NMR Fingerprinting via Variable RF Pulse Sequences
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Solution Overview
Problem
Conventional MRI techniques are limited in their ability to accurately and efficiently determine relaxation parameters of tissues, as they rely on coercive signal acquisition methods that constrain signal production, leading to subjective image interpretations and limitations in acquiring information about multiple relaxation parameters simultaneously.
Innovation Solution
The approach involves applying a series of varied sequence blocks to produce unique signal evolutions in resonant species, allowing for pattern recognition and characterization of tissues without forcing specific signals, enabling the determination of relaxation parameters through comparison with known or simulated signal evolutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MRI pulse sequences with preparation/wait/acquire phases are used to determine relaxation parameters, then qualitative images with specific weightings can be produced, but the process requires lengthy acquisition times and multiple repetitive sequences
Solution Approach 1:
The patent applies periodic RF pulse sequences with varying parameters (flip angles, echo times, inversion times) to excite resonant species, creating periodic signal evolutions that encode multiple relaxation parameters simultaneously. This periodic excitation approach replaces the need for multiple separate prepare/wait/acquire sequences, reducing total acquisition time while maintaining measurement precision through the systematic variation of sequence parameters across multiple periodic cycles
Solution Approach 2:
The patent systematically changes key pulse sequence parameters including flip angles, echo times, and inversion times across different excitations. By varying these parameters periodically, the method generates distinct signal evolution patterns that contain encoded information about multiple relaxation parameters (T1, T2, T2*), enabling their determination from a single continuous acquisition rather than multiple separate sequences
2Loss of information
If conventional MRI forces specific signal production through precise preparation conditions, then images can be reconstructed, but the approach constrains natural signal evolution and limits information about multiple relaxation parameters
Solution Approach 1:
The patent replaces the mechanical/constraint-based signal acquisition approach with a pattern recognition system. Instead of forcing signals to conform to predefined image reconstruction requirements, the method acquires natural signal evolutions and uses computational pattern matching (comparing acquired signals to simulated libraries) to extract relaxation parameters. This substitution of computational analysis for mechanical constraint reduces information loss while managing complexity through software rather than hardware constraints
Solution Approach 2:
The patent introduces a signal evolution library as an intermediary between the acquired NMR signals and the relaxation parameter determination. Simulated signal evolutions serve as reference patterns that mediate the interpretation of acquired signals, enabling the extraction of multiple relaxation parameters without direct constraint on the natural signal production process
3Measurement precision
If multiple separate pulse sequences are applied to acquire different weighted signals, then comprehensive tissue characterization is possible, but registering and aligning signals from these acquisitions becomes difficult
Solution Approach 1:
The patent merges the acquisition of multiple relaxation parameter information into a single continuous NMR signal evolution rather than requiring separate T1-weighted, T2-weighted, and other specialized sequences. By systematically varying pulse sequence parameters within one acquisition, the method simultaneously captures information about multiple relaxation parameters, eliminating the need to register and align signals from multiple separate acquisitions while maintaining comprehensive tissue characterization capability
4Productivity
If conventional MRI uses short wait times between preparations, then acquisition speed increases, but the ability to capture full relaxation evolution is limited
Solution Approach 1:
The patent employs dynamic variation of pulse sequence parameters (flip angles, echo times, inversion times) across successive excitations rather than using static, repeated sequences. This dynamic approach allows the system to efficiently sample the relaxation evolution at multiple points within a single acquisition, capturing complete relaxation information with shorter effective wait times between parameter variations, thereby maintaining both high productivity and 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 method enhances the accuracy and robustness of relaxation parameter determination, allowing for more precise and quantitative analysis of tissue characteristics without the limitations of conventional imaging sequences, enabling longer signal acquisition times and improved sensitivity to multiple relaxation parameters.
Implementation Method 1
controlling an NMR apparatus to apply RF energy to a volume containing one or more resonant species to produce individual NMR signals from the resonant species
Implementation Method 2
determine a signal evolution from the individual NMR signals... compare the signal evolution to one or more known, stored, simulated, and/or predicted signal evolutions... characterize at least one of the resonant species by comparing the signal evolution
Data Source
AI summary
Apparatus, methods, and other embodiments associated with NMR fingerprinting are described. One example NMR 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 flip angle, 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, a matching logic configured to compare a signal evolution to a known, simulated or predicted signal evolution, and a characterization logic configured to characterize a resonant species in the object as a result of the signal evolution comparisons.