Delay Alternating With Nutation For Tailored Excitation Research Articles

Efficacy of high-resolution vessel wall MRI in the postoperative assessment of intracranial aneurysms following flow diversion treatment.

Certain patients must undergo frequent postoperative digital subtraction angiography (DSA) after flow diversion (FD) therapy. No imaging modality with an efficacy comparable to that of DSA has been established. This study was conducted to determine the efficacy of contrast-enhanced delay alternating with nutation for tailored excitation (DANTE) T1-sampling perfection with application-optimized contrasts by using different flip angle evolution (SPACE), a high-resolution vessel wall magnetic resonance imaging technique for evaluating the occlusion status of intracranial aneurysms after FD treatment, with DSA serving as the reference standard. This retrospective study included 23 patients with 26 aneurysms who had undergone FD treatment between April 2016 and May 2022. Contrast-enhanced DANTE T1-SPACE and DSA were performed as postoperative follow-up imaging studies at 45 time points, both in the same period. The agreement rates for aneurysm occlusion status in the 45 imaging studies were examined. Contrast-enhanced DANTE T1-SPACE had a sensitivity and specificity of 96.3% (26/27) and 83.3% (15/18), respectively, for detecting aneurysm remnants. Overall, 91.1% (41/45) of findings detected on contrast-enhanced DANTE T1-SPACE were consistent with those on DSA. The findings detected on contrast-enhanced DANTE T1-SPACE were completely consistent with those of intraaneurysmal residual blood flow identified on DSA or high-resolution cone-beam computed tomography images in 74.1% (20/27) of the examinations that showed incomplete occlusion on DSA. Furthermore, parent artery status after FD treatment on contrast-enhanced DANTE T1-SPACE was consistent with that observed on DSA in 97.8% (44/45) of examinations. Contrast-enhanced DANTE T1-SPACE is a very useful option in the follow-up of aneurysms after FD treatment.

DANTE-CAIPI Accelerated Contrast-Enhanced 3D T1: Deep Learning-Based Image Quality Improvement for Vessel Wall MRI.

Accelerated and blood-suppressed postcontrast 3D intracranial vessel wall MRI (IVW) enables high-resolution rapid scanning but is associated with low SNR. We hypothesized that a deep-learning (DL) denoising algorithm applied to accelerated, blood-suppressed postcontrast IVW can yield high-quality images with reduced artifacts and higher SNR in shorter scan times. Sixty-four consecutive patients underwent IVW, including conventional postcontrast 3D T1-sampling perfection with application-optimized contrasts by using different flip angle evolution (SPACE) and delay alternating with nutation for tailored excitation (DANTE) blood-suppressed and CAIPIRINHIA-accelerated (CAIPI) 3D T1-weighted TSE postcontrast sequences (DANTE-CAIPI-SPACE). DANTE-CAIPI-SPACE acquisitions were then denoised by using an unrolled deep convolutional network (DANTE-CAIPI-SPACE+DL). SPACE, DANTE-CAIPI-SPACE, and DANTE-CAIPI-SPACE+DL images were compared for overall image quality, SNR, severity of artifacts, arterial and venous suppression, and lesion assessment by using 4-point or 5-point Likert scales. Quantitative evaluation of SNR and contrast-to-noise ratio (CNR) was performed. DANTE-CAIPI-SPACE+DL showed significantly reduced arterial (1 [1-1.75] versus 3 [3-4], P < .001) and venous flow artifacts (1 [1-2] versus 3 [3-4], P < .001) compared with SPACE. There was no significant difference between DANTE-CAIPI-SPACE+DL and SPACE in terms of image quality, SNR, artifact ratings, and lesion assessment. For SNR ratings, DANTE-CAIPI-SPACE+DL was significantly better compared with DANTE-CAIPI-SPACE (2 [1-2], versus 3 [2-3], P < .001). No statistically significant differences were found between DANTE-CAIPI-SPACE and DANTE-CAIPI-SPACE+DL for image quality, artifact, arterial blood and venous blood flow artifacts, and lesion assessment. Quantitative vessel wall SNR and CNR median values were significantly higher for DANTE-CAIPI-SPACE+DL (SNR: 9.71, CNR: 4.24) compared with DANTE-CAIPI-SPACE (SNR: 5.50, CNR: 2.64) (P < .001 for each), but there was no significant difference between SPACE (SNR: 10.82, CNR: 5.21) and DANTE-CAIPI-SPACE+DL. DL denoised postcontrast T1-weighted DANTE-CAIPI-SPACE accelerated and blood-suppressed IVW showed improved flow suppression with a shorter scan time and equivalent qualitative and quantitative SNR measures relative to conventional postcontrast IVW. It also improved SNR metrics relative to postcontrast DANTE-CAIPI-SPACE IVW. Implementing DL denoised DANTE-CAIPI-SPACE IVW has the potential to shorten protocol time while maintaining or improving the image quality of IVW.

An extended phase graph-based framework for DANTE-SPACE simulations including physiological, temporal, and spatial variations.

The delay alternating with nutation for tailored excitation (DANTE)-sampling perfection with application-optimized contrasts (SPACE) sequence facilitates 3D intracranial vessel wall imaging with simultaneous suppression of blood and CSF. However, the achieved image contrast depends closely on the selected sequence parameters, and the clinical use of the sequence is limited in vivo by observed signal variations in the vessel wall, CSF, and blood. This paper introduces a comprehensive DANTE-SPACE simulation framework, with the aim of providing a better understanding of the underlying contrast mechanisms and facilitating improved parameter selection and contrast optimization. An extended phase graph formalism was developed for efficient spin ensemble simulation of the DANTE-SPACE sequence. Physiological processes such as pulsatile flow velocity variation, varying flow directions, intravoxel velocity variation, diffusion, and effects were included in the framework to represent the mechanisms behind the achieved signal levels accurately. Intravoxel velocity variation improved temporal stability and robustness against small velocity changes. Time-varying pulsatile velocity variation affected CSF simulations, introducing periods of near-zero velocity and partial rephasing. Inclusion of diffusion effects was found to substantially reduce the CSF signal. Blood flow trajectory variations had minor effects, but differences along the trajectory reduced DANTE efficiency in low- areas. Introducing low-velocity pulsatility of both CSF and vessel wall helped explain the in vivo observed signal heterogeneity in both tissue types. The presented simulation framework facilitates a more comprehensive optimization of DANTE-SPACE sequence parameters. Furthermore, the simulation framework helps to explain observed contrasts in acquired data.

Improved Blood Suppression of Motion-Sensitized Driven Equilibrium in High-Resolution Whole-Brain Vessel Wall Imaging: Comparison of Contrast-Enhanced 3D T1-Weighted FSE with Motion-Sensitized Driven Equilibrium and Delay Alternating with Nutation for Tailored Excitation.

High-resolution vessel wall MR imaging is prone to slow-flow artifacts, particularly when gadolinium shortens the T1 relaxation time of blood. This study aimed to determine the optimal preparation pulses for contrast-enhanced high-resolution vessel wall MR imaging. Fifty patients who underwent both motion-sensitized driven equilibrium and delay alternating with nutation for tailored excitation (DANTE) preparation pulses with contrast-enhanced 3D-T1-FSE were retrospectively included. Qualitative analysis was performed using a 4-grade visual scoring system for black-blood performance in the small-sized intracranial vessels, overall image quality, severity of artifacts, and the degree of blood suppression in all cortical veins as well as transverse sinuses. Quantitative analysis of the M1 segment of the MCA was also performed. The qualitative analysis revealed that motion-sensitized driven equilibrium demonstrated a significantly higher black-blood score than DANTE in contrast-enhanced 3D-T1-FSE of the A3 segment (3.90 versus 3.58, P < .001); M3 (3.72 versus 3.26, P = .004); P2 to P3 (3.86 versus 3.64, P = .017); the internal cerebral vein (3.72 versus 2.32, P < .001); and overall cortical veins (3.30 versus 2.74, P < .001); and transverse sinuses (2.82 versus 2.38, P < .001). SNRlumen, contrast-to noise ratiowall-lumen, and SNRwall in the M1 vessel were not significantly different between the 2 preparation pulses (all, P > .05). Motion-sensitized driven equilibrium demonstrated improved blood suppression on contrast-enhanced 3D-T1-FSE in the small intracranial arteries and veins compared with DANTE. Motion-sensitized driven equilibrium is a useful preparation pulse for high-resolution vessel wall MR imaging to decrease venous contamination and suppress slow-flow artifacts when using contrast enhancement.

Image-Quality Assessment of 3D Intracranial Vessel Wall MRI Using DANTE or DANTE-CAIPI for Blood Suppression and Imaging Acceleration.

3D intracranial vessel wall MRI techniques are time consuming and prone to artifacts, especially flow artifacts. Our aim was to compare the image quality of accelerated and flow-suppressed 3D intracranial vessel wall MR imaging techniques relative to conventional acquisitions. Consecutive patients undergoing MR imaging had conventional postcontrast 3D T1-sampling perfection with application-optimized contrasts by using different flip angle evolution (SPACE) and either postcontrast delay alternating with nutation for tailored excitation (DANTE) flow-suppressed or DANTE-controlled aliasing in parallel imaging results in higher acceleration (CAIPI) flow-suppressed and accelerated T1-SPACE sequences performed. The sequences were evaluated using 4- or 5-point Likert scales for overall image quality, SNR, extent/severity of artifacts, motion, blood suppression, sharpness, and lesion assessment. Quantitative assessment of lumen and wall-to-lumen contrast ratios was performed. Eighty-nine patients were included. T1-DANTE-SPACE had significantly better qualitative ratings relative to T1-SPACE for image quality, SNR, artifact impact, arterial and venous suppression, and lesion assessment (P < .001 for each, respectively), with the exception of motion (P = .16). T1-DANTE-CAIPI-SPACE had significantly better image quality, lesion assessment, arterial and venous blood suppression, less artifact impact, and less motion compared with T1-SPACE (P < .001 for each, respectively). The SNR was higher with T1-SPACE compared with T1-DANTE-CAIPI-SPACE (P < .001). T1-DANTE-CAIPI-SPACE showed significantly worse lumen (P = .005) and wall-to-lumen contrast ratios (P = .001) compared with T1-SPACE, without a significant difference between T1-SPACE and T1-DANTE-SPACE. T1-DANTE-CAIPI-SPACE scan time was 5:11 minutes compared with 8:08 and 8:41 minutes for conventional T1-SPACE and T1-DANTE-SPACE, respectively. Accelerated postcontrast T1-DANTE-CAIPI-SPACE had fewer image artifacts, less motion, improved blood suppression, and a shorter scan time, but lower qualitative and quantitative SNR ratings relative to conventional T1-SPACE intracranial vessel wall MR imaging. Postcontrast T1-DANTE-SPACE had superior SNR, blood suppression, higher image quality, and fewer image artifacts, but slightly longer scan times relative to T1-SPACE.

Carotid arterial wall MRI of apolipoprotein e–deficient mouse at 7 T using DANTE-prepared variable-flip-angle rapid acquisition with relaxation enhancement

PurposeTo optimize a sequence combining the delay alternating with nutation for tailored excitation (DANTE) preparative module with the variable-flip-angle rapid acquisition with relaxation enhancement (VF-RARE) sequence (DANTE-VF-RARE) and to investigate its feasibility for vessel wall imaging in Apolipoprotein E–Deficient (ApoE−/−) mouse at 7 Tesla (T). Materials and methodsSpecific T1/T2 values were used for producing a sharper vessel wall in the variable-flip-angle optimization scheme. The DANTE RF pulse flip angle and pulse train length were optimized for maximizing the wall-lumen contrast.ApoE−/− (fed high fat diet for 20/40/ 60 weeks, n = 9/4/4) and wild-type mice (controls, n = 3) were imaged at 7 T using VF-RARE, DANTE-VF-RARE, time-of-flight (TOF) angiography, and multi-slice T1-weighted 2D RARE coupled with inflow outflow saturation bands (IOSB-RARE). Wall-lumen contrast-to-noise-ratio efficiency (CNReff), lumen area (LA), and wall area (WA) were compared between DANTE-VF-RARE and 2D IOSB-RARE sequences. Additionally, linear regression analysis was conducted between MR measurements and histomorphometric planimetry results. ResultsResidual blood signal was observed in the four out of eighteen carotids on VF-RARE images, whereas it was significantly suppressed on DANTE-VF-RARE images. Compared with IOSB-RARE, DANTE-VF-RARE offered significantly improved CNReff (P < 0.001). The LA and WA were both comparable (P = 0.085 and 0.112, respectively) and showed excellent agreement between DANTE-VF-RARE and IOSB-RARE (ICC = 0.96 and 0.95, respectively). The luminal stenosis identified by DANTE-VF-RARE was in consistent with the results of TOF. Strong correlations were found between MR measurements and histopathological analysis for both WA (DANTE-VF-RARE: r = 0.92, slope = 0.94, P < 0.001; IOSB-RARE: r = 0.93, slope = 0.94, P < 0.001) and LA (DANTE-VF-RARE: r = 0.82, slope = 0.54, P < 0.001; IOSB-RARE: r = 0.78, slope = 0.50, P < 0.001). ConclusionDANTE-VF-RARE achieves effective blood signal suppression and is a feasible approach for the 3D carotid arterial wall imaging of ApoE−/− mouse at 7 T.

Time-efficient and contrast-free magnetic resonance imaging approach to the diagnosis of deep vein thrombosis on black-blood gradient-echo sequence: a pilot study.

Black-blood thrombus imaging (BTI) has shown to be advantageous for the diagnosis of deep vein thrombosis (DVT). However, previous techniques using fast spin echo have a high specific absorption rate. As DANTE (delay alternating with nutation for tailored excitation) black-blood preparation can suppress blood flows over a broad range of velocities, we hypothesized that a DANTE black-blood preparation combined with a fast low-angle shot (FLASH) gradient-echo readout-DANTE-FLASH could be used to diagnose DVT. Eleven healthy volunteers and 30 suspected DVT patients were recruited to undergo DANTE-FLASH and magnetic resonance direct thrombus imaging (MRDTI). The suspected DVT patients were also examined by ultrasound (US). For the segment level, a total of 1,066 venous vessel segments were analyzed. Using US and MRDTI as the references, the sensitivity (SE), specificity (SP), positive and negative predictive values (PPV and NPV), and accuracy (ACC) of DANTE-FLASH were calculated. To quantitatively compare image quality between DANTE-FLASH and MRDTI, image signal-to-noise ratio (SNR), apparent contrast-to-noise ratio (CNR) between muscle and the venous lumen, and the apparent CNR between the thrombus and venous lumen were measured. Additionally, diagnostic confidence, image quality, and clot burden were also evaluated. Using the consensus results of US and MRDTI as a standard reference, the diagnostic SE, SP, PPV, NPV, and ACC of DANTE-FLASH for the 2 readers were 97.0% and 93.2%, 99.0% and 98.2%, 93.4% and 87.9%, 99.6% and 99.0%, and 98.8% and 97.6%, respectively. According to the image quantitative analysis results, DANTE-FLASH demonstrated higher image SNR and CNR than MRDTI. The image quality and diagnostic confidence scores of DANTE-FLASH were higher than MRDTI (3.66±0.44 vs. 3.52±0.52, P<0.001, and 3.84±0.36 vs. 3.76±0.41, P<0.001). There was excellent agreement between DANTE-FLASH and MRDTI on clot burden evaluation. DANTE-FLASH provided better image quality than MRDTI and accurately detected thrombi. It may, therefore, serve as a safe and convenient alternative for the diagnosis of DVT.

Integrated VASO and perfusion contrast: A new tool for laminar functional MRI

Earlier research in cats has shown that both cerebral blood volume (CBV) and cerebral blood flow (CBF) can be used to identify layer-dependent fMRI activation with spatial specificity superior to gradient-echo blood-oxygen-level-dependent (BOLD) contrast (Jin and Kim, 2008a). CBF contrast of perfusion fMRI at ultra-high field has not been widely applied in humans to measure laminar activity due to its low sensitivity, while CBV contrast for fMRI using vascular space occupancy (VASO) has been successfully used. However, VASO can be compromised by interference of blood in-flow effects and a temporally limited acquisition window around the blood-nulling time point. Here, we proposed to use DANTE (Delay Alternating with Nutation for Tailored Excitation) pulse trains combined with 3D-EPI to acquire an integrated VASO and perfusion (VAPER) contrast. The signal origin of the VAPER contrast was theoretically evaluated with respect to its CBV and CBF contributions using a four-compartment simulation model. The feasibility of VAPER to measure layer-dependent activity was empirically investigated in human primary motor cortex at 7 ​T. We demonstrated this new tool, with its highly specified functional layer profile, robust reproducibility, and improved sensitivity, to allow investigation of layer-specific cortical functions.

Cerebral Venous Thrombosis: MR Black-Blood Thrombus Imaging with Enhanced Blood Signal Suppression.

The residual blood flow artifact is a critical confounder for MR black-blood thrombus imaging of cerebral venous sinus thrombosis. This study aimed to conduct a validation of a new MR black-blood thrombus imaging technique with enhanced blood signal suppression. Twenty-six participants (13 volunteers and 13 patients) underwent conventional imaging methods followed by 2 randomized black-blood thrombus imaging scans, with a preoptimized delay alternating with nutation for tailored excitation (DANTE) preparation switched on and off, respectively. The signal intensity of residual blood, thrombus, brain parenchyma, normal lumen, and noise on black-blood thrombus images were measured. The thrombus volume, SNR of residual blood, and contrast-to-noise ratio for residual blood versus normal lumen, thrombus versus residual blood, and brain parenchyma versus normal lumen were compared between the 2 black-blood thrombus imaging techniques. Segmental diagnosis of venous sinus thrombosis was evaluated for each black-blood thrombus imaging technique using a combination of conventional imaging techniques as a reference. In the volunteer group, the SNR of residual blood (11.3 ± 2.9 versus 54.0 ± 23.4, P < .001) and residual blood-to-normal lumen contrast-to-noise ratio (7.5 ± 3.4 versus 49.2 ± 23.3, P < .001) were significantly reduced using the DANTE preparation. In the patient group, the SNR of residual blood (16.4 ± 8.0 versus 75.0 ± 35.1, P = .002) and residual blood-to-normal lumen contrast-to-noise ratio (12.4 ± 7.8 versus 68.8 ± 35.4, P = .002) were also significantly lower on DANTE-prepared black-blood thrombus imaging. The new black-blood thrombus imaging technique provided higher thrombus-to-residual blood contrast-to-noise ratio, significantly lower thrombus volume, and substantially improved diagnostic specificity and agreement with conventional imaging methods. DANTE-prepared black-blood thrombus imaging is a reliable MR imaging technique for diagnosing cerebral venous sinus thrombosis.

Insufficient slow-flow suppression mimicking aneurysm wall enhancement in magnetic resonance vessel wall imaging: a phantom study.

MR vessel wall imaging (VWI) is increasingly performed in clinical settings to support treatment decision-making regarding intracranial aneurysms. Aneurysm wall enhancement after contrast agent injection is expected to be related to aneurysm instability and rupture status. However, the authors hypothesize that slow-flow artifacts mimic aneurysm wall enhancement. Therefore, in this phantom study they assess the effect of slow flow on wall-like enhancement by using different MR VWI techniques. The authors developed an MR-compatible aneurysm phantom model, which was connected to a pump to enable pulsatile inflow conditions. For VWI, 3D turbo spin echo sequences-both with and without motion-sensitized driven equilibrium (MSDE) and delay alternating with nutation for tailored excitation (DANTE) preparation pulses-were performed using a 3-T MR scanner. VWI was acquired both before and after Gd contrast agent administration by using two different pulsatile inflow conditions (2.5 ml/sec peak flow at 77 and 48 beats per minute). The intraluminal signal intensity along the aneurysm wall was analyzed to assess the performance of slow-flow suppression. The authors observed wall-like enhancement after contrast agent injection, especially in low pump rate settings. Preparation pulses, in particular the DANTE technique, improved the performance of slow-flow suppression. Near-wall slow flow mimics wall enhancement in VWI protocols. Therefore, VWI should be carefully interpreted. Preparation pulses improve slow-flow suppression, and therefore the authors encourage further development and clinical implementation of these techniques.

Assessment of quantitative methods for enhancement measurement on vessel wall magnetic resonance imaging evaluation of intracranial atherosclerosis.

Quantitative measures of vessel wall magnetic resonance imaging (vwMRI) for the evaluation of intracranial atherosclerotic disease (ICAD) offers standardization not available with previously used qualitative approaches that may be difficult to replicate. vwMRI studies performed to evaluate ICAD that had caused a stroke were analyzed. Two blinded reviewers qualitatively rated culprit lesions for the presence of enhancement on T1 delay alternating with nutation for tailored excitation (DANTE) SPACE images. At least 3months later, quantitative analysis was performed of the same images, comparing lesion enhancement to reference structures. Cohen's kappa and intraclass correlation coefficients were calculated to assess agreement. Ratios of enhancement of lesions to references were compared to qualitative ratings. Studies from 54 patients met inclusion criteria. A mean of 49 (90.7%) lesions were qualitatively rated as enhancing, with good inter-rater agreement (κ = 0.783). Among reference structure candidates, low infundibulum demonstrated the highest inter-rater agreement on pre- and post-contrast imaging. The ratio of percentage increase in plaque signal following contrast to the same measure in low infundibulum demonstrated the highest agreement with qualitative assessment, with highest agreement seen with a ratio of 0.8 set as a threshold (κ = 0.675). Quantitative metrics can yield objective data to better standardize techniques and acceptance of vwMRI evaluation of ICAD. The low infundibulum had the highest inter-rater agreement on both pre- and post-contrast images and is best suited as a normally enhancing reference structure. Such quantitative techniques should be implemented in future research of vwMRI for the evaluation of ICAD.

Variable impact of CSF flow suppression on quantitative 3.0T intracranial vessel wall measurements.

Flow suppression techniques have been developed for intracranial (IC) vessel wall imaging (VWI) and optimized using simulations; however, simulation results may not translate in vivo. To evaluate experimentally how IC vessel wall and lumen measurements change in identical subjects when evaluated using the most commonly available blood and cerebrospinal fluid (CSF) flow suppression modules and VWI sequences. Prospective. Healthy adults (n = 13; age = 37 ± 15 years) were enrolled. A 3.0T 3D T1 /proton density (PD)-weighted turbo-spin-echo (TSE) acquisition with post-readout anti-driven equilibrium module, with and without Delay-Alternating-with-Nutation-for-Tailored-Excitation (DANTE) was applied. DANTE flip angle (8-12°) and TSE refocusing angle (sweep = 40-120° or 50-120°) were varied. Basilar artery and internal carotid artery (ICA) wall thicknesses, CSF signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and signal ratio (SR) were assessed. Measurements were made by two readers (radiology resident and board-certified neuroradiologist). A Wilcoxon signed-rank test was applied with corrected two-sided P < 0.05 required for significance (critical P = 0.008, 0.005, and 0.05 for SNR/CNR, SR, and wall thickness, respectively). A TSE pulse sweep = 40-120° and sweep = 50-120° provided similar (P = 0.55) CSF suppression. Addition of the DANTE preparation reduced CSF SNR from 17.4 to 6.7, thereby providing significant (P < 0.008) improvement in CSF suppression. The DANTE preparation also resulted in a significant (P < 0.008) reduction in vessel wall SNR, but variable vessel wall to CSF CNR improvement (P = 0.87). There was a trend for a difference in blood SNR with vs. without DANTE (P = 0.05). The outer vessel wall diameter and wall thickness values were lower (P < 0.05) with (basilar artery 4.45 mm, 0.81 mm, respectively) vs. without (basilar artery 4.88 mm, 0.97 mm, respectively) DANTE 8°. IC VWI with TSE sweep = 40-120° and with DANTE flip angle = 8° provides the best CSF suppression and CNR of the approaches evaluated. However, improvements are heterogeneous, likely owing to intersubject vessel pulsatility and CSF flow variations, which can lead to variable flow suppression efficacy in these velocity-dependent modules. 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;48:1120-1128.

The development and optimisation of 3D black-blood R2* mapping of the carotid artery wall

PurposeTo develop and optimise a 3D black-blood R2* mapping sequence for imaging the carotid artery wall, using optimal blood suppression and k-space view ordering. MethodsTwo different blood suppression preparation methods were used; Delay Alternating with Nutation for Tailored Excitation (DANTE) and improved Motion Sensitive Driven Equilibrium (iMSDE) were each combined with a three-dimensional (3D) multi-echo Fast Spoiled GRadient echo (ME-FSPGR) readout. Three different k-space view-order designs: Radial Fan-beam Encoding Ordering (RFEO), Distance-Determined Encoding Ordering (DDEO) and Centric Phase Encoding Order (CPEO) were investigated. The sequences were evaluated through Bloch simulation and in a cohort of twenty volunteers. The vessel wall Signal-to-Noise Ratio (SNR), Contrast-to-Noise Ratio (CNR) and R2*, and the sternocleidomastoid muscle R2* were measured and compared. Different numbers of acquisitions-per-shot (APS) were evaluated to further optimise the effectiveness of blood suppression. ResultsAll sequences resulted in comparable R2* measurements to a conventional, i.e. non-blood suppressed sequence in the sternocleidomastoid muscle of the volunteers. Both Bloch simulations and volunteer data showed that DANTE has a higher signal intensity and results in a higher image SNR than iMSDE. Blood suppression efficiency was not significantly different when using different k-space view orders. Smaller APS achieved better blood suppression. ConclusionThe use of blood-suppression preparation methods does not affect the measurement of R2*. DANTE prepared ME-FSPGR sequence with a small number of acquisitions-per-shot can provide high quality black-blood R2* measurements of the carotid vessel wall.

Black-blood T2* mapping with delay alternating with nutation for tailored excitation

PurposeTo develop a black-blood T2* mapping method using a Delay Alternating with Nutation for Tailored Excitation (DANTE) preparation combined with a multi-echo gradient echo (GRE) readout (DANTE-GRE). Materials and methodsSimulations of the Bloch equation for DANTE-GRE were performed to optimize sequence parameters. After optimization, the sequence was applied to a phantom scan and to neck and lower extremity scans conducted on 12 volunteers at 3T using DANTE-GRE, Motion-Sensitized Driven Equilibrium (MSDE)-GRE, and multi-echo GRE. T2* values were measured using an offset model. Statistical analyses were conducted to compare the T2* values between the three sequences. ResultsSimulation results showed that blood suppression can be achieved with various DANTE parameter adjustments. T2* maps acquired by DANTE-GRE were consistent and comparable to those acquired with multi-echo GRE in phantom experiments. In the in vivo experiments, DANTE-GRE was more comparable to multi-echo GRE than MSDE-GRE regarding the measurement of muscle T2* values. ConclusionDue to its high signal intensity retention and effective blood signal suppression, DANTE-GRE allows for robust and accurate T2* quantification, superior to that of MSDE-GRE, while overcoming blood flow artifacts associated with traditional multi-echo GRE.

T2‐Weighted intracranial vessel wall imaging at 7 Tesla using a DANTE‐prepared variable flip angle turbo spin echo readout (DANTE‐SPACE)

PurposeTo optimize intracranial vessel wall imaging (VWI) at 7T for sharp wall depiction and high boundary contrast.MethodsA variable flip angle turbo spin echo scheme (SPACE) was optimized for VWI. SPACE provides black‐blood contrast, but has less crushing effect on cerebrospinal fluid (CSF). However, a delay alternating with nutation for tailored excitation (DANTE) preparation suppresses the signal from slowly moving spins of a few mm per second. Therefore, we optimized a DANTE‐preparation module for 7T. Signal‐to‐noise ratio (SNR), contrast‐to‐noise ratio (CNR), and signal ratio for vessel wall, CSF, and lumen were calculated for SPACE and DANTE‐SPACE in 11 volunteers at the middle cerebral artery (MCA). An exemplar MCA stenosis patient was scanned with DANTE‐SPACE.ResultsThe 7T‐optimized SPACE sequence improved the vessel wall point‐spread function by 17%. The CNR between the wall and CSF was doubled (12.2 versus 5.6) for the DANTE‐SPACE scans compared with the unprepared SPACE. This increase was significant in the right hemisphere (P = 0.016), but not in the left (P = 0.090). The CNR between wall and lumen was halved, but remained at a high value (24.9 versus 56.5).ConclusionThe optimized SPACE sequence improves VWI at 7T. Additional DANTE preparation increases the contrast between the wall and CSF. Increased outer boundary contrast comes at the cost of reduced inner boundary contrast. Magn Reson Med 77:655–663, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Improved black-blood imaging using DANTE-SPACE for simultaneous carotid and intracranial vessel wall evaluation.

The purpose of this study was to develop a three-dimensional black blood imaging method for simultaneously evaluating the carotid and intracranial arterial vessel walls with high spatial resolution and excellent blood suppression with and without contrast enhancement. The delay alternating with nutation for tailored excitation (DANTE) preparation module was incorporated into three-dimensional variable flip angle turbo spin echo (SPACE) sequence to improve blood signal suppression. Simulations and phantom studies were performed to quantify image contrast variations induced by DANTE. DANTE-SPACE, SPACE, and two-dimensional turbo spin echo were compared for apparent signal-to-noise ratio, contrast-to-noise ratio, and morphometric measurements in 14 healthy subjects. Preliminary clinical validation was performed in six symptomatic patients. Apparent residual luminal blood was observed in five (pre-contrast) and nine (post-contrast) subjects with SPACE and only two (post-contrast) subjects with DANTE-SPACE. DANTE-SPACE showed 31% (pre-contrast) and 100% (post-contrast) improvement in wall-to-blood contrast-to-noise ratio over SPACE. Vessel wall area measured from SPACE was significantly larger than that from DANTE-SPACE due to possible residual blood signal contamination. DANTE-SPACE showed the potential to detect vessel wall dissection and identify plaque components in patients. DANTE-SPACE significantly improved arterial and venous blood suppression compared with SPACE. Simultaneous high-resolution carotid and intracranial vessel wall imaging to potentially identify plaque components was feasible with a scan time under 6 min. Magn Reson Med 75:2286-2294, 2016. © 2015 Wiley Periodicals, Inc.

Joint blood and cerebrospinal fluid suppression for intracranial vessel wall MRI.

To develop and evaluate a joint blood and cerebrospinal fluid (CSF) suppression technique for improved intracranial vessel wall MR imaging. The Delay Alternating with Nutation for Tailored Excitation (DANTE) prepulse was specifically optimized for CSF suppression to improve vessel wall and CSF contrast. It was evaluated on six patients and three healthy volunteers. CSF suppression efficiency, lumen signal to noise ratio, and wall-lumen contrast to noise ratio were compared between images with and without DANTE in major intercranial artery segments. Contrast changes in tissues were also compared with evaluate the technique's compatibility with multicontrast imaging techniques. The optimized DANTE images significantly improved intracranial vessel wall characterization on all images. Quantitatively, CSF to wall contrast improved by 28% (DANTE-VISTA 1.354 ± 0.216 versus VISTA 1.057 ± 0.13; P < 0.001). DANTE also significantly improved wall-lumen (10.55 ± 3.79 versus 9.34 ± 3.54; P < 0.001) and wall-CSF (4.62 ± 3.19 versus 0.78 ± 2.30; P < 0.001) contrast-to-noise ratios. DANTE prepared images were also found to make only minimal impact on static tissue contrast. DANTE prepared MR imaging can significantly improve contrast between the vessel wall and cerebral spinal fluid in major intracranial arteries, holding a good potential to be combined with multicontrast protocol for intracranial wall imaging.

DANTE‐prepared pulse trains: A novel approach to motion‐sensitized and motion‐suppressed quantitative magnetic resonance imaging

Delay alternating with nutation for tailored excitation (DANTE) pulse trains are well appreciated as frequency-selective excitation methods in Fourier transform NMR and for spatial tagging in MRI. In this study, nonselective DANTE pulse trains are used in combination with gradient pulses and short repetition times as motion-sensitive preparation modules. We show that while the longitudinal magnetization of static tissue is mostly preserved, flowing spins are largely (or fully) attenuated as they fail to establish transverse steady state due to a spoiling effect caused by flow along the applied gradient. The attenuation of flowing spins is effectively insensitive to spin velocity (above a low threshold) and can be approximately quantified with a simple T₁ longitudinal magnetization decay model. The relevant analytical equations for moving spins and static spins during DANTE module application are derived for both transient and steady state epochs. The equations are validated by comparing analytical solutions and numerical Bloch equation simulations against experimental observations in phantoms and in vivo. Based on this contrast mechanism, the application of the DANTE preparation to black blood vessel imaging is proposed. A simple demonstration of DANTE black blood imaging modules shows that it provides excellent blood signal suppression and static tissue signal preservation.