Contribution of the multi-echo approach in accelerated functional magnetic resonance imaging multiband acquisition.
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ABSTRACT:
SUBMITTER: Kovarova A
PROVIDER: S-EPMC8764472 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:ObjectivesTo apply the MB (multiband) excitation and blipped-CAIPI (blipped-controlled aliasing in parallel imaging) techniques in a spin and gradient-echo (SAGE) EPI sequence to improve the slice coverage for vessel architecture imaging (VAI).Materials and methodsBoth MB excitation and blipped-CAIPI with in-plane parallel imaging were incorporated into a gradient-echo (GE)/spin-echo (SE) EPI sequence for simultaneous tracking of the dynamic MR signal changes in both GE and SE contrasts after the injection of contrast agent. MB and singleband (SB) excitation were compared using a 20-channel head coil at 3 Tesla, and high-resolution MB VAI could be performed in 32 glioma patients.ResultsWhole-brain covered high resolution VAI can be achieved after applying multiband excitation with a factor of 2 and in-plane parallel imaging with a factor of 3. The quality of the images resulting from MB acceleration was comparable to those from the SB method: images were reconstructed without any loss of spatial resolution or severe distortions. In addition, MB and SB signal-to-noise ratios (SNR) were similar. A relative low g-factor induced from the MB acceleration method was achieved after using a blipped-CAIPI technique (1.35 for GE and 1.33 for SE imaging). Performing quantitative VAI, we found that, among all VAI parametric maps, microvessel type indicator (MTI), distance map (I) and vascular-induced bolus peak-time shift (VIPS) were highly correlated. Likewise, VAI parametric maps of slope, slope length and short axis were highly correlated.ConclusionsMultiband accelerated SAGE successfully doubles the number of readout slices in the same measurement time when compared to conventional readout sequences. The corresponding VAI parametric maps provide insights into the complexity and heterogeneity of vascular changes in glioma.
| S-EPMC6688807 | biostudies-literature
Project description:Dynamic contrast-enhanced quantitative first-pass perfusion using magnetic resonance imaging enables non-invasive objective assessment of myocardial ischemia without ionizing radiation. However, quantification of perfusion is challenging due to the non-linearity between the magnetic resonance signal intensity and contrast agent concentration. Furthermore, respiratory motion during data acquisition precludes quantification of perfusion. While motion correction techniques have been proposed, they have been hampered by the challenge of accounting for dramatic contrast changes during the bolus and long execution times. In this work we investigate the use of a novel free-breathing multi-echo Dixon technique for quantitative myocardial perfusion. The Dixon fat images, unaffected by the dynamic contrast-enhancement, are used to efficiently estimate rigid-body respiratory motion and the computed transformations are applied to the corresponding diagnostic water images. This is followed by a second non-linear correction step using the Dixon water images to remove residual motion. The proposed Dixon motion correction technique was compared to the state-of-the-art technique (spatiotemporal based registration). We demonstrate that the proposed method performs comparably to the state-of-the-art but is significantly faster to execute. Furthermore, the proposed technique can be used to correct for the decay of signal due to T2* effects to improve quantification and additionally, yields fat-free diagnostic images.
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Project description:AimsThe aim of the study was to assess the feasibility and accuracy of an integrated stress imaging algorithm with echo first and second-line Cardiac Magnetic Resonance (CMR) in selected cases. Stress echo (SE) is widely used for non-invasive diagnosis of coronary artery disease (CAD), but difficult patients and ambiguous responses may be met even with top-level technology and expertise. CMR might ideally complement SE in well-selected cases with unfeasible and/or ambiguous and/or submaximal results.Methods and results152 in-hospital patients with chest pain and normal baseline function were referred for SE and coronary angiography. Of the initial population, 33 were shunted to CMR due to poor acoustic window or ambiguous or submaximal SE test. The only criterion of positivity for both techniques was the presence of regional wall motion abnormalities in at least 2 contiguous segments. Coronary angiography was performed independently of test results. Significant CAD was identified by a >50% quantitatively assessed diameter reduction in at least 1 major coronary vessel.CAD was present in 88 patients. Interpretable and diagnostic stress test were obtained in 143 patients with the sequential algorithm. The sequential (SE in 110 + CMR in 33 patients) algorithm showed a sensitivity of 76% (95% CI 66% to 85%) specificity of 87% (95% CI 76% to 95%) and accuracy of 80% (95% CI 73% to 86%).ConclusionA sequential functional stress imaging algorithm with stress echo first and stress CMR in selected cases is feasible, clinically realistic and allows an efficient, radiation-free diagnosis of CAD.
| S-EPMC2262078 | biostudies-literature
Project description:PURPOSE:Diffusion spectrum imaging (DSI) provides us non-invasively and robustly with anatomical details of brain microstructure. To achieve sufficient angular resolution, DSI requires a large number of q-space samples, leading to long acquisition times. This need is mitigated here by combining the beneficial properties of Radial q-space sampling for DSI with a Multi-Echo Stimulated Echo Sequence (MESTIM). METHODS:Full 2D k-spaces for each of several q-space samples, along the same radially outward line in q-space, are acquired in one readout train with one spin and three stimulated echoes. RF flip angles are carefully chosen to distribute spin magnetization over the echoes and the DSI reconstruction is adapted to account for differences in diffusion time among echoes. RESULTS:Individual datasets and bootstrapped reproducibility analysis demonstrate image quality and SNR of the more-than-twofold-accelerated RDSI MESTIM sequence. Orientation distribution functions (ODF) and tractography results benefit from the longer diffusion times of the latter echoes in the echo train. CONCLUSION:A MESTIM sequence can be used to shorten RDSI acquisition times significantly without loss of image or ODF quality. Further acceleration is possible by combination with simultaneous multi-slice techniques. Magn Reson Med 79:306-316, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
| S-EPMC5623607 | biostudies-literature
Project description:BackgroundMagnetic resonance elastography (MRE) is an imaging technique that can noninvasively assess the shear properties of the intervertebral disc (IVD). Unlike the standard gradient recalled echo (GRE) MRE technique, a spin-echo echo-planar imaging (SE-EPI) sequence has the potential to improve imaging efficiency and patient compliance.PurposeTo validate the use of an SE-EPI sequence for MRE of the IVD compared against the standard GRE sequence.Study typeCross-over.SubjectsTwenty-eight healthy volunteers (15 males and 13 females, age range: 19-55).Field strength/sequence3 T; GRE, SE-EPI with breath holds (SE-EPI-BH) and SE-EPI with free breathing (SE-EPI-FB) MRE sequences.AssessmentMRE-derived shear stiffnesses were calculated via principal frequency analysis. SE-EPI derived shear stiffness and octahedral shear strain signal-to-noise ratios (OSS-SNR) were compared against those derived using the GRE sequence. The reproducibility and repeatability of SE-EPI stiffness measurements were determined. Shear stiffness was evaluated in the nucleus pulposus (NP) and annulus fibrosus (AF) regions of the disc. Scan times between sequences were compared.Statistical testsLinear mixed models, Bland-Altman plots, and Lin's concordance correlation coefficients (CCCs) were used with P < 0.05 considered statistically significant.ResultsGood correlation was observed between shear stiffnesses derived from the SE-EPI sequences with those derived from the GRE sequence with CCC values greater than 0.73 and 0.78 for the NP and AF regions, respectively. OSS-SNR was not significantly different between GRE and SE-EPI sequences (P > 0.05). SE-EPI sequences generated highly reproducible and repeatable stiffness measurements with CCC values greater than 0.97 in the NP and AF regions and reduced scan time by at least 51% compared to GRE. SE-EPI-BH and SE-EPI-FB stiffness measurements were similar with CCC values greater than 0.98 for both regions.Data conclusionSE-EPI-based MRE-derived stiffnesses were highly reproducible and repeatable and correlated with current standard GRE MRE-derived stiffness estimates while reducing scan times.Level of evidence1 TECHNICAL EFFICACY STAGE: 1.
| S-EPMC9475395 | biostudies-literature
Project description:BACKGROUND:To study gradient recalled echo (GRE) T2*-weighted imaging (T2*WI) for normal pancreas and acute pancreatitis (AP). METHODS:Fifty-one patients without any pancreatic disorders (control group) and 117 patients with AP were recruited. T2* values derived from T2*WI of the pancreas were measured for the two groups. The severity of AP was graded by the magnetic resonance severity index (MRSI) and the Acute Physiology and Chronic Healthy Evaluation II (APACHE II) scoring system. Logistic regression was used to analyze the relationship between the T2* values and AP severity. The usefulness of the T2* value for diagnosing AP and the relationship between the T2* values and the severity of AP were analyzed. RESULTS:On GRE-T2*WI, the normal pancreas showed a well-marinated and consistently homogeneous isointensity. Edematous AP, as well as the non-necrotic area in necrotizing AP, showed ill-defined but homogeneous signal intensity. AP with pancreatic hemorrhage showed a decreased T2* value and a signal loss on the signal decay curve. The T2* value of pancreas in the AP group was higher than that of the control group (t=-8.20, P<0.05). The T2* value tended to increase along with the increase in MRSI scores but not with the APACHE II scores (P>0.05). AP was associated with a one standard deviation increment in the T2* value (OR =1.37; 95% CI: 1.216-1.532). CONCLUSIONS:T2*WI demonstrates a few characteristics of the normal pancreas and AP, which could potentially be helpful for detecting hemorrhage, and contributes to diagnosing AP and its severity.
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Project description:The characterization of individual functional brain organization with Precision Functional Mapping has provided important insights in recent years in adults. However, little is known about the ontogeny of inter-individual differences in brain functional organization during human development, but precise characterization of systems organization during periods of high plasticity might be most influential towards discoveries promoting lifelong health. Collecting and analyzing precision fMRI data during early development has unique challenges and emphasizes the importance of novel methods to improve data acquisition, processing, and analysis strategies in infant samples. Here, we investigate the applicability of two such methods from adult MRI research, multi-echo (ME) data acquisition and thermal noise removal with Noise reduction with distribution corrected principal component analysis (NORDIC), in precision fMRI data from three newborn infants. Compared to an adult example subject, T2* relaxation times calculated from ME data in infants were longer and more variable across the brain, pointing towards ME acquisition being a promising tool for optimizing developmental fMRI. The application of thermal denoising via NORDIC increased tSNR and the overall strength of functional connections as well as the split-half reliability of functional connectivity matrices in infant ME data. While our findings related to NORDIC denoising are coherent with the adult literature and ME data acquisition showed high promise, its application in developmental samples needs further investigation. The present work reveals gaps in our understanding of the best techniques for developmental brain imaging and highlights the need for further developmentally-specific methodological advances and optimizations, towards precision functional imaging in infants.
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Project description:PurposeMagnetic resonance imaging (MRI) can provide unique information about extraocular muscle (EOM) structure and function. Previous high-resolution motility imaging studies used T1 weighting, which provides intrinsic contrast of dark-appearing EOMs against bright orbital fat and is suitable for intravenous contrast. However, time-consuming T1 sequences are subject to motion artifacts. We evaluated an alternative T2-weighted fast spin-echo pulse sequence that emphasizes tissue-free fluid.MethodsWe prospectively used high-resolution, surface coil technique for orbital MRI at 1.5T in 21 orthotropic and 113 living strabismic subjects and 2 monkey cadavers by using T2 fast spin-echo (T2FSE) weighting (long repetition time, short echo time). T2FSE was compared with T1 in 17 subjects, and with T1 in 506 different living subjects, and 12 cadavers.ResultsFor 2 mm thick coronal MRIs of 312 μm resolution spanning the entire orbit, T1 acquisition required 218 seconds, whereas T2FSE required 150 seconds (31% faster). T2-defined the globe border better, and provided intrinsic contrast between EOMs and their pulleys. Although both T1 and T2 demonstrated motor nerves to EOMs in living subjects, only T1 was satisfactory with injected contrast and in cadavers.ConclusionsFor motility imaging, T2FSE is faster than T1 MRI and demonstrates superior tissue details of EOMs and other orbital tissues. T2FSE of the orbits can be performed by the use of widely available standard equipment. We suggest that T2FSE be the preferred method for clinical imaging of EOM structure, function, and innervation, although T1 may be more appropriate when intravenous contrast must be used.
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Project description:Self-supervised learning has shown great promise because of its ability to train deep learning (DL) magnetic resonance imaging (MRI) reconstruction methods without fully sampled data. Current self-supervised learning methods for physics-guided reconstruction networks split acquired undersampled data into two disjoint sets, where one is used for data consistency (DC) in the unrolled network, while the other is used to define the training loss. In this study, we propose an improved self-supervised learning strategy that more efficiently uses the acquired data to train a physics-guided reconstruction network without a database of fully sampled data. The proposed multi-mask self-supervised learning via data undersampling (SSDU) applies a holdout masking operation on the acquired measurements to split them into multiple pairs of disjoint sets for each training sample, while using one of these pairs for DC units and the other for defining loss, thereby more efficiently using the undersampled data. Multi-mask SSDU is applied on fully sampled 3D knee and prospectively undersampled 3D brain MRI datasets, for various acceleration rates and patterns, and compared with the parallel imaging method, CG-SENSE, and single-mask SSDU DL-MRI, as well as supervised DL-MRI when fully sampled data are available. The results on knee MRI show that the proposed multi-mask SSDU outperforms SSDU and performs as well as supervised DL-MRI. A clinical reader study further ranks the multi-mask SSDU higher than supervised DL-MRI in terms of signal-to-noise ratio and aliasing artifacts. Results on brain MRI show that multi-mask SSDU achieves better reconstruction quality compared with SSDU. The reader study demonstrates that multi-mask SSDU at R = 8 significantly improves reconstruction compared with single-mask SSDU at R = 8, as well as CG-SENSE at R = 2.
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Project description:This pilot study tests the feasibility of rapid carotid MR angiography using the liver acquisition with volume acceleration-flex technique (LAVA MRA). Seven healthy volunteers and 21 consecutive patients suspected of carotid stenosis underwent LAVA and conventional time-of-flight (cTOF) MRAs. Artery-to-fat and artery-to-muscle signal intensity ratios were manually measured. LAVA MRA exhibited a significantly larger artery-to-fat signal intensity ratio compared with cTOF MRA in all slices (P < 0.001) and exhibited a larger (P < 0.001) or equivalent (P = 1.0) artery-to-muscle signal intensity ratio in the extracranial carotid arteries. The image quality of the cervical carotid bifurcation and the signal change on each MRA were visually assessed and compared among the MRAs. There was no significant difference between the two MRAs in visual assessment. LAVA MRA can provide visualization similar to cTOF MRA in the evaluation of the cervical carotid bifurcation while reducing scan time by one-fifth.
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