Presentation is loading. Please wait.

Presentation is loading. Please wait.

Samy Abo Seada, Joseph V Hajnal and Shaihan J Malik

Published byStella Wilkins Modified over 6 years ago

Similar presentations

Presentation on theme: "Samy Abo Seada, Joseph V Hajnal and Shaihan J Malik"β€” Presentation transcript:

1 Samy Abo Seada, Joseph V Hajnal and Shaihan J Malik
A simple optimization approach to making time efficient VERSE-multiband pulses feasible on non-ideal gradients Samy Abo Seada, Joseph V Hajnal and Shaihan J Malik

2 Motivation Aim Problem: Multiband RF pulses for SMS have long pulse durations [1,2] Solution: Use Time-Optimal VERSE to reduce pulse duration [3] Result: Not suitable for gradient system due to gradient imperfection Our solution: Iterative VERSE optimization with gradient correction Theory VERSE TO-VERSE GIRF-effect Iterative RF-correction Methods Results Simulations Experiment Conclusion A simple optimization approach to making time efficient VERSE-multiband pulses feasible on non-ideal gradients [1] Larkman et al. 2001 [2] Wong E. 2012 [3] Lee et al. 2009

3 Theory (1) - VERSE algorithm
Aim For flip angle πœƒ RF flips Magnetization down by an angle πœƒ and gradient ensures spatial selection Ultimately, net rotation πœƒ determined by angular precession [4] To achieve same signal, preserve net rotation πœƒ. Net rotation preserved if field strengths are halved and played out twice as long Theory VERSE TO-VERSE GIRF-effect πœƒ=πœ” dt Iterative RF-correction Methods Results Simulations Experiment Same net rotation πœƒ Conclusion A simple optimization approach to making time efficient VERSE-multiband pulses feasible on non-ideal gradients [4] Conolly 1988

4 Theory (2) Time Optimal VERSE
Aim Use VERSE to Minimise pulse duration, given System specification [5] Max gradient amplitude, max slew rate, max B1 Theory VERSE TO-VERSE GIRF-effect Iterative RF-correction Methods Results Simulations Experiment Conclusion Define arc-length parameter 𝑠 𝑑 =𝛾 0 𝑑 𝐺 𝜏 π‘‘πœ Excitation profiles preserved if π‘Š 𝑠 = 𝐡 1 𝑠 𝐺(𝑠) = 𝐡 1 𝑣 (𝑠) 𝐺 𝑣 (𝑠) A simple optimization approach to making time efficient VERSE-multiband pulses feasible on non-ideal gradients [5] Lee et al 2009

5 Theory (3) GIRF-effect Aim Previous work: Use VERSE to Minimise pulse duration, given hardware specs Does: Maximum peak RF (13πœ‡π‘‡), Maximum peak Gradient (40 π‘šπ‘‡ π‘š ), Maximum slew-rate (200 π‘šπ‘‡ π‘š π‘šπ‘  ) Does not take into account: Eddy currents, RF/G time-mismatch etc.. A measured Gradient Impulse Response function (GIRF) does! Theory VERSE TO-VERSE GIRF-effect Iterative RF-correction Methods Results Simulations 𝐺 π‘œπ‘’π‘‘ (𝑑)= 𝐺 𝑖𝑛 (𝑑)βˆ—πΊπΌπ‘…πΉ(𝑑) Experiment Conclusion A simple optimization approach to making time efficient VERSE-multiband pulses feasible on non-ideal gradients [6] Vannesjo 2013

6 Theory (3) GIRF-effect Simulated Profiles Gradient after TO-VERSE
RF after TO-VERSE Aim Theory VERSE TO-VERSE GIRF-effect Iterative RF-correction Methods Simulated Profiles Results Simulations Experiment Conclusion A simple optimization approach to making time efficient VERSE-multiband pulses feasible on non-ideal gradients

7 Theory (4) Iterative correction
Aim Holds for But Magnetization experiences Correct by substituting 𝑠 π‘Žπ‘π‘‘ into (1) and find 𝐡 1,π‘Žπ‘π‘‘π‘’π‘Žπ‘™ 𝑣 𝑠 π‘Žπ‘π‘‘ =π‘Š 𝑠 π‘Žπ‘π‘‘ 𝐺 π‘Žπ‘π‘‘π‘’π‘Žπ‘™ 𝑣 ( 𝑠 π‘Žπ‘π‘‘ ) Excitation profiles preserved if π‘Š 𝑠 = 𝐡 1 𝑠 𝐺(𝑠) = 𝐡 1 𝑣 (𝑠) 𝐺 𝑣 (𝑠) (1) Theory VERSE Corrected RF pulse overshoots initial 𝐡 1 constraint TO-VERSE GIRF-effect 𝑠 𝑑 =𝛾 0 𝑑 𝐺 π‘‘π‘’π‘šπ‘Žπ‘›π‘‘ 𝑣 𝜏 π‘‘πœ Iterative RF-correction Methods Simulated Profiles Results Simulations | 𝑀 π‘₯𝑦 | 𝑠 π‘Žπ‘π‘‘ 𝑑 =𝛾 0 𝑑 𝐺 π‘Žπ‘π‘‘π‘’π‘Žπ‘™ 𝑣 𝜏 π‘‘πœ Experiment Conclusion Space [cm] A simple optimization approach to making time efficient VERSE-multiband pulses feasible on non-ideal gradients

8 Theory (4) Iterative correction
Aim Theory VERSE TO-VERSE GIRF-effect Iterative RF-correction Methods Results Simulations Experiment Conclusion A simple optimization approach to making time efficient VERSE-multiband pulses feasible on non-ideal gradients

9 Methods Aim Simulations: Phase-optimized [Wong 2012] 180 π‘œ refocusing pulses Maximum gradient 40 π‘šπ‘‡ π‘š . Peak 𝐡 1 : 13πœ‡π‘‡ Maximum slew-rate: 200 π‘šπ‘‡ π‘š π‘šπ‘  GIRF: Measured for our Philips Achieva 3T Experiments: Philips Achieva 3T. Gradient echo sequence Spherical water phantom ( 𝑇 1 =270ms) Theory VERSE TO-VERSE GIRF-effect Iterative RF-correction Methods Results Simulations Experiment Conclusion A simple optimization approach to making time efficient VERSE-multiband pulses feasible on non-ideal gradients

10 Results (1): Simulations
Aim Effective duration defined as 𝑇 𝑒𝑓𝑓 = 𝛾 𝐡 1,π‘šπ‘Žπ‘₯ 𝑑𝑑 πœƒ where 𝛾:gyromagnetic ratio. dt: dwell-time. πœƒ: Flip angle Errorsbars show range of duration across different slice-separations Theory VERSE TO-VERSE GIRF-effect Iterative RF-correction Methods Results Simulations Experiment Conclusion VERSE:80% reduction VERSE + GIRF: 70 reduction VERSE:46% reduction VERSE + GIRF: 31% reduction A simple optimization approach to making time efficient VERSE-multiband pulses feasible on non-ideal gradients

11 Results (2) – In-vitro experiment
Aim Theory VERSE TO-VERSE GIRF-effect Iterative RF-correction Methods Results Simulations Experiment Conclusion A simple optimization approach to making time efficient VERSE-multiband pulses feasible on non-ideal gradients

12 Conclusion Aim Effective method to make Time-optimal VERSE-Multiband pulses feasible Applicable for any 1D pulse which suffers from gradient BW problems Three-stage design is sub-optimal High compression factor for Higher Time-bandwidth pulses Further work: Incorporate GIRF directly into VERSE for optimal design Is a measured GIRF necessary? Theory VERSE TO-VERSE GIRF-effect Iterative RF-correction Methods Results Simulations Experiment Conclusion A simple optimization approach to making time efficient VERSE-multiband pulses feasible on non-ideal gradients

Download ppt "Samy Abo Seada, Joseph V Hajnal and Shaihan J Malik"

Similar presentations

Assessment of tumoural ADC’s in rectal Tumours using Burst: New methodological Developments SJ Doran 1, ASK Dzik-Jurasz 2, J Wolber 2, C Domenig 1, MO.

Assessment of tumoural ADC’s in rectal Tumours using Burst: New methodological Developments SJ Doran 1, ASK Dzik-Jurasz 2, J Wolber 2, C Domenig 1, MO.
Tom Powers Practical Aspects of SRF Cavity Testing and Operations SRF Workshop 2011 Tutorial Session.

Tom Powers Practical Aspects of SRF Cavity Testing and Operations SRF Workshop 2011 Tutorial Session.
Pulse Techniques. Off-Resonance Effects Initial magnetization along z x-pulse (  = 0) On-resonance: M z -> -M y Off-resonance: phase 

Pulse Techniques. Off-Resonance Effects Initial magnetization along z x-pulse (  = 0) On-resonance: M z -> -M y Off-resonance: phase 
MR TRACKING METHODS Dr. Dan Gamliel, Dept. of Medical Physics,

MR TRACKING METHODS Dr. Dan Gamliel, Dept. of Medical Physics,
Figure 2. Signal level (left) degrades with slice offset and slice thickness when Z2 SEM is used in GradLoc imaging (ROI = FOV/2). To recover the full.

Figure 2. Signal level (left) degrades with slice offset and slice thickness when Z2 SEM is used in GradLoc imaging (ROI = FOV/2). To recover the full.
Stephen Molloy RF Group ESS Accelerator Division

Stephen Molloy RF Group ESS Accelerator Division
Parameters and Trade-offs

Parameters and Trade-offs
Principles of MRI: Image Formation

Principles of MRI: Image Formation
Chapter 9 Basic MRI I Mark D. Herbst, MD, PhD. Notice This lecture contained many drawings on the whiteboard, so get these from one of the other students.

Chapter 9 Basic MRI I Mark D. Herbst, MD, PhD. Notice This lecture contained many drawings on the whiteboard, so get these from one of the other students.
Magnetic Resonance Imaging

Magnetic Resonance Imaging
More MR Fingerprinting

More MR Fingerprinting
Protein NMR Spectroscopy: Principal and Practice Chapter 3.4 and 3.5: Pulse Techniques and Spin Decoupling Mar 19, 2009.

Protein NMR Spectroscopy: Principal and Practice Chapter 3.4 and 3.5: Pulse Techniques and Spin Decoupling Mar 19, 2009.
MRI. Magnetic Resonance 1.Principle first observed in 1946 2.Used for spectroscopy and imaging 3.Imaging techniques are a form of tomography, where slices.

MRI. Magnetic Resonance 1.Principle first observed in Used for spectroscopy and imaging 3.Imaging techniques are a form of tomography, where slices.
CARE07, 29 Oct. 2007 Alexej Grudiev, New CLIC parameters. The new CLIC parameters 29.10.2007 Alexej Grudiev.

CARE07, 29 Oct Alexej Grudiev, New CLIC parameters. The new CLIC parameters Alexej Grudiev.
FMRI: Biological Basis and Experiment Design Lecture 10: The Dreaded Drop-out Spin echo review Field maps Through-slice dephasing Β© Melissa Tillery

FMRI: Biological Basis and Experiment Design Lecture 10: The Dreaded Drop-out Spin echo review Field maps Through-slice dephasing Β© Melissa Tillery
Basics of Magnetic Resonance Imaging

Basics of Magnetic Resonance Imaging
Markus Strohmeier Sparse MRI: The Application of

Markus Strohmeier Sparse MRI: The Application of
Psy 8960, Fall β€˜06 Gradients and Fields1 Gradients and fields Static magnetic field Gradients –Effect of simultaneous gradients Excitation and slice selection.

Psy 8960, Fall β€˜06 Gradients and Fields1 Gradients and fields Static magnetic field Gradients –Effect of simultaneous gradients Excitation and slice selection.
FMRI: Biological Basis and Experiment Design Lecture 7: Gradients and k-space FFT examples –Sampling and aliasing Gradient Gradient echo K-space www.hoghaven.com.

FMRI: Biological Basis and Experiment Design Lecture 7: Gradients and k-space FFT examples –Sampling and aliasing Gradient Gradient echo K-space
Resonance condition. Pulse A coil of wire placed around the X axis will provide a magnetic field along the X axis when a direct current is passed through.

Resonance condition. Pulse A coil of wire placed around the X axis will provide a magnetic field along the X axis when a direct current is passed through.

Similar presentations

Ads by Google