Reducing SAR and Artifacts in T1rho MR Imaging via Segmented RF Pulses
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Solution Overview
Problem
Existing MR imaging systems for spin-lock magnetic field preparation are limited by SAR constraints, vulnerable to static magnet field (B0) and dynamic transmission RF field (B1) inhomogeneity, leading to longer imaging times and increased risk of patient motion and mis-registration artifacts.
Innovation Solution
A system that reduces the length of RF pulses needed for T1rho contrast generation and minimizes sensitivity to B0 and B1 inhomogeneity using a saturation pulse sequence, STEAM echo sequence, and rotary spin-lock method, incorporating magnetic field gradients for improved spin-lock magnetic field preparation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a long radiofrequency (RF) pulse is used to generate required T1rho contrast, then T1rho contrast quality is improved, but SAR constraints are violated and imaging time increases
Solution Approach 1:
The patent segments the spin-lock preparation into multiple discrete RF pulses separated by gradient moments, rather than using a single long continuous RF pulse. This segmentation allows the system to achieve the required T1rho contrast while reducing the duration of any individual RF pulse, thereby reducing SAR deposition and total imaging time.
Solution Approach 2:
The patent employs periodic RF pulses with specific timing and gradient applications to generate T1rho contrast. By using a series of periodic pulses rather than a continuous long pulse, the system maintains contrast quality while reducing the duty cycle and SAR constraints.
2Measurement precision
If a long radiofrequency (RF) pulse is used to generate required T1rho contrast, then T1rho contrast quality is improved, but SAR constraints are violated
Solution Approach 1:
The patent divides the spin-lock preparation into multiple short RF pulses separated by gradient moments, reducing the peak power and duty cycle requirements. This segmentation lowers SAR deposition while maintaining the cumulative effect needed for T1rho contrast generation.
Solution Approach 2:
The use of periodic RF pulses with controlled timing and gradient applications reduces the average power deposition compared to a continuous long pulse, thereby satisfying SAR constraints while achieving the required contrast.
3Measurement precision
If conventional spin-lock preparation is used, then T1rho contrast is generated, but sensitivity to static magnet field (B0) and dynamic transmission RF field (B1) inhomogeneity increases
Solution Approach 1:
By segmenting the spin-lock preparation into multiple pulses with gradient moments in between, the patent reduces the cumulative effect of B0 and B1 inhomogeneities. Each short pulse experiences less phase accumulation from field imperfections compared to a single long pulse.
Solution Approach 2:
The patent introduces gradient moments as intermediary elements between RF pulses. These gradients act as mediators to refocus spins and compensate for phase errors caused by B0 and B1 inhomogeneities, improving the reliability of T1rho contrast generation.
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 reduces imaging time, minimizes artifacts, and enhances the robustness of T1rho mapping by eliminating T1 contamination and reducing sensitivity to B1 and B0 inhomogeneities, resulting in high-quality MR images with reduced SAR deposition.
Implementation Method 1
acquiring image data of a 3D volume showing luminance contrast due to T1 spin lattice relaxation in a rotating frame
Implementation Method 2
system for acquiring MR imaging data of a portion of patient anatomy associated with spin lattice relaxation time in a rotating frame
Implementation Method 3
The magnetic field gradient generator generates anatomical volume select magnetic field gradients for phase encoding and readout RF data acquisition in a three dimensional (3D) anatomical volume
Data Source
AI summary
A system acquires MR image data of a portion of patient anatomy associated with spin lattice relaxation time in a rotating frame using an RF (Radio Frequency) signal generator and a magnetic field gradient generator. The RF (Radio Frequency) signal generator generates RF excitation pulses in anatomy and enables subsequent acquisition of associated RF echo data. The magnetic field gradient generator generates anatomical volume select magnetic field gradients for phase encoding and readout RF data acquisition in a three dimensional (3D) anatomical volume. The RF signal generator and the gradient generator use in order, a saturation pulse, a T1 spin lattice relaxation rotating frame preparation pulse sequence and a spoiler gradient, in acquiring image data of the 3D volume showing luminance contrast associated with T1 spin lattice relaxation in a rotating frame.