My research is focused on sequence design for MRS and MRI in human brain at 9.4T, aiming to tackle technical challenges introduced by the ultra-high field and therefore improve image quality and produce reliable image information for clinical diagnosis.
Parallel transmit spectral-spatial pulse design for ultra-high field MRS
Ultra high field MRI benefits 1H magnetic resonance spectroscopy (MRS) applications by offering increased chemical shift dispersion, improved SNR and reduced J-coupling, but also raises technical challenges such as shortened T2 and T2* relaxation times, severe chemical shift displacement artifacts and signal disuniformity due to high spatial B1+ field inhomogeneity. In this work, a parallel transmission based pulse design method that combines subspace preconditioned least squares optimization (LSQR) and optimal control (OC) approaches is proposed to achieve spectral-spatial pulses (SPSP) that tackle aforementioned technical challenges in ultra-high field 1H MRS.
Fig1 Transverse (a, c) and cut-away (b, d) views of the spectral-spatial saturation profiles (|Mxy|) of spatially selective excitation pulses designed by (a, b) using the LSQR method only, and (c, d) using the LSQR and OC methods in a combined manner.
Systematic investigation of influence factor on parallel transmit pulse performance
The parallel transmission technique helps to improve excitation uniformity and enables acceleration of related parallel transmit radiofrequency pulses in ultra-high field MRI. However, the overall performance of parallel transmission relates not only to the pulse design method and the specific arrangement of the transmit coil array, but is also influenced by several hardware and software imperfections. In this work, we systematically investigate the factors that could pose negative influence on the transmit pulse performance, including B1 mapping inaccuracy, B0 inhomogeneity, RF hardware and gradient hardware imperfection.
Fig 2 (a) Comparison of measured (blue) and theoretically designed (pink) k-space trajectory. (b) Measured (blue) and theoretically designed (pink) RF pulse shapes compared in two different voltage levels (upper row: 0~120V, lower row: 0~16V). (c) In vivo measured excitation profile (a vertical MPI figure shape) achieved by pulse designed by using B1 map acquired from AFI-corrected pre-conditioned TurboFLASH, with RF pulse delay calibration and consideration of k-space trajectory deviations.
Optimized transmit pulses for excellent whole-brain excitation homogeneity in high field MRI
Homogeneous whole-brain excitation is increasingly required in high field fMRI applications. To achieve homogeneous whole-brain coverage, we propose here an optimized 3D tailored RF (TRF) pulse for compensation of the severe RF field (B1) inhomogeneity, based on the recently developed parallel transmission technique. The RF pulse is designed with optimized stack-spiral trajectory tailored to fit into the high-weight k-space area that is most responsible for the desired excitation pattern. The feature of this pulsing approach is that it produces optimized pulses that provide homogeneous excitation over the entire brain volume with shortened pulse duration and peak RF energy.
Fig 3 ) Cut-away (a & c, on the plane y=0) and transverse (b & d, on the oblique plane shown as the gray line in a) views of (a, b) the overall sensitivity map of an 8-channel array over the head part of virtual human data, and (c, d) the simulation result of excitation profile driven by the designed pulse sequence.
11.2012 - now Postdoctoral Fellow, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
2.2008 - 9.2012 PhD in Biomedical Engineering, College of Biomedical Engineering &Instrument Science, Zhejiang University, China
9.2009 - 3.2010 Visiting student, School of Information Technology & Electrical Engineering, The University of Queensland, Australia
9.2006 - 1.2008 Master of Electromagnetic Fields & Micro-Wave Technology, College of Information Science and Engineering, Zhejiang University, China
9.2000 - 6.2005 Bachelor of Biomedical Engineering, College of Biomedical Engineering &Instrument Science, Zhejiang University, China
Shao T, Xia L, Liu F, and Crozier S (May-2012), Advanced Three-dimensional Tailored RF Pulse Design in Volumetric Selective Parallel Excitation, Medical Imaging, IEEE Transaction on, 31(5), 997-1007.
Chi J, Liu F, Xia L, Shao T, and Crozier S (Feb-2011), An Improved Cylindrical FDTD Algorithm and Its Application to Field-Tissue Interaction Study in MRI, Magnetics, IEEE Transactions on , 47(2), 466-470.
Xia L, Shao T, Liu F (Dec-2011), A design method of 3D selective excitation sequence in MRI, CN Patent CN102283649A.
Xia L, Shao T, Liu F (Dec-2011), An MRI excitation pulse sequence generator, CN Patent CN102288929A.
Shao T, Zhang Y, Avdievich N, Glaser S, Henning A (June-2015), A parallel transmit spectral-spatial pulse design method for ultra-high field MRS combining LSQR and optimal control based optimization, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Ontario, Canada
Shao T, Avdievich N, Chang YC, Hoffmann J, Scheffler K, Henning A (June-2015), Systematic investigation of influence factor on parallel transmit pulse performance at 9.4 Tesla, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Ontario, Canada
Hoffmann J, Shajan G, Mirkes C, Shao T, Henning A, Pohmann R, Scheffler K (June-2015), Towards routine application of dynamic parallel transmission for whole-brain imaging at 9.4 Tesla, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Ontario, Canada
Giapitzakis IA , Shao T, Avdievich N, Kreis R and Henning A (May-2014): Optimisation of Asymmetric Adiabatic Pulses for Single Voxel Metabolite Cycled 1H-MRS in the Human Brain at 9.4 Tesla, Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2014), Milano, Italy.
Shao T, Xia L, Liu F, and Crozier S (May-2012), Optimized transmit pulses for excellent whole-brain excitation homogeneity in high field MRI, in Proceedings of the 20th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2012), Melbourne, Victoria, Australia.
Xia L, Shao T, Zhu M, Shou G, Liu F, and Crozier S (May-2011),Accounting for B1 void using optimized transmit pulses in ultra high field MRI, 19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011), Montréal, Quebec, Canada.
Shao T, Zhu M, Xia L, Liu F (May-2011), Optimized slab selective parallel RF excitation at ultra high field, 5th International Conference on Bioinformatics and Biomedical Engineering (iCBBE 2011), Wuhan, China.