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Optimization of RF Pulse Parameters for 7T MRI: Design Space Exploration and Uniformity Analysis

This study investigates the design parameters for B1 mapping in a 7T MRI setup using a 2D 64x64 B1 map with a slice resolution of 5mm. Various iterations of kzfast3d_1ch.m were conducted to explore design options while ignoring B0 inhomogeneity. The focus was on achieving optimal uniformity based on criteria such as TR < 5ms and Max FA ≥ 60 degrees. Key questions addressed include the relationship between RF power, subpulse number, and width, alongside their influence on uniformity and SAR penalties. Findings reveal the need for 12-18 subpulses with varying RF penalties.

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Optimization of RF Pulse Parameters for 7T MRI: Design Space Exploration and Uniformity Analysis

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Presentation Transcript

  1. K-T Points Design Choices

  2. Scan Parameters • Phantom @7T, sagittal • 2D 64x64 B-S B1 map • 5mm slice resolution • Ran many iterations of kzfast3d_1ch.m to explore the design space and its predicted output B1 • B0 inhomogeneity is ignored

  3. Design Requirements • Choose parameters that has best uniformity given these constraints: • TR < 5ms • Max FA >= 60 deg. • SAR, need to figure out how to relate computed RF power to this

  4. Partial Dependence on # Subpulses and RF Power Penalty

  5. Questions • What is the criterion used for uniformity? • Given a # of subpulses and their width, should the error criterion be monotonically increasing with greater RF penalty? • Will always be achieving less uniformity, so 1st term is always increasing, can weighted RF power term be any smaller with a change in penalty?

  6. Partial Dependence on Subpulse Width and RF Power Penalty

  7. Partial Dependence on # Subpulses and Subpulse Width

  8. # Subpulses vs. RF Power Penalty with Subpulse Width changing in time

  9. Conclusions • 12-18 subpulses • 1-7 RF penalty • 0.12-0.2 ms subpulse width, but depends on B0

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