Multi-phase Pseudo-Continuous Arterial Spin Labeling for MRI Perfusion
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Solution Overview
Problem
Conventional pseudo-continuous arterial spin labeling (PCASL) methods are sensitive to phase tracking errors caused by gradient imperfections and off-resonance fields, leading to reduced tagging efficiency and inaccurate perfusion quantification in MRI applications.
Innovation Solution
The implementation of a multi-phase pseudo-continuous arterial spin labeling (MP-PCASL) method with multiple phases, which reduces sensitivity to phase tracking errors by fitting acquired data to a predefined inversion response function and compensating for phase errors using XY shim gradients, enabling more accurate and robust blood perfusion quantification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PCASL methods are used, then the tagging process is simple, but phase tracking errors occur due to gradient imperfections and off-resonance fields, reducing tagging efficiency and accuracy
Solution Approach 1:
The tagging process is divided into multiple phases (at least four phases with evenly distributed phase offsets) instead of using a simple two-phase approach. This segmentation allows the system to sample different phase points and fit the data to an inversion response function, thereby reducing sensitivity to phase tracking errors and improving perfusion quantification accuracy.
Solution Approach 2:
The patent changes the phase offset parameter across multiple tagging pulses, distributing phases evenly (e.g., 0, π/2, π, 3π/2 for four phases). This parameter variation enables the system to capture the inversion response curve and accurately determine the inversion time, compensating for phase errors caused by gradient imperfections and off-resonance effects.
2Reliability
If multi-phase tagging is implemented, then phase error sensitivity is reduced, but the number of RF pulses and processing complexity increase
Solution Approach 1:
The patent employs periodic modulation of the phase offset across multiple tagging pulses, creating a periodic pattern in the acquired signal. This periodic action allows the use of Fourier analysis or curve fitting to extract the inversion response, providing robust phase error compensation while maintaining a systematic and manageable pulse sequence structure.
Solution Approach 2:
The system acquires signals at multiple phase points and fits the data to an inversion response function, using the fitted parameters to determine the actual inversion time and phase corrections. This feedback mechanism allows the system to adapt to phase errors and optimize the tagging process, improving reliability despite the increased complexity of the pulse sequence.
3Measurement precision
If conventional two-phase PCASL is used, then the scan time is short, but the signal-to-noise ratio is lower and temporal resolution is limited
Solution Approach 1:
The patent acquires more phase information than the minimum required for basic tagging (excessive action by using at least four phases instead of two). This excess data acquisition improves the signal-to-noise ratio through better sampling of the inversion response curve and enables more accurate determination of perfusion parameters, justifying the increased scan time.
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
MP-PCASL provides consistent and robust blood perfusion quantification with higher signal-to-noise ratio (SNR) compared to conventional PCASL, improving the accuracy of cerebral blood flow measurements and reducing the impact of phase errors, while also offering faster processing options through signal demodulation.
Implementation Method 1
manipulating the magnetic spins in a body part and processing measured responses from the magnetic spins
Implementation Method 2
RF magnetic field to manipulate the spins
Implementation Method 3
gradient fields along mutually orthogonal x, y, or z directions to spatially select a body part for imaging
Implementation Method 4
MP-PCASL tagging scheme can be generalized in the equation below, where M represents the total number of phases. Δθm=θn,m−θn-1,m=γGtd+2πm/M
Implementation Method 5
acquiring magnetic resonance signals based on the applied train of RF pulses to sample the more than two phases
Data Source
AI summary
Techniques, systems and apparatus are described for magnetic resonance imaging. A magnetic resonance imaging (MRI) system comprises a scanner comprising a magnet, gradient coils and a radio frequency (RF) system to perform various operations. The scanner can apply a gradient field and a train of RF pulses comprising more than two phases to tag a target blood vessel, and acquire magnetic resonance signals based on the applied train of RF pulses to sample the more than two phases. The MRI system includes a data processing system in communication with the scanner to receive the acquired magnetic resonance signals and process the received magnetic resonance signal to generate images proportional to perfusion.