Gradient Echo MRI Sequence for Cardiac Phase Imaging
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Solution Overview
Problem
Current magnetic resonance tomography (MRT) techniques face challenges in acquiring fast image series of various heart phases with high resolution and consistent T1 contrast within a limited breathing pause, often requiring long measurement times or compromising on temporal or spatial resolution.
Innovation Solution
A method and apparatus for MRT imaging using a gradient echo sequence, where nuclear spins are excited and RF signals are measured, with a series of steps including pulse frequency determination, magnetization preparation, and repeated measurements along a trajectory established by projection gradients, allowing for temporal displacement of intervals relative to the pulse frequency to optimize image acquisition across multiple heart phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional MRT techniques are used to acquire fast image series of various heart phases, then temporal resolution is improved, but spatial resolution and measurement time are compromised
Solution Approach 1:
The patent segments the k-space data acquisition into multiple segments that are acquired at different temporal phases of the cardiac cycle. Each segment contains data from multiple heartbeats that are subsequently combined through sorting and averaging to reconstruct high-resolution images for specific cardiac phases, thereby achieving both high temporal and spatial resolution
Solution Approach 2:
The patent employs periodic RF pulse excitation synchronized with the cardiac cycle to acquire data at regular intervals corresponding to different heart phases. This periodic acquisition strategy allows consistent sampling of the cardiac cycle across multiple beats, enabling high temporal resolution imaging without sacrificing spatial detail
2Manufacturing precision
If measurement time is extended to improve image quality, then spatial resolution is improved, but the ability to acquire images within a breathing pause is compromised
Solution Approach 1:
The patent implements continuous data acquisition throughout the entire breathing pause without interruptions or pauses between segments. The RF pulse sequence runs continuously, collecting k-space data from multiple heartbeats in succession, thereby maximizing the utilization of the limited breathing hold time while maintaining high image quality through continuous sampling
3Manufacturing precision
If T1 contrast consistency is improved across heart phases, then image quality is improved, but measurement time increases
Solution Approach 1:
The patent applies preliminary magnetization preparation pulses (such as inversion recovery or saturation pulses) before the actual data acquisition to pre-establish the desired T1 contrast characteristics. This preliminary action ensures that when data is acquired during the brief breathing pause, the T1 contrast is already optimized and consistent across all cardiac phases, eliminating the need for extended measurement times to achieve contrast uniformity
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 acquisition of high-resolution images with consistent T1 contrast and improved temporal and spatial resolution for heart movement movies without extending measurement time, even during breath holds.
Implementation Method 1
MRT is based on the physical phenomenon of magnetic resonance and has been successfully used as an imaging modality for over 15 years in medicine and biophysics. In this examination modality, the subject is exposed to a strong, constant magnetic field. The nuclear spins of the atoms in the subject, which were previously randomly oriented, thereby align. Radio-frequency energy can now excite these 'ordered' nuclear spins to a specific oscillation. In MRT, this oscillation generates the actual measurement signal
Implementation Method 2
By the use of inhomogeneous magnetic fields generated by gradient coils, the measurement subject can be spatially coded in all three spatial directions. The slice selection (establishes an acquisition slice in the subject, for example the z-axis), the frequency coding (establishes a direction in the slice, for example the x-axis) and the phase coding (establishes the second dimension within the slice, typically the y-axis). Depending on the combination or interleaving (nesting) of the three gradients in an imaging sequence, the sampling of k-space can ensue in a Cartesian manner (line-by-line) or radially or helically
Data Source
AI summary
In a method and apparatus for magnetic resonance imaging on the basis of a gradient echo sequence by excitation of nuclear spins and measurement of radio-frequency signals indicating the excited nuclear spins, a) the pulse frequency of the person to be examined is determined, b) the magnetization of the spins is prepared by means of an RF pulse block, c) a number of steps of the spin excitation as well as measurement of an RF response signal are implemented, with the measurement data along a trajectory established by projection gradients being acquired along a first slice established by a slice-selection gradient, d) items b) through c) are repeated multiple times for the first slice, with each repetition of the steps b) through c) ensuing within a time interval that is fixed in duration, and the interval is temporally displaced relative to the determined pulse frequency for at least one portion of the repetitions, and e) items b) through d) are repeated for various slices.