MR Imaging Motion Detection via Gradient Image Comparison
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Solution Overview
Problem
Conventional MR imaging techniques face challenges in efficiently compensating for patient motion, particularly when using Cartesian k-space sampling schemes, as they either require additional navigator signals that extend scan time or are not compatible with motion-correction methods like PROPELLER.
Innovation Solution
The method involves acquiring MR signals as temporally successive subsets with sub-sampled k-space profiles, reconstructing single-subset images, computing gradient images to reduce central k-space influence, and detecting motion by comparing these gradient images, allowing for fast and robust motion detection without additional navigators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If navigator signals are acquired to detect patient motion, then motion detection capability is improved, but scan time is extended
Solution Approach 1:
The patent combines motion detection functionality with the standard k-space data acquisition process. Gradient images are computed from the same k-space profiles used for image reconstruction, eliminating the need for separate navigator signals. This merging of functions achieves motion detection capability without extending scan time.
2Reliability
If PROPELLER motion correction method is used, then motion compensation is improved, but compatibility with Cartesian sampling is lost
Solution Approach 1:
The patent changes the parameter of k-space sampling trajectory from the circular blade pattern required by PROPELLER to Cartesian sampling lines. By computing gradient images from Cartesian-sampled k-space data and comparing these gradient images for motion detection, the method adapts motion compensation to work with Cartesian sampling while maintaining the core principle of detecting motion through image comparison.
3Manufacturing precision
If k-space sampling density is increased to improve image quality, then manufacturing precision is improved, but acquisition time is extended
Solution Approach 1:
The patent performs preliminary computation of gradient images from the acquired k-space profiles. These gradient images are then used for motion detection and can guide whether full-resolution reconstruction is necessary. This preliminary processing allows for potential early termination or adaptive sampling strategies that prevent unnecessary acquisition time extension while maintaining image quality when needed.
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 efficient motion detection and correction in MR imaging, reducing artifacts and maintaining image quality by comparing gradient images, which are less affected by motion, and allows for the reconstruction of motion-compensated images without extending scan time.
Implementation Method 1
The magnetic field B0 produces different energy levels for the individual nuclear spins in dependence on the magnetic field strength which can be excited (spin resonance) by application of an electromagnetic alternating field (RF field) of defined frequency (so-called Larmor frequency, or MR frequency).
Implementation Method 2
The magnetic field B1 of this RF pulse extends perpendicular to the z-axis, so that the magnetization performs a precessional motion about the z-axis. The precessional motion describes a surface of a cone whose angle of aperture is referred to as flip angle.
Implementation Method 3
The transverse magnetization and its variation can be detected by means of receiving RF coils which are arranged and oriented within an examination volume of the MR device in such a manner that the variation of the magnetization is measured in the direction perpendicular to the z-axis.
Implementation Method 4
In order to realize spatial resolution in the body, constant magnetic field gradients extending along the three main axes are superposed on the uniform magnetic field B0, leading to a linear spatial dependency of the spin resonance frequency. The signal picked up in the receiving coils then contains components of different frequencies which can be associated with different locations in the body.
Data Source
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AI summary
The invention relates to a method of MR imaging of an object (10) placed in the examination volume of a MR device (1). It is an object of the invention to provide a method that enables efficient motion-compensation and/or motion-correction and that is compatible with Cartesian sampling of k-space. The method of the invention comprises: - generating MR signals by subjecting the object (10) to a MR imaging sequence of at least one RF pulse and switched magnetic field gradients; - acquiring the MR signals as a plurality of temporally successive subsets, each subset comprising a number of k-space profiles with sub-sampling of k-space, wherein the subsets complement each other to form a fully sampled set of k-space profiles; - reconstructing a single-subset MR image from each subset; - computing a gradient MR image from each single-subset MR image; and - detecting motion by comparing the gradient MR images with each other. Moreover, the invention relates to a MR device (1) and to a computer program for a MR device (1).