The Experts below are selected from a list of 870 Experts worldwide ranked by ideXlab platform
Yi Wang - One of the best experts on this subject based on the ideXlab platform.
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coronary mr angiography selection of acquisition window of minimal cardiac motion with electrocardiography triggered Navigator cardiac motion prescanning initial results
Radiology, 2001Co-Authors: Yi Wang, Richard Watts, Ian R Mitchell, Thanh D Nguyen, Jeffrey W Bezanson, Geoffrey Bergman, Martin R PrinceAbstract:The authors developed an electrocardiography-triggered M-mode Navigator-Echo technique to help monitor cardiac motion and identify the period of minimal cardiac motion in the cardiac cycle. Coronary magnetic resonance angiography was performed in eight healthy adult volunteers and one patient with heart disease. To minimize cardiac motion effects, trigger delays were estimated with the Navigator-Echo technique and two empirical formulas. The quality of images obtained with the different delay times was compared for clarity of depiction of the coronary arteries. Image quality was best with the delay calculated with the Navigator-Echo technique.
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Navigator Echo based real time respiratory gating and triggering for reduction of respiration effects in three dimensional coronary mr angiography
Radiology, 1996Co-Authors: Yi Wang, Phillip J Rossman, Roger C Grimm, Stephen J Riederer, Richard L EhmanAbstract:PURPOSE: To test the hypothesis that respiration effects in three-dimensional (3D) coronary magnetic resonance (MR) imaging can be reduced with Navigator-Echo-based gating or triggering according to the superior-inferior position of the diaphragm. MATERIALS AND METHODS: Real-time respiratory gating and respiratory triggering (breath hold with feedback) were implemented with Navigator Echoes in a magnetization-prepared, segmented, 3D coronary imaging sequence. The two techniques were first tested with a motion phantom. An imaging protocol that compared real-time respiratory-gated acquisition, real-time respiratory-triggered acquisition, and continuous acquisition was then evaluated in six healthy subjects. RESULTS: Real-time respiratory-gated and respiratory-triggered acquisition were superior to continuous acquisition with two signals averaged (P = .025). The performance of the gated acquisition was about the same as that of the triggered acquisition (P = .05). CONCLUSION: Navigator-Echo-based, real-time ...
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orbital Navigator Echoes for motion measurements in magnetic resonance imaging
Magnetic Resonance in Medicine, 1995Co-Authors: Yi Wang, Joel P Felmlee, Phillip J Rossman, Roger C Grimm, Stephen J Riederer, Richard L EhmanAbstract:A single "orbital" Navigator Echo, that has a circular k-space trajectory, is used to simultaneously measure in-plane rotational and multi-axis translational global motion. Rotation is determined from the shift in the magnitude profile of the Echo with respect to a reference Echo. Displacements are calculated from the phase difference between the current Echo and a reference Echo. Phantom studies show that this technique can accurately measure rotation and translations. Preliminary results from adaptive motion correction studies on phantom and human subjects indicate that the orbital Navigator Echo is an effective method for motion measurement in MRI.
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3d coronary mr angiography in multiple breath holds using a respiratory feedback monitor
Magnetic Resonance in Medicine, 1995Co-Authors: Yi Wang, Phillip J Rossman, Roger C Grimm, Stephen J Riederer, Josef P Debbins, Richard L EhmanAbstract:To reduce respiratory blur and ghosts in 3D coronary imaging, a data acquisition scheme using consistent multiple breath-holds was implemented. A Navigator Echo was acquired and processed in real time to dynamically measure diaphragm position. This information was provided as a visual prompt to the patient to maintain consistency in breath-hold levels such that the variation range of diastolic heart position was less than 2 mm. Preliminary results indicate that this multiple breath-hold acquisition scheme, compared with acquisition under respiration, can significantly reduce blur and ghost artifacts in 3D coronary imaging.
Richard L Ehman - One of the best experts on this subject based on the ideXlab platform.
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Navigator Echo based real time respiratory gating and triggering for reduction of respiration effects in three dimensional coronary mr angiography
Radiology, 1996Co-Authors: Yi Wang, Phillip J Rossman, Roger C Grimm, Stephen J Riederer, Richard L EhmanAbstract:PURPOSE: To test the hypothesis that respiration effects in three-dimensional (3D) coronary magnetic resonance (MR) imaging can be reduced with Navigator-Echo-based gating or triggering according to the superior-inferior position of the diaphragm. MATERIALS AND METHODS: Real-time respiratory gating and respiratory triggering (breath hold with feedback) were implemented with Navigator Echoes in a magnetization-prepared, segmented, 3D coronary imaging sequence. The two techniques were first tested with a motion phantom. An imaging protocol that compared real-time respiratory-gated acquisition, real-time respiratory-triggered acquisition, and continuous acquisition was then evaluated in six healthy subjects. RESULTS: Real-time respiratory-gated and respiratory-triggered acquisition were superior to continuous acquisition with two signals averaged (P = .025). The performance of the gated acquisition was about the same as that of the triggered acquisition (P = .05). CONCLUSION: Navigator-Echo-based, real-time ...
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orbital Navigator Echoes for motion measurements in magnetic resonance imaging
Magnetic Resonance in Medicine, 1995Co-Authors: Yi Wang, Joel P Felmlee, Phillip J Rossman, Roger C Grimm, Stephen J Riederer, Richard L EhmanAbstract:A single "orbital" Navigator Echo, that has a circular k-space trajectory, is used to simultaneously measure in-plane rotational and multi-axis translational global motion. Rotation is determined from the shift in the magnitude profile of the Echo with respect to a reference Echo. Displacements are calculated from the phase difference between the current Echo and a reference Echo. Phantom studies show that this technique can accurately measure rotation and translations. Preliminary results from adaptive motion correction studies on phantom and human subjects indicate that the orbital Navigator Echo is an effective method for motion measurement in MRI.
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3d coronary mr angiography in multiple breath holds using a respiratory feedback monitor
Magnetic Resonance in Medicine, 1995Co-Authors: Yi Wang, Phillip J Rossman, Roger C Grimm, Stephen J Riederer, Josef P Debbins, Richard L EhmanAbstract:To reduce respiratory blur and ghosts in 3D coronary imaging, a data acquisition scheme using consistent multiple breath-holds was implemented. A Navigator Echo was acquired and processed in real time to dynamically measure diaphragm position. This information was provided as a visual prompt to the patient to maintain consistency in breath-hold levels such that the variation range of diastolic heart position was less than 2 mm. Preliminary results indicate that this multiple breath-hold acquisition scheme, compared with acquisition under respiration, can significantly reduce blur and ghost artifacts in 3D coronary imaging.
Stephan Achenbach - One of the best experts on this subject based on the ideXlab platform.
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a direct comparison of noninvasive coronary angiography by electron beam tomography and Navigator Echo based magnetic resonance imaging for the detection of restenosis following coronary angioplasty
Investigative Radiology, 2002Co-Authors: Dieter Ropers, W. Moshage, M Regenfus, Werner G. Daniel, Nikolaos I Stilianakis, Susanne Birke, Winfried Kessler, Gerhard Laub, Stephan AchenbachAbstract:Ropers D, Regenfus M, Stilianakis N, et al. A direct comparison of noninvasive coronary angiography by electron beam tomography and Navigator-Echo-based magnetic resonance imaging for the detection of restenosis following coronary angioplasty. Invest Radiol 2002;37:386–392.rationale and objectives.
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usefulness of respiratory gated magnetic resonance coronary angiography in assessing narrowings 50 in diameter in native coronary arteries and in aortocoronary bypass conduits
American Journal of Cardiology, 1997Co-Authors: Winfried Kessler, Stephan Achenbach, W. Moshage, Gerhard Laub, Doris Zink, Randall Kroeker, Wolfgang Nitz, K BachmannAbstract:Abstract Magnetic resonance coronary angiography (MRCA) is a promising method for the assessment of proximal coronary artery stenosis. Conventional 2-dimensional techniques require repetitive breath holds to image multiple sections. This may lead to misregistrations if the respiratory level is not exactly reproduced. In the present study, MRCA was performed using a 3-dimensional approach with Navigator Echo-based respiratory gating. In 73 patients (55 men and 18 women) who were referred for cardiac catheterization, the assessment of significant stenoses (≥50%) was performed in the proximal and midsegments of the coronary arteries after multiplanar reconstruction of the visualized coronary arteries. In addition, in 8 patients with coronary artery bypass grafts the patency of the transplants was evaluated. After withdrawing 8 patients from analysis because of poor image quality, stenosis evaluation was possible in 236 of 455 reviewed coronary segments (52%). In the other 219 cases, either the visualization of the vessel segment was indistinct (30%) or the segment was located outside the imaging volume (18%). In total, 28 of 43 significant coronary stenoses could be correctly identified (65%). Evaluation of bypass graft patency was possible in 7 patients. All 4 occluded and 13 of 15 patent grafts were correctly classified. Thus, respiratory gated MRCA is a feasable method for the assessment of hemodynamically significant coronary stenoses and bypass graft patency. However, technical improvements are mandatory to improve accuracy of the method.
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visualization of the coronary arteries in three dimensional reconstructions using respiratory gated magnetic resonance imaging
Coronary Artery Disease, 1997Co-Authors: Stephan Achenbach, Dieter Ropers, W. Moshage, Winfried Kessler, Doris Zink, Randall Kroeker, Wolfgang Nitz, Gerhardt Laub, K BachmannAbstract:OBJECTIVE To assess the applicability of respiratory-gated magnetic resonance coronary angiography, combined with three-dimensional image reconstruction, for visualizing the coronary arteries. METHODS Twenty subjects (three healthy volunteers and 17 patients without stenoses detected by coronary angiography) were investigated. Magnetic resonance imaging was performed in a 1.5 T scanner using ECG-triggered gradient-Echo sequences to acquire a volume data set consisting of 24-48 contiguous axial cross-sections of the heart (2 mm slice thickness, 1.17 mm x 1.17 mm in-plane resolution). Navigator-Echo-based retrospective respiratory gating was used to minimize respiratory motion artifacts. Three-dimensional reconstructions of the heart were rendered using surface-display techniques. The length of the visualized coronary arteries was measured in curved multiplanar reconstructions. RESULTS In the three-dimensional reconstructions, the left main artery (LMA) and left anterior descending artery (LADA) were visualized in 17 cases, the left circumflex artery (LCXA) in 15, and the right coronary artery (RCA) in 16 cases. Vessel continuity was uninterrupted in all 17 cases for the LMA, in 14 for the LADA, eight for the LCXA, and 13 for the RCA. The mean lengths of the visualized vessels were 14 +/- 7 mm for the LMA, 65 +/- 13 mm for the LADA, 45 +/- 16 mm for the LCXA, and 37 +/- 26 mm for the RCA. Reasons for impaired visibility of the LCXA and RCA were poor image quality due to there being a low contrast:noise ratio, motion artifacts, and incomplete coverage by the imaging volume. CONCLUSIONS Navigator-Echo-based magnetic resonance imaging is a promising technique for investigating the coronary arteries. Acquisition of a volume data set permits three-dimensional displays of the coronary vessels.
John N Oshinski - One of the best experts on this subject based on the ideXlab platform.
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demonstration of circumferential heterogeneity in displacement and strain in the abdominal aortic wall by spiral cine dense mri
Journal of Magnetic Resonance Imaging, 2019Co-Authors: Elizabeth Iffrig, John S Wilson, Xiadong Zhong, John N OshinskiAbstract:Background Knowledge of tissue properties of the abdominal aorta can improve understanding of vascular disease and guide interventional approaches. Existing MRI methods to quantify aortic wall displacement and strain are unable to discern circumferential heterogeneity. Purpose To assess regional variation in abdominal aortic wall displacement and strain as a function of circumferential position using spiral cine displacement encoding with stimulated Echoes (DENSE). Study type Prospective. Population Cardiovascular disease-free men (n = 8) and women (n = 9) ages 30-42. Sequences Prospective electrocardiogram (ECG)-gated and Navigator Echo-gated spiral, cine 2D DENSE and retrospective ECG-gated phase contrast MR (PCMR) sequences at 3T. Assessment In-plane displacement values of the aortic wall acquired with DENSE were used to determine radial and circumferential aortic wall motion. A quadrilateral-based 2D strain calculation method was implemented to determine strain from the displacement field. Peak displacement and its radial and circumferential contributions as well as peak circumferential strain were compared among eight circumferential wall segments. Distensibility was calculated using PCMR and compared with homogenized circumferential strain. Statistical tests To account for repeated measurements in volunteers, linear mixed models for mean sector values were created for displacement magnitude, circumferential displacement, radial displacement, and circumferential strain. Comparisons were made between sectors. Calculated distensibility and homogenized circumferential strain were compared using Bland-Altman analysis. Statistical significance was defined as P Results Displacement was highest in the anterior wall (1.5 ± 0.7 mm) and was primarily in the radial as compared with circumferential direction (1.04 ± 0.05 mm vs. 0.81 ± 0.42 mm). Circumferential strain was highest in the lateral walls (left 0.16 ± 0.05 and right 0.21 ± 0.12) with homogenized circumferential strain of 0.14 ± 0.05. Data conclusion DENSE imaging in the abdominal aortic wall demonstrated that the anterior aortic wall exhibits the greatest displacement, while the lateral wall experiences the largest circumferential strain. Level of evidence 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:731-743.
Robert Frost - One of the best experts on this subject based on the ideXlab platform.
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Navigator based reacquisition and estimation of motion corrupted data application to multi Echo spin Echo for carotid wall mri
Magnetic Resonance in Medicine, 2020Co-Authors: Robert Frost, Luca Biasiolli, Katherine Hurst, Mohammad Alkhalil, Robin P Choudhury, Matthew D Robson, Aaron T Hess, Peter JezzardAbstract:Purpose To assess whether artifacts in multi-slice multi-Echo spin Echo neck imaging, thought to be caused by brief motion events such as swallowing, can be corrected by reacquiring corrupted central k-space data and estimating the remainder with parallel imaging. Methods A single phase-encode line (ky = 0, phase-encode direction anteroposterior) Navigator Echo was used to identify motion-corrupted data and guide the online reacquisition. If motion corruption was detected in the 7 central k-space lines, they were replaced with reacquired data. Subsequently, GRAPPA reconstruction was trained on the updated central portion of k-space and then used to estimate the remaining motion-corrupted k-space data from surrounding uncorrupted data. Similar compressed sensing-based approaches have been used previously to compensate for respiration in cardiac imaging. The g-factor noise amplification was calculated for the parallel imaging reconstruction of data acquired with a 10-channel neck coil. The method was assessed in scans with 9 volunteers and 12 patients. Results The g-factor analysis showed that GRAPPA reconstruction of 2 adjacent motion-corrupted lines causes high noise amplification; therefore, the number of 2-line estimations should be limited. In volunteer scans, median ghosting reduction of 24% was achieved with 2 adjacent motion-corrupted lines correction, and image quality was improved in 2 patient scans that had motion corruption close to the center of k-space. Conclusion Motion-corrupted Echo-trains can be identified with a Navigator Echo. Combined reacquisition and parallel imaging estimation reduced motion artifacts in multi-slice MESE when there were brief motion events, especially when motion corruption was close to the center of k-space.
