Echo Planar Slice Multiplexing Calibration
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Solution Overview
Problem
Current slice multiplexing techniques in magnetic resonance imaging face challenges in achieving high image quality due to inconsistencies between reference measurement data and acquired imaging data, particularly when using different acquisition methods for reference and imaging data, leading to increased noise and incomplete separation of slices.
Innovation Solution
A method involving the acquisition of reference measurement data using a gradient echo (GRE) technique with alternating polarities of readout gradients to determine polarity-specific calibration data, allowing for improved separation and unfolding of measurement data from collapsed echo planar simultaneous multi-slice (SMS) acquisitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If different acquisition methods are used for reference measurement data and imaging data, then acquisition time is reduced, but image quality deteriorates due to inconsistencies and increased noise
Solution Approach 1:
The patent applies homogeneity by using the same EPI acquisition method for both reference measurement data and imaging data. This ensures consistency in data characteristics and reduces noise artifacts that arise from mixing different acquisition methodologies. The unified approach maintains homogeneous processing conditions throughout the slice multiplexing workflow.
2Reliability
If EPI technique is used for reference measurement data, then consistency with imaging data is improved, but measurement time increases
Solution Approach 1:
The patent segments the k-space acquisition into different regions: fully sampled central k-space lines are used for reference measurement data, while peripheral k-space lines are undersampled for imaging data. This segmentation allows the reference data to maintain high consistency with the imaging data while reducing the overall measurement time through selective sampling strategies.
Solution Approach 2:
The patent applies partial sampling by acquiring only the necessary portion of k-space data at full resolution. Specifically, the central region of k-space is fully sampled to provide reference information, while the peripheral regions use accelerated undersampling. This partial action approach reduces measurement time while maintaining the consistency benefits of EPI acquisition for the critical reference portion.
3Productivity
If undersampling is applied to reduce measurement time, then productivity is improved, but N/2 ghosts and artifacts increase
Solution Approach 1:
The patent introduces an intermediary calibration process where reference measurement data acquired with full sampling is used to determine calibration factors. These calibration factors serve as intermediaries that correct the undersampled imaging data, thereby removing N/2 ghosts and artifacts while maintaining the productivity benefits of undersampling. The calibration data acts as a mediator between the fully sampled reference and the accelerated imaging acquisition.
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 noise and artifacts, providing robustness to physiological movements and magnetic field inhomogeneities, while significantly reducing measurement time and maintaining consistency with the acquired data.
Implementation Method 1
Radio frequency excitation pulses (RF pulses) are applied to the object under examination in order to induce nuclear spin resonances measurable as signals
Implementation Method 2
Rapidly switched gradient magnetic fields, called gradients for short, are superimposed on the main magnetic field for spatial encoding of the measurement data
Implementation Method 3
an oscillating, i.e., bipolar, readout gradient is deployed, which, with every change in polarity of the gradient, refocuses the transverse magnetization as far as the T2* relaxation allows, each time generating a gradient echo
Implementation Method 4
a so-called multiband RF pulse is used to excite or otherwise manipulate, e.g., refocus or saturate, two or more slices simultaneously
Implementation Method 5
refocuses the transverse magnetization as far as the T2* relaxation allows
Data Source
AI summary
Method for separating measurement data of an examination object, which data was acquired in collapsed form simultaneously for slices using an EPI SMS technique, into measurement data of individual slices, first and second sets of reference measurement data for separating the measurement data are acquired for each of the slices using a GRE acquisition technique, wherein the reference measurement data in the first set is acquired during switching of readout gradients of a first polarity, and the reference measurement data in the second set is acquired during switching of readout gradients of a second polarity. Based on the two sets of reference measurement data, corresponding separate first calibration data is determined from the reference measurement data acquired using a GRE acquisition technique while switching readout gradients of a first polarity, and second calibration data is determined from the reference measurement data acquired while switching readout gradients of a second polarity.