MRI Navigator and Image Data Synchronization
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Solution Overview
Problem
Conventional magnetic resonance imaging (MRI) methods face challenges in accurately correcting patient movement during scans, leading to image artifacts and increased scan times, particularly when using navigator images acquired at staggered intervals or with different contrast properties than the main image data.
Innovation Solution
The method involves simultaneously acquiring navigator and image data using different transverse magnetizations within the same scan period, allowing for precise movement correction and improved image quality by using the navigator data for real-time position correction of the field of view, and potentially applying retrospective corrections to reduce artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If navigator images are acquired at staggered intervals or with different contrast properties, then movement correction can be performed, but measurement precision and image quality deteriorate due to temporal and contrast mismatches
Solution Approach 1:
The patent merges the acquisition of navigator data and image data into a single simultaneous process. Multiple sub-volumes including navigator sub-volumes and image sub-volumes are excited and read out within the same scan period, eliminating temporal delays between navigator and image acquisition. This ensures that movement information and image data are captured at the same moment, improving movement correction precision while maintaining image quality.
Solution Approach 2:
The patent implements periodic acquisition of navigator and image data within structured scan periods. The sequence alternates between acquiring navigator sub-volumes and image sub-volumes in a regular pattern, ensuring synchronized temporal sampling. This periodic structure allows consistent movement tracking without compromising image quality, as both data types are acquired rhythmically within the same operational cycle.
2Productivity
If multiple sub-volumes are scanned simultaneously, then scan time is reduced, but device complexity increases due to coordinated pulse sequence management
Solution Approach 1:
The patent segments the imaging volume into multiple non-overlapping sub-volumes, each assigned to specific coil elements. Navigator sub-volumes and image sub-volumes are spatially separated and scanned simultaneously without interference. This segmentation allows parallel acquisition that reduces scan time while managing complexity through clear spatial and functional separation of different sub-volume acquisitions.
Solution Approach 2:
The patent creates a universal pulse sequence framework that handles both navigator and image sub-volumes using the same basic excitation and readout mechanisms. The same RF pulses and gradient fields serve dual purposes: acquiring navigator data for movement correction and image data for diagnostic purposes. This multi-functionality reduces device complexity by reusing existing hardware and sequence elements rather than requiring separate dedicated systems.
3Speed
If RF pulses are increased for faster imaging, then scan speed improves, but SAR exposure and RF peak output increase
Solution Approach 1:
The patent applies local quality by assigning different RF pulse characteristics to different sub-volumes. Navigator sub-volumes use RF pulses optimized for movement detection with lower flip angles, while image sub-volumes use pulses optimized for diagnostic quality. This local optimization allows faster scanning through parallel acquisition while reducing overall SAR exposure by using lower power pulses in the navigator portions.
Solution Approach 2:
The patent applies partial action by acquiring only the essential navigator information needed for movement correction rather than full diagnostic images. The navigator sub-volumes provide sufficient movement data with reduced RF energy input, while the main image sub-volumes provide diagnostic quality. This partial acquisition strategy maintains scan speed through parallel processing while reducing peak RF power requirements and SAR exposure.
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 the precision of movement correction and image quality by synchronizing navigator and image data acquisition, reducing artifacts and scan times, while also minimizing SAR exposure and RF peak output.
Implementation Method 1
In magnetic resonance tomography, a static basic magnetic field Bo, for initial orientation and homogenization of magnetic dipoles to be examined, is usually overlaid with a rapidly-switched magnetic field, known as the gradient field, for spatial resolution of the imaging signal.
Implementation Method 2
a rapidly-switched magnetic field, known as the gradient field, for spatial resolution of the imaging signal
Implementation Method 3
The value of magnetization (in particular the transverse magnetization, determined in a plane transverse to the above-described basic magnetic field) at a specific location of the examination object can be ascertained from k-space data with the use of a Fourier transformation.
Data Source
AI summary
In a magnetic resonance imaging apparatus and a method for generating magnetic resonance image data of a field of view of an examination object, magnetic resonance raw data are acquired by preferably different transverse magnetizations being excited in at least one sub-volume of a navigator volume and at least one sub-volume of an image volume, and are used for position determination and for imaging. These preferably different transverse magnetizations are simultaneously present in at least one period of the scan.