MR Pre-Scan Frequency Spectrum for Fat Suppression
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Solution Overview
Problem
Conventional MR imaging techniques face challenges in accurately determining parameters for fat suppression, leading to suboptimal image quality due to discrepancies between pre-scan and imaging conditions, often requiring repeated scans and time-consuming manual adjustments.
Innovation Solution
A method and system that acquire MR data in a pre-scan without a readout gradient, generating a frequency spectrum to allow users to interactively set parameters for the imaging sequence, ensuring relative signal levels match those expected in the imaging scan, thereby optimizing fat suppression and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional pre-scan pulse sequences are used with standard readout gradients, then data acquisition is efficient, but the relative signal levels in the frequency spectrum do not match those expected in the imaging scan, leading to suboptimal parameter setting
Solution Approach 1:
The patent applies parameter changes by modifying the pre-scan pulse sequence to use different gradient parameters (reduced or zeroed readout gradients, adjusted phase encoding gradients) and RF pulse parameters (adjusted flip angles, durations, and timing) to make the pre-scan signal levels match the imaging scan conditions. This allows accurate fat suppression parameter determination in a single scan without requiring repeated scans.
2Ease of operation
If manual fine tuning of saturation pulse parameters is performed using standard pre-scan sequences, then user interaction is possible, but the TR of the pre-scan is typically unrelated to the effective TR of the saturation pulse for the clinical scan, resulting in inaccurate parameter setting
Solution Approach 1:
The patent changes the timing parameters of the pre-scan pulse sequence to match the effective TR of the saturation pulse in the imaging sequence. The pre-scan TR is set equal to the imaging TR divided by the number of slices, and the RF pulse timing and duration are adjusted accordingly. This ensures that the saturation effects observed during interactive parameter adjustment accurately reflect the conditions in the clinical scan.
Solution Approach 2:
The patent implements feedback by displaying the frequency spectrum from the pre-scan data to the user, allowing interactive adjustment of saturation pulse parameters. The user can observe the effect of parameter changes on fat signal suppression in real-time, and the system provides feedback on the quality of suppression through the displayed spectrum, enabling precise parameter optimization.
3Ease of manufacture
If frequency selective saturation pulses are applied with empirically determined parameters, then the process is simple, but the nuances of the MR scanner and particulars of the object require pre-scan fine tuning for optimal results
Solution Approach 1:
The patent applies self-service by enabling the system to automatically perform the pre-scan and generate the frequency spectrum for parameter optimization without requiring external calibration equipment or complex manual procedures. The MR scanner itself provides all necessary functions: applying the modified pre-scan sequence, acquiring data, computing the frequency spectrum, and presenting it to the user for interactive parameter adjustment.
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 users to efficiently and effectively set parameters for optimal fat signal suppression and image quality, reducing the need for repeated scans and streamlining the pre-scan process while improving image quality.
Implementation Method 1
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or 'longitudinal magnetization ', MZ, may be rotated, or 'tipped ', into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B1 is terminated
Implementation Method 2
For example, if the region-of-interest is primarily composed of water and fat, each having a different chemical shift, through application of the appropriate chemical saturation, data collected and the resulting image would be of either water or fat, but not both
Data Source
AI summary
A method of calibrating an imaging sequence includes the application of a pre-scan pulse sequence to acquire MR signals from a region-of-interest to be imaged with an imaging pulse sequence. The pre-scan pulse sequence is interrupted to acquire pre-scan data in a low bandwidth acquisition window. A frequency spectrum is generated from the pre-scan data and displayed to interactively allow a user to establish scan parameters for the imaging pulse sequence.