MRI B1 Amplitude Correction for Stable Flip Angle Accuracy
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Solution Overview
Problem
Existing MRI systems face challenges in maintaining consistent B1 amplitude and flip angle accuracy due to variations in patient loading, coil absorption, and thermal changes in system components, leading to inaccurate RF transmitter gain levels and compromised image quality.
Innovation Solution
Interspersing B1 amplitude measurement sequences within MRI scan sequences to dynamically adjust RF parameter values, such as flip angle or transmit amplifier gain, based on real-time measurements to compensate for thermal and other environmental changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a per-patient calibration is performed to determine reference RF transmitter gain level, then B1 field measurement accuracy is improved, but thermal changes in system components during the examination cause drift in RF transmitter gain levels leading to degraded image quality
Solution Approach 1:
The patent performs a per-patient calibration before the examination to establish an initial reference RF transmitter gain level, and then periodically updates this calibration during the examination by inserting B1 amplitude measurement sequences between scan sequences. This preliminary action followed by periodic updates addresses both the initial accuracy requirement and the ongoing reliability maintenance despite thermal drift.
Solution Approach 2:
The patent implements a feedback mechanism where B1 amplitude measurement sequences are interspersed within the scan sequences to continuously monitor the actual B1 field amplitude. The measured values are compared against expected values, and the RF transmitter gain level is adjusted based on the deviation detected, thereby maintaining consistency despite thermal changes in system components.
2Manufacturing precision
If B1 amplitude measurement sequences are interspersed within MRI scan sequences to dynamically adjust RF parameters, then image quality is improved, but examination time is increased
Solution Approach 1:
The patent applies partial action by inserting B1 amplitude measurement sequences selectively between scan sequences rather than continuously during the entire examination. The system determines whether insertion is needed based on detected deviations in B1 amplitude, performing measurements only when necessary to correct RF parameter drift, thus minimizing time loss while maintaining image quality.
3Measurement precision
If RF parameter values are dynamically adjusted based on real-time measurements, then flip angle accuracy is improved, but system complexity is increased
Solution Approach 1:
The patent introduces an intermediary calibration module that acts as a mediator between the scan sequences and the RF parameter adjustment. This module inserts B1 amplitude measurement sequences, processes the measured values, compares them against expected values, and generates correction factors. By localizing the complexity to this dedicated intermediary component, the overall system manages complexity better while achieving improved flip angle accuracy through dynamic adjustment.
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
Ensures consistent B1 amplitude and flip angle accuracy, thereby improving image quality and patient safety by maintaining accurate RF parameter settings throughout the MRI examination.
Implementation Method 1
Sacolick et al. proposed in Magnetic Resonance in Medicine 66:1333-1338 (2011) (incorporated herein by reference), using a Bloch-Siegert Shift (BSS) method for RFL calibration.
Implementation Method 2
the B1 amplitude of the RF pulses has a direct relationship with the flip angle of the RF pulse, and the flip angle of the RF pulse is a primary determinant of MR signal intensity and image contrast
Data Source
AI summary
A method and system for modifying a series of magnetic resonance imaging (MRI) scan sequences for use in a single MRI examination. In one embodiment, a method and system intersperse a set of B1 amplitude measurement sequences within a received series of MRI scan sequences such that an RF parameter value of at least one scan sequence of the received series of MRI scan sequences is altered based on the results of at least one of the interspersed set of B1 amplitude measurement sequences.