Multi-Slice MR T1 Mapping via Concurrent Acquisition
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Solution Overview
Problem
Conventional Magnetic Resonance (MR) imaging systems face limitations in simultaneously achieving speed, signal-to-noise ratio (SNR), resolution, anatomical coverage, and accurate sampling of MR signal evolution for quantitative T1-mapping, often requiring a trade-off that compromises the number of anatomical slices and reduces accuracy.
Innovation Solution
The method involves generating RF excitation pulses and slice select magnetic field gradients to concurrently acquire T1 map image data of multiple slices using a pre-scan sequence, non-selective inversion recovery pulses, and echo-planar-imaging (EPI) acquisition, allowing for improved slice separation and image reconstruction while maintaining rapid sampling of the inversion recovery curve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional parallel imaging (GRAPPA) is used to improve imaging speed, then the number of anatomical slices can be increased, but the signal-to-noise ratio deteriorates
Solution Approach 1:
The imaging volume is divided into multiple slices that are excited and acquired concurrently using multi-slice RF pulses. Each slice is independently encoded in the phase-encoding direction, allowing simultaneous acquisition of multiple slices without the SNR penalty of parallel imaging techniques like GRAPPA.
Solution Approach 2:
The patent introduces slice acceleration as an additional dimension of parallelism independent of the phase-encoding direction. By encoding slices along the phase-encoding axis and using slice-selective RF pulses, the system achieves acceleration without compromising SNR, effectively adding a new degree of freedom to the imaging process.
2Area of stationary object
If interleaved multi-slice acquisitions are used to increase anatomical coverage, then more slices can be imaged, but different spin-histories and TI values occur for each slice which reduces quantitation accuracy
Solution Approach 1:
Multiple slices are merged into a single concurrent acquisition process using multi-slice RF pulses that excite all slices simultaneously. All slices share the same inversion recovery spin-history and TI values, ensuring consistent quantitation across the entire anatomical coverage while maintaining accelerated imaging speed.
Solution Approach 2:
A non-selective inversion recovery pulse is applied preliminary to all slice acquisitions to establish a unified spin-history for all slices. This preliminary action ensures that all subsequent slice measurements occur from the same magnetization state, enabling accurate quantitative T1 mapping across multiple slices.
3Measurement precision
If more TIs are measured for robust T1 fitting, then quantitation accuracy improves, but the imaging time increases
Solution Approach 1:
The system continuously acquires data from multiple slices at each TI point without interruption, maintaining the inversion recovery curve sampling across all slices simultaneously. This continuous multi-slice acquisition allows robust T1 fitting with multiple TI measurements while keeping the total imaging time short by processing all slices in parallel at each time point.
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 accelerates T1-mapping by increasing the number of slices acquired without sacrificing SNR, enabling more accurate and flexible quantitative imaging for applications like musculoskeletal, neurological, and cardiac imaging.
Implementation Method 1
generating radio frequency (RF) excitation pulses in a volume of patient anatomy to provide subsequent acquisition of associated RF echo data
Implementation Method 2
The magnetic field causes magnetic field vectors of protons (typically in hydrogen atoms) to align with the magnetic field. The RF pulses cause the magnetic field vectors of the protons to be displaced (e.g., rotate) relative to the magnetic field
Implementation Method 3
generating slice select magnetic field gradients for phase encoding and readout RF data acquisition in the patient anatomy
Implementation Method 4
inverting a longitudinal magnetization in the volume of patient anatomy using a non-selective inversion recovery pulse
Data Source
AI summary
A method for operating a Magnetic Resonance (MR) imaging system that includes generating radio frequency (RF) excitation pulses in a volume of patient anatomy and generating slice select magnetic field gradients for phase encoding and readout RF data acquisition in the patient anatomy. The method further includes concurrently acquiring T1 map image data of slices of an image by: (i) acquiring image calibration data using a pre-scan sequence; (ii) inverting a longitudinal magnetization in the volume of patient anatomy using a non-selective inversion recovery pulse; (iii) applying an excitation RF pulse to different slices in the volume of patient anatomy to rotate a portion of the longitudinal magnetization in a transverse direction; (iv) sampling individual slice image data of the slices in response to applying the excitation RF pulse; and (v) separating the concurrently acquired T1 map image into separate slices.