Stimulated Echo MR Reference Scan for Metal Susceptibility
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Solution Overview
Problem
Current MR imaging techniques face challenges in achieving fast and robust imaging of soft tissue near metal implants due to susceptibility issues, leading to signal voids and geometric distortions, particularly with standard SENSE reference scans being sensitive to metal susceptibility effects.
Innovation Solution
A stimulated echo sequence is employed, including preparation and reading RF pulses, with FID and stimulated echo signals acquired using parallel RF coils to derive spatial sensitivity profiles, enabling a fast and robust SENSE reference scan that is resistant to susceptibility effects, and allowing for simultaneous acquisition of B0 and B1 maps without additional scan time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If standard SENSE reference scan is used for MR imaging near metal implants, then scan duration is reduced, but susceptibility-induced artifacts (signal voids and geometric distortions) increase
Solution Approach 1:
The patent changes the imaging sequence parameters from standard gradient echo to stimulated echo sequence with specific timing parameters (TE, TR, flip angles) that are optimized to minimize susceptibility artifacts while maintaining fast scan duration. The stimulated echo sequence uses a specific parameter configuration where the first RF pulse has flip angle α, the second RF pulse has flip angle β, and the echo time TE is optimized to reduce artifact formation near metal implants.
2Reliability
If multispectral imaging techniques (SEMAC, MAVRIC) are used to counter susceptibility issues, then image quality improves, but scan duration increases
Solution Approach 1:
The patent segments the imaging process into a fast stimulated echo reference scan that acquires coil sensitivity data, followed by a compressed sensing-based parallel imaging reconstruction. This segmentation allows the reference scan to be completed quickly without the lengthy multi-spectral acquisition, while still providing the necessary sensitivity profiles for artifact reduction in the final image reconstruction.
Solution Approach 2:
The patent introduces stimulated echo signals as an intermediary mechanism that bridges the gap between fast single-spectral scanning and artifact-free multi-spectral imaging. The stimulated echo sequence serves as a mediator that provides susceptibility-resistant coil sensitivity data without requiring the extended scan times of SEMAC or MAVRIC techniques.
3Speed
If standard gradient echo sequence is used for reference scan, then acquisition speed is high, but sensitivity to susceptibility effects increases
Solution Approach 1:
The patent fundamentally changes the sequence type from gradient echo to stimulated echo, altering the physical parameters of signal generation. The stimulated echo sequence uses a different mechanism where magnetization is stored along the longitudinal axis between the second and third RF pulses, making it inherently less sensitive to susceptibility-induced dephasing while maintaining fast acquisition speed through optimized timing parameters.
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 accelerates multispectral MR imaging near metal, providing robust RF coil sensitivity information and adaptive frequency coverage, reducing scan duration and improving image quality by minimizing susceptibility-induced artifacts.
Implementation Method 1
Image-forming MR methods which utilize the interaction between magnetic fields and nuclear spins in order to form two-dimensional or three-dimensional images
Implementation Method 2
the magnetization in the z direction is built up again with a first time constant T1 (spin lattice or longitudinal relaxation time)
Implementation Method 3
the magnetization in the direction perpendicular to the z direction relaxes with a second time constant T2 (spin-spin or transverse relaxation time)
Implementation Method 4
The spin system can be excited (spin resonance) by application of an electromagnetic alternating field (radio frequency (RF) field, also referred to as B1 field) of defined frequency (so-called Larmor frequency, or MR frequency)
Implementation Method 5
The variation of the magnetization can be detected by means of one or more receiving RF coils which are arranged and oriented within an examination volume of the MR device in such a manner that the variation of the magnetization is measured in the direction perpendicular to the z-axis
Data Source
AI summary
The invention relates to a method of parallel MR imaging, wherein a reference scan is performed by means of a stimulated echo sequence including i) at least two preparation RF pulses (α) radiated toward a portion of a body (10) during a preparation period (21), and ii) one or more reading RF pulses (β) radiated toward the portion of the body (10) during an acquisition period (22) temporally subsequent to the preparation period (21). One or more FID signals (I1) and one or more stimulated echo signals (I2) are acquired during the acquisition period (22). The spatial receive and/or—if applicable—transmit4 sensitivity profiles of at least two RF coils (11, 12, 13) are derived from the acquired FID signals (I1) and/or from the acquired stimulated echo signals (I2). The parameters of the stimulated echo sequence are selected such that it is robust against susceptibility-induced artifacts. Moreover, 10 the invention relates to a MR device (1) and to a computer program for a MR device (1).