MRI T2 Mapping Using 3D Non-Slice Selective RF Pulses
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Solution Overview
Problem
Conventional T2 mapping in MRI using the Carr-Purcell-Meiboom-Gill (CPMG) sequence is affected by slice profile and B1 inhomogeneity issues, leading to non-ideal exponential decay curves and compounding errors, which complicates accurate T2 parameter mapping.
Innovation Solution
Implementing a T2 preparation phase with 3D non-slice selective block RF pulses followed by an in-out k-space trajectory for data acquisition, separating T2 weighting and signal acquisition, and using a 90x, 180y, 90x pulse sequence to mitigate slice profile and stimulated echo effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional SEMC approach with slice selective RF pulses is used for 2D acquisitions, then acquisition time is reduced, but slice profile effect and B1 inhomogeneity cause non-ideal decay curves and compounding errors
Solution Approach 1:
The patent segments the acquisition process into two distinct phases: a T2 preparation phase using 3D non-slice selective block RF pulses, and a separate signal acquisition phase using in-out k-space trajectory. This segmentation allows T2 weighting to be established without the harmful slice profile effects, then acquired separately to avoid compounding errors while maintaining efficiency.
Solution Approach 2:
The patent extracts the T2 weighting function from the signal acquisition process. By using 3D non-slice selective block RF pulses for T2 preparation and then acquiring signals with an in-out k-space trajectory, the harmful slice profile effects are removed from the T2 measurement while preserving the T2 weighting information.
2Loss of time
If T2 weighting and signal acquisition are mixed in conventional sequences, then acquisition time is reduced, but additive errors compound for later echoes
Solution Approach 1:
The patent divides the sequence into a T2 preparation phase (with 3D block RF pulses) and a signal acquisition phase (with in-out k-space trajectory). This segmentation prevents the compounding of additive errors while maintaining efficient acquisition timing, as each phase performs its specific function without interference from the other.
Solution Approach 2:
The patent performs T2 weighting preparation in advance using 3D non-slice selective block RF pulses before the signal acquisition phase. This preliminary action establishes the T2 contrast without introducing slice profile errors, which then remain consistent throughout the subsequent signal acquisition without compounding.
3Area of stationary object
If 2D slice selective pulses are used, then specific slice imaging is achieved, but imperfect slice profile varies inversely with slice size and causes non-homogeneous flip angles
Solution Approach 1:
The patent transitions from 2D slice selective imaging to 3D non-slice selective block RF pulses for T2 preparation. By moving to three dimensions and eliminating slice selection, the patent avoids the slice profile effects that cause non-homogeneous flip angles, achieving uniform T2 weighting across the entire imaged volume.
Solution Approach 2:
The patent removes the slice selection step from the T2 preparation process by using 3D non-slice selective block RF pulses. This extraction eliminates the source of slice profile effects and B1 inhomogeneity-related flip angle variations, achieving uniform T2 weighting without compromising spatial encoding in the subsequent signal acquisition phase.
4Object-generated harmful factors
If 180 degree refocusing RF pulses are applied in inhomogeneous B1 field, then spin echo is generated, but stimulated echoes are produced due to imperfect refocusing
Solution Approach 1:
The patent removes the 180 degree refocusing RF pulses from the T2 preparation phase and replaces them with 3D non-slice selective block RF pulses. This extraction eliminates the stimulated echo effect caused by imperfect refocusing in inhomogeneous B1 fields, while T2 weighting is still achieved through the alternative pulse sequence design.
Solution Approach 2:
The patent acknowledges that 180 degree refocusing pulses in inhomogeneous B1 fields produce stimulated echoes, but converts this problem into a solution by using 3D non-slice selective block RF pulses instead. This alternative approach achieves T2 weighting without the harmful stimulated echo effect, turning the recognition of the problem into a beneficial design choice.
Data Source
AI summary
Example apparatus and methods provide improved quantitative T2 mapping for magnetic resonance imaging (MRI). Conventional T2 (spin-spin) mapping in MRI may employ a spin echo with multiple echoes (SEMC) approach like the Carr-Purcell-Meiboom-Gill (CPMG) spin echo sequence. These conventional approaches may be negatively impacted by a slice profile effect that incorrectly and undesirably lowers the signal of a first echo and by a stimulated echo effect that incorrectly and undesirably raises the signal for even echoes. Example apparatus mitigate these issues by using a T2 preparation phase that uses three dimensional (3D) non-slice selective block RF pulses followed by a multi-echo data acquisition that uses an in-out k-space trajectory. The multi-echo acquisition may employ k-space segmentation to acquire one line of partition encodings per T2 preparation phase. While conventional systems mix T2 preparation and multi-echo acquisition, example apparatus and methods separate T2 preparation and multi-echo acquisition.