Echo Splitting for Magnetic Resonance Fingerprinting
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Solution Overview
Problem
Conventional MRI sequences face challenges in producing multiple echo pathways with varying signals over time, which limits the acquisition of rich and quantitative signal information, particularly in magnetic resonance fingerprinting (MRF), where constant signals are not desired, and multiple echo pathways are often refocused or spoiled.
Innovation Solution
The implementation of echo splitting techniques, such as the Quick Echo Split Technique (QUEST), which generates multiple echo paths by repeatedly de-phasing and exciting magnetization, allowing for the production of up to 3^k echo paths with a logarithmic growth in the number of echoes, reducing the need for gradient field switching and increasing the number of echoes acquired with a limited number of RF pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If multiple RF pulses are applied in conventional MRI sequences to generate multiple echo pathways, then the signal information richness is improved, but the acquisition time increases and SAR increases
Solution Approach 1:
The patent segments the echo acquisition process by using a single RF pulse to generate multiple echo pathways through controlled de-phasing and re-phasing of magnetization. Instead of applying multiple RF pulses sequentially, the method divides the magnetization into different echo paths using gradient fields, allowing simultaneous acquisition of multiple echo signals with different T1 and T2 weightings from one excitation event.
Solution Approach 2:
The patent employs periodic de-phasing and re-phasing gradient pulses to generate multiple echo pathways from a single RF excitation. The gradient fields are applied in a periodic pattern that creates controlled de-phasing followed by re-phasing, generating a series of echoes with varying contrast weights without requiring additional RF pulses, thus reducing SAR and acquisition time.
2Loss of information
If multiple RF pulses are used to generate multiple echo pathways, then the quantitative signal information is improved, but the specific absorption rate (SAR) increases
Solution Approach 1:
The patent segments the echo generation process by using gradient field manipulation rather than multiple RF pulses. A single RF pulse excites the magnetization, and subsequent gradient de-phasing and re-phasing events create multiple echo pathways with different T1 and T2 weightings. This segmentation approach maintains rich quantitative signal information while limiting RF energy deposition to one pulse per repetition cycle, thereby controlling SAR.
3Device complexity
If conventional MRI sequences use fixed flip angles to produce steady state signals, then the sequence simplicity is maintained, but the signal dynamics and information content are reduced
Solution Approach 1:
The patent introduces dynamics into the echo generation process by varying the de-phasing and re-phasing gradient strengths and timings across different repetition cycles. This creates dynamically varying echo pathways with different T1 and T2 weightings from a single RF pulse, enabling rich signal evolution that encodes multiple tissue parameters without requiring complex multi-pulse sequences or variable flip angle schemes.
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 significantly reduces acquisition time, increases the amount of information acquired per unit time, and decreases the specific absorption rate (SAR), enabling the generation of rich signal sets in a short period and facilitating the integration of additional parameters like diffusion sensitivity, while maintaining accurate T1 and T2 value quantification.
Implementation Method 1
magnetic resonance fingerprinting (MRF) involves applying a series of varied NMR excitations to an object
Implementation Method 2
echo splitting techniques, such as the Quick Echo Split Technique (QUEST), which generates multiple echo paths by repeatedly de-phasing and exciting magnetization
Data Source
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AI summary
Apparatus, methods, and other embodiments associated with nuclear magnetic resonance (NMR) fingerprinting using echo splitting are described. One example apparatus includes an NMR logic configured to repetitively and variably sample a (k, t, E) space associated with an object to acquire a set of NMR signals. Members of the set of NMR signals are associated with different points in the (k, t, E) space. Sampling is performed with t and/or E varying in a non-constant way. The varying parameters may include the number of echo splitting pulses, spacings between echo splitting pulses, flip angle of echo splitting pulses, echo time, RF amplitude, and other parameters. The NMR apparatus may also include a signal logic configured to produce an NMR signal evolution from the NMR signals, and a characterization logic configured to characterize a resonant species in the object as a result of comparing acquired signals to reference signals.