Adiabatic Pulse Sequence for Low SAR MR Imaging
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Solution Overview
Problem
Conventional MRI techniques for acquiring T1rho and T2rho imaging data face limitations due to high Specific Absorption Rate (SAR), long acquisition times, reduced spatial coverage, and sensitivity to B1 inhomogeneity and B0 field offsets, which restricts the ability to obtain multiple slices efficiently.
Innovation Solution
A system utilizing an RF signal generator and magnetic field gradient generator to provide a rotating frame preparation pulse sequence with adiabatic pulses and modulated RF and gradient pulses, specifically using Gradient Offset Independent Adiabaticity with Wurst modulation (GOIA-W) for slice selection, enabling efficient acquisition of multiple image slices with reduced SAR and accelerated imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional MRI techniques are used for T1rho and T2rho imaging, then imaging data can be acquired, but Specific Absorption Rate (SAR) is high and acquisition time is long
Solution Approach 1:
The patent applies adiabatic pulses with modified amplitude and frequency modulation parameters to achieve rotating frame preparation. By changing the pulse parameters (amplitude modulation, frequency sweep rates) and using gradient modulation, the method reduces SAR while maintaining imaging effectiveness, directly resolving the contradiction between acquisition time and energy consumption
2Area of stationary object
If conventional pulse sequences are used, then imaging can be performed, but spatial coverage is reduced and multiple slices cannot be acquired efficiently
Solution Approach 1:
The patent implements slice-selective adiabatic pulses with gradient modulation, dividing the imaging volume into multiple selectable slices. This segmentation allows efficient acquisition of multiple slices (e.g., 128 slices in 7.21 minutes) by independently controlling RF and gradient pulses for each slice, thereby increasing both spatial coverage and productivity
3Reliability
If conventional imaging methods are used, then T1rho and T2rho data can be obtained, but sensitivity to B1 inhomogeneity and B0 field offsets limits efficiency
Solution Approach 1:
The patent employs adiabatic pulses that inherently compensate for B1 inhomogeneity and B0 offsets during the preparation phase. The adiabatic condition ensures that the magnetization follows the effective field regardless of field variations, providing preliminary robustness that maintains reliability while enabling efficient imaging without requiring additional correction steps
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
The system achieves increased spatial coverage and shorter acquisition times, allowing for the acquisition of up to 128 slices in 7.21 minutes with reduced SAR, while being less sensitive to B0 and B1 inhomogeneities, thereby improving the efficiency and effectiveness of T1rho and T2rho imaging.
Implementation Method 1
MR imaging is a medical imaging technique that uses an applied magnetic field and RF pulses to make images of organs and structures inside the body. During MR imaging, the magnetic field causes magnetic field vectors of protons (typically in hydrogen atoms) to align with the magnetic field. The RF pulses cause the magnetic field vectors of the protons to be displaced from the magnetic field and re-align with the magnetic field.
Implementation Method 2
A magnetic field gradient generator generates magnetic field gradients for anatomical slice selection, phase encoding and readout
Data Source
AI summary
A system acquires MR imaging data of a portion of patient anatomy associated with proton spin lattice relaxation time in a rotating frame using an RF (Radio Frequency) signal generator configured to generate RF excitation pulses and a magnetic field gradient generator configured to generate anatomical volume select magnetic field gradients for phase encoding and readout RF data acquisition. The RF signal generator and the gradient generator are configured to provide a rotating frame preparation pulse sequence comprising at least one of, (a) a T1 spin lattice relaxation in a rotating frame (T1ρ) preparation pulse sequence of adiabatic pulses comprising modulated RF pulses and modulated magnetic field gradients for slice selection and (b) a T2 spin-spin relaxation in a rotating frame (T2ρ) preparation pulse sequence of adiabatic pulses comprising modulated RF pulses and modulated magnetic field gradients for slice selection.