Relaxation enhanced compressed sensing three-dimensional black-blood vessel wall MR imaging: Preliminary studies

Fast imaging of lenticulostriate arteries by high-resolution black-blood T1-weighted imaging with variable flip angles and acceleration by compressed sensitivity encoding

OBJECTIVE

We investigated the feasibility of using compressed sensitivity encoding (CS-SENSE) to accelerate high-resolution black-blood T1-weighted imaging with variable flip angles (T1WI-VFA) for efficient visualization and characterization of lenticulostriate arteries (LSAs) on a 3.0 T MR scanner.

MATERIALS AND METHODS

Twenty-five healthy volunteers and 18 patients with the cerebrovascular disease were prospectively enrolled. Healthy volunteers underwent T1WI-VFA sequences with different acceleration factors (AFs), including conventional sensitivity encoding (SENSE) AF = 3 and CS-SENSE AF = 3, 4, 5, and 6 (SENSE3, CS3, CS4, CS5, CS6, respectively) at 3 Tesla MRI scanner. Objective evaluation (contrast ratio and number, length, and branches of LSAs) and subjective evaluation (overall image quality and LSA visualization scores) were used to assess image quality and LSA visualization. Comparisons were performed among the 5 sequences to select the best AF. All patients underwent both T1WI-VFA with the optimal AF and digital subtraction angiography (DSA) examination, and the number of LSAs observed by T1WI-VFA was compared with that by DSA.

RESULTS

Pair-wise comparisons among CS3, CS4, and SENSE3 revealed no significant differences in both objective measurements and subjective evaluation (all P > 0.05). In patients, there was no significant difference in LSA counts on the same side between T1WI-VFA with CS4 and DSA (3, 3-4 and 3, 3-3, P = 0.243).

CONCLUSIONS

CS3 provided better LSA visualization but a longer scan duration compared to CS4. And, CS4 strikes a good balance between LSA visualization and acquisition time, which is recommended for routine clinical use.

Intracranial vessel wall imaging framework - Data acquisition, processing, and visualization

OBJECTIVE

Assessment of vessel walls is an integral part in diagnosis and disease monitoring of vascular diseases such as vasculitis. Vessel wall imaging (VWI), in particular of intracranial arteries, is the domain of Magnetic Resonance Imaging (MRI) - but still remains a challenge. The tortuous anatomy of intracranial arteries and the need for high resolution within clinically acceptable scan times require special technical conditions regarding the hardware and software environments.

MATERIALS AND METHODS

In this work a dedicated framework for intracranial VWI is presented offering an optimized, black-blood 3D T1-weighted post-contrast Compressed Sensing (CS)-accelerated MRI sequence prototype combined with dedicated 3D-GUI supported post-processing tool for the CPR visualization of tortuous arbitrary vessel structures.

RESULTS

Using CS accelerated MRI sequence, the scanning time for high-resolution 3D black-blood CS-space data could be reduced to under 10 min. These data are adequate for a further processing to extract straightened visualizations (curved planar reformats - CPR). First patient data sets could be acquired in clinical environment.

CONCLUSION

A highly versatile framework for VWI visualization was demonstrated utilizing a post-processing tool to extract CPR reformats from high-resolution 3D black-blood CS-SPACE data, enabling simplified and optimized assessment of intracranial arteries in intracranial vascular disorders, especially in suspected intracranial vasculitis, by stretching their tortuous course. The processing time from about 15-20 min per patient (data acquisition and further processing) allows the integration into clinical routine.

High-resolution Compressed-sensing T1 Black-blood MRI : A New Multipurpose Sequence in Vascular Neuroimaging?

BACKGROUND AND PURPOSE

In vasculopathies of the central nervous system, reliable and timely diagnosis is important against the background of significant morbidity and sequelae in cases of incorrect diagnosis or delayed treatment. Magnetic resonance imaging (MRI) plays a major role in the detection and monitoring of intracranial and extracranial vascular pathologies of different etiologies, in particular for evaluation of the vessel wall in addition to luminal information, thus allowing differentiation between various vasculopathies. Compressed-sensing black-blood MRI combines high image quality with relatively short acquisition time and offers promising potential in the context of neurovascular vessel wall imaging in clinical routine. This case review gives an overview of its application in the diagnosis of various intracranial and extracranial entities.

METHODS

An optimized high-resolution compressed-sensing black-blood 3D T1-weighted fast (turbo) spin echo technique (T1 CS-SPACE prototype) precontrast and postcontrast application at 3T was used for the evaluation of various vascular conditions in neuroradiology.

RESULTS

In this article seven cases of intracranial and extracranial arterial and venous vasculopathies with representative imaging findings in high-resolution compressed-sensing black-blood MRI are presented.

CONCLUSION

High-resolution 3D T1 CS-SPACE black-blood MRI is capable of imaging various vascular entities in high detail with whole head coverage and low susceptibility for motion artifacts and within acceptable scan times. It represents a highly versatile, non-invasive technique for the visualization and differentiation of a wide variety of neurovascular arterial and venous disorders.

Quantitative comparisons between relaxation enhanced compressed sensing 3D MERGE and conventional 3D MERGE for vessel wall imaging in equal scan time: preliminary studies

In this study, we quantitatively compared relaxation enhanced compressed sensing (RECS-3D MERGE) with conventional 3D MERGE techniques on blood suppression efficiency, wall-lumen contrast and plaque burden measurement for carotid atherosclerotic imaging in equal scan time. Twelve patients were recruited in the study. RECS-3D MERGE and conventional 3D MERGE were implemented. 2D DIR-FSE was carried out as a reference standard. The lumen signal-to-tissue ratio (STR) was used as the quantitative measure of blood suppression efficiency. The contrast-to-tissue ratio (CTR) was used as the quantitative measure of wall-lumen contrast. Vessel lumen area (LA) and wall area (WA) were measured for morphological comparisons. The lumen STR of RECS-3D MERGE was significantly lower than that of 3D MERGE while the wall-lumen CTR of RECS-3D MERGE was significantly higher. There were no significant differences in plaque burden measurements between RECS-3D MERGE and 2D DIR-FSE. For comparison between conventional 3D MERGE and 2D DIR-FSE, there were no significant differences in LA measurement. However, the WA of 3D MERGE was significantly larger. The RECS-3D MERGE sequence achieved more sufficient blood suppression and higher image contrast without prolonging the scan time. These improvements lead to more accurate morphological measurements of carotid atherosclerotic imaging.

Comparison of 3T Intracranial Vessel Wall MRI Sequences

BACKGROUND AND PURPOSE

Intracranial vessel wall MR imaging plays an increasing role in diagnosing intracranial vascular diseases. For a complete assessment, pre- and postcontrast sequences are required, and including other sequences, these result in a long scan duration. Ideally, the scan time of the vessel wall sequence should be reduced. The purpose of this study was to evaluate different intracranial vessel wall sequence variants to reduce scan duration, provided an acceptable image quality can be maintained.

MATERIALS AND METHODS

Starting from the vessel wall sequence that we use clinically (6:42 minutes), 6 scan variants were tested (scan duration ranging between 4:39 and 8:24 minutes), creating various trade-offs among spatial resolution, SNR, and contrast-to-noise ratio. In total, 15 subjects were scanned on a 3T MR imaging scanner: In 5 subjects, all 7 variants were performed precontrast-only, and in 10 other subjects, the fastest variant (4:39 minutes) and our clinically used variant (6:42 minutes) were performed pre- and postcontrast.

RESULTS

The fastest variant (4:39 minutes) had higher or comparable SNRs/contrast-to-noise ratios of the intracranial vessel walls compared with the reference sequence (6:42 minutes). Qualitative assessment showed that the contrast-to-noise ratio was most suppressed in the fastest variant of 4:39 minutes and the variant of 6:42 minutes pre- and postcontrast. SNRs/contrast-to-noise ratios of the fastest variant were all, except one, higher compared with the variant of 6:42 minutes (P < .008). Furthermore, the fastest variant (4:39 minutes) detected all vessel wall lesions identified on the 6:42-minute variant.

CONCLUSIONS

A 30% faster vessel wall sequence was developed with high SNRs/contrast-to-noise ratios that resulted in good visibility of the intracranial vessel wall.

A Comparison of Black-blood T2 Mapping Sequences for Carotid Vessel Wall Imaging at 3T: An Assessment of Accuracy and Repeatability

Purpose:

This study is to compare the accuracy of four different black-blood T₂ mapping sequences in carotid vessel wall.

Methods:

Four different black-blood T₂ mapping sequences were developed and tested through phantom experiments and 17 healthy volunteers. The four sequences were: 1) double inversion-recovery (DIR) prepared 2D multi-echo spin-echo (MESE); 2) DIR-prepared 2D multi-echo fast spin-echo (MEFSE); 3) improved motion-sensitized driven-equilibrium (iMSDE) prepared 3D FSE and 4) iMSDE prepared 3D fast spoiled gradient echo (FSPGR). The concordance correlation coefficient and Bland–Altman statistics were used to compare the sequences with a gold-standard 2D MESE, without blood suppression in phantom studies. The volunteers were scanned twice to test the repeatability. Mean and standard deviation of vessel wall T₂, signal-to-noise (SNR), the coefficient of variance and interclass coefficient (ICC) of the two scans were compared.

Results:

The phantom study demonstrated that T₂ measurements had high concordance with respect to the gold-standard (all r values >0.9). In the volunteer study, the DIR 2D MEFSE had significantly higher T₂ values than the other three sequences (P < 0.01). There was no difference in T₂ measurements obtained using the other three sequences (P > 0.05). iMSDE 3D FSE had the highest SNR (P < 0.05) compared with the other three sequences. The 2D DIR MESE has the highest repeatability (ICC: 0.96, [95% CI: 0.88–0.99]).

Conclusion:

Although accurate T₂ measurements can be achieved in phantom by the four sequences, in vivo vessel wall T₂ quantification shows significant differences. The in vivo images can be influenced by multiple factors including black-blood preparation and acquisition method. Therefore, a careful choice of acquisition methods and analysis of the confounding factors are required for accurate in vivo carotid vessel wall T₂ measurements. From the settings in this study, the iMSDE prepared 3D FSE is preferred for the future volunteer/patient scans.

Three-dimensional black-blood multi-contrast carotid imaging using compressed sensing: a repeatability study

OBJECTIVE

The purpose of this work is to evaluate the repeatability of a compressed sensing (CS) accelerated multi-contrast carotid protocol at 3 T.

MATERIALS AND METHODS

Twelve volunteers and eight patients with carotid disease were scanned on a 3 T MRI scanner using a CS accelerated 3-D black-blood multi-contrast protocol which comprises T ₁w, T ₂w and PDw without CS, and with a CS factor of 1.5 and 2.0. The volunteers were scanned twice, the lumen/wall area and wall thickness were measured for each scan. Eight patients were scanned once, the inter/intra-observer reproducibility of the measurements was calculated.

RESULTS

In the repeated volunteer scans, the interclass correlation coefficient (ICC) for the wall area measurement using a CS factor of 1.5 in PDw, T ₁w and T ₂w were 0.95, 0.81, and 0.97, respectively. The ICC for lumen area measurement using a CS factor of 1.5 in PDw, T ₁w and T ₂w were 0.96, 0.92, and 0.96, respectively. In patients, the ICC for inter/intra-observer measurements of lumen/wall area, and wall thickness were all above 0.81 in all sequences.

CONCLUSION

The results show a CS accelerated 3-D black-blood multi-contrast protocol is a robust and reproducible method for carotid imaging. Future protocol design could use CS to reduce the scanning time.

Flow artifact removal in carotid wall imaging based on black and gray-blood dual-contrast images subtraction

PURPOSE

To develop and validate a dual-contrast image subtraction (DCIS) strategy for eliminating the flow artifacts in black-blood carotid MRI.

METHODS

Twelve patients with carotid stenosis and eight healthy volunteers were imaged using the black and gray-blood dual-contrast imaging based on the relaxation-enhanced compressed sensing three-dimensional motion-sensitizing driven equilibrium prepared rapid-gradient-echo (RECS-3D MERGE) sequence. Subtraction of black-blood images (BBIs) and gray-blood images (GBIs), together with a preweighting procedure, was performed to eliminate the residual blood signal in BBIs. A wavelet denoising procedure was applied to offset the noise amplification. In addition to the lumen signal-to-noise ratio (SNR) and wall-lumen contrast-to-noise ratio (CNR), the signal variance ratio (SVR) and contrast variance ratio (CVR) were also used to evaluate the blood suppression efficiency.

RESULTS

By choosing the weighting factor of one, the lumen SNR of DCIS images was approximately 1% of that of the original BBIs, and the CNR showed a 91.4% improvement as compared with the BBIs. The median of the lumen SVR decreased to zero, and the CVR increased to 123% of that of the BBIs.

CONCLUSIONS

DCIS is demonstrated to be an effective strategy for sufficiently removing the residual flow signal from black-blood carotid MRI. Magn Reson Med 77:1612-1618, 2017. © 2016 International Society for Magnetic Resonance in Medicine.