Carotid artery: elliptic centric contrast-enhanced MR angiography compared with conventional angiography

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.

Simultaneous noncontrast angiography and intraplaque hemorrhage (SNAP) imaging: Comparison with contrast-enhanced MR angiography for measuring carotid stenosis

PURPOSE

To evaluate in a proof-of-concept study the feasibility of Simultaneous Noncontrast Angiography and intraPlaque hemorrhage (SNAP) imaging as a clinical magnetic resonance angiography (MRA) technique for measuring carotid stenosis. There is a growing interest in detecting intraplaque hemorrhage (IPH) during the clinical management of carotid disease, yet luminal stenosis has remained indispensable during clinical decision-making. SNAP imaging has been proposed as a novel IPH imaging technique that provides carotid MRA with no added scan time. Flowing blood shows negative signal on SNAP because of phase-sensitive inversion recovery.

MATERIALS AND METHODS

In all, 58 asymptomatic subjects with 16-79% stenosis on ultrasound were scanned at 3T by SNAP with 0.8 mm isotropic resolution and 16 cm longitudinal coverage. Two readers measured luminal stenosis of bilateral carotid arteries (n = 116) on minimum intensity projections of SNAP using the NASCET criteria. In the subset (48 arteries) with contrast-enhanced (CE) MRA available for comparison, luminal stenosis was also measured on maximum intensity projections of CE-MRA.

RESULTS

Intraclass correlation coefficients (ICCs) with 95% confidence intervals were 0.94 (0.90-0.96) and 0.93 (0.88-0.96) for intra- and interreader agreement on stenosis measurements, respectively. Corresponding kappas for grading stenosis (0-29%, 30-69%, 70-99%, and 100%) were 0.79 (0.67-0.89) and 0.80 (0.68-0.90). Agreement between SNAP and CE-MRA was high (ICC: 0.95 [0.90-0.98]; kappa: 0.82 [0.71-0.93]).

CONCLUSION

As a dedicated IPH-imaging sequence, SNAP also provided carotid stenosis measurement that showed high intra- and interreader consistency and excellent agreement with CE-MRA. Further comparisons with digital subtraction angiography and other noninvasive techniques are warranted.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2017;46:1045-1052.

Detection of carotid artery stenosis: a comparison between 2 unenhanced MRAs and dual-source CTA

BACKGROUND AND PURPOSE

Dual-source CTA and black-blood MRA are recently developed techniques for evaluating carotid stenosis. The purpose of this study was to compare dual-source CTA with black-blood MRA and conventional TOF MRA in both detecting carotid stenosis by using DSA as a reference standard and demonstrating plaque morphology.

MATERIALS AND METHODS

Thirty patients with suspected carotid artery stenosis underwent unenhanced MRA by using black-blood and TOF MRA and dual-source CTA. Source images from unenhanced MRAs and dual-source CTA were reconstructed with MIP or curved planar reconstruction. The degree of carotid artery stenosis was measured, and plaque surface morphology at the stenosis was analyzed and compared among different techniques.

RESULTS

Good correlation was observed for measuring the degree of carotid stenosis among dual-source CTA, black-blood MRA, TOF MRA, and DSA. Sensitivity and specificity for detecting severe stenosis were 100% and 97% with dual-source CTA, 100% and 95% with black-blood MRA, and 79% and 95% with TOF MRA. None of the 3 technologies resulted in stenosis of <50% being overestimated. Plaque surface irregularity or ulceration was more frequently detected with dual-source CTA and black-blood MRA than with TOF MRA and DSA.

CONCLUSIONS

This preliminary study shows that black-blood MRA is a promising technique, comparable with dual-source CTA and DSA, but better than TOF MRA, in the evaluation of carotid stenosis. Unlike dual-source CTA, black-blood MRA requires no intravenous contrast or radiation.

Guidelines for the early management of patients with acute ischemic stroke: a guideline for healthcare professionals from the American Heart Association/American Stroke Association

BACKGROUND AND PURPOSE

The authors present an overview of the current evidence and management recommendations for evaluation and treatment of adults with acute ischemic stroke. The intended audiences are prehospital care providers, physicians, allied health professionals, and hospital administrators responsible for the care of acute ischemic stroke patients within the first 48 hours from stroke onset. These guidelines supersede the prior 2007 guidelines and 2009 updates.

METHODS

Members of the writing committee were appointed by the American Stroke Association Stroke Council's Scientific Statement Oversight Committee, representing various areas of medical expertise. Strict adherence to the American Heart Association conflict of interest policy was maintained throughout the consensus process. Panel members were assigned topics relevant to their areas of expertise, reviewed the stroke literature with emphasis on publications since the prior guidelines, and drafted recommendations in accordance with the American Heart Association Stroke Council's Level of Evidence grading algorithm.

RESULTS

The goal of these guidelines is to limit the morbidity and mortality associated with stroke. The guidelines support the overarching concept of stroke systems of care and detail aspects of stroke care from patient recognition; emergency medical services activation, transport, and triage; through the initial hours in the emergency department and stroke unit. The guideline discusses early stroke evaluation and general medical care, as well as ischemic stroke, specific interventions such as reperfusion strategies, and general physiological optimization for cerebral resuscitation.

CONCLUSIONS

Because many of the recommendations are based on limited data, additional research on treatment of acute ischemic stroke remains urgently needed.

Current state-of-the-art 1.5 T and 3 T extracranial carotid contrast-enhanced magnetic resonance angiography

Recent advances in magnetic resonance (MR) hardware and software have improved the resolution and spatial coverage of head and neck first-pass contrast-enhanced (CE) MR angiography. Despite these improvements, high-quality submillimeter-resolution 1.5 T and 3 T carotid CE MR angiography is not consistently available in the general radiology practice. This article reviews the important imaging parameters and potential pitfalls that affect carotid CE MR angiography image quality, and the dose and timing of the gadolinium-based contrast agent, and summarizes vendor-specific protocols for high-quality submillimeter-resolution carotid CE MR angiography at 1.5 and 3 T.

A new computerized measurement approach of carotid artery stenosis on tomographic image sequence

RATIONALE AND OBJECTIVES

The stenosis degree of carotid artery (CA) can be a critical factor for treatment of cerebrovascular disease and for determining candidate of carotid endarterectomy. Currently, three different measuring methods are applied only on projectional cervical images. These measurement methods introduce several demerits such as a thromboembolic event, and three reference positions provide the different measurement results even on same subject. In addition, projection image could not provide the most severe stenosis position by nature; and the manual measurements also provide the inter-observer and intra-observer variability. Therefore, a computerized measuring scheme is necessary to overcome these drawbacks.

MATERIALS AND METHODS

By applying local adaptive thresholding technique on cervical magnetic resonance angiogram image sequence, CA objects are initially identified. These are used to determine the three-dimensional central axis of CA by using circumscribed quadrangle. The oblique slices are reformatted into two-dimensional image planes, which are perpendicular to the central axis of CA, to provide the circular shape of blood vessel provided that the artery runs horizontally across the scanning axis. After that, region growing technique is applied on obliquely reformatted image sequence followed by geometrically restoration of segmented CA objects.

RESULTS

The percentage of stenosis can be defined by the area ratio of segmented CA to restored CA object. The stenosis grading of is [(A-B)/A]×100%, where A represents area measure of restored object, B represents area measure of segmented CA object. Experiments have been conducted on both phantom that simulated the mild (30%), moderate (50%), and severe (70%) stenosis degree for validation of proposed measurement approach and 86 carotid arteries from 43 clinical data sets (including 5 occlusion cases).

CONCLUSIONS

The automated approach is recommended to measure the carotid stenosis by using axial image sequence. This technique is not only accurate as possible but also robust, simple to handle, and less time consuming as compared to manual measurements. In addition, a computerized carotid stenosis measuring method is necessary to overcome the drawbacks introduced by using the projectional image and measurement variability of inter-observer, intra-observer.

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.

Highly undersampled supraaortic MRA at 3.0 T: initial results with parallel imaging in two directions using a 16-channel neurovascular coil and parallel imaging factors up to 16

PURPOSE

To present the feasibility of highly undersampled contrast-enhanced MRA (CE-MRA) of the supraaortic arteries with a 16-channel neurovascular coil at 3.0 T using parallel imaging in two directions with parallel imaging factors (PIF) up to 16.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. In a prospective study, MRA protocols including PIF of 1, 2, 4, 9 and 16 yielding a spatial resolution from 0.81×0.81×1.0 mm(3) to 0.46×.46×0.98 mm(3) were acquired. In 32 examinations, image quality and vascular segments were rated independently by two radiologists. SNR estimations were performed for all MRA protocols.

RESULTS

The use of high PIF allowed to shorten acquisition time from 2:09 min down to 1:13 min and to increase the anatomic coverage while maintaining or even increasing spatial resolution down to 0.46×0.46×0.98 mm(3). The larger anatomic coverage that was achieved with the use of high PIF allowed for visualization of vascular structures that were not covered by the standard protocols. Despite the resulting lower SNR using high PIF, image quality was constantly rated to be adequate for diagnosis or better in all cases.

CONCLUSION

The use of high PIF yielded diagnostic image quality and allowed to increase the anatomic coverage while maintaining or even improving spatial resolution and shortening the acquisition time.

Comparison of real-time three-dimensional gadolinium-enhanced elliptic centric-ordered MR venography and two-dimensional time-of-flight MR venography of the intracranial venous system

BACKGROUND

To compare 3-dimensional gadolinium-enhanced elliptic centric-ordered (3D GEC) magnetic resonance venography (MRV) with traditional 2-dimensional time-of-flight (2D TOF) MRV for imaging of the intracranial venous system.

METHODS

Fifty-three patients underwent 2D and 3D MRV, whereby venous structures were evaluated by 2 neuroradiologists.

RESULTS

Of the 53 patients, 10 were diagnosed with dural venous sinus thrombosis and 12 with intracranial tumors. 3D GEC MRV displayed superior sensitivity/specificity (90.9%/96.8%) compared to 2D TOF MRV (63.6%/48.4%). Analysis of the areas under the receiver operating characteristic curves also showed superiority of 3D GEC (0.91) versus 2D TOF (0.53) MRV. Of the remaining 31 healthy patients, the rate of complete visibility of venous structures was also greater for 3D GEC (95.8%) than for 2D TOF (62.1%) MRV.

CONCLUSION

3D GEC MRV is superior to 2D TOF MRV for providing more detail of the intracranial venous system, and can lead to better diagnosis of venous conditions.

Contrast-enhanced MRA of the renal and aorto-iliac-femoral arteries: comparison of gadobenate dimeglumine and gadofosveset trisodium

RATIONALE AND OBJECTIVES

Dedicated contrast agents are now available for contrast-enhanced magnetic resonance angiography (CE-MRA). This study retrospectively compares the safety and diagnostic performance data from Phase III regulatory trials performed to evaluate gadobenate dimeglumine (MultiHance(®)) and gadofosveset trisodium (Vasovist®)) for renal and peripheral CE-MRA.

MATERIALS AND METHODS

Similar examination and blinded assessment methodology was utilized in all studies to determine the safety and diagnostic performance of the agents for detection of significant (>50%) steno-occlusive disease. Digital Subtraction Angiography (DSA) was used as the standard of truth. Diagnostic performance data (sensitivity, specificity, predictive values [PVs], and likelihood ratios [LRs]) were compared (Chi-square test).

RESULTS

CE-MRA with gadobenate dimeglumine was more specific (92.4% vs. 80.5%, p < 0.0001) and accurate (83.6% vs. 77.1%, p = 0.022) than CE-MRA with gadofosveset in the detection of significant renal artery stenosis. The average sensitivity was higher for gadofosveset (74.4% vs. 67.3%, p = 0.011) in peripheral vessels although gadobenate dimeglumine was more specific (93.0% vs. 88.2%, p < 0.0001) with no difference in accuracy (86.6% vs. 86.3%, p = 0.66). PPVs were higher (p < 0.0001) for gadobenate dimeglumine in both vascular territories. Pre- to post-test shifts in the probability of detecting significant disease were greater after gadobenate dimeglumine. Adverse events in the renal and peripheral studies were reported by 9.2% and 7.7% of patients after gadobenate dimeglumine compared with 30.3% and 22.1% of patients after gadofosveset.

CONCLUSION

The diagnostic performance of CE-MRA for the detection of significant steno-occlusive disease is similar with gadofosveset and gadobenate dimeglumine although the rate of adverse events appears higher with gadofosveset.

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.

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.

4D time-resolved MR angiography with keyhole (4D-TRAK): more than 60 times accelerated MRA using a combination of CENTRA, keyhole, and SENSE at 3.0T

PURPOSE

To present a new 4D method that is designed to provide high spatial resolution MR angiograms at subsecond temporal resolution by combining different techniques of view sharing with parallel imaging at 3.0T.

MATERIALS AND METHODS

In the keyhole-based method, a central elliptical cylinder in k-space is repeated n times (keyhole) with a random acquisition (CENTRA), and followed by the readout of the periphery of k-space. 4D-MR angiography with CENTRA keyhole (4D-TRAK) was combined with parallel imaging (SENSE) and partial Fourier imaging. In total, a speed-up factor of 66.5 (6.25 [CENTRA keyhole] x 8 [SENSE] x 1.33 [partial Fourier imaging]) was achieved yielding a temporal resolution of 608 ms and a spatial resolution of (1.1 x 1.4 x 1.1) mm(3) with whole-brain coverage 4D-TRAK was applied to five patients and compared with digital subtraction angiography (DSA).

RESULTS

4D-TRAK was successfully completed with an acceleration factor of 66.5 in all five patients. Sharp images were acquired without any artifacts possibly created by the transition of the central cylinder and the reference dataset. MRA findings were concordant with DSA.

CONCLUSION

4D time-resolved MRA with keyhole (4D-TRAK) is feasible using a combination of CENTRA, keyhole, and SENSE at 3.0T and allows for more than 60 times accelerated MRA with high spatial resolution.

Effects of doubling and tripling the spatial resolution in standard 3D contrast-enhanced magnetic resonance angiography of carotid artery disease

PURPOSE

To determine whether three-dimensional (3D) contrast-enhanced MR angiography (CE-MRA) of carotid artery disease may be more effective when performed at double or triple the spatial resolution of the present common clinical standard at 1.5T.

MATERIALS AND METHODS

A total of 110 consecutive patients with suspected carotid artery disease were imaged with elliptical centric 3D CE-MRA. The total acquisition time was increased from the standard clinical protocol of 21 seconds up to 60 seconds in 10-second steps, with corresponding voxel volume reductions from 0.95 mm(3) down to 0.35 mm(3). Quantitative and blinded qualitative measurements were then performed to determine the preferred imaging time.

RESULTS

In patients with significant stenosis, the 40-second acquisition with 0.53-mm(3) voxels produced significantly sharper images of the carotid bifurcation than the 21-second standard using 0.95-mm(3) voxels, but did not have a significant effect in patients without disease.

CONCLUSION

In patients with carotid artery stenosis, decreasing the voxel volume to 0.5 mm(3) by increasing the scan time from 21 to 40 seconds resulted in sharper depiction of the carotid stenosis. Further decreases in voxel volume, by extending the acquisition time further, did not improve the vessel depiction due to both signal-to-noise ratio (SNR) and sharpness losses.

Cerebral arteriovenous malformation: Spetzler-Martin classification at subsecond-temporal-resolution four-dimensional MR angiography compared with that at DSA

PURPOSE

To prospectively test the hypothesis that subsecond-temporal-resolution four-dimensional (4D) contrast material-enhanced magnetic resonance (MR) angiography at 3.0 T enables the same Spetzler-Martin classification (nidus size, venous drainage, eloquence) of cerebral arteriovenous malformation (AVM) as that at digital subtraction angiography (DSA).

MATERIALS AND METHODS

Institutional ethics committee approval and written informed consent were obtained. In a prospective intraindividual comparative study, 18 consecutive patients with cerebral AVM (nine men, nine women; mean age, 41.9 years +/- 14.0 [standard deviation]; range, 23-69 years) were examined with 4D contrast-enhanced MR angiography and DSA. Four-dimensional contrast-enhanced MR angiography combined randomly segmented central k-space ordering, keyhole imaging, sensitivity encoding, and half-Fourier imaging, which yielded a total acceleration factor of 60. Fifty dynamic scans were obtained every 608 msec at an acquired spatial resolution of 1.1 x 1.4 x 1.1 mm. Four-dimensional contrast-enhanced MR angiograms were independently reviewed by one neuroradiologist and one neurosurgeon according to Spetzler-Martin classification, overall diagnostic quality, and level of confidence. Kendall W coefficients of concordance (K) were computed to compare reader assessment of image quality, level of confidence, and Spetzler-Martin classification by using 4D contrast-enhanced MR angiography and to compare Spetzler-Martin classification as determined with DSA with that at 4D contrast-enhanced MR angiography.

RESULTS

Spetzler-Martin classification of cerebral AVM at 4D contrast-enhanced MR angiography and at DSA matched in 18 of 18 patients for both readers, which yielded 100% interobserver agreement (K = 1). Image quality of 4D contrast-enhanced MR angiography was judged to be at least adequate for diagnosis in all patients by both readers. In three of 18 patients, DSA depicted additional arterial feeders of cerebral AVM.

CONCLUSION

Subsecond-temporal-resolution 4D contrast-enhanced MR angiography at 3.0 T had 100% agreement with DSA with regard to Spetzler-Martin classification of cerebral AVM.

SUPPLEMENTAL MATERIAL

radiology.rsnajnls.org/cgi/content/full/2453061684/DC1.

Whole-body contrast-enhanced magnetic resonance angiography: new advances at 3.0 T

During the past decade, technical improvements and numerous advances in scanner hardware and software have significantly improved image quality, speed, and reliability of 3-dimensional (3-D) contrast-enhanced magnetic resonance angiography (CE-MRA). The accuracy of CE-MRA is now comparable with that of computed tomography angiography or even conventional catheter angiography. Peripheral vascular disease (PVD) accounts for 50,000 to 60,000 cases of percutaneous transluminal angioplasty and for about 100,000 cases of amputation annually in the United States. Proper treatment of the arterial disease requires a comprehensive assessment of the underlying vascular morphology because it is crucial to localize and gauge the severity of arterial lesions for further therapeutic decision making.Contrast-enhanced magnetic resonance angiography has been widely implemented in noninvasive evaluation of PVD with high diagnostic accuracy. The lack of ionizing radiation and the use of contrast agent with relatively small potential nephrotoxicity in population of PVD with high prevalence of renal impairment are the appealing features for broad acceptance of CE-MRA in initial diagnosis and repeated follow-up studies of patients with PVD. The minimum anatomical coverage for evaluation of PVD comprises the aortic bifurcation to the ankles; however, because of the systemic nature of atherosclerosis hypertension, renal or cerebrovascular disease frequently coexist. Thus, many clinicians regard evaluation of the whole-body arterial vasculature as desirable.

The vulnerable, or high-risk, atherosclerotic plaque: noninvasive MR imaging for characterization and assessment

"Vulnerable" plaques are atherosclerotic plaques that have a high likelihood to cause thrombotic complications, such as myocardial infarction or stroke. Plaques that tend to progress rapidly are also considered to be vulnerable. Besides luminal stenosis, plaque composition and morphology are key determinants of the likelihood that a plaque will cause cardiovascular events. Noninvasive magnetic resonance (MR) imaging has great potential to enable characterization of atherosclerotic plaque composition and morphology and thus to help assess plaque vulnerability. A classification for clinical, as well as pathologic, evaluation of vulnerable plaques was recently put forward in which five major and five minor criteria to define vulnerable plaques were proposed. The purpose of this review is to summarize the status of MR imaging with regard to depiction of the criteria that define vulnerable plaques by using existing MR techniques. The use of MR imaging in animal models and in human disease in various vascular beds, particularly the carotid arteries, is presented.

MRI of geometric and compositional features of vulnerable carotid plaque

Noninvasive imaging of atherosclerotic disease provides a powerful opportunity to gain insight into the complex chain of events underlying atherogenesis, plaque progression, and ultimately those processes that result in atherothrombosis with accompanying clinical symptoms. MRI is particularly attractive because it is noninvasive and is capable of providing a rich array of information on vascular disease. MR methods have been demonstrated to provide information on important features of vascular disease, including the geometric morphology of the flow lumen and the vessel wall, the composition of atheroma, measurement of flow velocities through vessels independent of overlying structures, and more recently insights into the presence and activity of specific molecules that are considered to be important participants in the inflammatory processes and that might differentiate the stable plaque from the vulnerable plaque.

Specificity of MR Angiography as a Confirmatory Test for Carotid Artery Stenosis: Is It Valid?

OBJECTIVE

We believe that many studies in the literature show a falsely elevated specificity for carotid MR angiography (MRA) in the detection of high-grade stenosis. The purpose of this study was to test the hypothesis that inclusion of a substantial proportion of normal carotid arteries in a study population will falsely elevate the specificity of MRA for confirming a high-grade carotid artery stenosis.

MATERIALS AND METHODS

Seventy-seven carotid arteries were evaluated in 63 patients suspected of having a high-grade carotid stenosis, and all vessels were evaluated with contrast-enhanced MRA. Two subgroups were created, and the specificity of MRA was calculated for each group using digital subtraction angiography (DSA) as the gold standard. Group 1 included 44 vessels classified as high-grade stenosis on sonography and all were evaluated with DSA. To test our hypothesis, group 2 included the 44 carotid arteries from group 1 plus 33 carotid arteries classified as normal or minimally narrowed on sonography and MRA.

RESULTS

In group 1, the specificity of MRA for accurately confirming a high-grade stenosis was 29% for contrast-enhanced maximum-intensity-projection (MIP) images alone and 75% for contrast-enhanced axially reformatted source images as compared with DSA. When the 33 normal arteries from group 2 were added to the data set, the specificities increased to 70% and 89%, respectively.

CONCLUSION

The calculated specificity of MRA as a confirmatory test for high-grade carotid stenosis is highly dependent on the proportion of normal carotid arteries included in the calculation. Based on our results, the specificity of MRA reported in the literature has likely been overstated because of spectrum bias.

Supraaortic arteries: contrast-enhanced MR angiography at 3.0 T--highly accelerated parallel acquisition for improved spatial resolution over an extended field of view

PURPOSE

To prospectively use 3.0-T breath-hold high-spatial-resolution contrast material-enhanced magnetic resonance (MR) angiography with highly accelerated parallel acquisition to image the supraaortic arteries of patients suspected of having arterial occlusive disease.

MATERIALS AND METHODS

Institutional review board approval and written informed consent were obtained for this HIPAA-compliant study. Eighty patients (44 men, 36 women; age range, 44-90 years) underwent contrast-enhanced MR angiography of the head and neck at 3.0 T with an eight-channel neurovascular array coil. By applying a generalized autocalibrating partially parallel acquisition algorithm with an acceleration factor of four, high-spatial-resolution (0.7 x 0.7 x 0.9 mm = 0.44-mm(3) voxels) three-dimensional contrast-enhanced MR angiography was performed during a 20-second breath hold. Two neuroradiologists evaluated vascular image quality and arterial stenoses. Interobserver variability was tested with the kappa coefficient. Quantitation of stenosis at MR angiography was compared with that at digital subtraction angiography (DSA) (n = 13) and computed tomographic (CT) angiography (n = 12) with Spearman rank correlation coefficient (R(s)).

RESULTS

Arterial stenoses were detected with contrast-enhanced MR angiography in 208 (reader 1) and 218 (reader 2) segments, with excellent interobserver agreement (kappa = 0.80). There was a significant correlation between contrast-enhanced MR angiography and CT angiography (R(s) = 0.95, reader 1; R(s) = 0.87, reader 2) and between contrast-enhanced MR angiography and DSA (R(s) = 0.94, reader 1; R(s) = 0.92, reader 2) for the degree of stenosis. Sensitivity and specificity of contrast-enhanced MR angiography for detection of arterial stenoses greater than 50% were 94% and 98% for reader 1 and 100% and 98% for reader 2, with DSA as the standard of reference. Vascular image quality was sufficient for diagnosis or excellent for 97% of arterial segments evaluated.

CONCLUSION

By using highly accelerated parallel acquisition, the described 3.0-T contrast-enhanced MR angiographic protocol enabled visualization and characterization of the majority of supraaortic arteries, with diagnostic or excellent image quality (97% of arterial segments) and diagnostic values comparable with those obtained by using CT angiography and DSA for detection of arterial stenoses.

Gadobenate dimeglumine-enhanced MR angiography: Diagnostic performance of four doses for detection and grading of carotid, renal, and aorto-iliac stenoses compared to digital subtraction angiography

PURPOSE

To determine the diagnostic performance of contrast-enhanced MR angiography (CE-MRA) with four doses of gadobenate dimeglumine for detection of significant steno-occlusive disease of the carotid, renal, and pelvic vasculature.

MATERIALS AND METHODS

Eighty-four patients with suspected disease of the renal (n = 16), pelvic (n = 41), or carotid (n = 27) arteries underwent CE-MRA (3D-spoiled gradient-echo sequences) at 1.5T. CE-MRA was performed with gadobenate dimeglumine at 0.025, 0.05, 0.1, or 0.2 mmol/kg (23, 24, 19, and 18 patients, respectively) administered at 2 mL/sec. Accuracy, sensitivity, specificity, and positive and negative predictive values (PPV and NPV, respectively) for detection of significant disease (>50% stenosis or occlusion for renal/pelvic arteries; >70% stenosis or occlusion for carotid arteries) was determined by three fully blinded, independent radiologists using conventional digital subtraction angiography (DSA) as reference standard. All comparisons were tested statistically (ANOVA, chi-square, and Mantel-Haenszel tests as appropriate) and reader agreement (kappa) was assessed.

RESULTS

Values for accuracy, sensitivity, specificity, PPV, and NPV on CE-MRA were consistently higher for 0.1 mmol/kg gadobenate dimeglumine (accuracy = 95.2-97.3%, sensitivity = 84.2% (all readers), specificity = 96.9-99.2%, PPV = 80.0-94.1%, NPV = 97.6-97.7%). The greater accuracy of the 0.1 mmol/kg dose was significant (P < 0.01, all readers) compared to all other dose groups. Agreement between the three readers was good for all dose groups (kappa >/=0.58), with the highest percent agreement (85.7%) noted for the 0.1 mmol/kg dose.

CONCLUSION

Significantly better diagnostic performance on CE-MRA of the renal, pelvic, and carotid arteries is achieved with a gadobenate dimeglumine dose of 0.1 mmol/kg bodyweight.

Effects of injection rate and dose on image quality in time-resolved magnetic resonance angiography (MRA) by using 1.0M contrast agents

In time-resolved MRA (TR MRA), injection parameters and contrast agent (CA) dose are important factors influencing image quality. In this study, three different injection schemes with different CA volumes were evaluated in 12 healthy volunteers. Injection rates between 0.2 and 0.8 ml/s were evaluated with CA volumes of 10 and 20 ml. To measure circulatory parameters, cine cardiac MRI was performed before each exam. Spatial resolution could be reduced to 2 x 1.4 x 2 mm3, temporal resolution was 2.25 s/frame. To exclude signal saturation at high CA concentrations, a phantom with fixed CA concentrations was placed in the field of view. SNR was measured, and the area under the curve of the arterial signal of the different injection schemes was calculated. Results showed the largest diagnostic window at a relatively slow injection rate of 0.4 ml/s and a CA volume of 10 ml. Circulatory parameters have an important impact on CA arrival, so delay times have to be set depending on these parameters.

Practical noninvasive neurovascular imaging of the neck arteries in patients with stroke, transient ischemic attack, and suspected arterial disease that may lead to ischemia, infarction, or flow abnormalities

Stroke is the third leading cause of death in the United States, killing nearly 157,000 people a year with an estimated society cost of dollar 58 billion in 2006. A large percentage of ischemic strokes is secondary to extracranial carotid and vertebral arterial disease. While digital subtraction angiography has traditionally been used for the initial evaluation of the degree of stenosis, noninvasive imaging has moved to the forefront in the extracranial arterial evaluation. The importance of understanding the imaging techniques, findings, interpretation, artifacts, and pitfalls is essential to appropriate patient management.

Three-Dimensional Cerebral Contrast-Enhanced Magnetic Resonance Venography at 3.0 Tesla

OBJECTIVE

The objective of this study was to evaluate a high spatial resolution 3-dimensional (3D) contrast-enhanced magnetic resonance (CE-MR) venography protocol for evaluation of intracranial venous system using highly accelerated parallel imaging at 3.0 T.

MATERIALS AND METHODS

Ten patients (4 male, 6 female; age, 38-76 years) with suspected cerebrovascular disease were prospectively studied on a 32-channel 3.0 T MR system. After a single intravenous contrast injection, high spatial resolution 3D CE-MR angiography of the entire supraaortic arteries was performed followed immediately by 3D cerebral CE-MR venography. By using a fast 3D gradient-recalled-echo sequence with elliptic centric k-space ordering and highly accelerated parallel acquisition (acceleration factor 3 and 2 in phase and slice encoding direction, respectively), 3D cerebral CE-MR venography was acquired with voxel dimensions of 0.7 x 0.7 x 0.8 mm in 24 seconds. Image evaluation was performed independently by 2 neuroradiologists for overall image quality, presence of noise, and artifacts. The image quality of 30 venous segments was evaluated in each subject using a 1 to 4 scoring scale. In 2 patients, catheter angiography was available for correlation. Statistical analysis of data was performed by using Wilcoxon rank sum test and kappa coefficient.

RESULTS

All studies were determined to be of diagnostic image quality by both observers. The majority (90%) of cerebral venous segments were evaluated to be of diagnostic image quality (median, 3; range, 3-4) by both readers and with excellent interobserver agreement (kappa = 0.86; 95% confidence interval, 0.79-0.93). One meningioma invading the superior sagittal sinus and one superior sagittal sinus fistula were detected subsequently confirmed by conventional angiography.

CONCLUSION

High spatial resolution 3D cerebral CE-MR venography is feasible and promising. Using a 32-channel 3.0 T system combined with multichannel array coils effectively supports highly accelerated parallel imaging, enabling subsequent acquisition of both high spatial resolution CE-MR angiography and CE-MR venography after a single contrast injection without impairing the image quality. More extensive clinical studies are warranted to establish the range of applications and confirm the accuracy of this technique.

MRI of atherosclerosis in clinical trials

Magnetic resonance imaging (MRI) of the arterial wall has emerged as a viable technology for characterizing atherosclerotic lesions in vivo, especially within carotid arteries and other large vessels. This capability has facilitated the use of carotid MRI in clinical trials to evaluate therapeutic effects on atherosclerotic lesions themselves. MRI is specifically able to characterize three important aspects of the lesion: size, composition and biological activity. Lesion size, expressed as a total wall volume, may be more sensitive than maximal vessel narrowing (stenosis) as a measure of therapeutic effects, as it reflects changes along the entire length of the lesion and accounts for vessel remodeling. Lesion composition (e.g. lipid, fibrous and calcified content) may reflect therapeutic effects that do not alter lesion size or stenosis, but cause a transition from a vulnerable plaque composition to a more stable one. Biological activity, most notably inflammation, is an emerging target for imaging that is thought to destabilize plaque and which may be a systemic marker of vulnerability. The ability of MRI to characterize each of these features in carotid atherosclerotic lesions gives it the potential, under certain circumstances, to replace traditional trials involving large numbers of subjects and hard end-points--heart attacks and strokes--with smaller, shorter trials involving imaging end-points. In this review, the state of the art in MRI of atherosclerosis is presented in terms of hardware, image acquisition protocols and post-processing. Also, the results of validation studies for measuring lesion size, composition and inflammation will be summarized. Finally, the status of several clinical trials involving MRI of atherosclerosis will be reviewed.

3.0 T versus 1.5 T MR angiography of the head and neck

This article presents the advantages and challenges of MR angiography of the intracranial and extracranial cerebral vasculature at 3.0 T with comparative assessment to 1.5 T approaches. The physical basis for the superiority of 3.0 T MR angiography is discussed in the context of evolving technological capabilities afforded by the synergistic advent of higher field scanners, improved coil design, and parallel imaging. This review emphasizes 3.0 T issues related to noncontrast three-dimensional time of flight MR angiography of the intracranial circulation, contrast enhanced three-dimensional time of flight MR angiography of the extracranial cerebral vasculature, and carotid plaque characterization.

High spatial resolution contrast-enhanced MR angiography of the supraaortic arteries using the quadrature body coil at 3.0T: A feasibility study

To examine whether the the increased signal-to-noise (S/N) available at 3.0T would permit the use of the quadrature body coil for high spatial resolution contrast-enhanced (CE) MR angiography (MRA), and whether the large FOV that was used in our routine 1.5T protocol would also be feasible at 3.0T. In a prospective study, 43 patients and five volunteers were examined on a clinical whole-body 3.0T MR unit (Intera, Philips Medical Systems, Best, The Netherlands) after institutional review board approval and informed consent. Three-dimensional CE MRA (T1 gradient echo-sequence with TR/TE = 5.7/1.93 msec.; acquisition time, 1:54 min.) using randomly segmented central k-space ordering (CENTRA) was acquired with the quadrature body coil, using over a FOV of 350 mm. A high-image matrix of 432x432 yielded a non-zero filled voxel size of 0.81 mm x 0.81 mm x 1.0 mm (0.66 mm(3)). For quantitative analysis, contrast ratios (CR) between vessels (S) and signal in surrounding tissue (ST) were calculated [(S-ST)/(S+ST)]. For qualitative analysis, image quality and presence of artifacts were rated by two radiologists in consensus on a five-point scale (1=excellent to 5=nondiagnostic). Digital subtraction angiography (DSA) served as the standard of reference in patients with vascular disease. In the five volunteers, 1.5T CE MRA using a phased array neurovascular coil was available for intraindividual comparison. 3.0T CE MRA was successfully performed in 48/48 subjects (100%). Mean CR+/- SD were 0.76 (139.30/182.42) and 0.87 (235.18/270.14) at 3.0T and 1.5T respectively . Mean image quality was 3.82+/-0.86. Intraindividual comparison between 1.5T and 3.0T CE MRA in the volunteers revealed no significant difference in image quality (4.2+/-0.74 vs 4.6+/-0.80; p>0.05). Vascular disease was correctly identified in 13/13 patients with DSA correlation. CE MRA of the supraaortic arteries is feasible at 3.0T using a large FOV of 350 mm. The signal gain at 3.0T enables high spatial resolution contrast-enhanced MR angiography by using the built-in quadrature body coil only.

Estudo da circulação hepatomesentérica pela angiografia por ressonância magnética com gadolínio: comparação entre doses simples e dupla no estudo de pacientes esquistossomóticos

OBJETIVO: Determinar a freqüência de visualização dos segmentos da circulação hepatomesentérica pela angiografia por ressonância magnética (angio-RM) com contraste e comparar o valor do método, utilizando-se duas diferentes dosagens de gadolínio (doses simples e dupla). MATERIAIS E MÉTODOS: Estudo prospectivo de 36 pacientes esquistossomóticos submetidos a angio-RM. Os exames foram realizados em equipamento de RM de 1,5 T, usando-se bobina de corpo e bomba injetora para a administração endovenosa do contraste. Foram utilizadas, de maneira randomizada, dose dupla do contraste paramagnético (0,2 mmol/kg de Gd-DTPA) em 21 pacientes e dose simples (0,1 mmol/kg) em outros 15 pacientes. Os exames foram interpretados por dois observadores em consenso, que classificaram o grau de visualização de 25 segmentos vasculares estabelecidos para análise, sem conhecimento da dose de gadolínio utilizada. RESULTADOS: Os segmentos vasculares proximais e de maior calibre foram as estruturas com melhor grau de visualização na maioria da amostra em estudo. O tronco celíaco, a artéria hepática comum, a artéria esplênica, a croça e terço médio da artéria mesentérica superior, a veia porta, a veia esplênica e a veia mesentérica superior apresentaram grau 2 de visualização em mais de 70% da amostra. Quanto à comparação das diferentes dosagens, não houve diferença significante (p < 0,05) no grau de visualização das diversas estruturas analisadas entre os grupos dose simples e dose dupla, com uma exceção isolada: na avaliação da artéria hepática direita (p = 0,008), o grupo dose simples apresentou maior freqüência de visualização grau 2, com valor significante. CONCLUSÃO: O grau de visualização dos segmentos vasculares hepatomesentéricos pela angio-RM com contraste é elevado, sendo maior nos segmentos proximais e de maior calibre. A comparação entre os grupos que utilizaram dose simples e dupla de contraste demonstrou resultados semelhantes.

Dissection of cervicocephalic arteries: early diagnosis and follow-up with magnetic resonance imaging

Evaluate Magnetic Resonance (MR) and Magnetic Resonance Angiography (MRA) sensibility in the diagnosis and follow-up of dissection of Internal Carotid and Vertebral Artery (ICA/VA). We revalued MR examination of 36 patients, 24 men, 12 women, aged 18-69 years. All patients underwent brain TC and MR (GE 1 Tesla); in 16 subjects 3D Time-of-Flight (TOF-3D) MRA was performed and in 20 subjects a Contrast-Enhanced MRA (CEMRA) of neck and head arteries. Thirty-one patients underwent a MRA follow-up. Dissection involved ICA in 30 and VA in 8. MR showed ischemic signs in 25 cases, wall hematoma in 19, and was normal in 11. MRA showed 25 vessels stenosis, 12 occlusions, and 9 aneurysm. Follow-up MRA showed 6 cases of complete resolution of stenosis, 17 partial resolution, 2 aneurysmal dissecanting, 6 luminal alteration unchanged, 1 aneurysma enlarged. MRA represented a non-invasive technique as investigation in suspected cervicocephalic arteries dissection.

Estudio no invasivo de las venas cerebrales y los senos durales: comparación de dos técnicas de angiografía con resonancia magnética

OBJECTIVE

To evaluate MR venography with bolus injection of intravenous contrast and elliptical filling of the K space, using three-dimensional fast spoiled gradient-echo (3D-FSPGR) sequences, and to compare it to the technique most frequently employed in the study of cerebral veins and dural sinuses, which is two-dimensional time-of-flight (2D-TOF) MR venography.

MATERIAL AND METHODS

Source images, multiplanar reconstructions, and maximum intensity projections (MIP) were obtained using both 2D-TOF venography and contrasted-enhanced 3D-FSPGR venography in 20 healthy volunteers. Two radiologists independently evaluated both techniques for the visualization of twenty-one predefined venous structures, classifying the depiction as completely visible, partially visible, or not visible.

RESULTS

The predefined venous structures were completely visible in 795 of 840 (94.6%) of the evaluations of contrast-enhanced 3D-FSPGR images versus 682 of 840 (81.1%) evaluations of 2D-TOF venography images. In the major dural sinuses, visualization was complete in 99.4% of the readings of contrast-enhanced 3D-FSPGR images versus 81% in the readings of the 2D-TOF images.

CONCLUSION

3D-FSPGR with elliptical filling of the K space and bolus injection of contrast material provides higher quality images of the intracranial venous system than those obtained using 2D-TOF sequences.

Extracranial Carotid MR Imaging at 3T

Some controversy exists over the accuracy and optimal parameters for carotid CE MR angiography at 1.5T. Spatial resolution remains more important than does temporal resolution to address the key question of vessel stenosis, based upon a review of the available literature that compares CE MR angiography with DSA. Specifically, CE MR angiograms with 0.9- to 1.2-mm resolution in all three planes before interpolation have a high reported sensitivity and specificity compared with DSA. To achieve this type of spatial resolution, cover the entire course of the carotid arteries from the aortic arch through the skull base, and achieve an absence of venous signal usually requires an elliptic-centric phase encoding CE MR angiogram that lasts for 50 to 60 seconds without the use of parallel imaging techniques. This near-millimeter resolution requires an accurate timing of the gadolinium bolus arrival to maximize intra-arterial SNR and to minimize venous contamination. Parallel imaging techniques can decrease the imaging time, but at a cost of some SNR. Initial experience with eight-channel or higher neurovascular coils at 3T indicates an increase in SNR/CNR compared with 1.5T. This should allow more consistent submillimeter-resolution carotid CE MR angiography with adequate SNR to maintain good IQ in a wide variety of clinical patients. Although a definite, prospective comparison of various CE MR angiography techniques,including a 20- to 30-second scan with 1.2- to 1.4-mm(3) voxel resolution and 50- to 60-second scan with 0.9- to 1.1-mm(3) voxel resolution at 1.5T, as well as 0.5- to 0.6-mm(3) voxel resolution with scan time of 50 to 60 seconds at 3T versus rotational DSA does not exist, the expectation is that the higher resolution and increased SNR that has resulted from 3T carotid CE MR angiography will have high sensitivity and specificity in detecting severe carotid stenosis. The most exciting application of 3T for carotid artery imaging may not be the higher resolution CE MR angiogram, however. Early work has demonstrated the potential of 3T, combined with sensitive surface coils, to depict carotid plaque with sufficient SNR to identify important plaque components consistently in most patients. This could help move MR imaging of the carotid arteries away from a strict evaluation of luminal narrowing to a focused evaluation of plaque morphology. Much work needs to be done. Although there is a growing body of literature to support the contention that plaque morphology is a predictor of subsequent thrombo-embolic disease, the natural history of these various plaque components in a large number of patients needs to be elucidated. If plaque characterization proves to be an independent risk factor that predicts stroke, more aggressive clinical treatment option strategies may be devised for patients who are at the highest risk. Currently, plaque characterization at 3T requires a different set of coils compared with the global assessment of the entire course of the carotid arteries. Future generations of 16- to 32-channel carotid coils should be able to combine the best features of current 4- to 8-channel surface carotid coils and neurovascular coils. These will enable a comprehensive evaluation of the entire course of the carotid artery and detailed carotid bifurcation plaque characterization at 3T within a clinically acceptable 1-hour time frame. This comprehensive carotid artery evaluation with 3T MR imaging would be far superior to that which is possible with US or CT.

Utility of MRA and CTA in the evaluation of carotid occlusive disease

Cervical carotid artery atherosclerotic disease is an important cause of thromboembolic stroke. Noninvasive imaging techniques have become preferred in initial diagnostic workup. We review the current approach to carotid imaging, and the clinical utility and limitations of carotid computed tomography angiography (CTA) and magnetic resonance angiography (MRA). Future directions of these modalities, including carotid plaque imaging, are also discussed.

Sensitivity encoding (SENSE) for contrast-enhanced 3D MR angiography of the abdominal arteries

PURPOSE

To assess sensitivity encoding (SENSE) for contrast-enhanced MR angiography (CE-MRA) of the abdominal arteries in comparison with standard MRA protocols.

MATERIALS AND METHODS

In 22 patients MRA of the abdominal arteries was performed twice (once using a standard protocol, and once with the additional use of SENSE). In 10 patients all examination parameters were kept constant (TR/TE/FA = 3.8 msec/1.3 msec/30 degrees ), and a reduction in scan time from 22 to 11 seconds was realized with the use of SENSE. In 12 patients, using SENSE the acquisition matrix was increased from 208 to 416, keeping the scan time constant. Image quality was scored on a five-point scale by three radiologists. Additionally, ROI-based measurements of CNR were performed.

RESULTS

For both protocols, image quality was significantly improved using SENSE. The time-reducing SENSE protocol yielded an average score of 4.2 points vs. 3.1 for the standard protocol. Using SENSE to increase the acquisition matrix, an average score of 4.3 was reached vs. 3.2 for the standard protocol (P < 0.05). The number of depictable small vessels and their bifurcations was significantly increased by either of the two SENSE protocols as compared to the standard imaging procedure.

CONCLUSION

SENSE for MRA of the abdominal arteries significantly increases image quality and permits a substantial reduction in breath-hold time or a significantly improved spatial resolution.

Contrast-Enhanced MR Angiography of Subclavian Steal Syndrome: Value of the 2D Time-of-Flight “Localizer” Sign

OBJECTIVE

Our objective was to determine if direction of flow within the vertebral artery could be reliably determined by evaluation of flow-sensitive, low-resolution 2D time-of-flight (TOF) localizer images taken before 3D contrast-enhanced MR angiography (3D CEMRA) sequences in patients with unsuspected subclavian steal syndrome.

CONCLUSION

Vertebral artery patency on 3D CEMRA in cases in which the vessel is absent on the TOF localizer in association with ipsilateral subclavian artery stenosis indicates reversal of flow in the vertebral artery and confirms the subclavian steal phenomenon. The combination of anatomic imaging with 3D CEMRA with functional information provided by the low-resolution TOF localizer confirms the diagnosis of subclavian steal without additional imaging.

Cardiovascular screening with parallel imaging techniques and a whole-body MR imager

The purpose of this study was to integrate parallel acquisition techniques into a comprehensive whole-body cardiovascular screening protocol to image all relevant organ systems without compromising spatial or temporal resolution. The study was approved by the institutional review board, and oral and written informed consent was obtained from each subject. Fifty subjects underwent whole-body magnetic resonance imaging that included imaging of heart, blood vessels, brain, lungs, and abdominal organs with a standard eight-channel imager. Image quality and pathologic findings were evaluated by two readers. The same protocol was then implemented with a new 32-channel whole-body imager. Depiction of 1476 (73.2%) of 2016 vessel segments was rated as good to excellent, and that of 1744 (86.5%), as without venous overlay. Interobserver agreement was good in evaluation of image quality and excellent in evaluation of pathologic findings. Acquisition time was reduced significantly (P < .05) with use of the whole-body imager and parallel acquisition techniques, which provided high-quality fast cardiovascular imaging.

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

PURPOSE

To compare three-dimensional (3D) time-of-flight (TOF) MR angiography, contrast-enhanced MR angiography, digital subtraction angiography (DSA), and rotational angiography for depiction of stenosis.

MATERIALS AND METHODS

The study had Ethics Committee approval, and each patient gave written informed consent. Forty-nine patients (18 women, mean age, 67.2 years +/- 9.1 [+/- standard deviation], and 31 men, mean age, 63.1 years +/- 8.0) with symptomatic stenosis of internal carotid artery (ICA) diagnosed at duplex ultrasonography underwent transverse 3D TOF MR angiography with sliding interleaved kY acquisition and coronal contrast-enhanced MR angiography, followed by DSA and rotational angiography within 48 hours. MR angiography was performed at 1.5-T with a cervical coil. Contrast-enhanced MR angiograms were obtained after a bolus injection of 20 mL of gadobenate dimeglumine. Maximum ICA stenosis on maximum intensity projection and source images was quantified according to NASCET criteria. Correlations for 3D TOF MR angiography, contrast-enhanced MR angiography, DSA, and rotational angiography were determined by means of cross tabulation, and accuracy for detection and grading of stenoses were calculated. Data were evaluated with analysis of variance, Wilcoxon signed rank test, and McNemar test, all at significance of P < .05.

RESULTS

Ninety-eight ICAs were evaluated at contrast-enhanced MR angiography, DSA, and rotational angiography, and 97 were evaluated at 3D TOF MR angiography. Correlations for contrast-enhanced MR angiography, 3D TOF MR angiography, and DSA relative to rotational angiography were r2 = 0.9332, r2 = 0.9048, and r2 = 0.9255, respectively. Lower correlation (r2 = 0.8593) was noted for contrast-enhanced MR angiography and DSA. Respective sensitivity and specificity for detection of hemodynamically relevant stenosis relative to rotational angiography were 100% and 90% for contrast-enhanced MR angiography, 95.5% and 87.2% for 3D TOF MR angiography, and 88.6% and 100% for DSA. Four of 31 severe stenoses were underestimated at DSA, and three were underestimated at contrast-enhanced MR angiography. Three severe stenoses were underestimated at 3D TOF MR angiography, and one was misclassified as occluded. Of 13 moderate (50%-69%) stenoses, one was overestimated at contrast-enhanced MR angiography, two were underestimated and three overestimated at 3D TOF MR angiography, and two were underestimated at DSA.

CONCLUSION

DSA results in an underestimation of ICA stenosis compared with rotational angiography. Contrast-enhanced MR angiography correlates best with rotational angiography.

Recommendations for Comprehensive Stroke Centers

Background and Purpose— To develop recommendations for the establishment of comprehensive stroke centers capable of delivering the full spectrum of care to seriously ill patients with stroke and cerebrovascular disease. Recommendations were developed by members of the Brain Attack Coalition (BAC), which is a multidisciplinary group of members from major professional organizations involved with the care of patients with stroke and cerebrovascular disease.

Summary of Review— A comprehensive literature search was conducted from 1966 through December 2004 using Medline and Pub Med. Articles with information about clinical trials, meta-analyses, care guidelines, scientific guidelines, and other relevant clinical and research reports were examined and graded using established evidence-based medicine approaches for therapeutic and diagnostic modalities. Evidence was also obtained from a questionnaire survey sent to leaders in cerebrovascular disease. Members of BAC reviewed literature related to their field and graded the scientific evidence on the various diagnostic and treatment modalities for stroke. Input was obtained from the organizations represented by BAC. BAC met on several occasions to review each specific recommendation and reach a consensus about its importance in light of other medical, logistical, and financial factors.

Conclusions— There are a number of key areas supported by evidence-based medicine that are important for a comprehensive stroke center and its ability to deliver the wide variety of specialized care needed by patients with serious cerebrovascular disease. These areas include: (1) health care personnel with specific expertise in a number of disciplines, including neurosurgery and vascular neurology; (2) advanced neuroimaging capabilities such as MRI and various types of cerebral angiography; (3) surgical and endovascular techniques, including clipping and coiling of intracranial aneurysms, carotid endarterectomy, and intra-arterial thrombolytic therapy; and (4) other specific infrastructure and programmatic elements such as an intensive care unit and a stroke registry. Integration of these elements into a coordinated hospital-based program or system is likely to improve outcomes of patients with strokes and complex cerebrovascular disease who require the services of a comprehensive stroke center.