Look-Locker MRI T1 Measurement Delay Compensation
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Solution Overview
Problem
The Look-Locker method for magnetic resonance imaging does not accurately account for the longitudinal relaxation time (T1) in its calculations, leading to deviations in measured relaxation times, especially when a delay time is present, which affects the accuracy of T1 mapping.
Innovation Solution
The method incorporates additional equations to account for both the modulated relaxation time (T1*) and the longitudinal relaxation time (T1) by fitting initial and steady-state magnetization quantities using specific formulas, allowing for accurate calculation of T1 regardless of the presence of a delay time, utilizing a series of accelerated scramble phase gradient echo pulse sequences for image acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the Look-Locker method uses only the modulated relaxation time T1* for calculation, then the calculation process is simple, but the measurement precision of longitudinal relaxation time T1 deteriorates
Solution Approach 1:
The patent segments the relaxation process into two distinct phases: the delay time period (governed by T1) and the image acquisition period (governed by T1*). By introducing separate equations for each phase (Equation 2 for delay time, Equation 1 for acquisition), the method accurately captures both relaxation processes without oversimplification, thereby resolving the contradiction between calculation simplicity and measurement precision.
Solution Approach 2:
The patent introduces additional parameters (M0, the initial magnetization quantity) to the calculation model. By fitting three parameters (M0, M0*, and T1*) using the system of equations, the method transforms the single-parameter T1* model into a multi-parameter model that accounts for both relaxation processes, thus improving T1 measurement precision while maintaining computational feasibility through standardized fitting procedures.
2Ease of operation
If a delay time is introduced in the Look-Locker method, then certain scanning requirements (spoiler gradient, flexible inversion time, elimination of magnetic transfer effect) are met, but the accuracy of T1 measurement deteriorates due to unaccounted relaxation processes
Solution Approach 1:
The patent applies preliminary action by explicitly accounting for the relaxation process during the delay time period before image acquisition begins. Equation (2) describes the magnetization evolution during this preliminary phase, ensuring that the relaxation occurring before data collection is properly modeled. This preliminary consideration of the delay time relaxation process prevents measurement errors while maintaining the operational flexibility provided by the delay time.
3Ease of manufacture
If the Look-Locker method assumes single relaxation process with T1*, then the method is easy to implement, but the reliability of T1 measurement deteriorates when delay time is present
Solution Approach 1:
The patent introduces M0 (initial magnetization quantity) as an intermediary parameter that connects the delay time relaxation process and the image acquisition relaxation process. This intermediary allows the two distinct relaxation phases to be mathematically linked through the relationship M(t)=M0-[M0-M(t-ft)]exp(-tf/T1), enabling reliable T1 measurement by bridging the gap between the two relaxation processes while maintaining a systematic and implementable calculation framework.
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 ensures accurate measurement of longitudinal relaxation time (T1) by considering both relaxation processes, thereby avoiding deviations and expanding the method's applicability to scenarios with and without delay times.
Implementation Method 1
hydrogen nuclei within the human tissue are excited by a radio-frequency pulse with the same frequency as the precession frequency of the hydrogen nuclei, so as to cause resonance of the hydrogen nuclei in the tissue
Implementation Method 2
a relaxation process of a longitudinal relaxation time (T1) in the delay time, and a relaxation process of a longitudinal relaxation time (T1*) modulated by an image acquisition sequence
Data Source
AI summary
In a method and apparatus for magnetic resonance imaging, an inverse recovery pulse is emitted and execution of an image acquisition sequence wherein, magnetic resonance image data are received is begun after a delayed recovery time of the inverse recovery pulse. A magnetic resonance image is reconstructed from the acquired magnetic resonance image data. The longitudinal relaxation time is obtained based on a known time after the inverse recovery pulse and a magnetization quantity of the known time. A second relaxation time is thereby able to be fully taken into account, so as to avoid a deviation of the longitudinal relaxation time. The range of application of the Look-Locker method is expanded, so that the present invention obtains an accurate longitudinal relaxation time no matter whether a delay exists before a sampled sequence.