Double Half RF Pulses for UTE Eddy Current Reduction
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Solution Overview
Problem
Ultrashort echo time (UTE) imaging faces challenges in achieving accurate slice selectivity and R2* quantitation due to eddy currents, which distort the slice profile and introduce errors in T2 measurements, especially for short T2 species like musculoskeletal tissues, lung, and frozen tissue during cryoablation, as conventional techniques are limited by long echo times and sensitive to gradient imperfections.
Innovation Solution
The Double Half RF (DHRF) and Inverted Double Half RF (IDHRF) pulses are introduced, which split a conventional full-sinc RF pulse into two halves with a time interval, improving slice selectivity for long T2 components and suppressing unwanted long T2 signals, thereby reducing the impact of eddy currents and enhancing the accuracy of short T2 imaging and quantitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional full-sinc RF pulses are used for UTE imaging, then the imaging can be performed with standard equipment, but eddy currents distort the slice profile and reduce measurement precision
Solution Approach 1:
The conventional full-sinc RF pulse is divided into two half-pulses separated by a time interval. This segmentation allows the first half-pulse to excite both short and long T2 species while the second half-pulse selectively refocuses only long T2 signals, thereby suppressing eddy current-induced artifacts and improving R2* quantitation accuracy for short T2 tissues.
Solution Approach 2:
The pulse sequence employs periodic application of half-pulses with a specific time interval between them. This periodic structure enables selective refocusing of long T2 signals while allowing short T2 signals to decay, creating a rhythm that suppresses eddy current effects and enhances measurement precision.
2Measurement precision
If conventional RF pulses are used, then the pulse sequence is simple, but slice selectivity is poor and long T2 signals contaminate short T2 imaging
Solution Approach 1:
The RF pulse is segmented into two distinct half-pulses with different functions: the first half-pulse provides broad excitation for both short and long T2 species, while the second half-pulse provides selective refocusing for long T2 signals. This segmentation achieves superior slice selectivity and signal suppression without requiring complex gradient characterization.
3Loss of time
If standard RF pulses are used for imaging, then the imaging speed is adequate, but the echo time is too long for accurate short T2 measurement
Solution Approach 1:
The pulse sequence rushes through the excitation and refocusing process by using half-pulses with a minimal time interval between them. This allows the acquisition to occur at ultra-short echo times, capturing short T2 signals before they decay, thereby reducing time loss and improving measurement accuracy.
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
These pulses significantly improve slice selectivity and R2* quantitation accuracy, reducing the influence of eddy currents and providing better contrast and signal-to-noise ratio for short T2 species by effectively suppressing long T2 signals, thus offering an alternative to time-consuming gradient characterization methods.
Implementation Method 1
nuclear magnetic moments are excited at specific spin precession frequencies which are proportional to the local magnetic field
Implementation Method 2
each nuclear spin responds to four different effects: precession about the main magnetic field, nutation about an axis perpendicular to the main field, and both transverse and longitudinal relaxation
Implementation Method 3
nutation about an axis perpendicular to the main field
Implementation Method 4
The radio-frequency signals resulting from the precession of these spins are received using pickup coils
Data Source
AI summary
A method for creating a magnetic resonance image of an object with at least a first species and a second species, wherein the first species has a first T2 time and the second species has a second T2 time longer than the first T2 time is provided. An excitation with an ultra short echo time using a pulse is provided, comprising a first subpulse that creates a transverse magnetization component for the first species and the second species and a second subpulse that creates a transverse magnetization for the first species and substantially returns the second species to a longitudinal axis, wherein the transverse magnetization component substantially decays for the first species during an interval between the first subpulse and the second subpulse. At least one echo is read. A magnetic resonance image is created from the at least one echo.