Adiabatic Half-Passage Spin-Lock MRI Sequence
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Magnetic resonance imaging (MRI) techniques face challenges in achieving robust imaging due to spatial inhomogeneity in B1 RF and B0 fields, leading to image artifacts such as banding effects, which reduce the diagnostic utility of T1rho imaging and other spin-lock based methods.
Innovation Solution
The implementation of a magnetization prep sequence that includes an adiabatic half-passage (AHP) followed by a spin-lock pulse and a reverse AHP, with amplitude and frequency modulation to align magnetization with the spin-lock field for both on-resonance and off-resonance frequencies, and a dual-acquisition approach to reduce errors in T1rho determination using a modified relaxation model.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional spin-lock pulse sequences are used, then T1rho imaging can be performed, but spatial inhomogeneity in B1 RF and B0 fields causes image artifacts such as banding effects
Solution Approach 1:
The patent applies adiabatic half passage (AHP) pulses before the spin-lock pulse to pre-align the magnetization vector with the effective field. This preliminary action ensures that spins are properly oriented before entering the spin-lock period, making the sequence robust against B1 and B0 field inhomogeneities and eliminating banding artifacts.
Solution Approach 2:
The patent modifies the conventional spin-lock sequence by introducing amplitude and frequency modulation through AHP pulses. The RF amplitude and frequency are varied during the AHP period to adiabatically rotate the magnetization, which compensates for field inhomogeneities and improves image reliability.
2Reliability
If adiabatic half passage pulses are added to align magnetization, then robustness against field inhomogeneity improves, but sequence complexity increases
Solution Approach 1:
The patent divides the magnetization preparation into distinct segments: an AHP pulse segment before the spin-lock pulse and a reverse AHP pulse segment after it. This segmentation allows each component to perform its specific function (alignment and re-alignment) while maintaining overall sequence structure and manageability.
Solution Approach 2:
The AHP pulses act as intermediary elements that mediate between the initial magnetization state and the spin-lock process. These intermediary pulses adiabatically rotate the magnetization to align with the effective field, facilitating robust spin-locking without requiring direct manipulation of the spin-lock parameters.
3Reliability
If reverse AHP is used to re-align magnetization, then spin alignment improves, but relaxation effects during reverse AHP introduce errors in T1rho determination
Solution Approach 1:
The patent incorporates a reverse AHP pulse after the spin-lock period to re-align the magnetization vector. This feedback action ensures that any deviations from proper alignment are corrected, maintaining robustness throughout the sequence. The relaxation effects during reverse AHP are accounted for in the data analysis to preserve measurement precision.
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 effectively reduces image artifacts and improves the accuracy of T1rho quantification by aligning spins with the spin-lock field, even in the presence of field inhomogeneities, and provides robust T1rho-weighted images with reduced errors.
Implementation Method 1
an adiabatic half passage (AHP) followed by a spin-lock pulse, followed by a reverse AHP
Implementation Method 2
RF pulses with magnetic field components (B1) transverse to the longitudinal field and frequencies tuned to the Larmor frequency of an isotope of interest
Implementation Method 3
an RF pulse, referred to as a spin-lock pulse, is applied to lock the magnetization around an effective magnetic field
Implementation Method 4
Magnetic resonance imaging (MRI) is a noninvasive diagnostic technique that can allow assessments of the composition and state of various tissues
Data Source
AI summary
MRI techniques provide robust imaging in the presence of inhomogeneity in the B1 (RF) and/or B0 magnetic fields. The techniques include using a magnetization prep sequence that includes an adiabatic half passage (AHP) followed by a spin-lock pulse, followed by a reverse AHP, after which a data acquisition sequence can be applied. The AHP and reverse AHP can have amplitude and frequency modulated to sweep through a region of frequency space. The RF amplitude of the AHP and reverse AHP can be designed to be equal to the spin-lock amplitude. Quantification of a magnetization relaxation parameter (e.g., T1rho) can use a modified relaxation model that accounts for relaxation effects during the reverse AHP. A dual-acquisition technique in which the reverse AHP of the second magnetization prep sequence has opposite frequency modulation to the reverse AHP of the first magnetization prep sequence can also be used.