MRI Shim Data Interleaving for Scan Time Reduction
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Solution Overview
Problem
Current MRI techniques face challenges in reducing the overall time required to acquire datasets due to the separate and time-consuming shim data acquisition process, which can be exacerbated by patient motion and the need for repeated shimming procedures during scans.
Innovation Solution
The integration or interleaving of shim data acquisition with slice acquisition using iterative processes that update shim currents continuously, allowing for simultaneous or alternating acquisition of shim and image data, particularly during quiescent phases of the heartbeat, to minimize the time gap and reduce scan duration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If shim data acquisition is performed separately before slice acquisition, then the magnetic field homogeneity is improved, but the total scan time increases
Solution Approach 1:
The patent merges shim data acquisition with slice acquisition into a single integrated process. The gradient echo sequence simultaneously performs both functions by acquiring phase data for shim calculation and image data for diagnostic purposes in the same scan, eliminating the need for separate shim acquisition and reducing total scan time while maintaining magnetic field homogeneity
2Manufacturing precision
If shim data acquisition is repeated during the scan, then the magnetic field homogeneity is maintained, but the scan time increases
Solution Approach 1:
The patent implements continuous shim monitoring and updating during the scan by periodically acquiring phase data from the gradient echo sequence and recalculating shim parameters on-the-fly. This continuous action maintains magnetic field homogeneity throughout the scan without requiring separate, time-consuming shim acquisition interruptions, thereby preserving scan efficiency
3Measurement precision
If a 3D multi-echo sequence is used for shim acquisition, then the field map accuracy is improved, but the acquisition time increases
Solution Approach 1:
The patent uses a gradient echo sequence that serves multiple functions simultaneously: it acquires phase data for field map generation, collects image data for diagnostic purposes, and provides T2* contrast information. This multi-functional approach achieves adequate field map accuracy without requiring the longer acquisition times of dedicated 3D multi-echo sequences
4Reliability
If 2D multi-slice acquisition is used instead of 3D DESS, then motion artifacts are reduced, but the shim correction coverage is limited
Solution Approach 1:
The patent implements a feedback mechanism where phase data is continuously acquired during the 2D multi-slice scan and used to dynamically update shim parameters. This real-time feedback allows the system to maintain accurate shim correction across the entire region of interest even when using faster 2D sequences, effectively overcoming the limited coverage issue while preserving motion artifact reduction benefits
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 reduces scan time, minimizes artifacts related to patient motion, and ensures improved image quality by continuously updating shim currents, making it feasible to acquire MRI datasets more efficiently, especially for large regions of interest like peripheral arteries or whole-body scans.
Implementation Method 1
Magnetic Resonance Imaging (MRI) measures tissue-specific responses to a radio frequency (RF) stimulus in a strong main magnetic field (B0). Specifically, the magnetization of tissue is aligned with B0. An initial RF pulse tips the magnetization out of this alignment and rotates with a tissue-specific RF frequency resulting in a signal that is picked up with a receiver coil.
Implementation Method 2
Additional magnetic field gradient pulses (G) are used to spatially encode the RF signal that, in turn, is used to reconstruct an image.
Implementation Method 3
The inhomogeneity of B0 can be compensated by adding additional magnetic fields generated by dedicated coils (shim coils) that are often described by a constant, linear, 2nd order and even higher order terms.
Implementation Method 4
The phase evolution between the echoes is proportional to B0 and the resulting phase map can be converted into a field map. Finally, the field map is being used to derive shim currents that generate additional magnetic fields that compensate the inhomogeneity of B0.
Data Source
AI summary
A method of acquiring magnetic resonance imaging (MRI) data of a subject includes dividing a region of interest into a plurality of slices, and acquiring the slices using an iterative process that interleaves acquisition of shim data covering the plurality of slices with acquisition of image data covering the slices over a plurality of iterations.