Magnetic Resonance Pulse Length Calculation for Artifact Reduction
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Solution Overview
Problem
Magnetic resonance imaging with ultrashort echo times (UTE) sequences faces artifacts due to insufficient excitation, particularly at image edges, caused by insufficient pulse bandwidth or strong gradients, leading to blurred image regions and reduced image quality.
Innovation Solution
A method to automatically calculate the maximum pulse length of RF excitation pulses, taking into account the desired field of view and maximum gradient strength, to optimize excitation and minimize artifacts while controlling Specific Absorption Rate (SAR) exposure, using a processor to calculate the pulse length and correct excitation errors through matrix inversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gradient strength is increased to improve spatial resolution, then the excitation bandwidth increases, but image artifacts appear at the edges due to insufficient excitation
Solution Approach 1:
The patent changes the pulse duration parameter to match the gradient strength. By calculating and setting the pulse length according to the formula T_pulse ≤ k / (γ * G_max), where G_max is the maximum gradient strength, the excitation bandwidth is optimized to cover the entire field of view without causing edge artifacts.
2Object-affected harmful factors
If the excitation pulse length is decreased to increase excitation bandwidth, then image artifacts are reduced, but the maximum flip angle and precision of RF excitation are reduced
Solution Approach 1:
The patent optimizes the pulse length parameter to achieve the maximum possible value that still prevents artifacts. By setting T_pulse ≤ k / (γ * G_max), the pulse is long enough to maintain high flip angles and precision, but short enough to cover the required bandwidth and avoid edge artifacts.
3Stability of the object's composition
If the gradient strength is reduced to avoid excitation artifacts, then image homogeneity improves, but the minimum repetition time increases and total measurement time increases
Solution Approach 1:
The patent changes the pulse duration parameter to match the gradient strength, allowing the use of higher gradient strengths without causing artifacts. This enables shorter repetition times and reduced measurement time while maintaining image homogeneity through proper excitation coverage.
4Stability of the object's composition
If the pulse bandwidth is increased to cover the entire field of view, then excitation uniformity improves, but the pulse length must be decreased which reduces flip angle
Solution Approach 1:
The patent optimizes the pulse length parameter by calculating the maximum value that satisfies both requirements: T_pulse ≤ k / (γ * G_max). This ensures the pulse is short enough to provide sufficient bandwidth for uniform excitation across the field of view, while being long enough to achieve the desired flip angle and maintain precision.
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
The method ensures reliable correction of artifacts, achieving higher flip angles and improved image quality by maximizing pulse length, which reduces SAR load and enhances image homogeneity across the field of view.
Implementation Method 1
Magnetic resonance (MR) is a known modality with which images of the inside of an examination subject can be generated. Expressed in a simplified form, the examination subject is positioned in a strong, static, homogeneous basic magnetic field (also called a B0 field) with a field strength from 0.2 Tesla to 7 Tesla or more in a magnetic resonance apparatus, such that the nuclear spins of the examination subject orient along the basic magnetic field.
Implementation Method 2
To trigger magnetic resonance signals, radio-frequency excitation pulses (RF pulses) are radiated into the examination subject, and the triggered magnetic resonance signals are detected
Implementation Method 3
For spatial coding of the measurement data, rapidly switched magnetic gradient fields are superimposed on the basic magnetic field
Data Source
AI summary
In a method and magnetic resonance apparatus for automatic calculation of a maximum pulse length of a non-selective excitation pulse for a magnetic resonance data acquisition pulse sequence in which gradients are switched during the radiation of at least one non-selective excitation pulse, a first parameter, which indicates the field of view (FOV) desired in the measurement for which the pulse length of the excitation pulse should be maximized, is loaded into a processor, and a second parameter, which indicates the maximum gradient strength (Gmax) which corresponds to the highest gradient strength applied in the entire measurement, is also loaded into the processor. The processor then calculates the maximum pulse length of the excitation pulse on the basis of the first and second parameter. By the maximization of the pulse length, the SAR exposure is reduced for the examination subject from whom the magnetic resonance data are acquired with the pulse sequence.