ihMT Sensitivity in MRI Steady-State Gradient Echo
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Solution Overview
Problem
Current MRI techniques for central nervous system imaging using inhomogeneous magnetization transfer (ihMT) have low sensitivity, particularly in steady-state gradient echo imaging, where repetition times are short, limiting the acquisition of significant volumes and sensitivity of ihMTR contrast.
Innovation Solution
Extending repetition times beyond 20 milliseconds, adjusting radiofrequency intensity to maintain a specific absorption rate, and using multiple lines acquisition within each repetition time, along with equally spaced Hann-shaped radiofrequency pulses, to enhance ihMTR contrast sensitivity and reduce susceptibility to RF non-uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If steady-state gradient echo imaging uses short repetition times (around 10 milliseconds), then acquisition time is reduced and three-dimensional imaging becomes feasible, but ihMTR contrast sensitivity remains low
Solution Approach 1:
The patent changes the repetition time parameter from the conventional 10 milliseconds to greater than 20 milliseconds (preferably greater than 30 milliseconds). This parameter change allows the magnetization to regenerate more fully between excitations, improving the ihMTR contrast sensitivity while still maintaining reasonable acquisition speeds for three-dimensional imaging.
2Measurement precision
If repetition time is extended beyond 20 milliseconds, then ihMTR contrast sensitivity increases, but acquisition time increases and productivity decreases
Solution Approach 1:
The patent applies partial action by acquiring multiple lines within each repetition time period. Instead of waiting for complete magnetization regeneration before acquiring the next line, the system acquires several lines partially during the extended repetition time, thereby improving sensitivity while mitigating the loss in acquisition speed.
3Productivity
If pre-saturation module duration TMT is kept short (around 5 milliseconds), then acquisition efficiency is maintained, but insufficient time remains within repetition time to readout significant portions of volume
Solution Approach 1:
The patent segments the volume acquisition into multiple lines that can be read out sequentially within each repetition time. By dividing the three-dimensional volume into manageable line segments, the system can acquire multiple lines per repetition time even with extended TR, thereby maintaining productivity while increasing volume coverage and sensitivity.
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 significantly increases ihMTR contrast sensitivity, achieving values up to 17% and reduces acquisition time by allowing multiple lines to be acquired per repetition time, while maintaining patient safety and reducing susceptibility to RF variations.
Implementation Method 1
inhomogeneous magnetization transfer (ihMT) techniques
Implementation Method 2
trapezoidal radiofrequency pulses are applied, having respective frequency offsets of +5 KHz and −5 KHz
Implementation Method 3
combination of three gradient coil control signals used for spatial encoding, typically named Slice, Phase and Frequency
Implementation Method 4
The Frequency signal waveform is configured to extract all x-positions in the selected line, in the form of an echo signal. The echo signal is sampled
Data Source
AI summary
A method for producing an MRI image includes the steps of acquiring lines of a volume under analysis using a steady-state gradient echo sequence in successive repetition times (TR); and applying an inhomogeneous magnetization transfer (ihMT) pre-saturation module (TMT) in each repetition time. The duration of the repetition times is greater than 20 milliseconds.