RF Spatial Encoding via Bloch-Siegert Effect
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Solution Overview
Problem
Magnetic resonance tomographs face challenges with large, expensive gradient coils that generate high energy costs, unpleasant noise, and limited encoding speed due to inductivity, causing discomfort for patients and inefficiencies in spatial encoding.
Innovation Solution
The use of a radio frequency unit generating specific frequency signals to create gradients via the Bloch-Siegert effect, allowing for spatial encoding without gradient coils, using antenna apparatuses arranged to emit these signals, which can be closer to the patient, reducing noise and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gradient coils are used for spatial encoding, then spatial encoding capability is achieved, but energy consumption increases and noise is generated
Solution Approach 1:
The patent replaces the mechanical gradient coil system with an electromagnetic field-based approach using radio frequency pulses and the Bloch-Siegert effect. Instead of using large gradient coils that consume high energy, the invention uses RF signals transmitted through antenna elements to induce frequency shifts in the Larmor precession of nuclear spins, thereby achieving spatial encoding without the need for high-power gradient coils
Solution Approach 2:
The invention changes the fundamental parameter used for spatial encoding from magnetic field gradient strength to radio frequency signal frequency. By varying the frequency of RF pulses applied through different antenna elements and utilizing the Bloch-Siegert effect, the system achieves spatial encoding through frequency modulation rather than through gradient field strength, significantly reducing energy requirements
2Productivity
If gradient coils are used for spatial encoding, then spatial encoding capability is achieved, but noise is generated causing patient discomfort
Solution Approach 1:
The patent replaces the mechanical gradient coil system with an electromagnetic field-based approach using radio frequency pulses and the Bloch-Siegert effect. Instead of using large gradient coils that generate audible noise, the invention uses RF signals transmitted through antenna elements to induce frequency shifts in the Larmor precession of nuclear spins, thereby achieving spatial encoding without noise-generating gradient coils
3Productivity
If gradient coils are used for spatial encoding, then spatial encoding is achieved, but encoding speed is limited due to inductivity
Solution Approach 1:
The patent replaces the inductive gradient coil system with a direct RF excitation system. By using radio frequency pulses transmitted through antenna elements and exploiting the Bloch-Siegert effect, the invention eliminates the inductive time constants that limit gradient coil switching speed. This allows for much faster transitions between encoding states since RF pulse durations can be significantly shorter than gradient coil rise times
Solution Approach 2:
The invention employs periodic RF pulse sequences with carefully controlled timing and frequency modulation. By using repetitive RF pulse trains with varying frequencies and phases across different antenna elements, the system achieves rapid spatial encoding through time-efficient pulse sequences that are not constrained by gradient coil inductivity
4Area of stationary object
If large gradient coils are used, then examination volume coverage is achieved, but device size and cost increase
Solution Approach 1:
The patent divides the examination volume into multiple segments or regions, each associated with specific antenna elements or element groups. By segmenting the RF transmission system into multiple independently controllable antenna elements, the invention can achieve full-volume coverage through coordinated activation of different element subsets, replacing the need for a single large gradient coil system
Solution Approach 2:
The antenna elements serve multiple functions: they transmit RF excitation pulses for spatial encoding, receive MR signals from the examination volume, and can be selectively activated to cover different regions. This multi-functionality eliminates the need for separate gradient coil systems for each encoding direction, reducing overall device complexity and size while maintaining full examination volume coverage
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 enables more efficient and patient-friendly spatial encoding with faster gradient generation and reduced energy costs, eliminating the need for bulky gradient coils and minimizing patient discomfort.
Implementation Method 1
The parameters are determined such that when transmitting signals according to the parameters over the antenna apparatus, a first gradient above the Larmor frequency of the nuclear spins is generated by the Bloch-Siegert effect
Data Source
AI summary
An apparatus and a method for spatial encoding in magnetic resonance tomography using a radio frequency signal are provided. A first set of parameters from a first frequency and from a first amplitude, and from a second frequency and a second amplitude is determined by the magnetic resonance tomograph, and corresponding signals are generated by a radio frequency device and transmitted by an antenna apparatus. A first gradient above the Larmor frequency of the nuclear spins is generated by the Bloch-Siegert effect. The same thing ensues with a second set of parameters that differs from the first set of parameters at least in one frequency or amplitude and therefore generates a second, different gradient.