Extracranial carotid arteries: evaluation with "black blood" MR angiography

Feasibility of Artificial Intelligence Constrained Compressed SENSE Accelerated 3D Isotropic T1 VISTA Sequence For Vessel Wall MR Imaging: Exploring the Potential of Higher Acceleration Factors Compared to Traditional Compressed SENSE

RATIONALE AND OBJECTIVES

Investigate the feasibility of using deep learning-based accelerated 3D T1-weighted volumetric isotropic turbo spin-echo acquisition (VISTA) for vessel wall magnetic resonance imaging (VW-MRI), compared to traditional Compressed SENSE and optimize acceleration factor (AF) to obtain high-quality clinical images.

METHODS

40 patients with atherosclerotic plaques in the intracranial or carotid artery were prospectively enrolled in our study from October 1, 2022 to October 31, 2023 underwent high-resolution vessel wall imaging on a 3.0 T MR system using variable Compressed SENSE (CS) AFs and reconstructed by an optimized artificial intelligence constrained Compressed SENSE (CS-AI). Images were reconstructed through both traditional CS and optimized CS-AI. Two radiologists qualitatively assessed the image quality scores of CS and CS-AI across different segments and quantitatively evaluated SNR (signal-to-noise ratio) and CNR (contrast-to-noise ratio) metrics. Paired t-tests, ANOVA, and Friedman tests analyzed image quality metrics. Written informed consent was obtained from all patients in this study.

RESULTS

CS-AI groups demonstrated good image quality scores compared to reference scans until AF up to 12 (P < 0.05). The CS-AI 10 protocol provided the best images in the lumen of both normal and lesion sites (P < 0.05). The plaque SNR was significantly higher in CS-AI groups compared to CS groups until the AF increased to 12 (P < 0.05). CS-AI protocols had higher CNR compared to CS with whichever AF on both pre-and post-contrast T1WI (P < 0.05), The CNR was highest in the CS-AI 10 protocol on pre-contrast T1WI and in CS-AI 12 on post-contrast T1WI (P < 0.05).

CONCLUSION

The study demonstrated the feasibility of using CS-AI technology to diagnose arteriosclerotic vascular disease with 3D T1 VISTA sequences. The image quality and diagnostic efficiency of CS-AI images were comparable or better than traditional CS images. Higher AFs are feasible and have potential for use in VW-MRI. The determination of standardized AFs for clinical scanning protocol is expected to help for empirical evaluation of new imaging technology.

Multimodal imaging approach for the diagnosis of intracranial atherosclerotic disease (ICAD): Basic principles, current and future perspectives

PURPOSE

To review the different imaging modalities utilized in the diagnosis of Intracranial Atherosclerotic Disease (ICAD) including their latest development and relevance in management of ICAD.

METHODS

A review of the literature was conducted through a search in google scholar, PubMed/Medline, EMBASE, Scopus, clinical trials.gov and the Cochrane Library. Search terms included, "imaging modalities in ICAD," "ICAD diagnostic," "Neuroimaging of ICAD," "Evaluation of ICAD". A summary and comparison of each modality's basic principles, advantages and disadvantages were included.

RESULTS

A total of 144 articles were identified and reviewed. The most common imaging used in ICAD diagnoses were DSA, CTA, MRA and TCD. They all had proven accuracy, their own benefits, and limitations. Newer modalities such as VWI, IVUS, OCT, PWI and CFD provide more detailed information regarding the vessel walls, plaque characteristics, and flow dynamics, which play a tremendous role in treatment guidance. In certain clinical scenarios, using more than one modality has been shown to be helpful in ICAD identification. The rapidly evolving software related to imaging studies, such as virtual histology, are very promising for the diagnostic and management of ICAD.

CONCLUSIONS

ICAD is a common cause of recurrent ischemic stroke. Its management can be both medical and/or procedural. Many different imaging modalities are used in its diagnosis. In certain clinical scenario, a combination of two more modalities can be critical in the management of ICAD. We expect that continuous development of imaging technique will lead to individualized and less invasive management with adequate outcome.

Vessel Wall Magnetic Resonance Imaging in Cerebrovascular Diseases

Cerebrovascular diseases are a leading cause of disability and death worldwide. The definition of stroke etiology is mandatory to predict outcome and guide therapeutic decisions. The diagnosis of pathological processes involving intracranial arteries is especially challenging, and the visualization of intracranial arteries’ vessel walls is not possible with routine imaging techniques. Vessel wall magnetic resonance imaging (VW-MRI) uses high-resolution, multiparametric MRI sequences to directly visualize intracranial arteries walls and their pathological alterations, allowing a better characterization of their pathology. VW-MRI demonstrated a wide range of clinical applications in acute cerebrovascular disease. Above all, it can be of great utility in the differential diagnosis of atherosclerotic and non-atherosclerotic intracranial vasculopathies. Additionally, it can be useful in the risk stratification of intracranial atherosclerotic lesions and to assess the risk of rupture of intracranial aneurysms. Recent advances in MRI technology made it more available, but larger studies are still needed to maximize its use in daily clinical practice.

Vessel wall imaging with advanced flow suppression in the characterization of intracranial aneurysms following flow diversion with Pipeline embolization device

BACKGROUND

High-resolution vessel wall MRI (VWI) is increasingly used to characterize intramural disorders of the intracranial vasculature unseen by conventional arteriography.

OBJECTIVE

To evaluate the use of VWI for surveillance of flow diverter (FD) treated aneurysms.

MATERIALS AND METHODS

Retrospective study of 28 aneurysms (in 21 patients) treated with a FD (mean 57 years; 14 female). All examinations included VWI and a contemporaneously obtained digital subtraction angiogram. Multiplanar pre- and post-gadolinium 3D, variable flip-angle T1 black-blood VWI was obtained using delay alternating nutation for tailored excitation (DANTE) at 3T. 3D time-of-flight MR angiography (MRA) was also carried out. Images were assessed for in-stent stenosis, aneurysm occlusion, presence and pattern/distribution of aneurysmal or parent vessel gadolinium enhancement.

RESULTS

The VWI-MRI was performed on average at 361±259 days after the intervention. Follow-up DSA was performed at 338±254 days postintervention. Good or excellent black-blood angiographic quality was recorded in 22/28 (79%) pre-contrast and 21/28 (75%) post-contrast VWI, with no cases excluded for image quality. Aneurysm enhancement was noted in 24/28 (85.7%) aneurysms, including in 79% of angiographically occluded aneurysms and 100% of angiographically non-occluded aneurysms. Enhancement of the stented parent-vessel wall occurred significantly more often when aneurysm enhancement was present (92% vs 33%, p=0.049).

CONCLUSION

Advanced VWI produces excellent depiction of FD-treated aneurysms, with robust evaluation of the parent vessel and aneurysm wall to an extent not achievable with conventional MRI/MRA. Gadolinium enhancement may, however, continue even after enduring catheter angiographic occlusion, confounding interpretation, and requiring cognizance of this potentially prolonged effect in such patients.

Current Clinical Applications of Intracranial Vessel Wall MR Imaging

Intracranial vessel wall MR imaging (VWI) is increasingly being used as a valuable adjunct to conventional angiographic imaging techniques. This article will provide an updated review on intracranial VWI protocols and image interpretation. We review VWI technical considerations, describe common VWI imaging features of different intracranial vasculopathies and show illustrative cases. We review the role of VWI for differentiating among steno-occlusive vasculopathies, such as intracranial atherosclerotic plaque, dissections and Moyamoya disease. We also highlight how VWI may be used for the diagnostic work-up and surveillance of patients with vasculitis of the central nervous system and cerebral aneurysms.

Essentials for Interpreting Intracranial Vessel Wall MRI Results: State of the Art

Intracranial vessel wall (VW) MRI has become widely available in clinical practice, providing multiple uses for evaluation of neurovascular diseases. The Vessel Wall Imaging Study Group of the American Society of Neuroradiology has recently reported expert consensus recommendations for the clinical implementation of this technique. However, the complexity of the neurovascular system and caveats to the technique may challenge its application in clinical practice. The purpose of this article is to review concepts essential for accurate interpretation of intracranial VW MRI results. This knowledge is intended to improve diagnostic confidence and performance in the interpretation of VW MRI scans. © RSNA, 2021 Online supplemental material is available for this article.

Evaluating renal arterial wall by non-enhanced 2D and 3D free-breathing black-blood techniques: Initial experience

OBJECTIVES

To evaluate the feasibility and reproducibility of 2D and 3D black-blood sequences in measuring morphology of renal arterial wall.

METHODS

The 2D and 3D imaging sequences used variable-refocusing-flip-angle and constant-low-refocusing-flip-angle turbo spin echo (TSE) readout respectively, with delicately selected black-blood scheme and respiratory motion trigger for free-breathing imaging. Fourteen healthy subjects and three patients with Takayasu arteritis underwent renal artery wall imaging with 3D double inversion recovery (DIR) TSE and 2D Variable Flip Angle-TSE (VFA-TSE) black-blood sequences at 3.0 T. Four healthy subjects were randomly selected for scan-rescan reproducibility experiments. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and morphology of arterial wall were measured and compared using paired-t-test or Wilcoxon signed-rank test between 2D and 3D sequences. The inter-observer, intra-observer and scan-rescan agreements of above measurements were determined using intraclass correlation coefficient (ICC).

RESULTS

The 2D and 3D imaging sequences showed similar morphological measurements (lumen area, wall area, mean wall thickness and maximum wall thickness) of renal arterial wall (all P > 0.05) and excellent agreement (ICC: 0.853-0.954). Compared to 2D imaging, 3D imaging exhibited significantly lower SNR_lumen (P < 0.01) and SNR_wall (P = 0.037), similar contrast-to-noise ratio (CNR) (P = 0.285), and higher CNR efficiency (CNR_eff) (P < 0.01). Both 2D and 3D imaging showed good to excellent inter-observer (ICC: 0.723-0.997), intra-observer (ICC: 0.749-0.996) and scan-rescan (ICC: 0.710-0.992) reproducibility in measuring renal arterial wall morphology, SNR and CNR, respectively.

CONCLUSIONS

Both high-resolution free-breathing 2D VFA-TSE and 3D DIR TSE black-blood sequences are feasible and reproducible in high-resolution renal arterial wall imaging. The 2D imaging has high SNR, whereas 3D imaging has high imaging efficiency.

Gadolinium-Enhanced 3D T1-Weighted Black-Blood MR Imaging for the Detection of Acute Optic Neuritis

BACKGROUND AND PURPOSE

A 3D T1-weighted black-blood sequence was recently shown to improve the detection of contrast-enhancing lesions in the brain in patients with MS compared with a 3D T1-weighted MPRAGE sequence. We compared a contrast-enhanced 3D T1-weighted black-blood sequence with a dedicated orbital contrast-enhanced T1-weighted Dixon sequence in patients with acute optic neuritis.

MATERIALS AND METHODS

MR imaging data (3T) of 51 patients showing symptoms of acute optic neuritis were analyzed retrospectively, including whole-brain contrast-enhanced 3D T1-weighted black-blood and dedicated orbital coronal 2D or 3D contrast-enhanced T1-weighted Dixon sequences. Two neuroradiologists assessed the images for overall image quality, artifacts, diagnostic confidence, and visual contrast enhancement. Furthermore, the standardized contrast-to-noise ratio was calculated. The final diagnosis of acute optic neuritis was established on the basis of clinical presentation, visually evoked potentials, and optical coherence tomography.

RESULTS

Thirty of 51 patients were diagnosed with acute optic neuritis. Of those, 21 showed contrast-enhancing lesions in the optic nerves, similarly detectable on contrast-enhanced T1-weighted Dixon and contrast-enhanced T1-weighted black-blood images. Thus, the accuracy for each sequence was identical, with a resulting sensitivity of 70% and specificity of 90% or 100% (depending on the reader). Overall image quality, diagnostic confidence, visual contrast enhancement, and artifacts were rated similarly in contrast-enhanced 3D T1-weighted black-blood and dedicated orbital contrast-enhanced T1-weighted Dixon sequences. There was no significant difference (P = .27) in the mean standardized contrast-to-noise ratio between contrast-enhanced T1-weighted black-blood (1.76 ± 1.07) and contrast-enhanced T1-weighted Dixon (2.29 ± 2.49) sequences.

CONCLUSIONS

Contrast-enhanced 3D T1-weighted black-blood imaging is comparable in accuracy and qualitative/quantitative features with dedicated orbital contrast-enhanced T1-weighted Dixon imaging for the detection of acute optic neuritis. Therefore, when used, it has the potential to considerably shorten total patient imaging time.

A Case of a Huge Inferior Vena Cava Leiomyosarcoma: Precise Preoperative Evaluation with Gadobutrol-Enhanced MRI

Background

Leiomyosarcoma of the inferior vena cava (IVC) is a rare malignant tumour with poor prognosis. Surgical resection is the first line of treatment to achieve the best possible outcome. However, precise preoperative evaluation is essential to guide therapeutic decisions. Here, the preoperative evaluation potential of gadobutrol-enhanced magnetic resonance imaging (MRI) was assessed in the management of a 42-year-old patient with a large IVC mass.

Methods

The patient first underwent enhanced computed tomography (CT), but the relationship between the left renal vein and the mass in the dilated IVC was ambiguous, and it remained unclear whether the right hepatic vein was invaded by the lesion. To make a precise assessment of the tumour, the patient subsequently underwent high-resolution MRI angiography examination combined with high-concentration contrast medium gadobutrol.

Results

MRI demonstrated the integrity of the right hepatic vein and the left renal vein. Following a multidisciplinary consultation, a complicated surgery including complete resection of the mass, artificial vessel replacement of IVC, total hepatectomy, and bilateral nephrectomy with liver and kidney auto-transplantation was performed successfully. The surgical plan formulated after reviewing the MRI preoperatively was adhered to the course of the surgery. Postoperative CT re-examination showed that the blood flow of the artificial blood vessel and the right hepatic vein was unobstructed. Histopathological examination confirmed the tumour to be a leiomyosarcoma.

Conclusion

Preoperative imaging diagnosis and assessment have important implications for the surgical planning of IVC leiomyosarcoma. High-resolution MRI angiography examination with high concentration contrast medium gadobutrol may be of particular benefit in IVC tumours.

Imaging of intracranial atherosclerotic plaques using 3.0 T and 7.0 T magnetic resonance imaging-current trends and future perspectives

Intracranial atherosclerotic disease (ICAD) is one of the most common causes of ischemic stroke and carries a relatively high risk of stroke recurrence. Advances in high-resolution magnetic resonance imaging (HRMRI) techniques of intracranial arteries now have made it possible to directly visualize atherosclerotic plaque itself, allowing detailed assessments of plaque morphology and components. Currently available intracranial HRMRI could be performed with 2-dimensional (2D) and 3D acquisitions, and multicontrast weightings in clinically reasonable scan times. Until now, HRMRI research of ICAD has focused on the identification of plaque vulnerability, and the relationship between plaque characteristics and ischemic stroke. HRMRI at ultra-high-field strength (7.0 T) holds promise in better visualizing intracranial vessel walls, as well as identifying early lesions and total burden of ICAD. As a result, intracranial HRMRI provides great insights into pathology of intracranial atherosclerotic plaques, stroke mechanisms, and future stroke risk. In this article, we will review the technical implementation, preclinical research, clinical applications, and future directions of HRMRI for the evaluation of ICAD at 3.0 T and 7.0 T.

Evaluation of chronic carotid artery occlusion by non-contrast 3D-MERGE MR vessel wall imaging: comparison with 3D-TOF-MRA, contrast-enhanced MRA, and DSA

OBJECTIVES

To analyze the accuracy of a non-contrast MR vessel wall imaging technique, three-dimensional motion-sensitized driven equilibrium prepared rapid gradient echo (3D-MERGE) for diagnosing chronic carotid artery occlusion (CCAO) characteristics compared with 3D time-of-flight (TOF) MRA, and contrast-enhanced MRA (CE-MRA), using digital subtraction angiography (DSA) as a reference standard.

METHODS

Subjects diagnosed with possible CCAO by ultrasound were retrospectively analyzed. Patients underwent 3.0-T MR imaging with 3D-MERGE, 3D-TOF-MRA, and CE-MRA followed by DSA within 1 week. Diagnostic accuracy of occlusion, occlusion site, and proximal stump condition were assessed independently on 3 MRI sequences and DSA. Agreement of the above indicators was evaluated in reference to DSA.

RESULTS

One hundred twenty-four patients with 129 suspected CCAO (5 with bilateral occlusions) met the inclusion criteria for our study. 3D-MERGE demonstrated a sensitivity, specificity, and accuracy of 97.0%, 86.7%, and 94.6%, respectively, with excellent agreement (Cohen's κ = 0.85; 95% CI, 0.71, 0.94) for diagnosing CCAO in reference to DSA. 3D-MERGE was superior in diagnosing CCAO compared with 3D-TOF-MRA (Cohen's κ = 0.61; 95% CI, 0.42, 0.77) and similar to CE-MRA (Cohen's κ = 0.93; 95% CI, 0.86, 1.00). 3D-MERGE also had excellent agreement compared with DSA for assessing occlusion sites (Cohen's κ = 0.85; 95% CI, 0.71, 0.97) and stump condition (Cohen's κ = 0.83; 95% CI, 0.71, 0.94). Moreover, 3D-MERGE provided additional information regarding the occluded segment, such as distal lumen collapse and vessel wall lesion components.

CONCLUSION

3D-MERGE can reliably assess chronic carotid occlusive characteristics and has the ability to identify other vessel wall features of the occluded segment. This non-contrast MR vessel wall imaging technique is promising for assessment of CCAO.

KEY POINTS

• Excellent agreement was found between 3D-MERGE and DSA for assessing chronic carotid artery occlusion, occlusion site, and proximal stump condition. • 3D-MERGE was shown to be a more accurate and efficient tool than 3D-TOF-MRA to detect the characteristics of the occluded segment. • 3D-MERGE provides not only luminal images for characterizing the proximal characteristics of occlusion but also vessel wall images for assessing the distal lumen and morphology of occlusion segment, which might help clinicians to optimize the treatment strategy for patients with chronic carotid artery occlusion.

Vascular wall imaging in reversible cerebral vasoconstriction syndrome - a 3-T contrast-enhanced MRI study

Background

Limited histopathology studies have suggested that reversible cerebral vasoconstriction syndromes (RCVS) does not present with vascular wall inflammation. Previous vascular imaging studies have had inconsistent vascular wall enhancement findings in RCVS patients. The aim of this study was to determine whether absence of arterial wall pathology on imaging is a universal finding in patients with RCVS.

Methods

We recruited patients with RCVS from Taipei Veterans General Hospital prospectively from 2010 to 2012, with follow-up until 2017 (n = 48). We analyzed the characteristics of vascular wall enhancement in these patients without comparisons to a control group. All participants received vascular wall imaging by contrasted T1 fluid-attenuated inversion recovery with a 3-T magnetic resonance machine. The vascular wall enhancement was rated as marked, mild or absent.

Results

Of 48 patients with RCVS, 22 (45.8%) had vascular wall enhancement (5 marked and 17 mild). Demographics, clinical profiles, and cerebral artery flow velocities were similar across patients with versus without vascular wall enhancement, except that patients with vascular wall enhancement had fewer headache attacks than those without (p = 0.04). Follow-up imaging completed in 14 patients (median interval, 7 months) showed reduced enhancement in 9 patients, but persistent enhancement in 5.

Conclusion

Almost half of our RCVS patients exhibited imaging enhancement of diseased vessels, and it was persistent for approximately a third of those patients with follow-up imaging. Both acute and persistent vascular wall enhancement may be unhelpful for differentiating RCVS from central nervous system vasculitis or subclinical atherosclerosis.

Cavernous brain malformations and their relation to black blood MRI in respect to vessel wall contrast enhancement

Background

Inflammatory responses are implicated as crucial patho-mechanisms of vascular brain malformations. Inflammation is suggested to be a key contributor to aneurysm rupture; however it is unclear whether inflammation contributes similarly to bleeding of cerebral cavernous malformations (CCMs). Black blood MRI is a sequence which identifies inflammation in blood vessel walls and in the present study is used to detect inflammatory response in CCMs.

Methods

Fifteen patients with 17 CCMs treated in our department in 2017 were retrospectively analysed. All patients received black blood MRIs and the results were analysed in correlation with, size and bleeding of CCMs.

Results

Size and bleeding status of CCMs did not correlate with contrast enhancement in the CCM wall. One of 3 patients with bleeding displayed contrast enhancement in black blood MRI, whereas the others had non enhancing lesions. Because of the small number of cases a statistical analysis was not performed.

Conclusion

In this limited cohort, inflammatory reactions in CCMs could not be detected by black blood MRI suggesting that the level of inflammation is minimal in these lesions and those different patho-mechanisms play a more important role in the rupture of CCMs.

Intracranial Vessel Wall Imaging with Magnetic Resonance Imaging: Current Techniques and Applications

Vessel wall magnetic resonance imaging (VW-MRI) is a modern imaging technique with expanding applications in the characterization of intracranial vessel wall pathology. VW-MRI provides added diagnostic capacity compared with conventional luminal imaging methods. This review explores the principles of VW-MRI and typical imaging features of various vessel wall pathologies, such as atherosclerosis, dissection, and vasculitis. Radiologists should be familiar with this important imaging technique, given its increasing use and future relevance to everyday practice.

Ferumoxytol enhanced black-blood cardiovascular magnetic resonance imaging

BACKGROUND

Bright-blood and black-blood cardiovascular magnetic resonance (CMR) techniques are frequently employed together during a clinical exam because of their complementary features. While valuable, existing black-blood CMR approaches are flow dependent and prone to failure. We aim to assess the effectiveness and reliability of ferumoxytol enhanced (FE) Half-Fourier Single-shot Turbo Spin-echo (HASTE) imaging without magnetization preparation pulses to yield uniform intra-luminal blood signal suppression by comparing FE-HASTE with pre-ferumoxytol HASTE imaging.

METHODS

This study was IRB-approved and HIPAA compliant. Consecutive patients who were referred for FE-CMR between June 2013 and February 2017 were enrolled. Qualitative image scores reflecting the degree and reliability of blood signal suppression were based on a 3-point Likert scale, with 3 reflecting perfect suppression. For quantitative evaluation, homogeneity indices (defined as standard deviation of the left atrial signal intensity) and signal-to-noise ratios (SNR) for vascular lumens and cardiac chambers were measured.

RESULTS

Of the 340 unique patients who underwent FE-CMR, HASTE was performed in 257. Ninety-three patients had both pre-ferumoxytol HASTE and FE-HASTE, and were included in this analysis. Qualitative image scores reflecting the degree and reliability of blood signal suppression were significantly higher for FE-HASTE images (2.9 [IQR 2.8-3.0] vs 1.8 [IQR 1.6-2.1], p < 0.001). Inter-reader agreement was moderate (k = 0.50, 95% CI 0.45-0.55). Blood signal suppression was more complete on FE-HASTE images than on pre-ferumoxytol HASTE, as indicated by lower mean homogeneity indices (24.5 [IQR 18.0-32.8] vs 108.0 [IQR 65.0-170.4], p < 0.001) and lower blood pool SNR for all regions (5.6 [IQR 3.2-10.0] vs 21.5 [IQR 12.5-39.4], p < 0.001).

CONCLUSION

FE-HASTE black-blood imaging offers an effective, reliable, and simple approach for flow independent blood signal suppression. The technique holds promise as a fast and routine complement to bright-blood cardiovascular imaging with ferumoxytol.

Flow-suppressed hyperpolarized 13 C chemical shift imaging using velocity-optimized bipolar gradient in mouse liver tumors at 9.4 T

PURPOSE

To optimize and investigate the influence of bipolar gradients for flow suppression in metabolic quantification of hyperpolarized ¹³ C chemical shift imaging (CSI) of mouse liver at 9.4 T.

METHODS

The trade-off between the amount of flow suppression using bipolar gradients and T2* effect from static spins was simulated. A free induction decay CSI sequence with alternations between the flow-suppressed and non-flow-suppressed acquisitions for each repetition time was developed and was applied to liver tumor-bearing mice via injection of hyperpolarized [1-¹³ C] pyruvate.

RESULTS

The in vivo results from flow suppression using the velocity-optimized bipolar gradient were comparable with the simulation results. The vascular signal was adequately suppressed and signal loss in stationary tissue was minimized. Application of the velocity-optimized bipolar gradient to tumor-bearing mice showed reduction in the vessel-derived pyruvate signal contamination, and the average lactate/pyruvate ratio increased by 0.095 (P < 0.05) in the tumor region after flow suppression.

CONCLUSION

Optimization of the bipolar gradient is essential because of the short ¹³ C T2* and high signal in venous flow in the mouse liver. The proposed velocity-optimized bipolar gradient can suppress the vascular signal, minimizing T2*-related signal loss in stationary tissues at 9.4 T. Magn Reson Med 78:1674-1682, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Voxel-based Histographic Analysis of the Basilar Artery in Patients with Isolated Pontine Infarction

Background and Purpose:

The signal information per voxels of magnetic resonance imaging (MRI) for vessel wall could reflect the pathologic features of atherosclerotic vessels. The aim of this study is to evaluate the usefulness of magnetic resonance voxel-based histogram (VBH) of atherosclerotic basilar artery in patients with isolated pontine infarctions (PIs).

Materials and Methods:

Wall and lumen of basilar artery were segmented from high resolution MR of 42 patients with isolated PI and 10 normal volunteers. VBHs were obtained after normalization by dividing the intensity of segmented wall with the intensity of non-infarcted area of pons. The variables of VBH included area (A), mean signal intensity (SI), standard deviation (SD), kurtosis (K), and skewness (SK) and area stenosis [AS; A^wall/(A^wall + A^lumen)] were compared according to the MRI-modified American Heart Association (AHA) atherosclerotic plaque schema, and between the subgroups of PI (lacunar: LPI and paramedian: PPI).

Results:

According to the MRI-modified AHA atherosclerotic plaque schema, A^wall/T₁ (mean area of wall on T₁-weighted MRI), SI^wall/T₁, SD^wall/T₁, SK^wall/T₁, K^wall/T₁, A^lumen/T₁, and AS^T₁ showed statistical differences. AHA IV–VII showed higher A^wall/T₁, SI^wall/T₁, and AS^T₁ than normal control. PPI showed statistical differences in A^wall/T₁, SI^wall/T₁, SK ^wall/T₁, and A^wall/T₂ than those of normal control after post hoc test, whereas LPI in A^wall/T₁ and A^wall/T₂ (P < 0.05, Kruskal-Wallis test, Dunnett T3 procedure).

Conclusions:

VBH analysis can provide the quantitative information with regard to volume as well as composition of the atherosclerotic plaque in the basilar artery. The difference in patterns of VBH might be further useful in characterizing PIs with presumably different pathogenesis.

MR Angiography of in Situ and Transplanted Renal Arteries

Three-dimensional (3D) time-of-flight (TOF) MR angiography (MRA) was performed in 34 patients with suspected renal artery disease. In situ (i.e., nontransplanted) renal arteries were studied with MRA in 14 patients. Of these, 12 had conventional angiography for comparison. Twenty-four MRAs of transplanted renal arteries were obtained in 20 patients; 8 of these had angiography as well. Significant stenoses of in situ renal arteries were diagnosed with a sensitivity of 100% and a specificity of 95%. The stenoses were all proximal; 3D TOF MRA proved inadequate for depiction of peripheral renal arteries. MRA and angiography showed good agreement between findings in 7 of 8 patients with renal transplants. In one patient with a renal transplant, MRA showed a significant stenosis of the arterial anastomosis which appeared completely normal at i.a. DSA, indicating that findings at MRA still need to be confirmed by more established alternative methods.

Three-Dimensional Black Blood Mr Angiography of the Liver during Breath Holding

In 2-D time-of-flight MR angiography (2-D TOF MRA) of the liver, artifacts caused by respiratory motion are unavoidable. Therefore, a 3-D black blood MRA of the liver was attempted in 7 healthy volunteers, using a 3-D gradient echo sequence which allows imaging during breath holding. 2-D TOF MRA was performed as well. In all subjects, 3-D MRA allowed visualization of the trunk, 1st-, and 2nd-order branches of the portal vein without interruption. Right 3rd-order branches were visualized without interruption in 6 of 7 subjects (85%). However, with 2-D MRA, the transverse portion of the left main portal vein could not be visualized in any subject, and the periphery of the portal vein was less clear than with 3-D MRA.

Intracranial Vessel Wall MRI: Principles and Expert Consensus Recommendations of the American Society of Neuroradiology

Intracranial vessel wall MR imaging is an adjunct to conventional angiographic imaging with CTA, MRA, or DSA. The technique has multiple potential uses in the context of ischemic stroke and intracranial hemorrhage. There remain gaps in our understanding of intracranial vessel wall MR imaging findings and research is ongoing, but the technique is already used on a clinical basis at many centers. This article, on behalf of the Vessel Wall Imaging Study Group of the American Society of Neuroradiology, provides expert consensus recommendations for current clinical practice.

Vessel wall imaging for intracranial vascular disease evaluation

Accurate and timely diagnosis of intracranial vasculopathies is important owing to the significant risk of morbidity with delayed and/or incorrect diagnosis both from the disease process and inappropriate therapies. Conventional luminal imaging techniques for analysis of intracranial vasculopathies are limited to evaluation of changes in the vessel lumen. Vessel wall MRI techniques can allow direct characterization of pathologic changes of the vessel wall. These techniques may improve diagnostic accuracy and improve patient outcomes. Extracranial carotid vessel wall imaging has been extensively investigated in patients with atherosclerotic disease and has been shown to accurately assess plaque composition and identify vulnerable plaque characteristics that may predict stroke risk beyond luminal stenosis alone. This review provides a brief history of vessel wall MRI, an overview of the intracranial vessel wall MRI techniques, its applications, and imaging findings of various intracranial vasculopathies pertinent to the neurointerventionalist, neurologist, and neuroradiologist. We searched MEDLINE, PubMed, and Google for English publications containing any of the following terms: 'intracranial vessel wall imaging', 'intracranial vessel wall', and 'intracranial vessel wall MRI'.

Assessment of carotid artery atherosclerotic disease by using three-dimensional fast black-blood MR imaging: comparison with DSA

PURPOSE

To assess fast three-dimensional (3D) black-blood (BB) magnetic resonance (MR) imaging as a noninvasive alternative to intraarterial digital subtraction angiography (DSA) at quantifying moderate to severe carotid artery atherosclerotic disease.

MATERIALS AND METHODS

Local ethics committee approval and written informed patient consent were obtained for this study. Sixty-five carotid arteries from 52 patients with at least 50% stenosis underwent 3D BB MR imaging and DSA. Quantitative measurements, including stenosis, lesion length, and the presence or absence of plaque ulceration, obtained with the two modalities were independently determined. Sensitivity and specificity, the intraclass correlation coefficient (ICC), Cohen κ, and Bland-Altman analysis were used to assess the agreement.

RESULTS

Excellent agreement in measuring luminal stenosis was found between 3D BB MR imaging and DSA (ICC, 0.96; 95% confidence interval [CI]: 0.93, 0.97). Three-dimensional BB MR imaging was also found to have high sensitivity (91.7%), specificity (96.2%), and agreement (Cohen κ, 0.85; 95% CI: 0.66, 0.99) with DSA for detection of ulcers. Good agreement was found between lesion length measured by using 3D BB MR imaging and DSA (ICC, 0.75; 95% CI: 0.51, 0.84). However, lesion length measurements by using 3D BB MR imaging were, on average, 4.0 mm longer than those measured by using DSA (P < .001).

CONCLUSION

Three-dimensional BB MR imaging is a noninvasive and accurate way to quantify moderate to severe carotid artery atherosclerotic disease. With fast acquisition and large coverage, 3D BB MR imaging has the potential to become an alternative imaging approach in evaluating the severity of atherosclerosis.

Visualization of lenticulostriate arteries at 3T: Optimization of slice-selective off-resonance sinc pulse-prepared TOF-MRA and its comparison with flow-sensitive black-blood MRA

RATIONALE AND OBJECTIVES

To optimize visualization of lenticulostriate artery (LSA) by time-of-flight (TOF) magnetic resonance angiography (MRA) with slice-selective off-resonance sinc (SORS) saturation transfer contrast pulses and to compare capability of optimal TOF-MRA and flow-sensitive black-blood (FSBB) MRA to visualize the LSA at 3T.

MATERIALS AND METHODS

This study was approved by the local ethics committee, and written informed consent was obtained from all the subjects. TOF-MRA was optimized in 20 subjects by comparing SORS pulses of different flip angles: 0, 400°, and 750°. Numbers of LSAs were counted. The optimal TOF-MRA was compared to FSBB-MRA in 21 subjects. Images were evaluated by the numbers and length of visualized LSAs.

RESULTS

LSAs were significantly more visualized in TOF-MRA with SORS pulses of 400° than others (P < .003). When the optimal TOF-MRA was compared to FSBB-MRA, the visualization of LSA using FSBB (mean branch numbers 11.1, 95% confidence interval (CI) 10.0-12.1; mean total length 236 mm, 95% CI 210-263 mm) was significantly better than using TOF (4.7, 95% CI 4.1-5.3; 78 mm, 95% CI 67-89 mm) for both numbers and length of the LSA (P < .0001).

CONCLUSIONS

LSA visualization was best with 400° SORS pulses for TOF-MRA but FSBB-MRA was better than TOF-MRA, which indicates its clinical potential to investigate the LSA on a 3T magnetic resonance imaging.

Spin echo magnetic resonance imaging

The spin echo sequence is a fundamental pulse sequence in MRI. Many of today's applications in routine clinical use are based on this elementary sequence. In this review article, the principles of the spin echo formation are demonstrated on which the generation of the fundamental image contrasts T1, T2, and proton density is based. The basic imaging parameters repetition time (TR) and echo time (TE) and their influence on the image contrast are explained. Important properties such as the behavior in multi-slice imaging or in the presence of flow are depicted and the basic differences with gradient echo imaging are illustrated. The characteristics of the spin echo sequence for different magnetic field strengths with respect to clinical applications are discussed.

MR diagnosis of vertebral artery dissection: value of 3D time-of-flight and true fast imaging with steady-state precession fusion imaging

OBJECTIVES

We hypothesized that 3D time-of-flight (TOF) and true fast imaging with steady-state precession (true-FISP) fusion imaging could provide more information regarding the arterial vessel wall. The purpose of this study was to compare the accuracy of lesion detection and the diagnostic confidence of VAD between TOF images alone and fused TOF and true-FISP images.

METHODS

Fifty patients were studied: 17 had VAD and 33 had vertebral artery hypoplasia. Fusion images of the vertebral artery were reconstructed using a workstation. A receiver-operating characteristic (ROC) analysis was conducted with a continuous rating scale from 1 to 100 to compare observer performance in VAD detection. Five radiologists participated in the observer performance test, and their performances with TOF images were compared with those using fused images.

RESULT

The observers found that the mean areas under the best-fit ROC curve for TOF images alone and fused TOF images were 0.66 ± 0.05 and 0.93 ± 0.04, which were significantly different (P < 0.01).

CONCLUSION

The fusion images provided more information regarding the arterial vessel wall. Fused images aided distinction between vertebral artery dissection versus vertebral artery hypoplasia.

KEY POINTS

• New MR techniques can help to differentiate flowing blood from static blood products. • Fused TOF and true-FISP images differentiate the lumen and the arterial wall, improving diagnostic performance. • Fused images may be superior to time-of-flight MR angiography alone.

CINE turbo spin echo imaging

High-resolution turbo spin echo (TSE) images have demonstrated important details of carotid artery morphology; however, it is evident that pulsatile blood and wall motion related to the cardiac cycle are still significant sources of image degradation. Although ECG gating can reduce artifacts due to cardiac-induced pulsations, gating is rarely used because it lengthens the acquisition time and can cause image degradation due to nonconstant repetition time. This work introduces a relatively simple method of converting a conventional TSE acquisition into a retrospectively ECG-correlated cineTSE sequence. The cineTSE sequence generates a full sequence of ECG-correlated images at each slice location throughout the cardiac cycle in the same scan time that is conventionally used by standard TSE sequences to produce a single image at each slice location. The cineTSE images exhibit reduced pulsatile artifacts associated with a gated sequence but without the increased scan time or associated nonconstant repetition time effects.

Carotid MRI: a tool for monitoring individual response to cardiovascular therapy?

Stroke remains a leading cause of morbidity and mortality. While stroke-related mortality has declined over the past four decades, data indicate that the mortality rate has begun to plateau. This change in trend may be attributable to variation in individual response to therapies that were derived from population-based studies. Further reductions in stroke mortality may require individualized care governed by directly monitoring the effects of cardiovascular therapy. In this article, carotid MRI is considered as a tool for monitoring in vivo carotid atherosclerotic disease, a principal etiology of stroke. Carotid MRI has been previously utilized to identify specific plaque features beyond luminal stenosis that are predictive of transient ischemic attack and stroke. To gain perspective on the possibility of monitoring plaque change within the individual, clinical trials and natural history studies that have used serial carotid MRI are considered. Data from these studies indicate that patients with a lipid-rich necrotic core with or without intraplaque hemorrhage may represent the desired phenotype for monitoring treatment effects in the individual. Advances in tissue-specific sequences, acquisition resolution, scan time, and techniques for monitoring inflammation and mechanical forces are expected to enable earlier detection of response to therapy. In so doing, cost-effective multicenter studies can be conducted to confirm the anticipated positive effects on outcomes of using carotid MRI for individualized care in patients with carotid atherosclerosis. In accordance, carotid MRI is poised to emerge as a powerful clinical tool for individualized management of carotid atherosclerotic disease to prevent stroke.

Current techniques for MR imaging of atherosclerosis

Vessel wall imaging of large vessels has the potential to identify culprit atherosclerotic plaques that lead to cardiovascular events. Comprehensive assessment of atherosclerotic plaque size, composition, and biological activity is possible with magnetic resonance imaging (MRI). Magnetic resonance imaging of the atherosclerotic plaque has demonstrated high accuracy and measurement reproducibility for plaque size. The accuracy of in vivo multicontrast MRI for identification of plaque composition has been validated against histological findings. Magnetic resonance imaging markers of plaque biological activity such as neovasculature and inflammation have been demonstrated. In contrast to other plaque imaging modalities, MRI can be used to study multiple vascular beds noninvasively over time. In this review, we compare the status of in vivo plaque imaging by MRI to competing imaging modalities. Recent MR technological improvements allow fast, accurate, and reproducible plaque imaging. An overview of current MRI techniques required for carotid plaque imaging including hardware, specialized pulse sequences, and processing algorithms are presented. In addition, the application of these techniques to coronary, aortic, and peripheral vascular beds is reviewed.

Imaging biomarkers of cardiovascular disease

Cardiovascular disease (CVD) is a leading cause of morbidity and mortality worldwide. Current clinical techniques that rely on stenosis measurement alone appear to be insufficient for risk prediction in atherosclerosis patients. Many novel imaging methods have been developed to study atherosclerosis progression and to identify new features that can predict future clinical risk. MRI of atherosclerotic vessel walls is one such method. It has the ability to noninvasively evaluate multiple biomarkers of the disease such as luminal stenosis, plaque burden, tissue composition and plaque activity. In addition, the accuracy of in vivo MRI has been validated against histology with high reproducibility, thus paving the way for application to epidemiological studies of disease pathogenesis and, by serial MRI, in monitoring the efficacy of therapeutic intervention. In this review, we describe the various MR techniques used to evaluate aspects of plaque progression, discuss imaging-based measurements (imaging biomarkers), and also detail their validation. The application of plaque MRI in clinical trials as well as emerging imaging techniques used to evaluate plaque compositional features and biological activities are also discussed.

Enhanced image quality in black-blood MRI using the improved motion-sensitized driven-equilibrium (iMSDE) sequence

PURPOSE

To propose an improved motion-sensitized driven-equilibrium (iMSDE) pulse sequence to enhance the tissue signal-to-noise ratio (SNR) while maintaining the same flow suppression capability in black-blood carotid artery magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Compared to the traditional MSDE sequence, the iMSDE sequence uses an extra refocusing pulse and two extra gradients to achieve SNR improvement. Computer simulation and phantom studies were used to evaluate both eddy currents and local B(1) inhomogeneity effects on SNR behaviors on both MSDE and iMSDE images. To further assess the SNR improvements brought by iMSDE in vivo, five healthy volunteers were also scanned with both sequences. The paired t-test was used for statistical comparison.

RESULTS

Both simulations and phantom studies demonstrated that eddy currents and local B(1) inhomogeneity will cause image SNR reduction in the MSDE sequence, and that these factors can be partially compensated for with the iMSDE sequence. In vivo comparison showed that the iMSDE sequence significantly improved the tissue-lumen contrast-to-noise ratio (CNR) and static tissue SNR (P < 0.001 for both), while maintaining low lumen SNR in carotid MRI.

CONCLUSION

Compared to the traditional MSDE sequence, the iMSDE sequence can achieve improved soft-tissue SNR and CNR in carotid artery MRI without sacrificing flow suppression capability and time efficiency.

Diagnosis of intracranial atherosclerosis

IMPORTANCE OF THE FIELD

Intracranial atherosclerosis is quickly becoming the most common stroke mechanism worldwide. Accurate diagnosis is important in making treatment decisions.

AREAS COVERED IN THE REVIEW

In this article the clinical and radiographic diagnosis of intracranial atherosclerosis is reviewed. An overview is provided of widely available invasive and non-invasive methods for the detection of intracranial atherosclerosis, including transcranial Doppler, magnetic resonance and computed tomography angiography, as well as conventional angiography.

WHAT THE READER WILL GAIN

The reader will become familiar with the advantages and limitations of various imaging modalities used in the diagnosis of intracranial atherosclerosis.

TAKE HOME MESSAGE

Non-invasive imaging modalities have a high negative predictive value in detecting intracranial atherosclerosis. The gold standard for confirmation of the diagnosis remains catheter angiography.

Effective motion-sensitizing magnetization preparation for black blood magnetic resonance imaging of the heart

PURPOSE

To investigate the effectiveness of flow signal suppression of a motion-sensitizing magnetization preparation (MSPREP) sequence and to optimize a 2D MSPREP steady-state free precession (SSFP) sequence for black blood imaging of the heart.

MATERIALS AND METHODS

Using a flow phantom, the effect of varying field of speed (FOS), b-value, voxel size, and flow pattern on the flow suppression was investigated. In seven healthy volunteers, black blood images of the heart were obtained at 1.5T with MSPREP-SSFP and double inversion recovery fast spin echo (DIR-FSE) techniques. Myocardium and blood signal-to-noise ratio (SNR) and myocardium-to-blood contrast-to-noise ratio (CNR) were measured. The optimal FOS that maximized the CNR for MSPREP-SSFP was determined.

RESULTS

Phantom data demonstrated that the flow suppression was induced primarily by the velocity encoding effect. In humans, FOS=10-20 cm/s was found to maximize the CNR for short-axis (SA) and four-chamber (4C) views. Compared to DIR-FSE, MSPREP-SSFP provided similar blood SNR efficiency in the SA basal and mid-views and significantly lower blood SNR efficiency in the SA apical (P=0.02) and 4C (P=0.01) views, indicating similar or better blood suppression.

CONCLUSION

Velocity encoding is the primary flow suppression mechanism of the MSPREP sequence and 2D MSPREP-SSFP black blood imaging of the heart is feasible in healthy subjects.

Spontaneous early recanalization of an acute symptomatic critical stenosis of the extracranial internal carotid artery: a case report

We present a 63-year-old female with critical stenosis of the extracranial portion of the internal carotid artery (ICA), diagnosed using color-coded Duplex ultrasonography (CCDU) and magnetic resonance imaging. Nine days later, the patient showed profound clinical improvement, at which time spontaneous recanalization of the previously highly stenosed ICA was seen in follow-up CCDU and magnetic resonance angiography (MRA) and confirmed by three-dimensional computed tomography angiography (CTA). The detection of recanalization is important in predicting the patient's prognosis and deciding a suboptimal secondary prophylaxis strategy of medical or surgical treatment. Therefore, we suggest performing imaging studies immediately in patients, especially potential surgical or stenting candidates showing great changes in neurological function, through examination with CCDU and confirmation with MRA or CTA, all safe and minimally invasive methods, to see whether recanalization has occurred.

Improved suppression of plaque-mimicking artifacts in black-blood carotid atherosclerosis imaging using a multislice motion-sensitized driven-equilibrium (MSDE) turbo spin-echo (TSE) sequence

In this study, a turbo spin-echo (TSE) based motion-sensitized driven-equilibrium (MSDE) sequence was used as an alternative black-blood (BB) carotid MRI imaging scheme. The MSDE sequence was first optimized for more efficient residual blood signal suppression in the carotid bulb of healthy volunteers. Effective contrast-to-noise ratio (CNR(eff)) and residual signal-to-noise ratio (SNR) in the lumen measured from MSDE images were then compared to those measured from inflow saturation (IS) and double inversion-recovery (DIR) images. Statistically significant higher CNR(eff) and lower lumen SNR were obtained from MSDE images. To assess MSDE sequence in a clinical carotid protocol, 42 locations from six subjects with 50% to 79% carotid stenosis by duplex ultrasound were scanned with both MSDE and multislice DIR. The comparison showed that MSDE images present significantly higher CNR and lower lumen SNR compared to corresponding multislice DIR images. The vessel wall area and mean wall thickness measurements in MSDE images were slightly but significantly lower than those obtained with other blood suppression techniques. In conclusion, in vivo comparisons demonstrated that MSDE sequence can achieve better blood suppression and provide a more accurate depiction of the lumen boundaries by eliminating plaque mimicking artifacts in carotid artery (CA) imaging.

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.

Blood attenuation with SSFP-compatible saturation (BASS)

PURPOSE

To investigate a rapid flow-suppression method for improving the contrast-to-noise ratio (CNR) between the vessel wall and the lumen for cardiovascular imaging applications.

MATERIALS AND METHODS

In this study a new dark-blood steady-state free precession (SSFP) sequence utilizing two excitation pulses per TR was developed. The first pulse is applied immediately adjacent to the slice of interest, while the second is a conventional slice-selective pulse designed to excite an SSFP signal for the static spins in the slice of interest. The slice-selective pulse is followed by fully refocused gradients along all three imaging axes over each TR. The signal amplitude (SA) from the moving spins excited by the "saturation" pulse is attenuated since they are not fully refocused at the TE.

RESULTS

This work provides confirmation, by both simulation and experiments, that modest adaptations of the basic True-FISP structure can limit unwanted "bright blood" signal within the vessels while simultaneously preserving the contrast and speed advantages of this well-established rapid imaging method.

CONCLUSION

Animal imaging trials confirm that dark-blood contrast is achieved with the BASS sequence, which substantially reverses the lumen-to-muscle CNR of a conventional True-FISP "bright blood" acquisition from 14.77 (bright blood) to -13.96 (dark blood) with a modest increase (24.2% of regular TR of SSFP for this implementation) in acquisition time to accommodate the additional slab-selective excitation pulse and gradient pulses.

A review on MR vascular image processing algorithms: acquisition and prefiltering: part I

Vascular segmentation has recently been given much attention. This review paper has two parts. Part I focuses on the physics of magnetic resonance angiography (MRA) generation and prefiltering techniques applied to MRA data sets. Part II of the review focuses on the vessel segmentation algorithms. The first section of this paper introduces the five different sets of receive coils used with the MRI system for magnetic resonance angiography data acquisition. This section then presents the five different types of the most popular data acquisition techniques: time-of-flight (TOF), phase-contrast, contrast-enhanced, black-blood, T2-weighted, and T2*-weighted, along with their pros and cons. Section II of this paper focuses on prefiltering algorithms for MRA data sets. This is necessary for removing the background nonvascular structures in the MRA data sets. Finally, the paper concludes with a clinical discussion on the challenges and the future of the data acquisition and the automated filtering algorithms.