B1-Corrected T1 Mapping in MRI Using Preliminary Field Acquisition
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Solution Overview
Problem
Existing T1 mapping methods in MRI are affected by B1 inhomogeneity, leading to inaccurate T1 values due to variations in the B1 field generated by the RF coil, which current methods attempt to address through adiabatic pulses or additional fitting parameters, but these approaches have limitations such as increased specific absorption rate and noise.
Innovation Solution
Acquire first MR data in the absence of a B1 field and second MR data shortly after its generation, processing these to determine a B1 field map, which is then used to generate a T1 map, thereby accounting for B1 inhomogeneity without the need for adiabatic pulses or additional fitting parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If adiabatic or optimized preparation pulses are applied to minimize sensitivity to B1 inhomogeneity, then T1 mapping accuracy is improved, but specific absorption rate increases
Solution Approach 1:
The patent extracts the B1 field map measurement as a separate preliminary step from the T1 mapping procedure. By acquiring the B1 field map first using a low-flip-angle sequence, the method separates the B1 inhomogeneity characterization from the T1 measurement, allowing accurate T1 mapping without requiring high-power adiabatic pulses that increase specific absorption rate.
Solution Approach 2:
The B1 field map is measured in advance before the actual T1 mapping sequence is executed. This preliminary measurement of the B1 field distribution allows the T1 fitting process to compensate for B1 inhomogeneity effects, achieving accurate T1 values without needing to apply corrective adiabatic pulses during the T1 measurement itself.
2Measurement precision
If additional fitting parameters are added to model saturation or inversion efficiency, then T1 mapping accuracy is improved, but noise increases
Solution Approach 1:
The B1 field map serves as an intermediary measurement that quantifies the B1 inhomogeneity distribution. Instead of adding complex fitting parameters to the T1 model, the method uses the pre-measured B1 field map as a mediator to correct for B1 effects during T1 fitting, thereby achieving accurate T1 values without introducing additional noise through extra fitting parameters.
3Device complexity
If B1 inhomogeneity is not accounted for, then device complexity is reduced, but T1 mapping accuracy deteriorates
Solution Approach 1:
The B1 field map is measured in advance before the actual T1 mapping sequence is executed. This preliminary measurement of the B1 field distribution allows the T1 fitting process to compensate for B1 inhomogeneity effects, achieving accurate T1 values without needing to apply corrective adiabatic pulses during the T1 measurement itself.
Solution Approach 2:
The patent divides the T1 mapping process into two separate segments: (1) B1 field map measurement using a low-flip-angle sequence, and (2) T1 mapping using the measured B1 field map for correction. This segmentation allows each step to be optimized independently, maintaining overall accuracy while reducing the complexity of individual sequence components.
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 method provides a more accurate and reliable T1 map by directly addressing B1 inhomogeneity, reducing noise and specific absorption rate, and requiring minimal modification to existing T1 mapping sequences.
Implementation Method 1
T1 relaxation time, also known as the spin-lattice or longitudinal relaxation time, is a measure of how fast the nuclear spin magnetization returns to its equilibrium state after an excitation pulse
Implementation Method 2
T1 is a key source of soft tissue contrast in MRI
Implementation Method 3
B1 inhomogeneity—that is variation in the B1 field generated by the RF coil of the MRI scanner
Data Source
AI summary
In a method of performing magnetic resonance imaging and a magnetic resonance apparatus, first MR data are acquired of a region of interest of a subject in the absence of a B1 field. Second MR data are acquired of the region of interest in the presence of a B1 field, and within a short time interval after generation of the B1 field. The first and second MR data are processed to determine a B1 field map, and a T1 map is generated using the B1 field map. The T1 map is a B1 corrected T1 map. The first and second MR data 103, 109 may be acquired as part of a T1 mapping sequence, such as a MOLLI or SASHA type cardiac T1 mapping sequence.