MR Imaging Sequence RF Phase Optimization
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Solution Overview
Problem
Conventional MR-imaging sequences struggle to optimize contrast between volume regions differing in magnetic resonance properties, often compromising on time-spatial resolution and image quality.
Innovation Solution
An MR-imaging sequence with adjustable RF-pulse phases according to the rule φk−φk-1=φ+k*Φ, where Φ is optimized to maximize the difference in signal strengths between voxel pairs, allowing for arbitrary contrast selection based on desired image representation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional MR-imaging sequences are used, then time-spatial resolution can be maintained, but contrast optimization between volume regions with different magnetic resonance properties is compromised
Solution Approach 1:
The patent implements dynamic adjustment of the RF-phase parameter Φ across different blocks of the imaging sequence. By making the phase progression dynamic rather than fixed, the system can adaptively optimize contrast for different tissue types and imaging objectives while maintaining temporal and spatial resolution. The phase parameter Φ is adjusted block-by-block to maximize signal differences between specific voxel pairs.
Solution Approach 2:
The invention changes the RF-phase parameter Φ as a controllable variable that can be optimized for different contrast requirements. By treating Φ as an adjustable parameter rather than a fixed sequence parameter, the system can tailor contrast optimization to specific imaging needs, such as enhancing differentiation between gray and white matter or optimizing for particular pathologies.
2Manufacturing precision
If fixed RF-phase sequences are used, then sequence simplicity is maintained, but contrast between specific voxel pairs cannot be optimized
Solution Approach 1:
The imaging sequence is divided into multiple blocks, each with its own RF-phase parameter Φk. This segmentation allows independent optimization of contrast for different blocks, enabling the system to target specific voxel pairs or tissue types in different phases of the imaging sequence while maintaining overall sequence manageability.
Solution Approach 2:
The RF-phase parameter Φ progresses periodically across blocks according to a defined rule (φk−φk-1=φ+k*Φ). This periodic progression creates a systematic way to explore different contrast optimizations across the sequence, allowing the system to cycle through different phase angles that maximize signal differences for various tissue comparisons.
3Adaptability or versatility
If standard T1-weighting or T2/T1 mixing contrasts are used, then conventional image representation is achieved, but enhanced contrast optimization for specific applications is limited
Solution Approach 1:
The patent creates a universal imaging sequence framework that can achieve multiple contrast types (T1-weighting, T2/T1 mixing, and application-specific contrasts) by adjusting the RF-phase parameter Φ. This multi-functional approach allows a single sequence design to serve various imaging objectives, from standard anatomical imaging to specialized contrast optimization for gray-white matter differentiation or pathology detection.
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 enables enhanced contrast optimization between volume regions, improving image representation by selectively adjusting the RF-phase parameter Φ to achieve optimal signal differences, surpassing the limitations of traditional T1-weighting and T2/T1 mixing contrasts.
Implementation Method 1
By the excitation of interesting spins by means of suitable radio frequency pulses or RF-pulses, of which the frequency must match the Larmor frequency of the spins which are to be excited, this net magnetization can be tilted about any 'flip angles'α about an axis which extends orthogonally with respect to B0 in the xy-plane. In this case, the equilibrium magnetization M0 produces a transversal component Mxy=M0*sin(α) and a longitudinal component Mz=M0*cos(α).
Implementation Method 2
The spins of the atomic nuclei used in imaging (generally these are the hydrogen protons) comprise a 'longitudinal' component in parallel with the main field, and a 'transversal' component which is perpendicular to said longitudinal component. The transversal component precesses about the z-axis at the Larmor frequency f=γ*B, where γ is the gyromagnetic ratio dependent upon the type of spin and B is the local magnetic field strength
Implementation Method 3
Reciprocal disturbances caused by adjacent spins effect a dephasing of the transversal magnetization Mxy and as a consequence produces a temporally exponential decrease in the measurement signal (T2-relaxation). The associated time constant is defined as the 'spin-spin-relaxation time' T2.
Implementation Method 4
Depending upon the type of measurement carried out, field inhomogeneities can further accelerate the time decrease in the measurement signal, which is then described by an effective time constant T2*2.
Implementation Method 5
At the same time as the decrease in the transversal magnetization Mxy, the longitudinal equilibrium magnetization (T1-relaxation) recovers. The time constant of this exponential process is defined as the 'spin-grid relaxation time' T1, where T1>T2 always applies.
Implementation Method 6
In order to achieve the excitation of selective layers (2D-imaging) or layer blocks (3D-imaging) as required for imaging purposes, and also for the purposes of actual location-coding during signal detection, defined magnetic field gradients are temporarily impressed upon the B0-field in selected spatial directions. This renders it possible to change the Larmor frequency linearly along a freely selectable spatial direction.
Data Source
AI summary
The invention relates to the obtainment of magnetic resonance measurement data for the reproduction of an image of an object volume, illustrating the contrast between volume elements (voxels) which differ from one another in the parameter vectors Pi of the magnetic resonance property of the respective inherent substance i. The object volume which is to be imaged is subjected within a stationary magnetic field to a sequence of repetitive blocks of effects, each containing an RF-pulse with a flip angle α<90° and magnetic field gradients, in order to obtain in each block N≧1 location-coded measurement signals and to achieve sufficient intravoxel dephasing, wherein the phase φ(k) of the RF-pulse is changed from block to block in accordance with the ruleφk−φk-1=φ+k*Φ,where k is the running index of the blocks within the sequence and φ is a randomly selected phase angle. In accordance with the invention, for the sequence parameter Φ a value Φc is selected, in which the set {Sij} of the difference valuesSij=∑n=1N[Sn(Φ,Q,Pi)-Sn(Φ,Q,Pj)]is optimized in accordance with a selected criterion K ({Sij}), where n with 1≦n≦N is the running index of the measurement signals detected within a respective block, Sn(Φ,Q,Pi) or Sn(Φ,Q,Pj) is the value of the transversal magnetization of the voxels, which contain the substance i or j, in the condition of dynamic equilibrium at the point in time of the maximum of the nth measurement signal, Q stands for the values of the remaining sequence parameters, and {Sij} includes all desired pairs of substances i and j.