MRI Gradient Pulse Waveform Shaping for NMR Signal Dynamic Range Control
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Solution Overview
Problem
Current MRI techniques face challenges in obtaining high SNR images due to the limited dynamic range of NMR signals, which requires extended measurement time or increased hardware and software costs when using multiple reception gains or companding methods.
Innovation Solution
The technique involves shifting the peak positions of NMR signals using frequency encoding gradient magnetic field pulses with different waveforms according to spatial positions, achieved by independently driving gradient magnetic field coils with varying electric currents, thereby narrowing the dynamic range of NMR signals without extending measurement time or increasing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the reception gain is increased to reduce noise ratio and improve image SNR, then the image quality is improved, but the dynamic range limitation of the A/D converter prevents further gain increase
Solution Approach 1:
The patent applies dynamic waveform design to gradient magnetic field pulses, where the waveform characteristics are adjusted based on spatial position. By making the gradient pulse waveforms dynamic (different for different positions), the system can shift peak positions of NMR signals from different locations to different time points, effectively spreading the signal energy over time and reducing the peak amplitude that needs to be handled by the A/D converter.
Solution Approach 2:
The patent changes the temporal parameters (waveform shapes) of gradient magnetic field pulses according to spatial position. By modifying the waveform parameters such as pulse duration, amplitude profile, and timing, the system achieves position-dependent peak shifting of NMR signals, which narrows the required dynamic range while maintaining signal quality.
2Adaptability or versatility
If multiple measurements with different reception gains are performed to obtain wide dynamic range, then the dynamic range is improved, but the measurement time is extended
Solution Approach 1:
The patent performs preliminary action by designing position-dependent gradient waveforms that pre-shift the peak positions of NMR signals before acquisition. This preliminary waveform design ensures that signals from different spatial locations are naturally distributed in time, achieving wide dynamic range coverage in a single measurement without requiring multiple sequential measurements with different gains.
Solution Approach 2:
The patent maintains continuous useful action by acquiring all necessary signal information in a single continuous measurement sequence. The position-dependent gradient waveforms ensure that throughout the continuous signal acquisition process, peaks from different positions are continuously distributed in time, eliminating the need to stop and restart measurements with different gain settings.
3Adaptability or versatility
If companding method is used to compress dynamic range, then the dynamic range is improved, but hardware costs increase due to non-linear amplifier
Solution Approach 1:
The patent replaces the mechanical/electronic companding system (non-linear amplifier hardware) with a magnetic field control system. Instead of using hardware non-linear amplification to compress dynamic range, the system uses position-dependent gradient magnetic field waveforms to achieve temporal distribution of signal peaks, substituting complex hardware processing with controlled magnetic field application.
4Adaptability or versatility
If companding method is used to compress dynamic range, then the dynamic range is improved, but software processing costs increase due to expansion processing
Solution Approach 1:
The patent extracts the dynamic range management function from the signal processing domain and moves it to the magnetic field control domain. By taking out the need for post-acquisition expansion processing and handling the dynamic range issue during the gradient pulse design and signal acquisition phase, the system eliminates complex software processing requirements.
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 allows for increased reception gain, reduced noise ratio, and improved image accuracy with high SNR without extending measurement time or increasing hardware and software processing costs.
Implementation Method 1
magnetic resonance imaging (hereinafter, referred to as MRI) technique for measuring nuclear magnetic resonance signals (hereinafter, referred to as NMR signals) from hydrogen, phosphorus, etc. of an object
Implementation Method 2
an excitation range is encoded to provide positional information by applying a phase encoding gradient magnetic field pulse and a frequency encoding gradient magnetic field pulse
Data Source
AI summary
In order to obtain highly accurate images with a high SNR without extending measurement time or increasing hardware costs and software processing costs, the present invention narrows a dynamic range (amplitude) of an NMR signal to be received by a reception coil (reception NMR signal) in an MRI apparatus. In order to narrow the amplitude of the reception NMR signal, according to the position of an imaging region, a peak position of the reception NMR signal is shifted from the said position in the present embodiment. The shift is achieved by applying frequency encoding gradient magnetic field pulses whose application amount in the time direction is different according to the position. This is realized by a plurality of gradient magnetic field generating systems that can be driven independently.