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

Simple Identification of Cerebrospinal Fluid Turbulent Motion Using a Dynamic Improved Motion-sensitized Driven-equilibrium Steady-state Free Precession Method Applied to Various Types of Cerebrospinal Fluid Motion Disturbance

The motion of cerebrospinal fluid (CSF) within the subarachnoid space and ventricles is greatly modulated when propagating synchronously with the cardiac pulse and respiratory cycle and path through the nerves, blood vessels, and arachnoid trabeculae. Water molecule movement that propagates between two spaces via a stoma, foramen, or duct presents increased acceleration when passing through a narrow area and can exhibit “turbulence.” Recently, neurosurgeons have started to perform fenestration procedures using neuroendoscopy to treat hydrocephalus and cystic lesions. As part of the postoperative evaluation, a noninvasive diagnostic technique to visualize the water molecules at the fenestrated site is necessary. Because turbulence is observed at this fenestrated site, an imaging technique appropriate for observing this turbulence is essential. We therefore investigated the usefulness of a dynamic improved motion-sensitized driven-equilibrium steady-state free precession (Dynamic iMSDE SSFP) sequence of magnetic resonance imaging that is superior for ascertaining turbulent motions in healthy volunteers and patients. Images of Dynamic iMSDE SSFP from volunteers revealed that CSF motion at the ventral surface of the brainstem and the third ventricle is augmented and turbulent. Moreover, our findings confirmed that this technique is useful for evaluating treatments that utilize neuroendoscopy. As a result, Dynamic iMSDE SSFP, a simple sequence for visualizing CSF motion, entails a short imaging time, can extensively visualize CSF motion, does not require additional processes such as labeling or trigger setting, and is anticipated to have wide-ranging clinical applications in the future.

Intracranial 3D and 4D MR Angiography Using Arterial Spin Labeling: Technical Considerations

In the 1980’s some of the earliest studies of arterial spin labeling (ASL) MRI have demonstrated its ability to generate MR angiography (MRA) images. Thanks to many technical improvements, ASL has been successfully moving its position from the realm of research into the clinical area, albeit more known as perfusion imaging than as MRA. For MRA imaging, other techniques such as time-of-flight, phase contrast MRA and contrast-enhanced (CE) MRA are more popular choices for clinical applications. In the last decade, however, ASL-MRA has been experiencing a remarkable revival, especially because of its non-invasive nature, i.e. the fact that it does not rely on the use of contrast agent. Very importantly, there are additional benefits of using ASL for MRA. For example, its higher flexibility to achieve both high spatial and temporal resolution than CE dynamic MRA, and the capability of vessel specific visualization, in which the vascular tree arising from a selected artery can be exclusively visualized. In this article, the implementation and recent developments of ASL-based MRA are discussed; not only focusing on the basic sequences based upon pulsed ASL or pseudo-continuous ASL, but also including more recent labeling approaches, such as vessel-selective labeling, velocity-selective ASL, vessel-encoded ASL and time-encoded ASL. Although these ASL techniques have been already utilized in perfusion imaging and their usefulness has been suggested by many studies, some additional considerations should be made when employing them for MRA, since there is something more than the difference of the spatial resolution of the readout sequence. Moreover, extensive discussion is included on what readout sequence to use, especially by highlighting how to achieve high spatial resolution while keeping scan-time reasonable such that the ASL-MRA sequence can easily be included into a clinical examination.

Compressed SENSE accelerated 3D T1w black blood turbo spin echo versus 2D T1w turbo spin echo sequence in pituitary magnetic resonance imaging

PURPOSE

To compare image quality between a 2D T1w turbo spin echo (TSE) sequence and a Compressed SENSE accelerated 3D T1w black blood TSE sequence (equipped with a black blood prepulse for blood signal suppression) in pre- and postcontrast imaging of the pituitary and to assess scan time reductions.

METHODS AND MATERIALS

For this retrospective study, 56 patients underwent pituitary MR imaging at 3T. 28 patients were scanned with the 2D- and 28 patients with the accelerated 3D sequence. Two board certified neuroradiologists independently evaluated 13 qualitative image features (12 features on postcontrast- and 1 feature on precontrast images).SNR and CNR measurements were obtained. Interreader agreement was assessed with the intraclass correlation coefficient while differences in scores were assessed with exact Wilcoxon rank sum tests.

RESULTS

The interreader agreement ranged from fair (visibility of the ophthalmic nerve, ICC = 0.57) to excellent (presence and severity of pulsation artefacts, ICC = 0.97). The Compressed SENSE accelerated 3D sequence outperformed the 2D sequence in terms of "overall image quality" (median: 4 versus 3, p = 0.04) and "presence and severity of pulsation artefacts" (median: 0 versus 1, p < 0.001). There were no significant differences in any other qualitative and quantitative (SNR, CNR) image quality features. Scan time was reduced by 03:53 min (33.1%) by replacing the 2D with the 3D sequence.

CONCLUSION

The Compressed SENSE accelerated 3D T1w black blood TSE sequence is a reliable alternative for the standard 2D sequence in pituitary imaging. The black blood prepulse may aid in suppression of pulsation artefacts.

High-resolution magnetic resonance imaging of intracranial vessel walls: Comparison of 3D T1-weighted turbo spin echo with or without DANTE or iMSDE

Background

The black-blood (BB) technique was developed to suppress the signal from blood and cerebrospinal fluid (CSF) to provide improved depiction of vessel walls.

Purpose

The aim was to compare three-dimensional turbo spin echo T1-weighted imaging (3D TSE T1WI) with or without two BB techniques (delay alternating with nutation for tailored excitation [DANTE], and improved motion-sensitized driven equilibrium [iMSDE]) for high-resolution magnetic resonance imaging (HR-MRI) of the vessel walls of intracranial arteries.

Study type

Prospective.

Population

Fourteen healthy volunteers who underwent 3D T1WI for examination of intracranial vessel walls.

Field strength/Sequence

3 Tesla, 3D TSE T1WI (SPACE and BrainVIEW) and BB (DANTE and iMSDE).

Assessment

SPACE with or without DANTE, and BrainVIEW with or without iMSDE, were acquired in each subject. Two neuroradiologists independently assessed image quality, vessel wall delineation, BB effect, CSF, and acceptability using visual scoring systems, and measured signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in vessel walls, lumen, and CSF, while blinded to the presence and type of BB technique used.

Statistical tests

Repeated measures ANOVA or Friedman tests were performed for the comparisons, followed by Bonferroni correction.

Results

The 3T T1WI sequences without BB are significantly superior in vessel wall delineation (P = 0.001). Black CSF scores were lower in SPACE with DANTE than SPACE without DANTE, and in BrainVIEW without iMSDE than SPACE without DANTE (P < 0.001). However, there were no significant differences in BB effect, image quality, and acceptability between the four 3D T1WI sequences (p > .05). The SNR_{Vessel wall}, CNR_Wall-Lumen, and CNR_Wall-CSF were higher (all p < .001) on SPACE with and without DANTE than on BrainVIEW with and without iMSDE. SNR_Lumen were higher (all p < .001) on BrainVIEW with and without iMSDE than on SPACE with and without DANTE. SNRCSF was higher (all p < .001) on BrainVIEW with iMSDE than on SPACE with DANTE.

Data conclusion

Both 3D TSE T1WI sequences were acceptable for intracranial vessel wall evaluation, with or without BB techniques. Therefore, BB techniques may not necessarily be required with 3D TSE T1WI with a long ETL and TR (below 1160 ms).

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

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Reproducibility of 3.0T High-Resolution Magnetic Resonance Imaging for the Identification and Quantification of Middle Cerebral Arterial Atherosclerotic Plaques

OBJECTIVE

To assess the reproducibility of 3.0T high-resolution magnetic resonance imaging for the identification and quantification of atherosclerotic plaques in the middle cerebral artery.

METHODS

Sixty-nine consecutive patients with ischemic stroke or asymptomatic stenosis (>30%) of the middle cerebral artery underwent 3.0T high-resolution magnetic resonance imaging examinations. Two independent investigators reviewed all images with 1 investigator re-evaluating all images 4 weeks later. Wall characteristics of the middle cerebral artery, including plaque surface morphology, plaque location, plaque components, and burden were identified and measured.

RESULTS

Intraobserver and interobserver agreement were all substantial in identifying plaque surface irregularity (k = 0.741, 0.555-0.897; k = 0.685, 0.490-0.843; respectively) and intraplaque hemorrhage (k = 0.654, 0.446-0.838; k = 0.605, 0.369-0.792; respectively). Intraobserver agreement was substantial (k = 0.654) and interobserver agreement was moderate (k = 0.553) for the identification of plaque fibrous caps. The total intraobserver and interobserver reproducibility was almost excellent for the identification of plaque position. With regards to vessel area measurement at the site of maximal lumen narrowing, intraobserver and interobserver reproducibility was excellent (intraclass correlation coefficient was 0.886 and 0.885, respectively) and moderate for lumen area at the site of maximal lumen narrowing (intraclass correlation coefficient was 0.695 and 0.558, respectively). In addition, intraobserver and interobserver reproducibility was excellent for vessel area and lumen area measurements at the reference sites.

CONCLUSIONS

The reproducibility of 3.0T high-resolution magnetic resonance imaging for the identification and quantification of artery wall characteristics was overall acceptable. However, the reliability for lumen area measurement at the maximum narrowing site and identification of the fibrous cap needs to be improved.

Intracranial arterial wall imaging: Techniques, clinical applicability, and future perspectives

Purpose

To review the current state of the art and future development of intracranial vessel wall imaging.

Methods

Recent literature review and expert opinion about intracranial arterial wall imaging.

Results

Intracranial large artery diseases represent an important cause of stroke and vascular cognitive impairment worldwide. Our traditional understanding of intracranial large artery diseases is based on the observation of luminal narrowing or occlusion with angiographic or ultrasound techniques. Recently, novel imaging techniques have made the intracranial artery wall accessible for noninvasive visualization. The main advantage of vessel-wall imaging as compared to conventional imaging techniques for visualization of intracranial arteries is the ability to detect vessel wall changes even before they get to cause any significant luminal stenosis. This diagnostic capacity is provoking a revolutionary change in the way we see the intracranial circulation. In this article, we will review the current state of magnetic resonance imaging and computed tomography-based intracranial arterial wall imaging, focusing on technical considerations and their clinical applicability. Moreover, we will provide the readers with our vision on the future development of vessel-wall imaging techniques.

Conclusion

Intracranial arterial wall imaging methods are gaining increasing potential to impact the diagnosis and treatment of patients with cerebrovascular diseases.

Respiratory- and cardiac-triggered three-dimensional sheath inked rapid acquisition with refocused echoes imaging (SHINKEI) of the abdomen for magnetic resonance neurography of the celiac plexus

The visualisation of the celiac plexus using respiratory- and cardiac-triggered three-dimensional (3D) sheath inked rapid acquisition with refocused echoes imaging (SHINKEI) was evaluated. After ethical approval and written informed consent, eight volunteers (age 27 ± 5 years, mean ± standard deviation) were scanned at 1.5 and 3 T. Displacement of the celiac ganglia due to aortic pulsatility was studied on axial single-slice breath-hold balanced turbo field-echo cine sequences in five volunteers and found to be 3.0 ± 0.5 mm (left) and 3.1 ± 0.4 mm (right). Respiratory- and cardiac-triggered 3D SHINKEI images were compared to respiratory- and cardiac-triggered fat-suppressed 3D T2-weighted turbo spin-echo and respiratory-triggered 3D SHINKEI in all volunteers. Visibility of the celiac ganglia was rated by three radiologists as visible or non-visible. On 3D SHINKEI with double-triggering at 1.5 T, the left and right ganglia were seen by all observers in 7/8 and 8/8 volunteers, respectively. At 3 T, this was the case for 6/8 and 7/8 volunteers, respectively. The nerve-to-muscle signal ratio increased from 1.9 ± 0.5 on fat-suppressed 3D T2-weighted turbo spin-echo to 4.7 ± 0.8 with 3D SHINKEI. Anatomical validation was performed in a human cadaver. An expert in anatomy confirmed that the hyperintense structure visible on ex vivo 3D SHINKEI scans was the celiac plexus. In conclusion, double-triggering allowed visualisation of the celiac plexus using 3D SHINKEI at both 1.5 T and 3 T.

Simultaneous 3D whole-heart bright-blood and black blood imaging for cardiovascular anatomy and wall assessment with interleaved T2 prep-IR

PURPOSE

To develop a motion-corrected 3D flow-insensitive imaging approach interleaved T₂ prepared-inversion recovery (iT₂ prep-IR) for simultaneous lumen and wall visualization of the great thoracic vessels and cardiac structures.

METHODS

A 3D flow-insensitive approach for simultaneous cardiovascular lumen and wall visualization (iT₂ prep) has been previously proposed. This approach requires subject-dependent weighted subtraction to completely null the arterial blood signal in the black-blood volume. Here, we propose an (T₂ prep-IR) approach to improve wall visualization and remove need for weighted subtraction. The proposed sequence is based on the acquisition and direct subtraction of 2 interleaved 3D whole-heart data sets acquired with and without T₂ prep-IR preparation. Image navigators are acquired before data acquisition to enable 2D translational and 3D non-rigid motion correction allowing 100% respiratory scan efficiency. The proposed approach was evaluated in 10 healthy subjects and compared with the conventional 2D double inversion recovery (DIR) sequence and the 3D iT₂ prep sequence. Additionally, 5 patients with congenital heart disease were acquired to test the clinical feasibility of the proposed approach.

RESULTS

The proposed iT₂ prep-IR sequence showed improved blood nulling compared to both DIR and iT₂ prep techniques in terms of SNR (SNR_blood = 6.9, 12.2, and 18.2, respectively) and contrast-to-noise-ratio (CNR_myoc-blood = 28.4, 15.4, and 15.3, respectively). No statistical difference was observed between iT₂ prep-IR, iT₂ prep and DIR atrial and ventricular wall thickness quantification.

CONCLUSION

The proposed interleaved T₂ prep-IR sequence enables the simultaneous lumen and wall visualization of cardiac structures and shows promising results in terms of SNR, CNR, and wall thickness measurement.

Regional assessment of carotid artery pulse wave velocity using compressed sensing accelerated high temporal resolution 2D CINE phase contrast cardiovascular magnetic resonance

BACKGROUND

Cardiovascular magnetic resonance (CMR) allows for non-invasive assessment of arterial stiffness by means of measuring pulse wave velocity (PWV). PWV can be calculated from the time shift between two time-resolved flow curves acquired at two locations within an arterial segment. These flow curves can be derived from two-dimensional CINE phase contrast CMR (2D CINE PC CMR). While CMR-derived PWV measurements have proven to be accurate for the aorta, this is more challenging for smaller arteries such as the carotids due to the need for both high spatial and temporal resolution. In this work, we present a novel method that combines retrospectively gated 2D CINE PC CMR, high temporal binning of data and compressed sensing (CS) reconstruction to accomplish a temporal resolution of 4 ms. This enables accurate flow measurements and assessment of PWV in regional carotid artery segments.

METHODS

Retrospectively gated 2D CINE PC CMR data acquired in the carotid artery was binned into cardiac frames of 4 ms length, resulting in an incoherently undersampled ky-t-space with a mean undersampling factor of 5. The images were reconstructed by a non-linear CS reconstruction using total variation over time as a sparsifying transform. PWV values were calculated from flow curves by using foot-to-foot and cross-correlation methods. Our method was validated against ultrasound measurements in a flow phantom setup representing the carotid artery. Additionally, PWV values of two groups of 23 young (30 ± 3 years, 12 [52%] women) and 10 elderly (62 ± 10 years, 5 [50%] women) healthy subjects were compared using the Wilcoxon rank-sum test.

RESULTS

Our proposed method produced very similar flow curves as those measured using ultrasound at 1 ms temporal resolution. Reliable PWV estimation proved possible for transit times down to 7.5 ms. Furthermore, significant differences in PWV values between healthy young and elderly subjects were found (4.7 ± 1.0 m/s and 7.9 ± 2.4 m/s, respectively; p < 0.001) in accordance with literature.

CONCLUSIONS

Retrospectively gated 2D CINE PC CMR with CS allows for high spatiotemporal resolution flow measurements and accurate regional carotid artery PWV calculations. We foresee this technique will be valuable in protocols investigating early development of carotid atherosclerosis.

Proximal internal carotid artery stenosis associates with diffuse wall thickening in petrous arterial segment of moyamoya disease patients: a three-dimensional magnetic resonance vessel wall imaging study

PURPOSE

To investigate the association between proximal internal carotid artery (ICA) luminal narrowing and diffuse wall thickening (DWT) in ipsilateral petrous ICA in moyamoya disease (MMD) patients.

METHODS

Forty-one MMD (mean age 42.8 ± 11.0 years, 19 males) and 36 atherosclerotic patients (mean age 61.5 ± 7.1 years, 31 males) and 41 healthy controls were recruited and underwent carotid MR vessel wall imaging. The luminal narrowing of proximal ICA was evaluated by the diameter ratio of ICA to common carotid artery (DR_ICA/CCA). The wall thickness of petrous ICA was measured on T1-VISTA images. The enhancement degree of petrous ICA was recorded and graded into four grades (none to marked) on the CE-T1-VISTA images. The correlation between wall thickness in petrous ICA and DR_ICA/CCA was analyzed_. RESULTS: In total, 81 arteries of MMD patients and 64 arteries of atherosclerotic patients were included for analysis. The DR_ICA/CCA was significantly correlated with the wall thickness in petrous ICA in MMD (r = - 0.434, P < 0.001) and atherosclerotic groups (r = - 0.604, P < 0.001). Logistic regression analysis revealed that odds ratio (OR) of DR_ICA/CCA was 4.433 (95% CI 1.980-9.925, P < 0.001) and 2.212 (95% CI 1.253-3.905, P = 0.006) in MMD and atherosclerotic groups in discriminating petrous ICA DWT after adjusting for confounding factors. An increasing trend was found in prevalence of DWT and wall thickness with enhancement grades in petrous ICA in MMD (P = 0.02 and P = 0.01) and atherosclerotic groups (P < 0.001 and P < 0.001), respectively.

CONCLUSIONS

The proximal ICA luminal narrowing is significantly associated with wall thickness and diffuse wall thickening in ipsilateral petrous ICA in patients with carotid steno-occlusive diseases regardless of MMD or atherosclerosis.

Deep-learned 3D black-blood imaging using automatic labelling technique and 3D convolutional neural networks for detecting metastatic brain tumors

Black-blood (BB) imaging is used to complement contrast-enhanced 3D gradient-echo (CE 3D-GRE) imaging for detecting brain metastases, requiring additional scan time. In this study, we proposed deep-learned 3D BB imaging with an auto-labelling technique and 3D convolutional neural networks for brain metastases detection without additional BB scan. Patients were randomly selected for training (29 sets) and testing (36 sets). Two neuroradiologists independently evaluated deep-learned and original BB images, assessing the degree of blood vessel suppression and lesion conspicuity. Vessel signals were effectively suppressed in all patients. The figure of merits, which indicate the diagnostic performance of radiologists, were 0.9708 with deep-learned BB and 0.9437 with original BB imaging, suggesting that the deep-learned BB imaging is highly comparable to the original BB imaging (difference was not significant; p = 0.2142). In per patient analysis, sensitivities were 100% for both deep-learned and original BB imaging; however, the original BB imaging indicated false positive results for two patients. In per lesion analysis, sensitivities were 90.3% for deep-learned and 100% for original BB images. There were eight false positive lesions on the original BB imaging but only one on the deep-learned BB imaging. Deep-learned 3D BB imaging can be effective for brain metastases detection.

A case report: C2 radiculopathy induced by neck flexion due to the cord compression of C2 segmental type vertebral artery relieved by microvascular decompression

Background:

Decompression of an anomalous vertebral artery (VA) may effectively treat cervical myelopathy/radiculopathy due to resultant spinal cord or nerve compression. Here we report a case of C2 radiculopathy induced by neck flexion due to cord compression of the C2 segmental type VA relieved by microvascular decompression.

Case Description:

A 30-year-old female presented with left occipitalgia, sensory abnormalities in the left upper and lower extremities, and neck pain induced by neck flexion. The magnetic resonance imaging (MRI) revealed an abnormal flow void, confirming that the VA was compressing the spinal cord at the C1 level. Three-dimensional computed tomography (3D-CT) showed an anomalous course of the left VA, which entered the spinal canal between the axis and atlas. Microvascular decompression was performed by transposing the artery (e.g., anchoring it to the dura using PTEF): this effectively relieved cord compression.

Conclusion:

An anomalous VA rarely causes cervical radiculopathy induced by neck flexion. When it occurs, microvascular decompression effectively relieves pressure resulting in a resolution of symptoms.

Utility of the variable flip angle 3D fast-spin echo (isoFSE) sequence on 3T MR for diagnosing vertebrobasilar artery dissection

We aimed to investigate the utility of the isoFSE sequence, one of the variable flip angle 3D fast-spin echo sequences, on 3T-MR for displaying vessel walls and diagnosing vertebrobasilar artery dissection (VAD). We retrospectively evaluated 12 initial and 28 follow-up images from 12 patients diagnosed with either intracranial VAD or carotid artery dissection. The image quality for displaying the vessel wall was scored using a five-point scale (1 poor, 5 excellent) on initial T1-weighted isoFSE images for each region of the arteries. The intracranial artery dissection findings assessed at time points after onset were evaluated on initial and follow-up T1/T2-weighted isoFSE images. For small arteries, including the anterior/posterior inferior cerebellar artery, similar high scores were obtained on both unenhanced and contrast-enhanced T1-weighted isoFSE images (average: 4.7-5.0, p > 0.2). On unenhanced images, dissected vertebral arteries showed significantly lower scores than non-dissected vertebral arteries for both readers (p = 0.017 and 0.015, respectively), but the scores were high (3.9 and 4.0, respectively). Definitive findings of VAD were observed on the initial images except in one case. For all cases, definitive findings were seen on at least one of the initial or follow-up images. Temporal changes in the findings could be observed for all cases. In conclusion, we showed favorable wall visualization on T1-weighted isoFSE images and the utility of follow-up imaging using unenhanced-T1/T2-weighted and contrast-enhanced T1-weighted isoFSE sequences with acceptable scan times, which could promote the regular use of 3D black-blood vessel wall imaging.

Three-dimensional black blood contrast enhanced magnetic resonance imaging in patients with acute ischemic stroke and negative susceptibility vessel sign

PURPOSE

The purpose of this study was to evaluate the enhancement patterns of three-dimensional (3D) black blood (BB) contrast enhanced magnetic resonance (MR) imaging in acute stroke patients with negative susceptibility vessel sign (SVS).

MATERIALS AND METHODS

From January 2014 to August 2016 we retrospectively reviewed MR imaging and MR angiography findings of patients who presented with acute stroke symptoms of less than 24 h duration. For the 394 patients enrolled, we assessed the frequency of patients who exhibited negative SVS on susceptibility weighted MR imaging (SWI) and positive enhancement in 3D BB contrast enhanced MR imaging. We subdivided the enrolled group according to whether the MR angiography findings suggested stenosis (stenosis group) or occlusion (occlusion group). Enhancement patterns on BB contrast enhanced MR imaging were compared between the two groups according to several qualitative parameters: intensity (weak or strong), morphology (linear/eccentric or round/concentric), length (focal or segmental) and multiplicity (single or multiple).

RESULTS

Sixty-two of 394 patients (15.7%) showed positive findings on BB contrast-enhanced MR imaging with negative SVS. Forty-two patients were classified into the stenosis group, and 20 patients were assigned to the occlusion group. Enhancement patterns of the stenosis group showed weak intensity, linear or eccentric morphology and focal lesion length on BB contrast enhanced MR imaging, compared to the occlusion group (P < 0.001). In contrast, enhancement patterns of the occlusion group showed strong intensity, round or concentric morphology and longer segmental lesion length, compared to the stenosis group (P < 0.001).

CONCLUSION

Three-dimensional BB contrast enhanced MR imaging in acute stroke patients with stenotic lesions and negative SVS shows enhancement patterns of linear or eccentric morphology and shorter, more focal lesions.

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 arterial spin labeling imaging with a DANTE preparation pulse

On arterial spin-labeled (ASL) images, areas of bright intravascular signal will appear when the post labeling delay time is shorter than arterial transit time. Vascular suppression (VS) schemes reduce artefactual bright signal by dephasing intravascular labeled spins. However, existing VS methods, such as Motion-Sensitized Driven-Equilibrium (MSDE), decrease the uniformity of the signal intensity distribution and extend the echo time. The purpose of this study is to compare VS using a Delays Alternating with Nutation for Tailored Excitation (DANTE) preparation pulse, with MSDE for ASL imaging on a flow phantom and volunteer data. In the phantom study, the signal decay pattern of moving water was similar for both methods. In the volunteer study, the bright intravascular signal artifact was decreased by both methods. However right-left differences in signal intensity were smaller using DANTE-prepared ASL. The proposed DANTE-prepared ASL sequence has a vessel suppression effect while maintaining a uniform signal intensity distribution. This study indicates that DANTE is a potentially useful method for vessel suppression in ASL imaging.

Contrast-enhanced magnetic resonance imaging for the detection of ruptured coronary plaques in patients with acute myocardial infarction

Purpose

X-ray coronary angiography (XCA) is the current gold standard for the assessment of lumen encroaching coronary stenosis but XCA does not allow for early detection of rupture-prone vulnerable plaques, which are thought to be the precursor lesions of most acute myocardial infarctions (AMI) and sudden death. The aim of this study was to investigate the potential of delayed contrast-enhanced magnetic resonance coronary vessel wall imaging (CE-MRCVI) for the detection of culprit lesions in the coronary arteries.

Methods

16 patients (13 male, age 61.9±8.6 years) presenting with sub-acute MI underwent CE-MRCVI within 24-72h prior to invasive XCA. CE-MRCVI was performed using a T1-weighted 3D gradient echo inversion recovery sequence (3D IR TFE) 40±4 minutes following the administration of 0.2 mmol/kg gadolinium-diethylenetriamine-pentaacetic acid (DTPA) on a 3T MRI scanner equipped with a 32-channel cardiac coil.

Results

14 patients were found to have culprit lesions (7x LAD, 1xLCX, 6xRCA) as identified by XCA. Quantitative CE-MRCVI correctly identified the culprit lesion location with a sensitivity of 79% and excluded culprit lesion formation with a specificity of 99%. The contrast to noise ratio (CNR) of culprit lesions (9.7±4.1) significantly exceeded CNR values of segments without culprit lesions (2.9±1.9, p<0.001).

Conclusion

CE-MRCVI allows the selective visualization of culprit lesions in patients immediately after myocardial infarction (MI). The pronounced contrast uptake in ruptured plaques may represent a surrogate biomarker of plaque activity and/or vulnerability.

Investigation of 3D reduced field of view carotid atherosclerotic plaque imaging

To investigate the feasibility of using CUBE based reduced field of view imaging in atherosclerotic plaque imaging. Twenty-four patients were enrolled in this prospective study (13 males, 11 females, age 63±10). All patients underwent MRI exams consisting of 3D TOF, MPRAGE, iMSDE, DANTE, full FOV and reduced FOV CUBE imaging; 18 patients under went contrast enhanced imaging. The resulting images from different imaging sequences were assessed in terms of blood suppression, SNR, motion artifacts and vascular clarity. Reduced field of view CUBE outperformed MPRAGE, iMSDE and full FOV CUBE in blood suppression (P<0.05); outperformed MPRAGE, iMSDE and DANTE in SNR(P<005); outperformed MPRAGE and iMSDE in motion artifacts (P<005); outperformed MPRAGE and iMSDE in vascular clarity (P<0.05). The identifications of hemorrhage and calcification components were consistent between full FOV CUBE and reduced FOV CUBE (P<0.05). Overall, CUBE combined with reduced field of view imaging would be a promising method in atherosclerotic plaque imaging.

Vessel wall characterization using quantitative MRI: what's in a number?

The past decade has witnessed the rapid development of new MRI technology for vessel wall imaging. Today, with advances in MRI hardware and pulse sequences, quantitative MRI of the vessel wall represents a real alternative to conventional qualitative imaging, which is hindered by significant intra- and inter-observer variability. Quantitative MRI can measure several important morphological and functional characteristics of the vessel wall. This review provides a detailed introduction to novel quantitative MRI methods for measuring vessel wall dimensions, plaque composition and permeability, endothelial shear stress and wall stiffness. Together, these methods show the versatility of non-invasive quantitative MRI for probing vascular disease at several stages. These quantitative MRI biomarkers can play an important role in the context of both treatment response monitoring and risk prediction. Given the rapid developments in scan acceleration techniques and novel image reconstruction, we foresee the possibility of integrating the acquisition of multiple quantitative vessel wall parameters within a single scan session.

Learning-based automated segmentation of the carotid artery vessel wall in dual-sequence MRI using subdivision surface fitting

PURPOSE

The quantification of vessel wall morphology and plaque burden requires vessel segmentation, which is generally performed by manual delineations. The purpose of our work is to develop and evaluate a new 3D model-based approach for carotid artery wall segmentation from dual-sequence MRI.

METHODS

The proposed method segments the lumen and outer wall surfaces including the bifurcation region by fitting a subdivision surface constructed hierarchical-tree model to the image data. In particular, a hybrid segmentation which combines deformable model fitting with boundary classification was applied to extract the lumen surface. The 3D model ensures the correct shape and topology of the carotid artery, while the boundary classification uses combined image information of 3D TOF-MRA and 3D BB-MRI to promote accurate delineation of the lumen boundaries. The proposed algorithm was validated on 25 subjects (48 arteries) including both healthy volunteers and atherosclerotic patients with 30% to 70% carotid stenosis.

RESULTS

For both lumen and outer wall border detection, our result shows good agreement between manually and automatically determined contours, with contour-to-contour distance less than 1 pixel as well as Dice overlap greater than 0.87 at all different carotid artery sections.

CONCLUSIONS

The presented 3D segmentation technique has demonstrated the capability of providing vessel wall delineation for 3D carotid MRI data with high accuracy and limited user interaction. This brings benefits to large-scale patient studies for assessing the effect of pharmacological treatment of atherosclerosis by reducing image analysis time and bias between human observers.

Diffusion-prepared stimulated-echo turbo spin echo (DPsti-TSE): An eddy current-insensitive sequence for three-dimensional high-resolution and undistorted diffusion-weighted imaging

In this study, we present a new three-dimensional (3D), diffusion-prepared turbo spin echo sequence based on a stimulated-echo read-out (DPsti-TSE) enabling high-resolution and undistorted diffusion-weighted imaging (DWI). A dephasing gradient in the diffusion preparation module and rephasing gradients in the turbo spin echo module create stimulated echoes, which prevent signal loss caused by eddy currents. Near to perfect agreement of apparent diffusion coefficient (ADC) values between DPsti-TSE and diffusion-weighted echo planar imaging (DW-EPI) was demonstrated in both phantom transient signal experiments and phantom imaging experiments. High-resolution and undistorted DPsti-TSE was demonstrated in vivo in prostate and carotid vessel wall. 3D whole-prostate DWI was achieved with four b values in only 6 min. Undistorted ADC maps of the prostate peripheral zone were obtained at low and high imaging resolutions with no change in mean ADC values [(1.60 ± 0.10) × 10^-3 versus (1.60 ± 0.02) × 10^-3  mm² /s]. High-resolution 3D DWI of the carotid vessel wall was achieved in 12 min, with consistent ADC values [(1.40 ± 0.23) × 10^-3  mm² /s] across different subjects, as well as slice locations through the imaging volume. This study shows that DPsti-TSE can serve as a robust 3D diffusion-weighted sequence and is an attractive alternative to the traditional two-dimensional DW-EPI approaches.

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.

Large coverage black-bright blood interleaved imaging sequence (LaBBI) for 3D dynamic contrast-enhanced MRI of vessel wall

PURPOSE

To propose a large coverage black-bright blood interleaved imaging sequence (LaBBI) for 3D dynamic contrast-enhanced MRI (DCE-MRI) of the vessel wall.

METHODS

LaBBI consists of a 3D black-blood stack-of-stars golden angle radial acquisition with high spatial resolution for vessel wall imaging and a 2D bright-blood Cartesian acquisition with high temporal resolution for arterial input function estimation. The two acquisitions were performed in an interleaved fashion within a single scan. Simulations, phantom experiments, and in vivo tests in three patients were performed to investigate the feasibility and performance of the proposed LaBBI.

RESULTS

In simulation tests, the estimated K^trans and v_p by LaBBI were more accurate than conventional bright-blood DCE-MRI with lower root mean square error in all the tested conditions. In phantom test, no signal interference was found on the 2D scan in LaBBI. Pharmacokinetic analysis of the patients' data acquired by LaBBI showed that K^trans was higher in fibrous tissue (0.0717 ± 0.0279 min^-1 ), while lower in necrotic core (0.0206 ± 0.0040 min^-1 ) and intraplaque hemorrhage (0.0078 ± 0.0007 min^-1 ), compared with normal vessel wall (0.0273 ± 0.0052 min^-1 ).

CONCLUSION

The proposed LaBBI sequence, with high spatial and temporal resolution, and large coverage blood suppression, was promising to probe the perfusion properties of vessel wall lesions. Magn Reson Med 79:1334-1344, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Efficacy of Maximum Intensity Projection of Contrast-Enhanced 3D Turbo-Spin Echo Imaging with Improved Motion-Sensitized Driven-Equilibrium Preparation in the Detection of Brain Metastases

Objective

To evaluate the diagnostic benefits of 5-mm maximum intensity projection of improved motion-sensitized driven-equilibrium prepared contrast-enhanced 3D T1-weighted turbo-spin echo imaging (MIP iMSDE-TSE) in the detection of brain metastases. The imaging technique was compared with 1-mm images of iMSDE-TSE (non-MIP iMSDE-TSE), 1-mm contrast-enhanced 3D T1-weighted gradient-echo imaging (non-MIP 3D-GRE), and 5-mm MIP 3D-GRE.

Materials and Methods

From October 2014 to July 2015, 30 patients with 460 enhancing brain metastases (size > 3 mm, n = 150; size ≤ 3 mm, n = 310) were scanned with non-MIP iMSDE-TSE and non-MIP 3D-GRE. We then performed 5-mm MIP reconstruction of these images. Two independent neuroradiologists reviewed these four sequences. Their diagnostic performance was compared using the following parameters: sensitivity, reading time, and figure of merit (FOM) derived by jackknife alternative free-response receiver operating characteristic analysis. Interobserver agreement was also tested.

Results

The mean FOM (all lesions, 0.984; lesions ≤ 3 mm, 0.980) and sensitivity ([reader 1: all lesions, 97.3%; lesions ≤ 3 mm, 96.2%], [reader 2: all lesions, 97.0%; lesions ≤ 3 mm, 95.8%]) of MIP iMSDE-TSE was comparable to the mean FOM (0.985, 0.977) and sensitivity ([reader 1: 96.7, 99.0%], [reader 2: 97, 95.3%]) of non-MIP iMSDE-TSE, but they were superior to those of non-MIP and MIP 3D-GREs (all, p < 0.001). The reading time of MIP iMSDE-TSE (reader 1: 47.7 ± 35.9 seconds; reader 2: 44.7 ± 23.6 seconds) was significantly shorter than that of non-MIP iMSDE-TSE (reader 1: 78.8 ± 43.7 seconds, p = 0.01; reader 2: 82.9 ± 39.9 seconds, p < 0.001). Interobserver agreement was excellent (κ > 0.75) for all lesions in both sequences.

Conclusion

MIP iMSDE-TSE showed high detectability of brain metastases. Its detectability was comparable to that of non-MIP iMSDE-TSE, but it was superior to the detectability of non-MIP/MIP 3D-GREs. With a shorter reading time, the false-positive results of MIP iMSDE-TSE were greater. We suggest that MIP iMSDE-TSE can provide high diagnostic performance and low false-positive rates when combined with 1-mm sequences.

Association between proximal internal carotid artery steno-occlusive disease and diffuse wall thickening in its petrous segment: a magnetic resonance vessel wall imaging study

PURPOSE

Significant stenosis or occlusion in carotid arteries may lead to diffuse wall thickening (DWT) in the arterial wall of downstream. This study aimed to investigate the correlation between proximal internal carotid artery (ICA) steno-occlusive disease and DWT in ipsilateral petrous ICA.

METHODS

Symptomatic patients with atherosclerotic stenosis (>0%) in proximal ICA were recruited and underwent carotid MR vessel wall imaging. The 3D motion sensitized-driven equilibrium prepared rapid gradient-echo (3D-MERGE) was acquired for characterizing the wall thickness and longitudinal extent of the lesions in petrous ICA and the distance from proximal lesion to the petrous ICA. The stenosis degree in proximal ICA was measured on the time-of-flight (TOF) images.

RESULTS

In total, 166 carotid arteries from 125 patients (mean age 61.0 ± 10.5 years, 99 males) were eligible for final analysis and 64 showed DWT in petrous ICAs. The prevalence of severe DWT in petrous ICA was 1.4%, 5.3%, 5.9%, and 80.4% in ipsilateral proximal ICAs with stenosis category of 1%-49%, 50%-69%, 70%-99%, and total occlusion, respectively. Proximal ICA stenosis was significantly correlated with the wall thickness in petrous ICA (r = 0.767, P < 0.001). Logistic regression analysis showed that proximal ICA stenosis was independently associated with DWT in ipsilateral petrous ICA (odds ratio (OR) = 2.459, 95% confidence interval (CI) 1.896-3.189, P < 0.001].

CONCLUSION

Proximal ICA steno-occlusive disease is independently associated with DWT in ipsilateral petrous ICA.

Technical Note: Measurement of common carotid artery lumen dynamics using black-blood MR cine imaging

PURPOSE

To demonstrate the feasibility of measuring the common carotid artery (CCA) lumen dynamics using a black-blood cine (BB-cine) imaging method.

METHODS

Motion-sensitized driven-equilibrium (MSDE) prepared spoiled gradient sequence was used for the BB-cine imaging. CCAs of eleven healthy volunteers were studied using this method. Lumen dynamics, including lumen area evolution waveforms and distension values, were measured and evaluated by comparing this method with bright-blood cine (BrB-cine) imaging.

RESULTS

Compared with the BrB-cine images, flow artifacts were effectively suppressed in the BB-cine images. BrB-cine images generally show larger lumen areas than BB-cine images. The lumen area waveforms and distension measurements from BB-cine imaging showed smaller variances among different subjects than BrB-cine imaging.

CONCLUSIONS

The proposed BB-cine imaging technique can suppress the flow artifacts effectively and reduce the partial volume effects from the vessel wall. This might allow more accurate lumen dynamics measurements than traditional BrB-cine imaging, which may further be valuable for investigating biomechanical and functional properties of the cardiovascular system.

Assessment of acute thermal damage volumes in muscle using magnetization-prepared 3D T2 -weighted imaging following MRI-guided high-intensity focused ultrasound therapy

PURPOSE

To evaluate magnetization-prepared 3D T₂ -weighted magnetic resonance imaging (MRI) measurements of acute tissue changes produced during ablative MR high-intensity focused ultrasound (MR-HIFU) exposures.

MATERIALS AND METHODS

A clinical MR-HIFU system (3T) was used to generate thermal lesions (n = 24) in the skeletal muscles of three pigs. T₁ -weighted, 2D T₂ -weighted, and magnetization-prepared 3D T₂ -weighted sequences were acquired before and after therapy to evaluate tissue changes following ablation. Tissues were harvested shortly after imaging, fixed in formalin, and gross-sectioned. Select lesions were processed into whole-mount sections. Lesion dimensions for each imaging sequence (length, width) and for gross sections (diameter of lesion core and rim) were assessed by three physicists. Contrast-to-background ratio between lesions and surrounding muscle was compared.

RESULTS

Lesion dimensions on T₁ and 2D T₂ -weighted imaging sequences were well correlated (R² ∼0.7). The contrast-to-background ratio between lesion and surrounding muscle was 7.4 ± 2.4 for the magnetization-prepared sequence versus 1.7 ± 0.5 for a conventional 2D T₂ -weighted acquisition, and 7.0 ± 2.9 for a contrast-enhanced T₁ -weighted sequence. Compared with diameter measured on gross pathology, all imaging sequences overestimated the lesion core by 22-33%, and underestimated the lesion rim by 6-13%.

CONCLUSION

After MR-HIFU exposures, measurements of the acute thermal damage patterns in muscle using a magnetization-prepared 3D T₂ -weighted imaging sequence correlate with 2D T₂ -weighted and contrast-enhanced T₁ -weighted imaging, and all agree well with histology. The magnetization-prepared sequence offers positive tissue contrast and does not require IV contrast agents, and may provide a noninvasive imaging evaluation of the region of acute thermal injury at multiple times during HIFU procedures.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:354-364.

Intracranial arterial wall enhancement using gadolinium-enhanced 3D black-blood T1-weighted imaging

PURPOSE

We investigated the enhancement of the intracranial arterial walls with gadolinium-enhanced, black-blood three-dimensional T1-weighted imaging (Gd-3DBB) by using an improved motion-sensitized driven-equilibrium (iMSDE)-prepared volumetric isotropic turbo spin-echo acquisition (VISTA).

METHODS

A total of 115 patients underwent FLAIR, 3D-TOF-MRA and Gd-3DBB with a 1.5-T scanner. The degree and distribution of the arterial wall enhancement on Gd-3DBB was assessed. The association of the degree of wall enhancement with brain infarction/ischemic lesions on FLAIR, luminal changes on 3D-TOF-MRA, and cardiovascular risk factors (CVRFs) was investigated by univariate and multiple logistic regression analyses.

RESULTS

Strong enhancement of the arterial walls was observed in 77 vertebral arteries (33.5%), 4 basilar arteries (3.5%), 31 supraclinoid internal carotid arteries (ICAs) (13.5%) and 8 middle cerebral arteries (3.5%). In addition, 221 intrapetrous ICAs (96.1%) showed strong enhancement. After adjusting for confounding factors, multivariate analyses showed that the patient age was independently associated with the strong wall enhancement of the arteries for both the posterior (OR, 1.088; 95% CI, 1.034-1.146) and the anterior circulation (OR, 1.098, 95% CI 1.029-1.172). In addition, the presence of the supratentorial brain infarctions was independently associated with the strong wall enhancement in the anterior circulation excluding the intrapetrous ICAs (OR, 4.097; 95% CI, 1.483-11.319).

CONCLUSIONS

Although the arterial wall enhancement on the Gd-3DBB probably reflects normal aging, the enhancement in the anterior circulation might be related to brain infarctions. On the other hand, the intrapetrous ICA enhancement is considered a nonspecific finding and should not be mistaken for arterial pathologies such as atherosclerosis or arteritis.

Black-blood native T1 mapping: Blood signal suppression for reduced partial voluming in the myocardium

PURPOSE

To study the feasibility of black-blood contrast in native T₁ mapping for reduction of partial voluming at the blood-myocardium interface.

METHODS

A saturation pulse prepared heart-rate-independent inversion recovery (SAPPHIRE) T₁ mapping sequence was combined with motion-sensitized driven-equilibrium (MSDE) blood suppression for black-blood T₁ mapping at 3 Tesla. Phantom scans were performed to assess the T₁ time accuracy. In vivo black-blood and conventional SAPPHIRE T₁ mapping was performed in eight healthy subjects and analyzed for T₁ times, precision, and inter- and intraobserver variability. Furthermore, manually drawn regions of interest (ROIs) in all T₁ maps were dilated and eroded to analyze the dependence of septal T₁ times on the ROI thickness.

RESULTS

Phantom results and in vivo myocardial T₁ times show comparable accuracy with black-blood compared to conventional SAPPHIRE (in vivo: black-blood: 1562 ± 56 ms vs. conventional: 1583 ± 58 ms, P = 0.20); Using black-blood SAPPHIRE precision was significantly lower (standard deviation: 133.9 ± 24.6 ms vs. 63.1 ± 6.4 ms, P < .0001), and blood T₁ time measurement was not possible. Significantly increased interobserver interclass correlation coefficient (ICC) (0.996 vs. 0.967, P = 0.011) and similar intraobserver ICC (0.979 vs. 0.939, P = 0.11) was obtained with the black-blood sequence. Conventional SAPPHIRE showed strong dependence on the ROI thickness (R² = 0.99). No such trend was observed using the black-blood approach (R² = 0.29).

CONCLUSION

Black-blood SAPPHIRE successfully eliminates partial voluming at the blood pool in native myocardial T₁ mapping while providing accurate T₁ times, albeit at a reduced precision. Magn Reson Med 78:484-493, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Magnetic Resonance Imaging Technique for Visualization of Irregular Cerebrospinal Fluid Motion in the Ventricular System and Subarachnoid Space

BACKGROUND

Many studies have shown that cerebrospinal fluid (CSF) behaves irregularly, rather than with laminar flow, in the various CSF spaces. We adapted a modified previously known magnetic resonance imaging technique to visualize irregular CSF motion. Subsequently, we assessed the usefulness and clinical significance of the present method.

MATERIALS AND METHODS

Normal CSF motion in 10 healthy volunteers was visualized with the dynamic improved, motion-sensitized, driven-equilibrium steady-state free precession technique. Subsequently, CSF motion visualization with a modified sequence was applied to 3 patients.

RESULTS

In healthy volunteers, we achieved visualization of the irregularity of CSF flow in the ventricles and spinal canal, whereas CSF motion was diminished in the peripheral part of the intracranial subarachnoid space. In one case, we confirmed the patency of the patient's third ventriculostomy fenestration site. In the other, we verified the usefulness of the proposed sequence for determining the communication between the ventricle or subarachnoid space and the cyst.

CONCLUSIONS

Using the present sequence, we obtained images that accentuated CSF motion, which is largely composed of irregular motion. This method does not require pulse triggering or complex post-processing of images and allows visualization of CSF motion in a short period of time in selected whole imaging planes. It can therefore be applied clinically to diagnose various diseases that cause abnormalities in the CSF space.

Acceleration-selective arterial spin labeling for intracranial MR angiography with improved visualization of cortical arteries and suppression of cortical veins

PURPOSE

A new approach for intracranial MR angiography (MRA) is introduced, using acceleration-selective arterial spin labeling (AccASL). The aim of this study was to investigate the arterial visualization and venous suppression using AccASL.

METHODS

Intracranial MRA images obtained by AccASL and time-of-flight (TOF) were compared in seven healthy volunteers and one patient with occlusion of the terminal portion of the left internal carotid artery. The volunteer images were assessed by measuring the contrast-to-noise ratio (CNR) between the middle cerebral artery (MCA) and white matter (WM) and between the confluence of sinuses and WM. Additionally, visualized peripheral arteries were counted and qualitative scoring of the MCA visualization and vein signal contamination was conducted.

RESULTS

The CNR at the M4 branch and the number of visualized arteries was significantly higher using AccASL compared with that in TOF (P < 0.05). In the qualitative comparison, the score for artery visualization was higher using AccASL (P < 0.05), while minimizing signal contamination by cortical veins. Additionally, in patient examination, the collateral flow visualization was better with AccASL.

CONCLUSION

AccASL enables better efficiency for visualizing peripheral arteries compared with TOF, while suppressing cortical vein signal. Magn Reson Med 77:1996-2004, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Breath-hold black blood quantitative T1rho imaging of liver using single shot fast spin echo acquisition

BACKGROUND

Liver fibrosis is a key feature in most chronic liver diseases. T1rho magnetic resonance imaging is a potentially important technique for noninvasive diagnosis, severity grading, and therapy monitoring of liver fibrosis. However, it remains challenging to perform robust T1rho quantification of liver on human subjects. One major reason is that the presence of rich blood signal in liver can cause artificially high T1rho measurement and makes T1rho quantification susceptible to motion.

METHODS

A pulse sequence based on single shot fast/turbo spin echo (SSFSE/SSTSE) acquisition, with theoretical analysis and simulation based on the extended phase graph (EPG) algorithm, was presented for breath-hold single slice quantitative T1rho imaging of liver with suppression of blood signal. The pulse sequence was evaluated in human subjects at 3.0 T with 500 Hz spinlock frequency and time-of-spinlock (TSL) 0, 10, 30 and 50 ms.

RESULTS

Human scan demonstrated that the entire T1rho data sets with four spinlock time can be acquired within a single breath-hold of 10 seconds with black blood effect. T1rho quantification with suppression of blood signal results in significantly reduced T1rho value of liver compared to the results without blood suppression.

CONCLUSIONS

A signal-to-noise ratio (SNR) efficient pulse sequence was reported for T1rho quantification of liver. The black blood effect, together with a short breath-hold, mitigates the risk of quantification errors as would occur in the conventional methods.

Improved motion-sensitized driven-equilibrium preparation for 3D turbo spin echo T1 weighted imaging after gadolinium administration for the detection of brain metastases on 3T MRI

OBJECTIVE

To evaluate the clinical usefulness of an improved motion-sensitized driven-equilibrium (iMSDE) preparation for three-dimensional turbo spin echo (TSE) T1 weighted imaging after gadolinium administration in 3.0-T MRI for the detection of brain metastases compared with conventional gradient echo (C-GRE) T1 weighted imaging with gadolinium.

METHODS

40 patients with suspected brain metastases underwent MR studies, including two contrast-enhanced sequences, iMSDE-TSE and C-GRE. Post-enhancement images of 14 patients with suspected metastatic brain lesions were retrospectively analyzed, and comparisons between iMSDE-TSE and C-GRE were made using the Wilcoxon signed-rank test.

RESULTS

C-GRE detected 86 metastatic lesions, whereas iMSDE-TSE detected 97, including one false-positive lesion on both sequences. 11 of 96 metastases were detected on iMSDE-TSE only. On C-GRE, 15 of 85 metastases were equivocal. There was a significant difference between C-GRE and iMSDE-TSE in terms of the number of detected lesions (p = 0.024). Notably, the interobserver agreement for diagnosing metastases and identifying non-metastases was nearly identical. Overall, iMSDE-TSE achieves higher detectability of metastatic brain lesions, especially equivocal lesions.

CONCLUSION

Compared with C-GRE, iMSDE-TSE detected more brain metastases. This method is especially helpful in discerning equivocal metastases.

ADVANCES IN KNOWLEDGE

Previous studies have offered limited clinically useful information because they have all been preliminary studies such as comparing the contrast-to-noise ratio of each sequence without evaluating iMSDE-TSE. This study, however, is unique because we evaluate the clinical usefulness of iMSDE-TSE for the detection of brain metastases, and we compare these results to C-GRE.

Slice-selective adiabatic magnetization T2 -preparation (SAMPA) for efficient T2 -weighted imaging at ultrahigh field strengths

PURPOSE

At high field, T₂ -weighted (T₂ w) imaging is limited by transmit field inhomogeneity and increased radiofrequency power deposition. In this work, we introduce SAMPA (Slice-selective Adiabatic Magnetization T₂ PrepAration) and demonstrate its use for efficient brain T₂ w imaging at 7 Tesla (T).

METHODS

SAMPA was designed by subsampling an optimized B₁ insensitive rotation (BIR4) waveform with small tip angle linear subpulses. To perform T₂ w imaging, SAMPA was inserted before a fast gradient echo acquisition. The off-resonance behavior, B₁ robustness, and slice selectivity of the novel T₂ preparation module were analyzed using Bloch simulations. The performance of SAMPA for T₂ w imaging was demonstrated in phantom experiments as well as in the brains of healthy volunteers at 7T.

RESULTS

Based on simulations, the proposed design operates at peak B₁ of 15 μT and higher, within a 400 Hz bandwidth. T₂ values were in strong agreement with spin echo-based T₂ mapping in phantom experiments. Whole brain, interleaved multislab three-dimensional imaging could be acquired with 0.8 mm³ isotropic resolution in 5:36 min per T₂ weighting.

CONCLUSION

Compared with previous adiabatic T₂ preparation techniques, SAMPA allows for slice-selectivity, which can lead to efficient and robust acquisitions for T₂ w imaging at high field. Magn Reson Med 76:1741-1749, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Three-Dimensional Carotid Plaque MR Imaging

There has been significant progress made in 3-dimensional (3D) carotid plaque MR imaging techniques in recent years. Three-dimensional plaque imaging clearly represents the future in clinical use. With effective flow-suppression techniques, choices of different contrast weighting acquisitions, and time-efficient imaging approaches, 3D plaque imaging offers flexible imaging plane and view angle analysis, large coverage, multivascular beds capability, and even can be used in fast screening.