Gradient And Spin Echo Research Articles

A Test-Retest Study of Single- and Multi-Delay pCASL for Choroid Plexus Perfusion Imaging in Healthy Subjects Aged 19 to 87 Years.

There is a growing interest in the choroid plexus (ChP) due to its critical role in cerebrospinal fluid (CSF) production and its involvement in neurodegenerative and cerebrovascular diseases. However, comprehensive studies comparing the accuracy and reliability of single- and multi-PLD (post-labeling delay) arterial spin labeling (ASL) techniques, specifically in relation to the ChP, remain limited. This study systematically evaluated the test-retest reliability and quantification accuracy of cerebral blood flow (CBF) measurements, focusing on the ChP, using single-delay and multi-delay 3D gradient-and-spin echo (GRASE) pseudo-continuous ASL (pCASL) on 28 subjects (aged 19 to 87 years, 14 males/14 females) at 3.0 tesla. Both single-delay (2 sec) and 5-PLD (0.5 - 2.5 sec) pCASL scans were repeated approximately one week apart with a spatial resolution of 2.5×2.5×3 mm³. Voxel-wise and regional CBF and arterial transit time (ATT) measurements were compared to assess test-retest reliability, with a particular focus on ChP perfusion changes with age. In this study, 12.15% of ChP voxels exhibited ATTs longer than 2 sec, potentially leading to a significant underestimation of CBF using single-delay ASL. Multi-delay ASL showed improved accuracy in estimating CBF values for the ChP compared to single-delay ASL when ATT > PLD. Additionally, ChP volume (mean ± std = 1.72± 0.85 ml) increased (p < 0.01) and ChP perfusion (43.07±14.18 mL/100 g/min) decreased (p = 0.04) with age. These findings underscore the robustness of multi-delay ASL with model-fitting quantification in assessing ChP perfusion, making it the preferred method for accurate CBF and ATT estimation, particularly in regions with prolonged transit time such as ChP.

Enhanced 3D Magnetic Resonance Cholangiopancreatography with Fast Gradient and Spin Echo Sequence: Technical Advancements and Clinical Implications

Objective: The application of fast gradient and spin echo (GRASE) sequence in 3D magnetic resonance cholangiopancreatography (MRCP) was investigated. Methods: Sixty patients who underwent 3D MRCP examination using the Philips Ingenia 3.0T superconducting MR imaging system and a 32-channel phased array direct digital RF receiving coil in the hospital from June 2021 to June 2023 were selected. The acquisition times of the two sequences were compared, and the scanned images of the two sequences were subjectively and objectively evaluated, with the scanning sequence including turbo spin echo (TSE) sequence and GRASE sequence. Results: The display scores, image artifact scores, and overall image quality scores of the GRASE sequence on the common bile duct, gallbladder duct, main pancreatic duct, left and right hepatic ducts were higher than those of the TSE sequence, and the differences were statistically significant (P&lt;0.05). The acquisition time of GRASE sequence was 16 seconds, which was about 96% shorter than that of TSE sequence (399.06±84.53) seconds. The contrast to noise ratio (CNR) of the GRASE sequence was higher than that of the TSE sequence, and the difference was statistically significant (P &lt; 0.05); The signal to noise ratio (SNR) of the GRASE sequence was slightly higher than that of the TSE sequence, but the difference was not statistically significant (P &gt; 0.05). Conclusion: The use of the GRASE sequence in 3D MRCP examinations can improve image quality, shorten acquisition time, and ensure CNR.

Free-breathing three-dimensional simultaneous myocardial T1 and T2 mapping based on multi-parametric SAturation-recovery and Variable-flip-Angle

BackgroundQuantitative myocardial tissue characterization with T1 and T2 parametric mapping can provide an accurate and complete assessment of tissue abnormalities across a broad range of cardiomyopathies. However, current clinical T1 and T2 mapping tools rely predominantly on two-dimensional (2D) breath-hold sequences. Clinical adoption of three-dimensional (3D) techniques is limited by long scan duration. The aim of this study is to develop and validate a time-efficient 3D free-breathing simultaneous T1 and T2 mapping sequence using multi-parametric SAturation-recovery and Variable-flip-Angle (mSAVA). MethodsmSAVA acquires four volumes for simultaneous whole-heart T1 and T2 mapping. We validated mSAVA using simulations, phantoms, and in-vivo experiments at 3T in 11 healthy subjects and 11 patients with diverse cardiomyopathies. T1 and T2 values by mSAVA were compared with modified Look-Locker inversion recovery (MOLLI) and gradient and spin echo (GraSE), respectively. The clinical performance of mSAVA was evaluated against late gadolinium enhancement (LGE) imaging in patients. ResultsPhantom T1 and T2 by mSAVA showed a strong correlation to reference sequences (R2 = 0.98 and 0.99). In-vivo imaging with an imaging resolution of 1.5 × 1.5 × 8 mm3 could be achieved. Myocardial T1 and T2 of healthy subjects by mSAVA were 1310 ± 46 and 44.6 ± 2.0 ms, respectively, with T1 standard deviation higher than MOLLI (105 ± 12 vs 60 ± 16 ms) and T2 standard deviation lower than GraSE (4.5 ± 0.8 vs 5.5 ± 1.0 ms). mSAVA T1 and T2 maps presented consistent findings in patients undergoing LGE. Myocardial T1 and T2 of all patients by mSAVA were 1421 ± 79 and 47.2 ± 3.3 ms, respectively. ConclusionmSAVA is a fast 3D technique promising for clinical whole-heart T1 and T2 mapping.

Robust unenhanced peripheral magnetic resonance angiography using single-slab 3D chemical-shift-encoded GRASE.

Objective.To develop a novel, unenhanced magnetic resonance angiography (MRA) exploiting cardiac-gated, single-slab 3D chemical-shift-encoded gradient- and spin-echo (GRASE) imaging for robust background suppression.Approach.The proposed single-slab 3D GRASE employs variable-flip-angles (VFA) in the refocusing radio-frequency (RF) pulse train to promote sensitivity to blood flow as well as imaging encoding efficiency. Phase encoding blips are inserted between adjacent lobes of the switching readout gradients such that chemical shift-induced phase information is encoded into different locations in k-space. Based on the assumption that most background signals in the angiogram come from the fatty tissues, the proposed method directly separates angiograms from fatty background tissue signals from highly incomplete measurements by solving a constrained optimization problem with sparsity prior. Numerical simulations and experiments were performed to validate the effectiveness of the proposed method in healthy volunteers as compared with conventional fresh blood imaging (FBI).Main results.Compared with conventional FBI, the proposed method yields clearer delineation of small branching arteries and robust fatty background suppression without apparent loss of signals.Significance.We have successfully demonstrated the feasibility of the proposed, single-slab 3D VFA GRASE with chemical-shift-encoded reconstruction for the generation of robust unenhanced peripheral MRA.

Blood-Brain Barrier Permeability to Water Measured Using Multiple Echo Time Arterial Spin Labeling MRI in the Aging Human Brain.

The blood-brain barrier (BBB) plays a vital role in maintaining brain homeostasis, but the integrity of this barrier deteriorates slowly with aging. Noninvasive water exchange magnetic resonance imaging (MRI) methods may identify changes in the BBB occurring with healthy aging. To investigate age-related changes in the BBB permeability to water using multiple-echo-time (multi-TE) arterial spin labeling (ASL) MRI. Prospective, cohort. Two groups of healthy humans-older group (≥50 years, mean age = 56 ± 4 years, N = 13, females = 5) and younger group (≤20 years, mean age = 18 ± 1, N = 13, females = 7). A 3T, multi-TE Hadamard pCASL with 3D Gradient and Spin Echo (GRASE) readout. Two different approaches of variable complexity were applied. A physiologically informed biophysical model with a higher complexity estimating time ( ) taken by the labeled water to move across the BBB and a simpler model of triexponential decay measuring tissue transition rate ( . Two-tailed unpaired Student t-test, Pearson's correlation coefficient and effect size. P < 0.05 was considered significant. Older volunteers showed significant differences of 36% lower , 29% lower cerebral perfusion, 17% pronged arterial transit time and 22% shorter intra-voxel transit time compared to the younger volunteers. Tissue fraction ( ) at the earliest TI = 1600 msec was significantly higher in the older group, which contributed to a significantly lower compared to the younger group. at TI = 1600 msec showed significant negative correlation with (r = -0.80), and and showed significant positive correlation (r = 0.73). Both approaches of Multi-TE ASL imaging showed sensitivity to detect age-related changes in the BBB permeability. High tissue fractions at the earliest TI and short in the older volunteers indicate that the BBB permeability increased with age. 2 TECHNICAL EFFICACY: Stage 1.

Impact of susceptibility-induced distortion correction on perfusion imaging by pCASL with a segmented 3D GRASE readout

PurposeThe consensus for the clinical implementation of arterial spin labeling (ASL) perfusion imaging recommends a segmented 3D Gradient and Spin-Echo (GRASE) readout for optimal signal-to-noise-ratio (SNR). The correction of the associated susceptibility-induced geometric distortions has been shown to improve diagnostic precision, but its impact on ASL data has not been systematically assessed and it is not consistently part of pre-processing pipelines. Here, we investigate the effects of susceptibility-induced distortion correction on perfusion imaging by pseudo-continuous ASL (pCASL) with a segmented 3D GRASE readout. MethodsData acquired from 28 women using pCASL with 3D GRASE at 3T was analyzed using three pre-processing options: without distortion correction, with distortion correction, and with spatial smoothing (without distortion correction) matched to control for blurring effects induced by distortion correction. Maps of temporal SNR (tSNR) and relative perfusion were analyzed in eight regions-of-interest (ROIs) across the brain. ResultsDistortion correction significantly affected tSNR and relative perfusion across the brain. Increases in tSNR were like those produced by matched spatial smoothing in most ROIs, indicating that they were likely due to blurring effects. However, that was not the case in the frontal and temporal lobes, where we also found increased relative perfusion with distortion correction even compared with matched spatial smoothing. These effects were found in both controls and patients, with no interactions with the participant group. ConclusionCorrection of susceptibility-induced distortions significantly impacts ASL perfusion imaging using a segmented 3D GRASE readout, and this step should therefore be considered in ASL pre-processing pipelines. This is of special importance in clinical studies, reporting perfusion across ROIs defined on relatively undistorted images and when conducting group analyses requiring the alignment of images across different subjects.

Myelin‐weighted MR Imaging in Patients with Alzheimer’s Disease

AbstractBackgroundDeveloping an imaging technique to map myelin changes in the brain within a short scan time is needed due to the inability of Alzheimer’s disease (AD) patients to remain motionless during MRI scanning.PurposeTo investigate myelin loss in both AD and mild cognitive impairment (MCI) patients with a new myelin water mapping technique within reasonable scan time and evaluate the clinical relevance of the apparent myelin water fraction (MWF) values by assessing the relationship between decreases in myelin water and the degree of memory decline or aging.MethodIn this prospective study from March 2019 to October 2021, the participants were allocated as follows: 29 individuals were assigned to the cognitively normal (CN) elderly group (mean ± SD, 73 ± 5 years, 16 females), 32 participants were assigned to the MCI group (74 ± 5 years, 21 females), and 31 patients were assigned to the AD group (74 ± 6 years, 26 females). A 3D visualization of the short transverse relaxation time component (ViSTa)‐gradient and spin‐echo (GraSE) sequence was developed to map apparent MWF. Then, the MWF values were compared between the three participant groups, and was evaluated the relationship with the degree of memory loss.ResultA total of 92 participants were evaluated. The AD group showed a reduced apparent MWF compared to the CN and MCI groups. Moreover, the MWF was decreased with age and positively correlated with Mini‐Mental State Examination scores. The largest AUC value (0.799) was in the corpus callosum and used to classify the CN and AD groups using the apparent MWF.ConclusionThe ViSTa‐GraSE sequence can be a useful tool to map the MWF in a reasonable scan time. Combining the MWF in the corpus callosum with the detection of atrophy in the hippocampus can be valuable for group classification.FundingThe research was supported by the National Research Foundation of Korea (NRF) grant funded by Ministry of Science and ICT (No. 2020R1A2C1004749, GHJ), Republic of Korea.

Evaluation of 3D stack-of-spiral turbo FLASH acquisitions for pseudo-continuous and velocity-selective ASL-derived brain perfusion mapping.

The most-used 3D acquisitions for ASL are gradient and spin echo (GRASE)- and stack-of-spiral (SOS)-based fast spin echo, which require multiple shots. Alternatively, turbo FLASH (TFL) allows longer echo trains, and SOS-TFL has the potential to reduce the number of shots to even single-shot, thus improving the temporal resolution. Here we compare the performance of 3D SOS-TFL and 3D GRASE for ASL at 3T. The 3D SOS-TFL readout was optimized with respect to fat suppression and excitation flip angles for pseudo-continuous ASL- and velocity-selective (VS)ASL-derived cerebral blood flow (CBF) mapping as well as for VSASL-derived cerebral blood volume (CBV) mapping. Results were compared with 3D GRASE readout on healthy volunteers in terms of perfusion quantification and temporal SNR (tSNR) efficiency. CBF and CBV mapping derived from 3D SOS-TFL-based ASL was demonstrated on one stroke patient, and the potential for single-shot acquisitions was exemplified. SOS-TFL with a 15° flip angle resulted in adequate tSNR efficiency with negligible image blurring. Selective water excitation was necessary to eliminate fat-induced artifacts. For pseudo-continuous ASL- and VSASL-based CBF and CBV mapping, compared to the employed four-shot 3D GRASE with an acceleration factor of 2, the fully sampled 3D SOS-TFL delivered comparable performance (with a similar scan time) using three shots, which could be further undersampled to achieve single-shot acquisition with higher tSNR efficiency. SOS-TFL had reduced CSF contamination for VSASL-CBF. 3D SOS-TFL acquisition was found to be a viable substitute for 3D GRASE for ASL with sufficient tSNR efficiency, minimal relaxation-induced blurring, reduced CSF contamination, and the potential of single-shot, especially for VSASL.

Quantification of blood-brain barrier water exchange and permeability with multidelay diffusion-weighted pseudo-continuous arterial spin labeling.

To present a pulse sequence and mathematical models for quantification of blood-brain barrier water exchange and permeability. Motion-compensated diffusion-weighted (MCDW) gradient-and-spin echo (GRASE) pseudo-continuous arterial spin labeling (pCASL) sequence was proposed to acquire intravascular/extravascular perfusion signals from five postlabeling delays (PLDs, 1590-2790 ms). Experiments were performed on 11 healthy subjects at 3 T. A comprehensive set of perfusion and permeability parameters including cerebral blood flow (CBF), capillary transit time (τc ), and water exchange rate (kw ) were quantified, and permeability surface area product (PSw ), total extraction fraction (Ew ), and capillary volume (Vc ) were derived simultaneously by a three-compartment single-pass approximation (SPA) model on group-averaged data. With information (i.e., Vc and τc ) obtained from three-compartment SPA modeling, a simplified linear regression of logarithm (LRL) approach was proposed for individual kw quantification, and Ew and PSw can be estimated from long PLD (2490/2790 ms) signals. MCDW-pCASL was compared with a previously developed diffusion-prepared (DP) pCASL sequence, which calculates kw by a two-compartment SPA model from PLD = 1800 ms signals, to evaluate the improvements. Using three-compartment SPA modeling, group-averaged CBF = 51.5/36.8 ml/100 g/min, kw = 126.3/106.7 min-1 , PSw = 151.6/93.8 ml/100 g/min, Ew = 94.7/92.2%, τc = 1409.2/1431.8 ms, and Vc = 1.2/0.9 ml/100 g in gray/white matter, respectively. Temporal SNR of MCDW-pCASL perfusion signals increased 3-fold, and individual kw maps calculated by the LRL method achieved higher spatial resolution (3.5 mm3 isotropic) as compared with DP pCASL (3.5 × 3.5 × 8 mm3 ). MCDW-pCASL allows visualization of intravascular/extravascular ASL signals across multiple PLDs. The three-compartment SPA model provides a comprehensive measurement of blood-brain barrier water dynamics from group-averaged data, and a simplified LRL method was proposed for individual kw quantification.

Orientation dependence of R2 relaxation in the newborn brain

In MRI the transverse relaxation rate, R2 = 1/T2, shows dependence on the orientation of ordered tissue relative to the main magnetic field. In previous studies, orientation effects of R2 relaxation in the mature brain's white matter have been found to be described by a susceptibility-based model of diffusion through local magnetic field inhomogeneities created by the diamagnetic myelin sheaths. Orientation effects in human newborn white matter have not yet been investigated. The newborn brain is known to contain very little myelin and is therefore expected to exhibit a decrease in orientation dependence driven by susceptibility-based effects. We measured R2 orientation dependence in the white matter of human newborns. R2 data were acquired with a 3D Gradient and Spin Echo (GRASE) sequence and fiber orientation was mapped with diffusion tensor imaging (DTI). We found orientation dependence in newborn white matter that is not consistent with the susceptibility-based model and is best described by a model of residual dipolar coupling. In the near absence of myelin in the newborn brain, these findings suggest the presence of residual dipolar coupling between rotationally restricted water molecules. This has important implications for quantitative imaging methods such as myelin water imaging, and suggests orientation dependence of R2 as a potential marker in early brain development.

Customized whole brain-covering 3D GRASE in multi-delay pseudo-continuous arterial spin labeling for duplex distinct hemodynamic mapping contrasts of brain tissues and circulation pathways

Gradient and spin echo (GRASE) is widely employed in arterial spin labeling (ASL) as an efficient readout sequence. Hemodynamic parameter mappings of perfusion, such as cerebral blood flow (CBF) and arterial transit time (ATT), can be derived via multi-delay ASL acquisitions. Multi-delay ASL perfusion imaging inevitably suffers limited signal-to-noise ratio (SNR) since a motion-sensitized vessel suppressing module has to be employed to highlight perfusion signals. The present work reveals that in multi-delay ASL, manipulation of GRASE sequence on either planar imaging echo echo train for adjusted spatial resolutions or FSE echo train for modulated extent of T 2-blurring can significantly alter the mapping contrasts among tissues and among cerebral lobes under different pathways of blood circulation, and meanwhile regulates SNR. Four separate multi-delay ASL scans with different echo train designs in 3D whole brain covering GRASE were carried out for healthy subjects to evaluate the variations in regard to the parameter quantifications and SNR. Based on the quantification mappings, the GRASE acquisition with moderate spatial resolution (3.5 × 3.5 × 4 mm3) and segmented k z scheme was recognized for the first time to be recommended for more unambiguous CBF and ATT contrasts between GM and WM in conjunction with more enhanced ATT contrast between anterior and posterior cerebral circulations, with reasonably good SNR. The technical proposal is of great value for the cutting-edge research of a variety of neurological diseases of global concerns.

Comparison between gradient and spin-echo (GRASE) and compressed sensing sequences for single breath-hold three-dimensional magnetic resonance cholangiopancreatography in patients with T1 hyperintense bile

PurposeTo compare image quality and the detectability of gallstones in patients with T1 hyperintense bile between single breath-hold three-dimensional (3D) magnetic resonance cholangiopancreatography (MRCP) with gradient and spin-echo (GRASE) and with compressed sensing (CS). MethodsWe retrospectively evaluated patients who underwent MRCP using GRASE and CS and had hyperintense bile on T1-weighted fat-suppressed images. The relative duct-to-periductal contrast ratios (RCs) of each bile duct segment were calculated. Pancreaticobiliary duct visibility, motion artifacts, background suppression, and overall image quality were scored on a 5-point scale. The Wilcoxon signed-rank test was used to analyze differences in qualitative and quantitative results. Diagnostic performance in detecting common bile duct (CBD) and gallbladder stones was assessed using receiver operating characteristic (ROC) curves. ResultsIn total, 96 patients were included in the study. RCs of all bile duct segments in GRASE MRCP were significantly lower than those in CS MRCP (p < 0.001). All biliary duct visibility and overall image quality had significantly higher scores in GRASE MRCP than in CS MRCP (p < 0.001–0.003). Area under ROC curves of GRASE MRCP and CS MRCP were 1.00 and 0.88 for CBD stone (p = 0.14) and 0.93 and 0.82 for gallbladder stone (p = 0.08), respectively. ConclusionsGRASE MRCP provides better image quality than CS MRCP in patients with hyperintense bile on T1-weighted images. The detectability of biliary stones was also higher in GRASE MRCP than in CS MRCP, although not significantly.

Three-dimensional static-fluid MR urography with gradient- and spin-echo (GRASE) at 3.0T: comparison of image quality and diagnostic performance with respiratory-triggered fast spin-echo (FSE)

PurposeTo compare the performance of 3D MRU based on a breath-hold gradient- and spin-echo (BH-GRASE) technique with conventional 3D respiratory-triggered FSE (RT-FSE) sequence in patients with urinary tract dilation.MethodsWe prospectively included 90 patients with urinary tract dilation who underwent both 3D BH-GRASE and RT-FSE MRU at 3T. The acquisition time of two MRU sequences was recorded. Three readers blinded to the protocols reviewed the image quality using a five-point scale and assessed the diagnostic performance related to urinary tract dilation. The relative contrast ratio (CR) between the urinary tract and adjacent area was measured quantitatively.ResultsAcquisition time was 14.8 s for BH-GRASE MRU and 213.6 ± 52.2 s for RT-FSE MRU. The qualitative image analysis demonstrated significant equivalence between the two MRU protocols. 3D BH-GRASE MRU better depicted bilateral renal calyces than RT-FSE MRU (p < 0.05). The CR values of the urinary tract were lower on BH-GRASE MRU compared with RT-FSE MRU (p < 0.05). There were excellent agreements in the assessment of urinary tract dilation between BH-GRASE and RT-FSE MRU, including the dilated degree, obstructive level, and obstructive imaging features (inter-sequence κ = 0.924–1).Conclusion3D BH-GRASE MRU significantly decreased the acquisition time and achieved comparable image quality, urinary tract visualization, and diagnostic performance with conventional 3D RT-FSE MRU. Breath-hold 3D MRU with GRASE may provide a feasible evaluation of urinary tract dilation.Graphical abstract

Myelin-Weighted Imaging Presents Reduced Apparent Myelin Water in Patients with Alzheimer's Disease.

The purpose of this study was to investigate myelin loss in both AD and mild cognitive impairment (MCI) patients with a new myelin water mapping technique within reasonable scan time and evaluate the clinical relevance of the apparent myelin water fraction (MWF) values by assessing the relationship between decreases in myelin water and the degree of memory decline or aging. Twenty-nine individuals were assigned to the cognitively normal (CN) elderly group, 32 participants were assigned to the MCI group, and 31 patients were assigned to the AD group. A 3D visualization of the short transverse relaxation time component (ViSTa)-gradient and spin-echo (GraSE) sequence was developed to map apparent MWF. Then, the MWF values were compared between the three participant groups and was evaluated the relationship with the degree of memory loss. The AD group showed a reduced apparent MWF compared to the CN and MCI groups. The largest AUC (area under the curve) value was in the corpus callosum and used to classify the CN and AD groups using the apparent MWF. The ViSTa-GraSE sequence can be a useful tool to map the MWF in a reasonable scan time. Combining the MWF in the corpus callosum with the detection of atrophy in the hippocampus can be valuable for group classification.

Joint estimation and correction of motion and geometric distortion in segmented arterial spin labeling.

Arterial spin labeling allows noninvasive measurement of cerebral blood flow by magnetically labeling inflowing blood, using it as endogenous tracer. Unfortunately, sensitivity to subject motion is high due to the subtractive nature of arterial spin labeling, which is especially problematic if Cartesian segmented 3D gradient and spin echo (GRASE) is applied. Using a 3D GRASE PROPELLER (3DGP) segmentation, retrospective correction of in-plane rigid body motion is possible before final combination of different segments. However, the standard 3DGP reconstruction is affected by off-resonance effects and has not yet been validated with different motion patterns and levels of background suppression. The standard algorithm (1) and a Cartesian segmented 3D GRASE (2), as well as a new 3DGP reconstruction algorithm, which allows joint estimation of motion and geometric distortion (called 3DGP-JET), are validated in 5 healthy volunteers. Image quality of perfusion-weighted images was investigated for background suppression levels of 0%, 5%, and 10% in combination with no motion, as well as slow and fast intentional motion patterns during the scan. The proposed 3DGP-JET algorithm allowed robust estimation of field maps and motion for all scenarios, and greatly reduced motion-related artifacts in perfusion-weighted images when compared with Cartesian segmented 3D GRASE. Further improvements of the presented 3DGP-JET routine and a combination with prospective motion correction are recommended to compensate for through-plane motion, making the presented technique a good candidate for dealing with motion-related artifacts in arterial spin labeling images in clinical reality.

Three-dimensional gradient and spin-echo readout for time-encoded pseudo-continuous arterial spin labeling: Influence of segmentation factor and flow compensation.

PurposeTo monitor the complete passage of the labeled blood through the vascular tree into tissue and improve the quantification of ASL maps, we evaluated the effect of 3D gradient and spin‐echo (GRASE) readout segments on temporal SNR (tSNR) and image blurriness for time‐encoded pseudo‐continuous arterial spin labeling and the effect of flow‐compensation gradients on the presence of intravascular signal.MethodsFifteen volunteers were scanned using time‐encoded pCASL with 2D EPI and single‐segment, two‐segments, and three‐segments 3D‐GRASE readouts with first‐order flow compensation (FC) gradients. Two‐segments 3D‐GRASE scans were acquired with 25%, 50%, 75%, and 100% of full first‐order FC. Temporal SNR was assessed, and cerebral blood flow and arterial blood volume were quantified for all readout strategies.ResultsFor single‐segment 3D GRASE, tSNR was comparable to 2D EPI for perfusion signal but worse for the arterial signal. Two‐segments and three‐segments 3D GRASE resulted in higher tSNR than 2D EPI for perfusion and arterial signal. The arterial signal was not well visualized for 3D‐GRASE data without FC. Visualization of the intravascular signal at postlabeling delays of 660 ms and 1060 ms was restored with FC. Adequate visualization of the intravascular signal was achieved from 75% of FC gradient strength at a postlabeling delay of 660 ms. For a postlabeling delay of 1060 ms, full‐FC gradients were the best option to depict intravascular signal.ConclusionSegmented GRASE provided higher effective tSNR compared with 2D‐EPI and single‐segment GRASE. Flow compensation with GRASE readout should be carefully controlled when applying for time‐encoded pCASL to visualize intravascular signal.

Comparisons between image quality and diagnostic performance of 2D- and breath-hold 3D magnetic resonance cholangiopancreatography at 3T.

To compare the image quality and diagnostic performance of 2D MRCP to those of breath-hold 3D MRCP using compressed sensing (CS-MRCP) and gradient and spin-echo (GRASE-MRCP) at 3T. From January to November 2018, patients who underwent pancreatobiliary MRI including 2D MRCP and two breath-hold 3D MRCP using CS and GRASE at 3T were included. Three radiologists independently evaluated image quality, motion artifact, and pancreatic cyst conspicuity. Diagnostic performance was assessed for bile duct anatomic variation, bile duct, and pancreatic diseases using a composite algorithm as reference standards. Pancreatic lesion detectability and conspicuity were evaluated using JAFROC and generalized estimating equation analysis. One hundred patients (male = 50) were included. Bile duct anatomic variation, bile duct and pancreatic diseases were present in respectively 31, 15, and 79 patients. Breath-hold 3D MRCP provided better image quality than 2D MRCP (3.5 ± 0.6 in 2D MRCP; 4.0 ± 0.7 in GRASE-MRCP and 3.9 ± 0.8 in CS-MRCP, p < 0.001 for both). There was no difference in motion artifact between 2D and breath-hold 3D MRCP (p = 0.1). Breath-hold 3D CS-MRCP provided better pancreatic cyst conspicuity than 2D MRCP (2.7 [95% CI: 2.5-3.0] vs. 2.3 [95% CI: 2.1-2.5], p = 0.001). There were no significant differences between the diagnostic performance of the three sequences in the detection of bile duct anatomic variation or pancreatic lesions (p > 0.05). Breath-hold 3D MRCP with GRASE or CS can provide better image quality than 2D MRCP in a comparable scan time. • Breath-hold 3D MRCP using compressed sensing (CS) or gradient and spin-echo (GRASE) provided a better image quality with less image blurring than 2D MRCP. • There were no significant differences between 2D MRCP and breath-hold 3D MRCP in either motion artifact or the number of non-diagnostic exams. • There were no significant differences between 2D MRCP and either type of breath-hold 3D MRCP in the diagnosis of bile duct anatomic variation or detection of pancreatic lesions.

In vivo investigation of the multi-exponential T2 decay in human white matter at 7 T: Implications for myelin water imaging at UHF.

Multi-component T2 mapping using a gradient- and spin-echo (GraSE) acquisition has become standard for myelin water imaging at 3 T. Higher magnetic field strengths promise signal-to-noise ratio benefits but face specific absorption rate limits and shortened T2 times. This study investigates compartmental T2 times in vivo and addresses advantages and challenges of multi-component T2 mapping at 7 T. We acquired 3D multi-echo GraSE data in seven healthy adults at 7 T, with three subjects also scanned at 3 T. Stimulated echoes arising from B1+ inhomogeneities were accounted for by the extended phase graph (EPG) algorithm. We used the computed T2 distributions to determine T2 times that identify different water pools and assessed signal-to-noise and fit-to-noise characteristics of the signal estimation. We compared short T2 fractions and T2 properties of the intermediate water pool at 3 T and 7 T. Flip angle mapping confirmed that EPG accurately determined the larger B1+ inhomogeneity at 7 T. Multi-component T2 analysis demonstrated shortened T2 times at 7 T compared with 3 T. Fit-to-noise and signal-to-noise ratios were improved at 7 T but depended on B1+ homogeneity. Adjusting the shortest T2 to 8 ms and the T2 threshold that separates different water compartments to 20 ms yielded short T2 fractions at 7 T that conformed to 3 T data. Short T2 fractions in myelin-rich white matter regions were lower at 7 T than at 3 T, and higher in iron-rich structures. Adjusting the T2 compartment boundaries was required due to the shorter T2 relaxation times at 7 T. Shorter echo spacing would better sample the fast decaying signal but would increase peripheral nerve stimulation. Multi-channel transmission will improve T2 measurements at 7 T. We used a multi-echo 3D GraSE sequence to characterize the multi-exponential T2 decay at 7 T. We adapted T2 parameters for evaluation of the short T2 fraction. Obtained 7 T multi-component T2 maps were in good agreement with 3 T data.

Associations Between Findings From Myelin Water Imaging and Cognitive Performance Among Individuals With Multiple Sclerosis

Cognitive impairment is a debilitating symptom of multiple sclerosis (MS) that affects up to 70% of patients. An improved understanding of the underlying pathology of MS-related cognitive impairment would provide considerable benefit to patients and clinicians. To determine whether there is an association between myelin damage in tissue that appears completely normal on standard clinical imaging, but can be detected by myelin water imaging (MWI), with cognitive performance in MS. In this cross-sectional study, participants with MS and controls underwent cognitive testing and magnetic resonance imaging (MRI) from August 23, 2017, to February 20, 2019. Participants were recruited through the University of British Columbia Hospital MS clinic and via online recruitment advertisements on local health authority websites. Cognitive testing was performed in the MS clinic, and MRI was performed at the adjacent academic research neuroimaging center. Seventy-three participants with clinically definite MS fulfilling the 2017 revised McDonald criteria for diagnosis and 22 age-, sex-, and education-matched healthy volunteers without neurological disease were included in the study. Data analysis was performed from March to November 2019. MWI was performed at 3 T with a 48-echo, 3-dimensional, gradient and spin-echo (GRASE) sequence. Cognitive testing was performed with assessments drawn from cognitive batteries validated for use in MS. The association between myelin water measures, a measurement of the T2 relaxation signal from water in the myelin bilayers providing a specific marker for myelin, and cognitive test scores was assessed using Pearson correlation. Three white matter regions of interest-the cingulum, superior longitudinal fasciculus (SLF), and corpus callosum-were selected a priori according to their known involvement in MS-related cognitive impairment. For the 95 total participants, the mean (SD) age was 49.33 (11.44) years. The mean (SD) age was 50.2 (10.7) years for the 73 participants with MS and 46.4 (13.5) for the 22 controls. Forty-eight participants with MS (66%) and 14 controls (64%) were women. The mean (SD) years of education were 14.7 (2.2) for patients and 15.8 (2.5) years for controls. In MS, significant associations were observed between myelin water measures and scores on the Symbol Digit Modalities Test (SLF, r = -0.490; 95% CI, -0.697 to -0.284; P < .001; corpus callosum, r = -0.471; 95% CI, -0.680 to -0.262; P < .001; and cingulum, r = -0.419; 95% CI, -0.634 to -0.205; P < .001), Selective Reminding Test (SLF, r = -0.444; 95% CI, -0.660 to -0.217; P < .001; corpus callosum, r = -0.411; 95% CI, -0.630 to -0.181; P = .001; and cingulum, r = -0.361; 95% CI, -0.602 to -0.130; P = .003), and Controlled Oral Word Association Test (SLF, r = -0.317; 95% CI, -0.549 to -0.078; P = .01; and cingulum, r = -0.335; 95% CI, -0.658 to -0.113; P = .006). No significant associations were found in controls. This study used MWI to demonstrate that otherwise normal-appearing brain tissue is diffusely damaged in MS, and the findings suggest that myelin water measures are associated with cognitive performance. MWI offers an in vivo biomarker feasible for use in clinical trials investigating cognition, providing a means for monitoring changes in myelination and its association with symptom worsening or improvement.

T2 Relaxation Times at Cardiac MRI in Healthy Adults: A Systematic Review and Meta-Analysis.

Background T2 mapping is an important cardiac MRI technique with applications in various conditions. However, a comprehensive evaluation of the T2 literature for normal values is lacking. Purpose To characterize the ranges of normal values and variability of myocardial T2 relaxation times using a systematic review and meta-analysis of the T2 literature. Materials and Methods PubMed and Cochrane Central were searched from June 2019 to January 2020 for myocardial T2 measurements in healthy adults. Studies quantifying T2 relaxation times conducted at 1.5 T or 3.0 T using gradient and spin-echo (GRASE) or T2-prepared balanced steady-state free precession sequences were included. Summary means were generated using a random-effects model. Subgroup analysis and meta-regression were performed to assess factors causing heterogeneity. Results Of the 2481 articles retrieved, 42 studies were included with 954 healthy adults (mean age, 42.4 years ± 10.5 [standard deviation]; 538 men). The pooled mean of T2 across studies was 52 msec at 1.5 T (95% confidence interval [CI]: 51 msec, 53 msec) and 46 msec at 3.0 T (95% CI: 44 msec, 48 msec) (P ≤ .001). I2 was 98% at 1.5 T and 3.0 T. Meta-regression at 1.5 T and 3.0 T identified vendor (β at 1.5 T = -4 msec [with Philips as reference], P < .001; β at 3.0 T = -5 msec, P = .02) and pulse sequence (β at 1.5 T = -5 msec [with GRASE as reference], P < .001; β at 3.0 T = -6 msec, P = .002) as significant covariates, but it did not identify any association with covariates of age (β at 1.5 T = 0 msec per year, P = .70; β at 3.0 T = 0 msec per year, P = .83) or sex (β at 1.5 T = -1 msec, P = .88; β at 3.0 T = 6 msec, P = .42). Conclusion The pooled mean of T2 relaxation times in healthy adults had marked heterogeneity across studies with field strength, vendor, and pulse sequence identified as covariates associated with T2. T2-prepared measurements were similar between vendors at each field strength. © RSNA, 2020 Online supplemental material is available for this article.