Multi-shot RF Excitation for EPI Calibration
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Solution Overview
Problem
Echo-planar imaging (EPI) in MRI suffers from geometric distortion, blurring, and reduced signal-to-noise ratio (SNR) due to physiological noise, particularly in single-shot EPI with Fast Low-Angle Excitation Echo Planar Technique (FLEET) Auto-Calibration Scans (ACS), which compromises image quality.
Innovation Solution
A method involving multi-shot RF excitation with predetermined flip angles and rewinder pulses during the calibration phase of EPI data acquisition, optimizing k-space data acquisition to improve image quality by matching echo train lengths and applying rewinder gradients to minimize motion artifacts and eddy currents, while using higher flip angles for calibration without sacrificing motion protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If FLEET ACS is used to reduce physiological noise, then motion artifacts are reduced, but signal-to-noise ratio and image quality deteriorate
Solution Approach 1:
The patent divides the k-space data acquisition into multiple interleaved segments, each containing a subset of phase encoding steps. This segmentation allows the system to acquire calibration data in a structured manner that reduces physiological noise while maintaining adequate signal-to-noise ratio through proper segment organization and reconstruction.
Solution Approach 2:
The patent performs auto-calibration scans before the actual imaging acquisition to characterize the system response and correct for distortions. This preliminary action allows the system to compensate for physiological noise and geometric distortions during the main imaging sequence, improving overall image quality without extending total scan time.
2Manufacturing precision
If multi-shot EPI is used to reduce geometric distortion, then image accuracy improves, but acquisition time increases
Solution Approach 1:
The patent segments the phase encoding steps into multiple interleaved groups, where each group corresponds to a separate shot. This segmentation enables the system to acquire k-space data in a way that reduces geometric distortion through proper phase encoding while maintaining efficient acquisition timing through interleaved processing.
Solution Approach 2:
The patent employs periodic phase encoding patterns across multiple shots, where phase encoding steps are systematically varied and repeated in a periodic manner. This periodic action allows for consistent geometric encoding that reduces distortion while maintaining a regular acquisition rhythm that optimizes scan time efficiency.
3Measurement precision
If higher flip angles are used for calibration, then contrast and calibration quality improve, but motion artifacts increase
Solution Approach 1:
The patent segments the calibration process into multiple interleaved segments with different flip angles. This segmentation allows the system to use higher flip angles for improved contrast and calibration quality in specific segments while using lower flip angles in other segments to minimize motion artifacts, with the final reconstruction combining information from all segments.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances image quality by reducing motion artifacts and improving SNR, achieving better contrast and calibration without extending calibration time, thus addressing the trade-offs in existing FLEET ACS methods.
Implementation Method 1
providing a multi-shot radio frequency (RF) excitation to an RF coil that excites spins in a slice of patient tissue
Implementation Method 2
providing a series of frequency encoding pulses equal to the predetermined number of readout lines throughout a readout period
Implementation Method 3
providing a series of phase encoding pulses during a middle portion of the readout period corresponding to a middle section of the k-space
Implementation Method 4
each frequency and phase encoding pulse each include a rewinder pulse before a spoiler pulse after the magnetic resonance signals are captured
Implementation Method 5
each frequency and phase encoding pulse each include a rewinder pulse before a spoiler pulse after the magnetic resonance signals are captured
Data Source
AI summary
Systems and methods for improving calibration of MRI imaging using echo-planar imaging (EPI) include a multi-shot radio frequency (RF) excitation during a calibration phase and a processor that calibrates the k-space for a slice by acquiring k-space data through multi-shot EPI data acquisition for a plurality of interleaved segments in the slice, each divided into a predetermined number of readout lines. Each EPI data acquisition includes providing a series of frequency encoding pulses throughout a readout period equal to the predetermined number of readout lines, providing a series of phase encoding pulses during a middle portion of the readout period corresponding to a middle section of the k-space, capturing magnetic resonance signals during the middle portion. The frequency and phase encoding pulse each include a rewinder pulse before a spoiler pulse after the magnetic resonance signals are captured. The processor creates a calibration model from the acquired k-space data based on the magnetic resonance signals during the middle portion, wherein k-space data corresponding to each segment in the slice is acquired before acquiring data for subsequent slices.