Multiphoton MRI Using Z-Axis RF Coils to Reduce Patient Heating
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Solution Overview
Problem
Conventional MRI systems rely on single-photon excitation, which can cause patient heating, limit spatial encoding, and restrict the acquisition of certain patient properties due to strong RF pulses, necessitating improved imaging methods.
Innovation Solution
The implementation of multiphoton MRI techniques using an additional RF coil oriented along the z-axis parallel to the main magnetic field, allowing for the development of new pulses and imaging approaches, including the use of oscillating gradients to create multiphoton resonances and transform standard pulse sequences into multiband ones without modifying the RF pulse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If strong RF pulses are used for excitation, then transverse magnetization is generated, but patient heating increases
Solution Approach 1:
The patent changes the fundamental excitation parameter from single-photon resonance at Larmor frequency to multiphoton processes involving multiple lower-energy photons. This parameter change allows achieving the same transverse magnetization effect with lower peak RF power, thereby reducing patient heating while maintaining imaging capability
Solution Approach 2:
The patent employs periodic oscillating gradient fields applied along with RF pulses to create time-varying resonance conditions. This periodic action enables multiphoton excitation where the cumulative effect of multiple lower-energy photons achieves the desired spin excitation, distributing energy delivery over time and reducing instantaneous heating
2Productivity
If single-photon excitation is used, then imaging is achieved, but spatial encoding ability is limited
Solution Approach 1:
The patent adds a temporal dimension to the excitation process by using oscillating gradients that modulate the resonance frequency over time. This time-varying gradient approach creates additional spatial encoding dimensions, enabling more sophisticated localization and imaging capabilities beyond conventional static gradient methods
3Productivity
If conventional single-photon excitation is used, then imaging is performed, but flexibility for acquiring certain patient properties is limited
Solution Approach 1:
The patent introduces dynamic control over the excitation process through time-varying gradient fields and multiphoton sequences. This dynamics enables adaptive adjustment of imaging parameters during the scan, allowing flexible acquisition of different tissue properties and contrast mechanisms that are inaccessible to static single-photon excitation methods
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 enhances imaging flexibility by enabling excitation beyond the Larmor frequency, reducing patient heating, and improving spatial encoding, while maintaining comparable signal-to-noise ratios to single-photon excitation.
Implementation Method 1
at least one additional RF Coil producing a magnetic field oriented in the z-direction
Implementation Method 2
simultaneously oscillating gradients along a z-axis, parallel to the main magnetic field B0 field
Implementation Method 3
multiphoton effects occur when more RF fields are added along the z-axis, parallel to the main magnetic field B0
Data Source
AI summary
Systems and methods are provided for multiphotonic magnetic resonance imaging. The system uses one or more (B1,z) RF coils or oscillating gradients oriented along the z-axis to provide multiphoton resonances. The B1,z coils can be implemented as planar coils or solenoids. With the additional coils, standard slice-selective pulse sequences have all standard excitations replaced with multiphoton excitations that excite extra resonances. In vivo imaging using multiphoton excitation has signal to noise ratios comparable to single-photon excitations when similar pulse sequences are used. Since excitation is not bound to the Larmor frequency, new RF pulse sequences can be designed with imaging methods patterned after single-photon excitation concepts.