B1 Mapping Using Stimulated Echo and Flow Suppression
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Solution Overview
Problem
Current B1 mapping techniques are slow, making them unsuitable for clinical workflows, particularly in cardiac imaging where rapid acquisition is necessary, and are sensitive to blood flow, degrading image quality in MRA and cardiac imaging.
Innovation Solution
A method combining a suppression sequence with a stimulated echo sequence to acquire B1 maps quickly, using FID and stimulated echo signals, and applying efficient sampling schemes like EPI or parallel imaging, with optional ECG-gating and black-blood preparation to minimize blood signal interference, enabling real-time dynamic RF shimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional B1 mapping techniques are used, then measurement precision is achieved, but acquisition time is too long for clinical workflows
Solution Approach 1:
The B1 mapping process is segmented into multiple independent measurements at different flip angles, with each measurement acquired rapidly using a single-shot stimulated echo sequence. This allows parallel or sequential acquisition of multiple data points without requiring long acquisition times for each individual measurement, thereby maintaining precision while reducing total acquisition time to under one heartbeat.
Solution Approach 2:
The patent applies preliminary RF pulses to prepare the magnetization state before the actual B1 mapping measurement. By pre-positioning the magnetization in a specific state using preparation pulses, the subsequent measurement can be performed rapidly with a single-shot sequence, eliminating the need for lengthy relaxation periods and enabling fast acquisition while preserving measurement accuracy.
2Speed
If standard stimulated echo sequence is used for fast acquisition, then speed is improved, but sensitivity to blood flow degrades image quality
Solution Approach 1:
The patent applies a preliminary flow suppression sequence before the stimulated echo sequence to counteract the harmful effect of blood flow. This preliminary action dephases or saturates the magnetization of flowing blood, so that when the rapid stimulated echo sequence is executed, the blood flow artifacts are already suppressed, allowing fast acquisition without degradation of image quality in MRA and cardiac imaging.
3Measurement precision
If multiple measurements are performed for accurate B1 mapping, then measurement precision is improved, but acquisition time increases
Solution Approach 1:
The patent implements continuous useful action by acquiring multiple B1 mapping measurements in rapid succession without idle relaxation periods between them. The stimulated echo sequence allows immediate sequential acquisition of multiple flip angle measurements, maintaining continuous data collection and eliminating wasted time, thereby achieving both high precision through multiple measurements and high productivity through efficient continuous scanning.
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
Enables rapid and accurate B1 mapping within a heartbeat, reducing artifacts from blood flow and allowing continuous adaptation of RF shim settings to the patient's motion state, improving image quality and integrating seamlessly into clinical workflows.
Implementation Method 1
the magnetic field produces different energy levels for the individual nuclear spins in dependence on the magnetic field strength which can be excited (spin resonance) by application of an electromagnetic alternating field (RF field, also referred to as B1 field) of defined frequency
Implementation Method 2
the magnetization performs a precessional motion about the z-axis. The precessional motion describes a surface of a cone whose angle of aperture is referred to as flip angle
Implementation Method 3
the magnetization in the z direction is built up again with a first time constant T1 (spin lattice or longitudinal relaxation time)
Implementation Method 4
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 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
Implementation Method 6
linear magnetic field gradients extending along the three main axes are superposed on the uniform magnetic field, leading to a linear spatial dependency of the spin resonance frequency
Implementation Method 7
The dephasing can be compensated by means of a refocusing pulse (for example a 180° pulse). This produces an echo signal (spin echo) in the receiving coils
Data Source
AI summary
A method of MR imaging, wherein a portion of a body placed in the examination volume of a MR device is subjected to an imaging sequence of RF pulses and switched magnetic field gradients. The imaging sequence is a stimulated echo sequence including i) at least two preparation RF pulses (α) radiated toward the portion of the body during a preparation period, and ii) one or more reading RF pulses (β) radiated toward the portion of the body during an acquisition period temporally subsequent to the preparation period. One or more FID signals and one or more stimulated echo signals are acquired during the acquisition period. A B1 map indicating the spatial distribution of the RF field of the RF pulses within the portion of the body is derived from the acquired FID and stimulated echo signals.