Asymmetric RF Pulse Shaping for Low-Energy MRI Inversion
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Solution Overview
Problem
Magnetic resonance (MR) perfusion imaging techniques, particularly arterial spin labeling (ASL) at high magnetic fields, face challenges with high RF energy deposition and sensitivity to B0- and B1-field inhomogeneities, leading to suboptimal inversion profiles.
Innovation Solution
A computer-implemented method constructs an asymmetric RF pulse by optimizing a combined RF amplitude curve using a loss function that includes an energy term, combining RF amplitudes for different parts of the time interval to reduce energy deposition and improve inversion profile accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional RF pulses are used for ASL at high magnetic fields, then magnetization labeling is achieved, but RF energy deposition is excessive and inversion profile accuracy deteriorates
Solution Approach 1:
The patent applies asymmetry by designing an RF pulse with different amplitude characteristics in its first and second halves. The first half uses a higher amplitude to achieve accurate magnetization inversion, while the second half reduces amplitude to minimize RF energy deposition. This asymmetric time-profile resolves the contradiction between achieving accurate inversion profiles and reducing excessive RF energy deposition at high magnetic fields.
Solution Approach 2:
The RF pulse is segmented into distinct temporal portions with different amplitude characteristics. By dividing the pulse into a first half and second half with different energy levels, the invention optimizes each segment's contribution - the first segment ensures accurate magnetization labeling while the second segment reduces overall energy deposition, thereby resolving the technical contradiction.
2Measurement precision
If RF amplitude is increased to improve inversion profile accuracy, then magnetization labeling precision improves, but RF energy deposition increases
Solution Approach 1:
The patent implements local quality by applying different amplitude characteristics to different temporal portions of the RF pulse. The first half of the pulse uses higher amplitude locally to ensure accurate inversion profile, while the second half uses reduced amplitude locally to minimize energy loss. This spatial-temporal differentiation resolves the contradiction between precision and energy efficiency.
3Use of energy by moving object
If pulse duration is extended to reduce peak RF amplitude, then RF energy deposition decreases, but inversion profile accuracy deteriorates
Solution Approach 1:
The patent employs periodic action by structuring the RF pulse with distinct temporal phases - an initial high-amplitude phase for accurate inversion followed by a lower-amplitude phase. This periodic variation in amplitude over time allows the pulse to achieve both accurate magnetization labeling and reduced overall energy deposition, resolving the contradiction between pulse duration, peak amplitude, and inversion accuracy.
Data Source
AI summary
For constructing an asymmetric RF pulse for an MRI system, a first RF amplitude for a first part of a time interval is determined and an RF amplitude curve, which depends on at least one RF curve parameter is received. A combined RF amplitude curve for the time interval is determined by combining the first RF amplitude for the first part of the time interval and the RF amplitude curve for a second part of the time interval, which succeeds the first part of the time interval. The combined RF amplitude curve is optimized using a loss function, which comprises an energy loss term, which depends on a pulse energy of the combined RF amplitude curve, and using the at least one RF curve parameter as at least one optimization variable. A combined amplitude of the asymmetric RF pulse is given by the optimized combined RF amplitude curve.