Retrospective MRI Motion Compensation via Navigator Echo Averaging
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Solution Overview
Problem
Current MRI techniques face challenges in generating clear images of both moving and static objects due to motion artifacts, particularly in abdominal imaging, where respiratory triggering lengthens scan time and navigator echo techniques blur static objects, requiring separate scans for optimal results.
Innovation Solution
A magnetic resonance imaging system with motion compensation means that uses navigator echo techniques to track and average image data from multiple acquisitions, allowing for separate image processing of moving and static objects within the same imaging session, reducing motion artifacts and maintaining efficient scan times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If respiratory triggering is used to synchronize measurements, then motion artifacts are reduced, but scan time is lengthened by two or three times
Solution Approach 1:
The patent applies preliminary action by performing navigator echo measurements before the actual imaging data acquisition. The navigator echoes detect respiratory motion in advance, and this motion information is stored and later used to retrospectively adjust the imaging data. This allows the main imaging sequence to proceed without waiting for respiratory synchronization, thus reducing scan time while still enabling motion correction.
Solution Approach 2:
The patent uses navigator echoes as an intermediary to transfer motion information from the moving object to the imaging system. The navigator echoes separately detect respiratory displacement, and this information acts as a mediator that enables retrospective adjustment of the main imaging data without requiring real-time synchronization during the actual image acquisition.
2Measurement precision
If navigator echo technique is applied to focus on moving objects, then motion artifacts are reduced, but static objects become blurred
Solution Approach 1:
The patent applies segmentation by separating the processing of moving and static objects. After acquiring all imaging data with navigator echoes, the system sorts the data based on detected respiratory motion and then performs separate averaging operations: one for moving objects that benefits from motion compensation, and another for static objects that uses the original unadjusted data to avoid blurring.
Solution Approach 2:
The patent applies local quality by applying different processing strategies to different regions or object types within the same image dataset. Moving objects receive motion-compensated processing while static objects receive standard processing, allowing each to be optimized for its specific characteristics rather than applying a uniform approach that would compromise both.
3Loss of information
If multiple measurements are averaged to improve signal to noise ratio, then SNR is improved, but blurring occurs on moving objects
Solution Approach 1:
The patent performs preliminary detection of respiratory motion using navigator echoes before averaging the main imaging data. By knowing the motion state in advance, the system can sort and average data from similar respiratory phases together, maintaining both high SNR through averaging and image sharpness by ensuring that averaged data corresponds to the same anatomical position.
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 enables clear and sharp images of both moving and static objects without extending scan time, improving image quality and reducing blurring, while preventing scan failures associated with respiratory triggering.
Implementation Method 1
the object area which is to be examined, i.e. the 'sample', is disposed in a stationary magnetic field B0 and is subjected to a sequence of at least one electromagnetic high-frequency pulse (HF-pulse) of a selected frequency and to subsequent pulses of magnetic field gradients in various spatial directions, such that the HF-excitations cause echoes to occur which are detected as the MR-signal
Implementation Method 2
Navigator echo is another motion compensation technique, which detects motion prior to data acquisition and modifies data acquisition accordingly. Navigator techniques use image space navigator echoes for detecting motion during image data acquisition.
Data Source
AI summary
A magnetic resonance imaging apparatus comprises a data acquisition system with motion compensation means for acquiring an image data set in respect of a moving object within an imaging region, the image data set comprising a plurality of acquisitions each in respect of one or more slice planes. Further there are means for averaging, on a slice-by-slice basis, said plurality of acquisitions to generate a single, average image set of said moving object. Also means are provided for calculating the actual scan location of all of said slice planes from all of said acquisitions, means for averaging a selected set of slice planes to generate a single, average image set of a static object within said imaging region. This averaging results in a high image quality in respect of the moving object (12) because for the static object, slice locations change for each acquisition.