UTE MRI Frequency Map Generation via Phase Contribution Segmentation
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Solution Overview
Problem
Ultrashort TE (UTE) MRI struggles to generate accurate frequency maps due to limited time for phase difference development in short T2 tissues, resulting in high phase contrast in phase images but lacking a systematic method for quantifying this contrast.
Innovation Solution
An MR imaging system and method that calculates a frequency map by reconstructing phase images from UTE sequence data, accounting for phase contributions during the RF pulse and data acquisition gradient pulse, using Bloch equations and gradient coil positioning to determine off-resonance frequencies on a pixel-by-pixel basis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If UTE sequences use very short TE periods to detect signals from short T2 tissues, then signal detection capability is improved, but phase difference development time is reduced leading to limited phase contrast
Solution Approach 1:
The patent segments the phase image into multiple frequency components by calculating phase contributions from different time periods (during RF pulse, during data acquisition gradient pulse, and during TE period). This allows separate quantification of phase differences that would otherwise be mixed in a single short TE measurement.
Solution Approach 2:
The patent performs preliminary calculations of phase contributions during the RF pulse and gradient pulse application before final frequency map generation. This preliminary segmentation of phase components enables accurate frequency quantification even with ultrashort TE periods.
2Measurement precision
If phase images are reconstructed from UTE sequence data, then phase contrast is enhanced, but systematic quantification of frequency information is lacking
Solution Approach 1:
The patent uses an iterative feedback approach where the phase image is reconstructed, phase contributions are calculated and subtracted, and the process is repeated to generate frequency maps. This feedback loop enables systematic quantification of frequency information while preserving phase contrast.
Solution Approach 2:
The patent performs preliminary calculation and removal of known phase contributions (from RF pulse and gradient pulses) before final frequency map generation. This preliminary action isolates the tissue-specific phase differences and enables accurate frequency quantification.
3Measurement precision
If multiple phase contributions are calculated and removed from phase images, then frequency map accuracy is improved, but processing complexity increases
Solution Approach 1:
The patent segments the total phase into distinct components (RF pulse phase, gradient pulse phase, TE period phase) that can be calculated and removed separately. This segmentation simplifies the processing by breaking down a complex quantification problem into manageable sequential steps.
Solution Approach 2:
The patent performs preliminary calculation of phase contributions using known pulse sequence parameters before final frequency map generation. This preliminary action reduces processing complexity during the main reconstruction by pre-computing removable phase components.
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
Enables the generation of precise frequency maps from UTE sequence data, enhancing phase contrast analysis independent of steady-state longitudinal magnetization, thereby improving image quality and tissue differentiation in short T2 tissues.
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.
Implementation Method 2
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.
Implementation Method 3
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed.
Data Source
AI summary
A system and method for quantifying MR data acquired during a UTE sequence include a computer programmed to execute an MR scan comprising an application of an RF pulse, an echo time (TE) period, and an application of a data acquisition gradient pulse, wherein the TE period begins after the RF pulse and ends before the data acquisition gradient pulse. MR data of an imaging object are acquired during application of the data acquisition gradient pulse, and a phase image is reconstructed based on the acquired MR data. The computer is also programmed to calculate a first contribution of phase to the phase image during the application of the RF pulse, to calculate a second contribution of phase to the phase image by the application of the data acquisition gradient pulse, and to generate a frequency map based on the phase image and based on the first and second contributions of phase.