Search

Your search keyword '"Zhang, Shelley HuaLei"' showing total 9 results
Start Over Author "Zhang, Shelley HuaLei"
9 results on '"Zhang, Shelley HuaLei"'

6. Gradient-Induced Voltages on 12-Lead ECGs during High Duty-Cycle MRI Sequences and a Method for Their Removal considering Linear and Concomitant Gradient Terms

Author

Zhang, Shelley HuaLei, Ho Tse, Zion Tsz, Dumoulin, Charles L., Kwong, Raymond Y., Stevenson, William G., Watkins, Ronald, Ward, Jay, Wang, Wei, and Schmidt, Ehud J.

Subjects
Adult, Male, Models, Statistical, Cardiac-Gated Imaging Techniques, Reproducibility of Results, Middle Aged, Magnetic Resonance Imaging, Article, Healthy Volunteers, Electrocardiography, Image Processing, Computer-Assisted, Linear Models, Humans, Artifacts, Electrodes, Algorithms
Abstract

To restore 12-lead electrocardiographic (ECG) signal fidelity inside MRI by removing magnetic field gradient-induced voltages during high gradient duty cycle sequences.A theoretical equation was derived to provide first- and second-order electrical fields induced at individual ECG electrodes as a function of gradient fields. Experiments were performed at 3T on healthy volunteers using a customized acquisition system that captured the full amplitude and frequency response of ECGs, or a commercial recording system. The 19 equation coefficients were derived via linear regression of data from accelerated sequences and were used to compute induced voltages in real-time during full resolution sequences to remove ECG artifacts. Restored traces were evaluated relative to ones acquired without imaging.Measured induced voltages were 0.7 V peak-to-peak during balanced steady state free precession (bSSFP) with the heart at the isocenter. Applying the equation during gradient echo sequencing, three-dimensional fast spin echo, and multislice bSSFP imaging restored nonsaturated traces and second-order concomitant terms showed larger contributions in electrodes further from the magnet isocenter. Equation coefficients are evaluated with high repeatability (ρ = 0.996) and are dependent on subject, sequence, and slice orientation.Close agreement between theoretical and measured gradient-induced voltages allowed for real-time removal. Prospective estimation of sequence periods in which large induced voltages occur may allow hardware removal of these signals.

Published
2015

7. Myocardial perfusion quantification using simultaneously acquired 13NH3‐ammonia PET and dynamic contrast‐enhanced MRI in patients at rest and stress.

Author

Kunze, Karl P., Nekolla, Stephan G., Rischpler, Christoph, Zhang, Shelley HuaLei, Hayes, Carmel, Langwieser, Nicolas, Ibrahim, Tareq, Laugwitz, Karl‐Ludwig, and Schwaiger, Markus

Abstract

Purpose: Systematic differences with respect to myocardial perfusion quantification exist between DCE‐MRI and PET. Using the potential of integrated PET/MRI, this study was conceived to compare perfusion quantification on the basis of simultaneously acquired 13NH3‐ammonia PET and DCE‐MRI data in patients at rest and stress. Methods: Twenty‐nine patients were examined on a 3T PET/MRI scanner. DCE‐MRI was implemented in dual‐sequence design and additional T1 mapping for signal normalization. Four different deconvolution methods including a modified version of the Fermi technique were compared against 13NH3‐ammonia results. Results: Cohort‐average flow comparison yielded higher resting flows for DCE‐MRI than for PET and, therefore, significantly lower DCE‐MRI perfusion ratios under the common assumption of equal arterial and tissue hematocrit. Absolute flow values were strongly correlated in both slice‐average (R2 = 0.82) and regional (R2 = 0.7) evaluations. Different DCE‐MRI deconvolution methods yielded similar flow result with exception of an unconstrained Fermi method exhibiting outliers at high flows when compared with PET. Conclusion: Thresholds for Ischemia classification may not be directly tradable between PET and MRI flow values. Differences in perfusion ratios between PET and DCE‐MRI may be lifted by using stress/rest‐specific hematocrit conversion. Proper physiological constraints are advised in model‐constrained deconvolution. [ABSTRACT FROM AUTHOR]

Published
2018
Full Text
View/download PDF

9. Myocardial perfusion quantification using simultaneously acquired 13 NH 3 -ammonia PET and dynamic contrast-enhanced MRI in patients at rest and stress.

Author

Kunze KP, Nekolla SG, Rischpler C, Zhang SH, Hayes C, Langwieser N, Ibrahim T, Laugwitz KL, and Schwaiger M

Subjects
Aged, Ammonia chemistry, Blood Flow Velocity, Contrast Media, Coronary Circulation, Exercise Test, Female, Humans, Image Interpretation, Computer-Assisted methods, Image Processing, Computer-Assisted, Male, Middle Aged, Motion, Tomography, X-Ray Computed, Magnetic Resonance Imaging, Myocardial Perfusion Imaging, Positron-Emission Tomography
Abstract

Purpose: Systematic differences with respect to myocardial perfusion quantification exist between DCE-MRI and PET. Using the potential of integrated PET/MRI, this study was conceived to compare perfusion quantification on the basis of simultaneously acquired 13 NH 3 -ammonia PET and DCE-MRI data in patients at rest and stress., Methods: Twenty-nine patients were examined on a 3T PET/MRI scanner. DCE-MRI was implemented in dual-sequence design and additional T 1 mapping for signal normalization. Four different deconvolution methods including a modified version of the Fermi technique were compared against 13 NH 3 -ammonia results., Results: Cohort-average flow comparison yielded higher resting flows for DCE-MRI than for PET and, therefore, significantly lower DCE-MRI perfusion ratios under the common assumption of equal arterial and tissue hematocrit. Absolute flow values were strongly correlated in both slice-average (R 2  = 0.82) and regional (R 2  = 0.7) evaluations. Different DCE-MRI deconvolution methods yielded similar flow result with exception of an unconstrained Fermi method exhibiting outliers at high flows when compared with PET., Conclusion: Thresholds for Ischemia classification may not be directly tradable between PET and MRI flow values. Differences in perfusion ratios between PET and DCE-MRI may be lifted by using stress/rest-specific hematocrit conversion. Proper physiological constraints are advised in model-constrained deconvolution., (© 2018 International Society for Magnetic Resonance in Medicine.)

Published
2018
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results