MR Phase Encoding for Multi-Spin Dixon Imaging
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Solution Overview
Problem
Conventional magnetic resonance imaging techniques face challenges in recording magnetic resonance data of objects with multiple spin species due to limitations in echo spacing, which lead to increased measurement time, reduced signal-to-noise ratio, and artifacts such as FID artifacts and incomplete fat suppression, especially in 3D TSE sequences.
Innovation Solution
A method involving RF excitation pulses that generate specific phase differences between spin species within echo trains, allowing for simultaneous recording of MR datasets without extending echo spacing, thereby avoiding the need for phase shifts and associated disadvantages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional TSE sequences are used to record MR data of objects with multiple spin species, then the measurement can be performed, but the echo spacing must be extended to achieve phase differences between spin species, which increases measurement time and reduces signal-to-noise ratio
Solution Approach 1:
The patent applies parameter changes by using RF excitation pulses with specific flip angles (different from conventional 90 degrees) to generate the required phase differences between spin species. By optimizing the flip angle parameter, the system achieves the necessary phase separation without extending echo spacing, thus resolving the contradiction between measurement precision and time loss.
Solution Approach 2:
The patent implements preliminary action by introducing a phase shift element before the RF excitation pulse that pre-establishes the phase difference between spin species. This preliminary phase modulation allows the echo train to capture the phase information without requiring extended echo spacing, thereby reducing measurement time while maintaining measurement precision.
2Adaptability or versatility
If echo spacing is extended to generate phase differences between spin species, then Dixon reconstruction becomes possible, but artifacts such as FID artifacts increase and measurement time increases
Solution Approach 1:
The patent changes the RF excitation pulse parameters (flip angle and phase) to generate phase differences between spin species without extending echo spacing. This parameter optimization enables Dixon reconstruction capability while preventing FID artifacts, as the phase information is encoded during the excitation process rather than requiring extended echo times that would generate harmful artifacts.
Solution Approach 2:
The patent substitutes the conventional approach of using temporal separation (extended echo spacing) with a phase-based encoding mechanism. By using phase shift elements and optimized RF pulses, the system replaces the mechanical/time-based separation method with a phase-space approach, enabling Dixon reconstruction without the harmful FID artifacts that plague extended echo spacing methods.
3Quantity of substance
If conventional RF excitation pulses are used, then standard imaging is achieved, but phase differences between spin species cannot be generated without extending echo spacing
Solution Approach 1:
The patent optimizes RF excitation pulse parameters (flip angle, phase, and timing) to simultaneously maintain high signal intensity and generate precise phase differences between spin species. By carefully selecting non-conventional flip angles and introducing phase shift elements, the system achieves both high signal quantity and measurement precision without extending echo spacing.
Solution Approach 2:
The patent applies preliminary phase modulation before the main RF excitation pulse to pre-establish the phase differences between spin species. This preliminary action ensures that when the echo train is recorded, the phase information is already encoded, allowing high signal intensity capture while achieving the required measurement precision for Dixon reconstruction without extending echo spacing.
4Adaptability or versatility
If phase shifts are introduced to generate phase differences between spin species, then Dixon reconstruction is enabled, but measurement time increases and signal-to-noise ratio decreases
Solution Approach 1:
The patent optimizes the phase shift element parameters and RF excitation pulse parameters to generate the necessary phase differences with minimal disruption to signal intensity. By carefully controlling the phase shift magnitude and timing, the system enables Dixon reconstruction while maintaining high signal-to-noise ratio, avoiding the penalties associated with conventional phase shift methods.
Solution Approach 2:
The patent implements preliminary phase modulation that efficiently encodes phase differences between spin species before the echo train recording begins. This preliminary action is designed to minimize the impact on signal intensity while achieving the required phase separation, thereby enabling Dixon reconstruction capability without sacrificing signal-to-noise ratio or significantly increasing measurement time.
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 efficient and rapid recording of MR datasets with phase differences suitable for Dixon reconstruction, reducing measurement time and artifacts, and improving image quality by separating spin species signals effectively.
Implementation Method 1
Magnetic resonance technology (hereinafter, the abbreviation MR stands for magnetic resonance) is a known technology which can be used to generate images of the inside of an object under examination. In simple terms, for this purpose, the object under examination is placed in a magnetic resonance device in a comparatively strong static homogeneous main magnetic field, also called the B0 field
Implementation Method 2
In order to trigger nuclear spin resonances that can be measured as signals, radio-frequency excitation pulses (RF pulses) are irradiated into the object under examination and the triggered nuclear spin resonances are measured in the frequency space as so-called k-space data
Implementation Method 3
The most commonly used method for generating echo signals after excitation of the nuclear spins is the so-called spin echo method. Herein, in the simplest case, the transverse magnetization is so to speak 'flipped' by irradiating at least one RF refocusing pulse after the irradiation of the RF excitation pulse, whereby the dephased magnetization is rephased again and thus a so-called spin echo SE is formed
Data Source
AI summary
In an MR data recording method, different desired phase differences between spins of a first spin species and spins of a second spin species are generated by irradiated RF excitation pulses in each case and corresponding MR datasets are recorded in respective echo trains after irradiation of the RF excitation pulses. This makes it possible to eliminate the need to shift the readout interval away from the spin-echo time, as was previously necessary to generate different phase differences and the associated extension of echo spacings in order to generate the different phase differences between the spin species. Thus, the disadvantages of a previously necessary extension of the echo spacing can be avoided with the method according to the disclosure.