SEMAC MRI Slice-Selective Imaging with Varying Flip Angles
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Magnetic resonance imaging (MRI) techniques face challenges in reducing measurement time and specific absorption rate (SAR) due to metal artifacts caused by magnetic field inhomogeneities, which increase the time required for data acquisition and RF radiation exposure.
Innovation Solution
The method involves slice-selective MR imaging by acquiring data from multiple readout partitions of a target slice and adjacent slices, using time-correlated slice selection gradients and refocusing pulses with varying flip angles to reduce image artifacts and SAR, while maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If SEMAC technique with additional phase coding steps is used to correct metal artifacts, then image quality is improved, but measurement time increases linearly
Solution Approach 1:
The patent divides k-space into multiple readout partitions along the slice selection direction, acquiring data from the target slice and adjacent slices separately. This segmentation allows parallel processing and reduces the total measurement time while maintaining the artifact correction capability through the SEMAC technique.
Solution Approach 2:
The patent acquires SEMAC data not only from the target slice but also from adjacent slices above and below it. This partial extension to neighboring slices provides the necessary phase encoding information for artifact correction without requiring complete phase encoding of the entire imaging volume, thus reducing measurement time.
2Manufacturing precision
If multiple refocusing pulses with RF portions are radiated per time unit in SEMAC sequence, then metal artifact correction is improved, but SAR increases
Solution Approach 1:
The patent applies different flip angles to refocusing pulses based on their position in k-space. Pulses associated with readout partitions farther from the k-space center use smaller flip angles to reduce SAR, while pulses near the center maintain larger flip angles to preserve image quality. This local optimization resolves the contradiction between artifact correction and SAR reduction.
Solution Approach 2:
The patent dynamically changes the flip angle parameter of refocusing pulses based on the readout partition distance from the k-space center. This parameter modulation allows the system to reduce RF energy deposition (SAR) in regions where less signal contribution is needed, while maintaining adequate signal strength in critical regions.
3Use of energy by moving object
If additional downtimes are provided to limit SAR, then SAR is reduced, but measurement time increases
Solution Approach 1:
The patent dynamically adjusts the flip angle of refocusing pulses based on the readout partition position, replacing static SAR management with dynamic parameter optimization. This allows continuous SAR reduction without requiring additional downtimes, as the flip angle modulation continuously optimizes the RF energy deposition throughout the acquisition.
Solution Approach 2:
By changing the flip angle parameter of refocusing pulses according to readout partition distance, the system reduces SAR through parameter optimization rather than temporal separation. This eliminates the need for additional downtimes while maintaining SAR within acceptable limits.
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 allows for reduced measurement time and lower SAR exposure, effectively minimizing metal artifacts and maintaining image quality by varying the flip angles of refocusing pulses based on their distance from the k-space center, thereby optimizing the tradeoff between SAR reduction and image quality.
Implementation Method 1
In magnetic resonance (MR) imaging, nuclear spins in a subject are aligned or polarized by the application of a basic magnetic field, and that nuclear spins are subsequently by radiation of one or more radio-frequency (RF) pulses, deflected out of the steady state
Implementation Method 2
For each additional slice selection gradient with an associated refocusing pulse, the method includes: activation of at least one kz-phase coding gradient along the first direction, to define a readout partition, and activation of at least one ky-phase coding gradient along a second direction to acquire MR data
Implementation Method 3
The multiple refocusing pulses have at least two different flip angles
Data Source
AI summary
In a SEMAC-like magnetic resonance imaging, MR data of multiple readout partitions of a target slice are used in order to reduce image artifacts due to magnetic field inhomogeneities. Slice-selectively excited nuclear spins are refocused via radiation of multiple refocusing pulses. For each refocusing pulse, at least one kz-phase coding gradient is respectively applied along a first direction (to define a readout partition) and at least one ky-phase coding gradient is applied along a second direction to acquire MR data, wherein the first and second directions are orthogonal to one another. The multiple refocusing pulses have at least two different flip angles.