Multiple contrast fast spin-echo approach to black-blood intracranial MRA: use of complementary and supplementary information

Three-dimensional spin-echo-based black-blood MRA in the detection of vasospasm following subarachnoid hemorrhage

BACKGROUND

Black-blood MR angiography (BBMRA), which utilizes a non-T₁ contrast spin-echo type technique, has been expected to overcome several issues associated with time-of-flight (TOF) MRA.

PURPOSE

To investigate the efficacy of BBMRA to detect vasospasms following subarachnoid hemorrhage (SAH).

STUDY TYPE

Retrospective.

SUBJECTS

Seventeen patients with SAH in their early posttreatment period.

FIELD STRENGTH/SEQUENCE

BBMRA, which uses a volumetric isotropic turbo spin-echo acquisition (VISTA), and TOF-MRA on 1.5T scanners.

ASSESSMENT

Visualization of supratentorial arteries and veins in BBMRA was rated on a 4-point scale by two neuroradiologists. Another neuroradiologist independently assessed TOF-MRA. The degree of the vasospasm was then evaluated using a 3-point scale by the same readers. The diagnostic performance of the MRAs was evaluated using computed tomography angiography (CTA) or digital subtraction angiography (DSA) as the standard of reference.

STATISTICAL TESTS

Wilcoxon signed rank test, McNemar test, and Cohen's kappa coefficient.

RESULTS

BBMRA provided superior visualization of the anterior and middle cerebral arteries than TOF-MRA (P < 0.05). The depiction of the veins was more pronounced on BBMRA (P < 0.01). Of the 166 arterial segments evaluated by CTA or DSA, 23 (13.9%) could not be assessed using TOF-MRA because of high signal hemorrhage, whereas BBMRA enabled visualization of all the segments. Vasospasm was confirmed in 30 segments by CTA or DSA. The sensitivity, specificity, and positive and negative predictive values were 73, 96, 76, and 95 for TOF-MRA and 91, 100, 100, and 98 for BBMRA, respectively (P = 0.13 for sensitivity, P = 0.06 for specificity). The agreement of the degree of vasospasm between MRA and the standard of reference, as indicated by kappa value, was 0.71 (95% confidence interval [CI], 0.55-0.87) for TOF-MRA and 0.91 (95% CI, 0.82-0.99) for BBMRA.

DATA CONCLUSION

BBMRA, owing to its contrast properties, may be superior to TOF-MRA for the evaluation of intracranial arteries after SAH.

LEVEL OF EVIDENCE

3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:800-807.

Vascular disorders--magnetic resonance angiography: brain vessels

Magnetic resonance angiography (MRA) of the brain obtained at 3 T imaging has made a significant clinical impact. MRA benefits from acquisition at higher magnetic field strength because of higher available signal-to-noise ratio and improved relative background suppression due to magnetic field strength-related T1 lengthening. Parallel imaging techniques are ideally suited for high-field MRA. Many of the developments that have made 3 T MRA of the brain successful can be regarded as enabling technologies that are essential for further development of 7 T MRA, which brings additional challenges.

Does black blood MRA have a role in the assessment of intracerebral aneurysms?

The aim of this study was to assess whether the addition of a black blood (BB) sequence to standard three-dimensional time-of-flight (3D-TOF) imaging yields improved quantitative assessment of intracranial aneurysms. Thirty seven patients with 42 proven intracranial aneurysms underwent intra-arterial digital subtraction angiography, 3D-TOF and BB MRI imaging. This multimodality imaging was used to create a composite reference aneurysm description. The 3D-TOF and BB imaging were graded on a subjective seven-point scale to determine what improvement if any the addition of BB imaging yielded. Comparison of measurements from all imaging modalities demonstrated no significant difference (p < 0.01) in aneurysm length/width or parent vessel width. Aneurysm neck measurements were underestimated on 3D-TOF images although there was still a significant correlation (R(2) = 0.72, p < 0.05). Comparison of TOF and BB examinations to the composite reference using the Wilcoxon signed-rank test showed significant improvement in the demonstration of the aneurysm to parent/branch vessels and the morphology/size of the aneurysm neck, particularly in the setting of local haematoma or slow flow (p < 0.001). We propose the addition of the BB sequence as a useful adjunct to 3D-TOF imaging particularly when detailed aneurysm morphology is required or there is thrombus in subarachnoid space.

MR angiography in the follow-up of intracranial aneurysms treated with Guglielmi detachable coils: systematic review and meta-analysis

INTRODUCTION

The aim of this study was to systematically review published data on the diagnostic performance of magnetic resonance angiography (MRA) compared with digital subtraction angiography as reference standard in the follow-up of intracranial aneurysms treated with Guglielmi detachable coils.

METHODS

A systematic search for relevant studies was performed of the PubMed/MEDLINE and Embase databases. Two reviewers independently assessed the methodological quality of each study. A meta-analysis of the reported sensitivity and specificity of each study was performed.

RESULTS

The inclusion criteria were met by 16 studies. The studies had moderate methodological quality. Pooled sensitivity and specificity of non-enhanced time-of-flight MRA (TOF-MRA) for the detection of residual flow (within the aneurysmal neck and/or coil mesh) were 83.3% (95% CI 70.3-91.3%) and 90.6% (95% CI 80.4-95.8%), respectively. Pooled sensitivity and specificity of contrast-enhanced MRA (CE-MRA) for the detection of residual flow were 86.8% (95% CI 71.4-94.5%) and 91.9% (95% CI 79.8-97.0%), respectively. All pooled estimates were subject to heterogeneity. There were no statistically significant differences in pooled sensitivity and specificity between TOF-MRA and CE-MRA.

CONCLUSION

The results of this study suggest that both TOF-MRA and CE-MRA achieve a moderate to high diagnostic performance. However, the findings should be interpreted with caution because the included studies were of moderate methodological quality and all pooled estimates were subject to heterogeneity. More well-designed studies are required to confirm the current results and MRA at higher field strength (>1.5 T) needs to be further explored.

Motion artifact reduction technique for dual-contrast FSE imaging

There is considerable similarity between proton density-weighted (PDw) and T2-weighted (T2w) images acquired by dual-contrast fast spin-echo (FSE) sequences. The similarity manifests itself in image space as consistency between the phases of PDw and T2w images and in k-space as correspondence between PDw and T2w k-space data. A method for motion artifact reduction for dual-contrast FSE imaging has been developed. The method uses projection onto convex sets (POCS) formalism and is based on image space phase consistency and the k-space similarity between PDw and T2w images. When coupled with a modified dual-contrast FSE phase encoding scheme the method can yield considerable artifact reduction, as long as less than half of the acquired data is corrupted by motion. The feasibility and efficiency of the developed method were demonstrated using phantom and human MRI data.