Abstract
OBJECTIVE: Ultrahigh field MRI provides great opportunities for medical diagnostics and research. However, ultrahigh field MRI also brings challenges, such as larger magnetic susceptibility induced field changes. Parallel-transmit radio-frequency pulses can ameliorate these complications while performing advanced tasks in routine applications. To address one class of such pulses, we propose an optimal-control algorithm as a tool for designing advanced multi-dimensional, large flip-angle, radio-frequency pulses. We contrast initial conditions, constraints, and field correction abilities against increasing pulse trajectory acceleration factors.
MATERIALS AND METHODS: On an 8-channel 7T system, we demonstrate the quasi-Newton algorithm with pulse designs for reduced field-of-view imaging with an oil phantom and in vivo with scans of the human brain stem. We used echo-planar imaging with 2D spatial-selective pulses. Pulses are computed sufficiently rapid for routine applications.
RESULTS: Our dataset was quantitatively analyzed with the conventional mean-square-error metric and the structural-similarity index from image processing. Analysis of both full and reduced field-of-view scans benefit from utilizing both complementary measures.
CONCLUSION: We obtained excellent outer-volume suppression with our proposed method, thus enabling reduced field-of-view imaging using pulse trajectory acceleration factors up to 4.
Original language | English |
---|---|
Pages (from-to) | 29-39 |
Number of pages | 11 |
Journal | Magnetic Resonance Materials in Physics Biology and Medicine |
Volume | 30 |
Issue number | 1 |
DOIs | |
Publication status | Published - Feb 2017 |
Keywords
- MRI
- RF pulse design
- Parallel transmit
- Ultrahigh field MRI
- DESIGN
- EXCITATION
- TRANSMISSION
- TRAJECTORIES
- MULTISLICE
- DREAM