MRI Pulse Sequences for Artifact Compensation
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Solution Overview
Problem
Current MRI systems face challenges in producing high-contrast, artifact-free images within acceptable Specific Absorption Rate (SAR) levels, as high-power RF pulses can cause tissue damage and conventional techniques require harmful contrast agents or result in reduced image quality.
Innovation Solution
A method and system that compensate for external and radiofrequency magnetic-field inhomogeneities by applying pulse sequences with arbitrary-excitation flip angles and spin-locking pulses, both on and off resonance, to minimize artifacts and reduce RF power usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high-power RF pulses are used to maximize tissue contrast, then image contrast is improved, but tissue damage and SAR levels worsen
Solution Approach 1:
The patent changes the frequency parameter of RF pulses from on-resonance to off-resonance, and modifies pulse sequence parameters by incorporating spin-locking pulses and refocusing composite pulses. This allows achieving adequate tissue contrast without requiring high RF power, thereby reducing SAR levels and avoiding tissue damage while maintaining diagnostic image quality
Solution Approach 2:
The patent employs periodic pulse sequences including spin-locking pulses applied at specific intervals between excitation pulses. These periodic applications of lower-power pulses with specific timing achieve the desired contrast enhancement through cumulative effect, replacing the need for single high-power pulses
2Object-affected harmful factors
If RF power is reduced to meet acceptable SAR levels, then safety is improved, but image quality and tissue contrast worsen
Solution Approach 1:
The patent introduces spin-locking pulses as intermediary elements between excitation pulses. These intermediate pulses manipulate the spin state to enhance contrast without requiring high RF power for the main excitation, allowing safe SAR levels while maintaining image quality through the mediating action of spin-locking sequences
Solution Approach 2:
By changing the frequency to off-resonance and adjusting pulse timing parameters, the system achieves enhanced tissue contrast at low RF power levels. The parameter modifications allow the MRI system to operate within safe SAR limits while producing diagnostic-quality images with adequate contrast
3Ease of operation
If conventional pulse sequences are used, then ease of operation is maintained, but image artifacts increase due to magnetic field inhomogeneities
Solution Approach 1:
The patent incorporates refocusing composite pulses and spin-locking pulses as preliminary actions before signal acquisition. These pre-applied pulses compensate for magnetic field inhomogeneities by realigning spins and eliminating phase errors before imaging, preventing artifacts from forming during the scan while maintaining operational simplicity
Solution Approach 2:
The patent employs refocusing composite pulses that provide feedback correction for magnetic field inhomogeneities. The sequence design includes built-in compensation mechanisms that detect and correct field variations, ensuring artifact-free images without requiring complex external adjustments or sophisticated real-time feedback systems
4Manufacturing precision
If intravenous contrast agents are used to compensate for field inhomogeneities, then image quality is improved, but patient safety and side effects worsen
Solution Approach 1:
The patent replaces the chemical mechanism of intravenous contrast agents with a physical pulse sequence mechanism. By using spin-locking pulses and refocusing composite pulses, the system achieves enhanced image contrast and artifact reduction through electromagnetic field manipulation rather than chemical substances, eliminating the safety risks associated with contrast agents
Solution Approach 2:
The patent enables the MRI system to self-compensate for field inhomogeneities through built-in pulse sequence design. The refocusing composite pulses and spin-locking sequences automatically correct for magnetic field variations without requiring external contrast agents, allowing the system to serve its own diagnostic needs without additional patient intervention
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 the production of high-contrast, artifact-free MR images at low RF power levels, within safe SAR limits, potentially eliminating the need for intravenous contrast agents and improving image quality.
Implementation Method 1
Radio-frequency (RF) pulses are emitted by the coils, causing the target atoms to absorb energy. In response to the RF pulses, photons are emitted by the target atoms and detected as signals in receiver coils.
Implementation Method 2
The scanner provides a magnetic field that causes target atoms to align with the magnetic field.
Data Source
AI summary
Methods of, and systems for, simultaneously compensating for external-magnetic-field inhomogeneity as well as radiofrequency magnetic-field inhomogeneity in an MRI system. In one method embodiment, a pulse sequence is applied when the transmitter-reference frequency is delivered on resonance. The pulse sequence includes radiofrequency pulses which may be applied at arbitrary-excitation-flip angles that are not necessarily 90° degrees. The pulse sequence also includes spin-locking pulses applied in concert with a refocusing-composite pulse. In another method embodiment, a pulse sequence is applied when the transmitter-reference frequency is delivered off resonance. This off-resonance-pulse sequence includes radiofrequency pulses which may be applied at arbitrary-excitation-flip angles that are not necessarily 90° degrees. Sandwiched between the excitation-flip angles are at least two off-resonance-spin-lock pulses applied at an inverse phase and frequency from each other.