MRI Pulse Sequence for Selective Slice Magnetization
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Solution Overview
Problem
Magnetic resonance imaging (MRI) systems face challenges in achieving spatially selective excitation with shorter high-frequency pulses, leading to long pulse durations and artifacts, as well as limitations in power deposition and excitation efficiency.
Innovation Solution
A pulse sequence comprising four slice-selective excitation pulses is used, where each pulse is designed to selectively excite a specific area, with the third and fourth pulses canceling out magnetization in non-target areas, allowing for efficient and selective magnetization of the intersection area, utilizing sinc pulses and gradient signals to define slice thickness and planes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional single-pulse excitation methods are used, then spatial selectivity is achieved, but pulse duration becomes excessively long leading to artifacts
Solution Approach 1:
The patent divides a single long excitation pulse into multiple shorter pulses (first, second, third, and fourth excitation pulses) applied in sequence. Each pulse excites a specific spatial region, and through controlled cancellation effects, the net result achieves the desired spatial selectivity without requiring any single pulse to be excessively long, thereby reducing artifacts while maintaining selectivity.
Solution Approach 2:
The patent employs preliminary anti-action by designing the pulse sequence so that certain pulses create magnetization that will be subsequently canceled by later pulses. Specifically, the third and fourth pulses are designed to cancel magnetization in non-target areas created by the first two pulses, ensuring that only the intersection region maintains the desired magnetization. This preemptive cancellation strategy prevents artifacts while achieving spatial selectivity.
2Duration of action of moving object
If shorter high-frequency pulses are used to reduce artifacts, then pulse duration is reduced, but spatial selectivity and excitation efficiency deteriorate
Solution Approach 1:
The patent combines multiple short excitation pulses into a composite pulse sequence that achieves the spatial selectivity of a single long pulse. By merging the effects of four shorter pulses with carefully controlled phases and amplitudes, the system attains the same spatial selectivity as a conventional long pulse but without the associated artifacts and extended duration.
Solution Approach 2:
The patent utilizes periodic action by applying a sequence of periodically spaced excitation pulses rather than a single continuous pulse. The periodic application of these pulses, with specific timing and phase relationships, allows the system to build up the desired spatial pattern through constructive interference in the target region while maintaining short individual pulse durations to avoid artifacts.
3Manufacturing precision
If multiple excitation pulses are applied to improve spatial selectivity, then selectivity is enhanced, but power deposition increases
Solution Approach 1:
The patent applies the discarding and recovering principle by intentionally creating magnetization in non-target areas with early pulses and then systematically discarding it through subsequent cancellation pulses. The third and fourth pulses are specifically designed to cancel the magnetization created by the first two pulses in non-target regions, ensuring that only the intersection region retains the desired magnetization. This approach achieves high spatial selectivity while controlling overall power deposition by eliminating wasted energy in non-target areas.
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
This approach enables shorter pulse sequences, improved selectivity, and reduced artifacts, while maintaining efficient energy deposition, allowing for precise 3D magnetization and enhanced imaging quality by ensuring only the target area is magnetized.
Implementation Method 1
The nuclear spins of the atoms in the object of investigation are excited by these HF pulses such that the nuclear spins are deflected from an equilibrium position around an 'excitation flip angle' that runs parallel to the basic magnetic field B0
Implementation Method 2
a static basic magnetic field (e.g., a B0 field) that is as homogeneous as possible. This static basic magnetic field may be generated by a basic field magnet of the magnetic resonance measuring device
Implementation Method 3
Rapidly switched gradient fields generated by gradient coils are superimposed on the basic magnetic field during the recording of the magnetic resonance images for the purpose of spatial encoding
Implementation Method 4
The nuclear spins precess around the direction of the basic magnetic field B0
Implementation Method 5
After excitation, the nuclear spins relax and revert to a starting position oriented toward the B0 field. When the nuclear spins are relaxed, high-frequency signals (i.e., magnetic resonance signals) are emitted
Data Source
AI summary
A method for controlling a magnetic resonance system outputs a pulse sequence including a first slice-selective excitation pulse that excites a first slice with a first magnetization. The pulse sequence includes a second slice-selective excitation pulse that excites a second slice with the first magnetization and a third slice-selective excitation pulse that excites the first slice with a second magnetization that cancels the first magnetization. The pulse sequence also includes and a fourth slice-selective excitation pulse that excites the second slice with a magnetization that cancels the first magnetization. The first slice and the second slice intersect.