PASL MRI Motion Correction Using Volumetric EPI Navigator
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Solution Overview
Problem
Current 3D arterial spin labeling (ASL) magnetic resonance imaging techniques are prone to motion corruption and artifacts due to segmented k-space acquisition and subtraction methods, which compromise the effectiveness of perfusion imaging, especially in procedures like stroke evaluation, where patient head motion is a significant issue.
Innovation Solution
A magnetic resonance system and method for real-time prospective motion correction using pulsed arterial spin labeling (PASL) with a volumetric EPI-based navigator, allowing for synchronization of RF pulses and magnetic field gradients to correct motion between control and tagged sequences with different magnetization histories, thereby minimizing artifacts and enhancing image accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If segmented k-space acquisition and subtraction methods are used in 3D ASL MRI, then perfusion imaging can be performed, but motion corruption and artifacts occur
Solution Approach 1:
The patent applies preliminary action by acquiring navigator echoes before the main imaging data to detect head position and orientation. These navigator measurements are taken in advance to establish a reference frame, allowing subsequent motion correction to be applied to the perfusion images. This proactive approach prevents motion corruption from compromising the final perfusion measurement.
Solution Approach 2:
The patent implements feedback by continuously monitoring head motion through navigator echoes and using this information to correct the perfusion images in real-time. The system measures actual head position and orientation during the scan, then applies corrective transformations to align the images properly, creating a closed-loop system that compensates for motion artifacts.
2Measurement precision
If many repetitions of ASL data acquisitions are averaged to increase signal-to-noise ratio, then noise effects are reduced, but imaging time increases and motion corruption accumulates
Solution Approach 1:
The patent introduces navigator echoes as an intermediary element that enables motion correction during the ASL acquisition process. These additional navigator measurements act as a mediator between the control and tagged images, providing the necessary information to align them properly even when acquired at different times. This allows the system to maintain multiple repetitions for noise reduction without proportionally increasing motion artifacts.
3Measurement precision
If control and tagged images are acquired at different times, then perfusion measurement can be performed, but head motion causes misalignment between images
Solution Approach 1:
The patent uses feedback by measuring actual head position and orientation through navigator echoes acquired at different times, then using these measurements to calculate corrective transformations. The system continuously monitors motion and applies real-time corrections to align control and tagged images, creating a closed-loop system that maintains image registration despite temporal separation.
Solution Approach 2:
The patent applies preliminary action by acquiring navigator echoes that capture head position and orientation information before the main perfusion imaging sequences. These preliminary measurements establish a reference framework that enables subsequent alignment of control and tagged images, ensuring proper registration even though the images are acquired at different times.
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
The system achieves real-time motion correction, reducing artifacts and improving the accuracy of perfusion imaging by aligning successive tagged and control images, resulting in clearer perfusion maps and increased signal-to-noise ratio, even during patient movement.
Implementation Method 1
Radio-frequency (RF) excitation pulses are directed into the examination subject to excite nuclear magnetic resonances, and subsequent relaxation of the excited nuclear magnetic resonances can generate RF signals
Implementation Method 2
Rapidly switched magnetic gradient fields can be superimposed on the base magnetic field, in various orientations, to provide spatial coding of the RF signal data
Implementation Method 3
a spatially selective inversion or saturation of water protons in arterial blood is used to label or 'tag' blood flowing into the region to be imaged
Implementation Method 4
When the labeled or tagged blood reaches the tissue within the imaging region, it attenuates the MR signal emanating from the perfused tissue following spatially-selective excitation of the region
Data Source
AI summary
A magnetic resonance method and system are provided for generating real-time motion-corrected perfusion images based on pulsed arterial spin labeling (PASL) with a readout sequence such as a 3D gradient and spin echo (GRASE) image data acquisition block. The real-time motion correction is achieved by using a volumetric 3D EPI navigator that is provided during an intrinsic delay in the PASL sequence, which corrects for motion prospectively and does not extend the image data acquisition time as compared to a similar non-motion-corrected imaging procedure.