluation at 3T. Material and Methods. Twenty-three patients (5 f, 18 m; mean age 61 y, age range 45–78 y) with internal carotid artery stenosis detected with ultrasonography were examined on a 3.0T MR system. The MR examination included both 3D TOF MRA and CEMRA of the carotid arteries. MR images were evaluated independently by two board-certified radiologists. Stenosis evaluation was based on a five-point scale. Stenosis grades determined by TOF and CEMRA were compared using Spearman's rank correlation coefficient and the Wilcoxon test. Cohen's Kappa was used to evaluate interrater reliability. Results. CEMRA detected stenosis in 24 (52%) of 46 carotids evaluated, while TOF detected stenosis in 27 (59%) of 46 carotids. TOF MRA yielded significantly higher results for stenosis grade in comparison to CEMRA (P = 0.014). Interrater agreement was very good for both TOF MRA (κ = 0.93) and CEMRA (κ = 0.93). Conclusion. At 3T, 3D TOF MRA should not be used as replacement for contrast-enhanced MRA of the carotid arteries, as it results in significantly higher stenosis grades.

Dynamic and static magnetic resonance angiography of the supra-aortic vessels at 3.0 T: intraindividual comparison of gadobutrol, gadobenate dimeglumine, and gadoterate meglumine at equimolar dose

PURPOSE

The purpose of this study was the intraindividual comparison of a 1.0 M and two 0.5 M gadolinium-based contrast agents (GBCA) using equimolar dosing in dynamic and static magnetic resonance angiography (MRA) of the supra-aortic vessels.

MATERIALS AND METHODS

In this institutional review board-approved study, a total of 20 healthy volunteers (mean ± SD age, 29 ± 6 years) underwent 3 consecutive supra-aortic MRA examinations on a 3.0 T magnetic resonance system. The order of GBCA (Gadobutrol, Gadobenate dimeglumine, and Gadoterate meglumine) was randomized with a minimum interval of 48 hours between the examinations. Before each examination and 45 minutes after each examination, circulatory parameters were recorded. Total GBCA dose per MRA examination was 0.1 mmol/kg with a 0.03 mmol/kg and 0.07 mmol/kg split for dynamic and static MRA, respectively, injected at a rate of 2 mL/s. Two blinded readers qualitatively assessed static MRA data sets independently using pairwise rankings (superior, inferior, and equal). In addition, quantitative analysis was performed with signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) evaluation as well as vessel sharpness analysis of static MRA using an in-house-developed semiautomated tool. Dynamic MRA was evaluated for maximal SNR. Statistical analysis was performed using the Cohen κ, the Wilcoxon rank sum tests, and mixed effects models.

RESULTS

No significant differences of hemodynamic parameters were observed. In static MRA, Gadobutrol was rated superior to Gadoterate meglumine (P < 0.05) and equal to Gadobenate dimeglumine (P = 0.06) with good to excellent reader agreement (κ, 0.66-0.83). In static MRA, SNR was significantly higher using 1.0 M Gadobutrol as compared with either 0.5 M agent (P < 0.05 and P < 0.05) and CNR was significantly higher as compared with Gadoterate meglumine (P < 0.05), whereas CNR values of Gadobutrol data sets were not significantly different as compared with Gadobenate dimeglumine (P = 0.13). Differences in CNR between Gadobenate dimeglumine and Gadoterate meglumine were not significant (P = 0.78). Differences in vessel sharpness between the different GBCAs were also not significant (P > 0.05). Maximal SNR in dynamic MRA using Gadobutrol was significantly higher than both comparators at the level of the proximal and distal internal carotid artery (P < 0.05 and P < 0.05; P < 0.05 and P < 0.05).

CONCLUSIONS

At equimolar doses, 1.0 M Gadobutrol demonstrates higher SNR/CNR than do Gadobenate dimeglumine and Gadoterate meglumine, with superior image quality as compared with Gadoterate meglumine for dynamic and static carotid MRA. Despite the shortened bolus with Gadobutrol, no blurring of vessel edges was observed.

Multicenter, intraindividual comparison of single-dose gadobenate dimeglumine and double-dose gadopentetate dimeglumine for MR angiography of the supra-aortic arteries (the Supra-Aortic VALUE study)

BACKGROUND AND PURPOSE

Gadobenate dimeglumine has markedly higher R1 relaxivity compared to gadopentetate dimeglumine meaning that lower doses can be used to achieve similar contrast enhancement. Our aim was to prospectively compare single-dose gadobenate dimeglumine with double-dose gadopentetate dimeglumine for contrast-enhanced MRA of the supra-aortic vasculature.

MATERIALS AND METHODS

Forty-six patients (37 men, 9 women; mean age, 63.5±10.1 years) with known or suspected steno-occlusive disease of the supra-aortic vessels underwent 2 identical CE-MRA examinations at 1.5T. Contrast agents were administered in randomized order, with the 2-fold greater volume of gadopentetate dimeglumine injected at a 2 times faster rate. Image assessment was performed by 3 independent blinded readers for vessel anatomic delineation, detection/exclusion of pathology, and global preference. Diagnostic performance (sensitivity, specificity, accuracy, PPV, and NPV) for detection of ≥60% stenosis was determined for 39/46 patients who underwent preinterventional DSA. Data were analyzed by using the Wilcoxon signed-rank, McNemar, and Wald tests in terms of the noninferiority of single-dose gadobenate dimeglumine compared with double-dose gadopentetate dimeglumine. Quantitative enhancement (signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR)) was also compared.

RESULTS

All images were technically adequate. No differences (P=1.0) were noted by any reader for any qualitative parameter. All readers considered single-dose gadobenate dimeglumine and double-dose gadopentetate dimeglumine equivalent in at least 42/46 patients (91.3% three-reader agreement) for all parameters. Nonsignificant superiority for gadobenate dimeglumine was reported for all diagnostic performance indicators (sensitivity: 82.7%-88.5% versus 75.0%-80.8%; specificity: 96.4%-98.6% versus 94.6%-98.6%; accuracy: 94.6%-96.1% versus 92.4%-94.9%; PPV: 81.5%-91.5% versus 73.7%-90.7%; NPV: 96.8%-97.8% versus 95.4%-96.4%). No differences (P>.05) in quantitative enhancement were noted.

CONCLUSIONS

The image quality and diagnostic performance achieved with 0.1-mmol/kg gadobenate dimeglumine is at least equivalent to that achieved with 0.2-mmol/kg gadopentetate dimeglumine.

Contrast-enhanced magnetic resonance angiography

Magnetic resonance (MR) angiography is a powerful tool for the evaluation of cervical and intracranial vasculature. Both noncontrast and contrast-enhanced MR angiography can provide exquisite vascular contrast and detail without the use of ionizing radiation. More advanced techniques such as time-resolved MR angiography and parallel imaging provide dynamic information in rapid fashion. This article describes the basic principles and techniques of MR angiography image acquisition.

Imaging of the carotid artery

In the study of carotid arteries, modern techniques of imaging allow to analyze various alterations beyond simple luminal narrowing, including the morphology of atherosclerotic plaques, the arterial wall and the surrounding structures. By using CTA and MRI it is possible to obtain three-dimensional rendering of anatomic structures with excellent detail for treatment planning. This paper will detail the role of various imaging methods for the assessment of carotid artery pathology with emphasis on the detection, analysis and characterization of carotid atherosclerosis.

Whole-body MR angiography: initial experience in imaging pediatric vasculopathy

Radiological assessment of vasculopathy in children is typically undertaken with ultrasonography, echocardiography, conventional angiography, computed tomography and, more recently, positron emission tomography. Drawbacks of these modalities include radiation exposure or, in the case of ultrasonography, the dependence on operator skills and sufficient acoustic windows. With advancements in MR technology, which have improved sensitivity and shortened scan times, whole-body magnetic resonance angiography (WB-MRA) lends itself as a potential "one-stop shop" for vascular imaging. Currently, WB-MRA is primarily used in adult patients with atherosclerosis or multifocal regional vasculopathy. WB-MRA has not been employed in the routine assessment of pediatric vascular disease. The purpose of this article is to describe and illustrate our WB-MRA imaging technique for evaluation of pediatric vasculopathy.

Evaluation of inflammatory status of atherosclerotic carotid plaque before thromboendarterectomy using delayed contrast-enhanced subtracted images after magnetic resonance angiography

OBJECTIVE

To investigate the correlation among carotid plaque contrast enhancement (CPCE) at MRI, inflammatory cell infiltration (ICI) at histopathology, and carotid stenosis degree.

MATERIALS AND METHODS

Twenty-eight patients (19 males; mean age 67±9 years) scheduled for thromboendarterectomy prospectively underwent 1.5-T MR imaging using: (a) axial T1-weighted gradient-echo (T1wGRE) sequence centered on carotid bifurcations; (b) contrast-enhanced MR angiography (CE-MRA) with 0.1 mmol/kg of gadobenate dimeglumine; (c) enhanced axial T1wGRE sequence as in (a), 3 min after contrast injection. A three-point score system (absent, focal, wide) was used to assess CPCE on native and subtracted MRI images (c minus a) and ICI at histopathology. Carotid stenosis degree was determined on CE-MRA.

RESULTS

Six CPCE studies were discarded due to patient movement. In the remaining 22 studies, CPCE was absent, focal and wide in 13, 6 and 3 cases, respectively; ICI was absent, focal and wide in 13, 7 and 2 cases, respectively (k=0.57). On CE-MRA 21/28 stenoses were severe and 7/28 moderate. There was no correlation either with ICI (p=1.000, n=28) or CPCE (p=0.747, n=22).

CONCLUSION

The correlation between CPCE and ICI suggests a role for CPCE as an independent marker of plaque inflammation.

Overestimation of moderate carotid stenosis assessed by both Doppler US and contrast enhanced 3D-MR angiography in the CARMEDAS study

PURPOSE

To evaluate the agreement and diagnostic accuracy of Contrast enhanced magnetic resonance angiography (CE-MRA), Doppler ultrasound (DUS) and Digital subtraction angiography (DSA) in the assessment of carotid stenosis.

METHODS

DUS, CE-MRA and DSA were performed in 56 patients included in the Carotide-angiographie par résonance magnétique-échographie-doppler-angioscanner (CARMEDAS) multicenter study with a carotid stenosis ≥ 50%. Three readers evaluated stenoses on CE-MRA and DSA (NASCET criteria). Velocities criteria were used for stenosis estimation on DUS.

RESULTS

CE-MRA had a sensitivity and specificity of 96-98% and 66-83% respectively for carotid stenoses ≥ 50% and a sensitivity and specificity of 94% and 76-84% respectively for carotid stenoses ≥ 70%. The interobserver agreement of CE-MRA was excellent, except for moderate stenoses (50-69%). DUS had a sensitivity and specificity of 88 and 75% respectively for carotid stenoses ≥ 50% and a sensitivity and specificity of 83 and 86% respectively for carotid stenoses ≥ 70%. Combined concordant CE-MRA and DUS had a sensitivity and specificity of 100 and 85-90% respectively for carotid stenoses ≥ 50% and a sensitivity and specificity of 96-100% and 80-87% respectively for carotid stenoses ≥ 70%. The positive predictive value of the association CE-MRA and DUS for carotid stenoses ≥ 70% is calculated between 77 and 82% while the negative predictive value is calculated between 97 and 100%. CE-MRA and DUS have concordant findings in 63-72%, and the overestimations cases were recorded only for carotid stenosis ≤ 69%.

CONCLUSION

Combined DUS-CE-MRA is excellent for evaluation of severe stenosis but remains debatable in moderate stenosis (50-69%) due to the risk of overestimations.

[CT diagnostics of carotid artery stenosis]

CT angiography can be used to evaluate carotid artery stenosis with high diagnostic safety. In contrast to the gold standard digital subtraction angiography (DSA) it is a non-invasive procedure which yields information regarding the degree of stenosis as well as information about plaque morphology. Due to multiple reconstruction planes in 3 levels in maximum intensity projections (MIP) and the possibility to perform volume rendering (VR) reconstruction more information about the extent of carotid disease can be acquired. Due to the bolus tracking technique optimum contrast medium enhancement of the carotid artery with simultaneous minimization of venous artifacts is possible.

Randomized trial of predilation versus direct stenting for treatment of carotid artery stenosis

BACKGROUND

A controversial aspect of carotid artery stenting (CAS) is the placement of a stent with or without predilation. The study was designed to test the hypothesis that direct stenting (DS) was not inferior to CAS with predilation.

METHODS

Elective CAS with filter protection was performed in 205 consecutive, unselected patients with carotid artery stenosis (>50% if symptomatic and > or =75% if asymptomatic by Doppler assessment) who were randomly assigned to CAS with predilation (n=100) or direct stenting (DS, n=105). Filter and stent selection were left to the operator's discretion. The study end-point was the angiographic success, defined as < or =30% angiographic residual stenosis after CAS without abnormal angiographic findings in cerebral circulation and without cross-over to predilation in the DS group.

RESULTS

At baseline, patient clinical characteristics and stenosis anatomic features did not differ between groups. Angiographic success was 99% and 97%, p=0.33, in predilation and DS, respectively. No cross-over to predilation occurred in the DS group. Procedural time was shorter in DS as compared to predilation (24.3+/-7% versus 19.9+/-6%, p=0.001) and visible debris were more frequently captured in predilation as compared to DS (50% versus 36%, p=0.003). No peri-procedural and 30-day death or major stroke occurred in both groups. Minor stroke and TIA rates were similar in either group (2% versus 0% and 8% versus 5.7%, p=ns, respectively).

CONCLUSION

In an unselected, consecutive series of patients submitted to CAS, DS is a feasible technique and is not inferior to CAS with predilation.

Measurement of carotid stenosis on computed tomographic angiography: reliability depends on postprocessing technique

PURPOSE

We previously demonstrated the validity of axial source (AxS) image quantification of computed tomographic angiography (CTA) visualized carotid stenosis. There is concern that AxS images may not accurately measure stenosis in patients with obliquely orientated stenosis and that measurements on axial oblique (AxO) multiplanar reformats (MPR), maximum intensity projections (MIP) images, or Doppler ultrasound (DUS) are superior. We tested the performance of AxS images against AxO MPRs, MIPs, and DUS techniques for stenosis quantification.

METHODS

A total of 120 consecutive patients with CTA and DUS detected carotid disease were enrolled; carotids with occlusion, near occlusion, or stenosis <40% were excluded. Proximal and distal carotid diameters and North American Symptomatic Carotid Endarterectomy Trial (NASCET) style ratios were measured independently by 2 neuroradiologists on AxS, AxO, and MIP images on separate occasions in a blinded protocol. Intra- and interobserver agreements were determined for all measurements. The performance of different image types to identify > or =70% stenosis was assessed against a NASCET-style reference standard.

RESULTS

Intra- and interobserver reliabilities for stenosis measurements were higher for both AxS (interclass correlation coefficients [ICC], 0.87-0.93 and 0.84-0.89) and AxO images (ICCs, 0.82-0.89 and 0.86-0.92) than for MIPs (ICCs, 0.66-0.86 and 0.79-0.82), respectively. Intra- and interobserver agreements on the NASCET ratio tended to be lower than proximal stenosis measurements. AxS and AxO image proximal stenosis measurements most accurately distinguished patients with > or =70% stenosis (0.90), followed by DUS (0.83) and MIP images (0.76).

CONCLUSIONS

A single AxS image stenosis measurement was highly reproducible and accurate in the estimation of carotid stenosis, which precluded the need for AxO MPRs.

Magnetic resonance angiography of the extracranial carotid system

OBJECTIVES

To discuss the role of magnetic resonance angiography (MRA) in the evaluation of the extracranial carotid system with an emphasis on atherosclerosis and to briefly address the role of magnetic resonance imaging in imaging of carotid atherosclerotic plaque.

METHODS

Literature and institutional review.

DISCUSSION

The North American Symptomatic Carotid Endarterectomy Trial and European Carotid Surgery Trial studies have emphasized the importance of recognition and treatment of carotid stenosis in the prevention of ischemic stroke. Magnetic resonance angiography is a viable tool in the screening and quantification of this entity. Both time of flight and contrast-enhanced MRA techniques are available for clinical use, each with distinct advantages and limitations. A thorough understanding of these is vital for correct performance and interpretation of these studies. Plaque imaging with magnetic resonance imaging offers new insights into the pathophysiology of the atherosclerotic process and may be used in the future to monitor response to lipid-lowering drug therapy.

CONCLUSION

Magnetic resonance angiography is a robust imaging technique for evaluation of the extracranial carotid circulation. The radiologist must be aware of the advantages and limitations of the different techniques available. Contrast-enhanced MRA is now the most widely performed technique. It can be used to replace digital subtraction angiography in the evaluation of carotid stenosis in most clinical settings.

Neurovascular imaging at 1.5 tesla versus 3.0 tesla

The primary advantage of high field strength MR imaging over imaging on modern 1.5 Tesla (T) systems is increased signal-to-noise ratio, which can be used to improve image quality or shorten scan acquisition time. In the years since 3.0T scanners were first approved for clinical use, one of the areas which has benefited greatly from its introduction is neurovascular MR angiography (MRA). Early experience has shown significant improvements in resolution and image quality. Whether high field strength MRA is robust or accurate enough to replace digital subtraction angiography in the foreseeable future remains to be seen. This article discusses the current state of neurovascular MRA at 3.0T, basic physical differences between MR imaging at 1.5T and 3.0T, and their effects on MRA sequences. The literature regarding the efficacy of 3.0T MRA techniques for diagnosing specific neurovascular pathologies and carotid steno occlusive disease is reviewed.

Gadofosveset-enhanced MR angiography of carotid arteries: does steady-state imaging improve accuracy of first-pass imaging? Comparison with selective digital subtraction angiography

PURPOSE

To evaluate the diagnostic accuracy of gadofosveset-enhanced magnetic resonance (MR) angiography in the assessment of carotid artery stenosis, with digital subtraction angiography (DSA) as the reference standard, and to determine the value of reading first-pass, steady-state, and "combined" (first-pass plus steady-state) MR angiograms.

MATERIALS AND METHODS

This study was approved by the local ethics committee, and all subjects gave written informed consent. MR angiography and DSA were performed in 84 patients (56 men, 28 women; age range, 61-76 years) with carotid artery stenosis at Doppler ultrasonography. Three readers reviewed the first-pass, steady-state, and combined MR data sets, and one independent observer evaluated the DSA images to assess stenosis degree, plaque morphology and ulceration, stenosis length, and tandem lesions. Interobserver agreement regarding MR angiographic findings was analyzed by using intraclass correlation and Cohen kappa coefficients. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated by using the McNemar test to determine possible significant differences (P < .05).

RESULTS

Interobserver agreement regarding all MR angiogram readings was substantial. For grading stenosis, sensitivity, specificity, PPV, and NPV were, respectively, 90%, 92%, 91%, and 91% for first-pass imaging; 95% each for steady-state imaging; and 96%, 99%, 99%, and 97% for combined imaging. For evaluation of plaque morphology, respective values were 84%, 86%, 88%, and 82% for first-pass imaging; 98%, 97%, 98%, and 97% for steady-state imaging; and 98%, 100%, 100%, and 97% for combined imaging. Differences between the first-pass, steady-state, and combined image readings for assessment of stenosis degree and plaque morphology were significant (P < .001).

CONCLUSION

Gadofosveset-enhanced MR angiography is a promising technique for imaging carotid artery stenosis. Steady-state image reading is superior to first-pass image reading, but the combined reading protocol is more accurate.

Diagnostic accuracy of contrast-enhanced MR angiography in severe carotid stenosis: meta-analysis with metaregression of different techniques

Contrast-enhanced magnetic resonance angiography (CE-MRA) has become a well-established noninvasive imaging method for the assessment of severe carotid stenosis (70-99% by NASCET criteria). However, CE-MRA is not a standardised technique, but encompasses different concurrent techniques. This review analyses possible differences. A bivariate random effects meta-analysis of 17 primary diagnostic accuracy studies confirmed a high pooled sensitivity of 94.3% and specificity of 93.0% for carotid CE-MRA in severe carotid stenosis. Sensitivity was fairly uniform among the studies, while specificity showed significant variation (I (2) = 73%). Metaregressions found significant differences for specificity with two covariates: specificity was higher when using not only maximum intensity projection (MIP) images, but also three-dimensional (3D) images (P = 0.01). Specificity was also higher with electronic images than with hardcopies (P = 0.02). The timing technique (bolus-timed, fluoroscopically triggered or time-resolved) did not result in any significant differences in diagnostic accuracy. Some nonsignificant trends were found for the percentages of severe carotid disease, acquisition time and voxel size. In conclusion, in CE-MRA of severe carotid stenosis the three major timing techniques yield comparably high diagnostic accuracy, electronic images are more specific than hardcopies, and 3D images should be used in addition to MIP images to increase the specificity.

Carotid artery stenosis: accuracy of noninvasive tests--individual patient data meta-analysis

PURPOSE

To find clinically relevant estimates of the accuracy of noninvasive imaging-Doppler ultrasonography (US), computed tomographic (CT) angiography, magnetic resonance (MR) angiography, and contrast material-enhanced MR angiography-in diagnosing both severe and moderate symptomatic carotid artery stenosis; to ascertain the effect of prespecified clinical factors and clinical setting on diagnostic accuracy; and to estimate the probability of agreement between two noninvasive tests.

MATERIALS AND METHODS

Original principal investigators obtained ethics approval for each data set. All data were anonymized. Individual patient data sets (IPDs) for noninvasive imaging tests were used to determine sensitivity, specificity, and agreement between the tests for symptomatic carotid artery stenosis; to compare ipsilateral with contralateral arteries; to compare IPDs with literature estimates; to compare routine audit and research data; and to determine the effect of age and sex on sensitivity and specificity.

RESULTS

Contrast-enhanced MR angiography was the most accurate (sensitivity, 0.85 [30 of 35]; 95% confidence interval [CI]: 0.69, 0.93; and specificity, 0.85 [67 of 78]; 95% CI: 0.76, 0.92) for 70%-99% symptomatic stenosis. Sensitivity for a 50%-69% stenosis was poor, although data were limited. Sensitivity and specificity were generally lower in the ipsilateral than in the contralateral artery. IPD estimates were lower than literature values. Results of comparison of research with audit-derived data were inconclusive. Neither age nor sex affected accuracy. Agreement was better between two Doppler US tests and between two contrast-enhanced MR angiographic tests than it was between Doppler US and contrast-enhanced MR angiography, except for a 70%-99% symptomatic stenosis.

CONCLUSION

Primary studies should distinguish ipsilateral from contralateral arteries and carefully describe the patients' characteristics and study environment. The literature overestimates noninvasive imaging accuracy. More data are needed to inform physicians in routine clinical practice.

Correlation between US-PSV and MDCTA in the quantification of carotid artery stenosis

PURPOSE

Stroke is a major cause of death and serious long-lasting neurological disability and the severity of carotid artery stenosis is one of the most important determinants of cerebrovascular events. The purpose of this paper is to evaluate the correlation between multi-detector-row CT angiography (MDCTA) and ultra-sound peak-systolic-velocity (US-PSV) in the quantification of carotid artery stenosis.

METHODS AND MATERIAL

52 patients were retrospectively studied by using four-detector row CT and ultra-sound. Each patient was assessed for stenosis degree by using NASCET method when studied by using MDCT and by using PSV when studied by using US. Statistic analysis was performed to determine the entity of correlation (method of Pearson) between MDCTA and US-PSV. The Bland-Altman analysis was applied to assess the level of inter-technique agreement.

RESULTS

Sonographic PSV measurements ranged from 70 to 589cm/s. Distal ICA velocities ranged from 29 to 238cm/s. Linear regression analysis showed a good correlation (r(2)=0.613) between MDCTA-NASCET linear percentage stenosis and PSV and measured. PSV value that corresponded to a NASCET linear percentage stenosis of 70% was 283cm/s and with this values sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were 75%, 88.6%, 90.7% and 70.5%, respectively.

CONCLUSIONS

Results of our study suggest that NASCET stenosis measured in MDCTA and PSV values have a good correlation. The use of a threshold of 283cm/s allows obtaining good value of sensitivity and specificity.