Motion-Triggered APT/CEST MR Imaging with Continuous RF Saturation
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Solution Overview
Problem
Current APT/CEST MR imaging techniques are inefficient for moving body parts due to the long time required for selective saturation, which is further compromised by motion triggering methods that delay image acquisition, leading to reduced scan efficiency and motion artifacts.
Innovation Solution
A method where preparation RF pulses are continuously applied during motion phases, with MR signal acquisition triggered by detected motion signals, allowing for efficient and motion-compensated imaging by recognizing specific motion states, such as full expiration, and optionally using a pre-determined time delay for initiating acquisitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If motion triggering is used to acquire MR signals, then motion artifacts are reduced, but scan time efficiency deteriorates due to delays in image acquisition
Solution Approach 1:
The preparation RF pulses are applied in advance continuously to achieve selective saturation before the motion-triggered image acquisition, so that when the trigger signal arrives, the saturation is already established and no delay is needed
Solution Approach 2:
The preparation RF pulses are applied continuously without interruption during the waiting period for the motion trigger signal, ensuring that the selective saturation process continues uninterrupted and efficiently, maximizing the use of preparation time
2Reliability
If selective saturation is applied for APT/CEST imaging, then tissue contrast is improved, but the time required for saturation increases scan duration
Solution Approach 1:
Selective saturation is achieved as a preliminary action before the motion-triggered image acquisition, allowing the saturation process to complete in advance without compromising the timing of the actual image capture
Solution Approach 2:
The preparation RF pulses are applied continuously to maintain and build up selective saturation throughout the waiting period, ensuring optimal saturation levels are achieved efficiently without time loss
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 scan time efficiency and robustness, reducing motion artifacts and ensuring high-quality MR imaging by synchronizing RF pulses with body motion, while maintaining safety by monitoring and limiting RF exposure to prevent heat deposition issues.
Implementation Method 1
A particularly promising approach for contrast enhancement and increase of MR detection sensitivity (by orders of magnitude) is the known method based on 'Chemical Exchange Saturation Transfer' (CEST)
Implementation Method 2
Image-forming MR methods which utilize the interaction between magnetic fields and nuclear spins in order to form two-dimensional or three-dimensional images
Implementation Method 3
The magnetic field 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
Implementation Method 4
After termination of the RF pulse, the magnetization relaxes back to the original state of equilibrium, in which the magnetization in the z direction is built up again with a first time constant T1 (spin lattice or longitudinal relaxation time)
Implementation Method 5
the magnetization in the direction perpendicular to the z direction relaxes with a second time constant T2 (spin-spin or transverse relaxation time)
Implementation Method 6
In order to realize spatial resolution in the body, linear magnetic field gradients extending along the three main axes are superposed on the uniform magnetic field, leading to a linear spatial dependency of the spin resonance frequency
Data Source
AI summary
A method of MR imaging a moving portion of a body includes detecting a motion signal from the body while continuously subjecting the moving portion of the body to one or more preparation RF pulses; subjecting the moving portion of the body to an imaging sequence including an excitation RF pulse and switched magnetic field gradients, wherein the imaging sequence is triggered by the detected motion signal; acquiring MR signals from the moving portion of the body; and reconstructing an MR image from the acquired MR signals.