Variable Flip Angle Echo Train for Multi-Contrast MRI
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Solution Overview
Problem
Current magnetic resonance imaging techniques are inefficient in acquiring multiple types of contrast weightings simultaneously, requiring separate data sets and longer measurement times for each weighting type.
Innovation Solution
A method and apparatus that utilize a magnetic resonance pulse sequence with a refocusing-RF-pulse flip angle evolution to generate an echo train, allowing for simultaneous extraction of multiple contrast weightings from the same signal evolution, preferably using a turbo or fast spin-echo pulse sequence like the SPACE sequence, where different portions of the echo train are sampled to obtain proton density-weighted and T2-weighted images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate data sets are acquired for each contrast weighting type, then optimal contrast representation is achieved, but measurement time increases
Solution Approach 1:
The patent combines multiple contrast weighting acquisitions into a single data set by utilizing different portions of the echo train from one excitation pulse. The echo train contains signal evolutions that can be segmented into different time portions, each contributing to different contrast weightings (e.g., early echoes for proton density, later echoes for T2 weighting), thereby merging multiple contrast acquisitions into one measurement process.
Solution Approach 2:
The patent segments the echo train into different portions that can be assigned to different contrast weighting types. By dividing the echo train temporally, the method extracts useful signal information for multiple contrasts from a single continuous signal evolution, allowing simultaneous acquisition of proton density-weighted and T2-weighted images without requiring separate measurements.
2Adaptability or versatility
If multiple data sets are acquired for different contrast weightings, then comprehensive tissue contrast is achieved, but data processing complexity increases
Solution Approach 1:
The patent creates a universal data acquisition approach where a single echo train serves multiple functions by providing signal data for different contrast weightings. The same excitation pulse and resulting echo train generate information that can be processed into proton density-weighted images, T2-weighted images, or other contrast types, making the acquisition system multi-functional without requiring separate dedicated sequences for each contrast.
3Reliability
If separate excitation pulses are used for each contrast weighting, then optimal signal evolution is achieved, but the number of RF pulses increases
Solution Approach 1:
The patent maintains continuous useful action by utilizing the entire echo train generated from a single excitation pulse for multiple contrast weightings. Instead of terminating the signal evolution after one contrast is acquired and starting a new excitation for the next contrast, the method continuously extracts information from the ongoing signal evolution, maximizing the utility of each RF pulse and reducing the total number of pulses required.
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 the acquisition of multiple contrast weightings in a more efficient manner, reducing total measurement time while allowing for optimal contrast representation between tissues, such as in proton density and T2-weighted images, with the potential to generate additional contrast types.
Implementation Method 1
Magnetic resonance technology has been increasingly used in recent years to generate cross-sectional images of the human body
Implementation Method 2
The return to the equilibrium state is referred to as 'relaxation', and the return of the component of the magnetization vector parallel to the direction of the basic magnetic field to the original longitudinal direction (equilibrium) is therefore referred to as longitudinal relaxation. Since this relaxation is determined by the spin-lattice (T1) interactions, it is also referred to as spin-lattice or T1 relaxation.
Implementation Method 3
There are also spin-spin interactions, designated as T2 interactions, which result in a loss of phase coherence among the magnetization vectors. This loss of phase coherence is manifest as a decay of the transverse (i.e., perpendicular to the longitudinal axis) component of the magnetization vectors, and is therefore also referred to as transverse or T2 relaxation.
Implementation Method 4
The examination subject is exposed to radio-frequency (RF) excitation pulses to excite nuclear magnetic resonances
Implementation Method 5
For spatial encoding of the measurement data, rapidly switched magnetic gradient fields are superimposed on the basic magnetic field
Implementation Method 6
An associated MR image can be reconstructed from the k-space matrix populated with such values by means of, for example, a multi-dimensional Fourier transformation
Data Source
AI summary
In a method and an apparatus for acquiring magnetic resonance data, a region of a subject is exposed to a spin echo magnetic resonance pulse sequence that includes a refocusing radio-frequency pulse flip angle evolution that causes magnetic resonance signals to be emitted from the region with a signal evolution following each excitation radio-frequency pulse. The signal evolution is sampled to extract two or more sets of sampled data therefrom respectively with different contrast weightings of tissues in the region. The multiple sets of sampled data are made available as respective outputs in a form allowing multiple different images of the region to be generated therefrom, respectively with said different contrast weightings. For example, a spin density-weighted image and a T2-weighted image, or a T2-weighted image and a heavily T2-weighted image, thus can be generated by sampling from the same variable-flip-angle echo train.