MRI RF Pulse Sequences for Metal Artifact Correction
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Solution Overview
Problem
Magnetic resonance imaging (MRI) scans of patients with metal implants often result in significant distortion and signal loss due to the higher susceptibility of metals to magnetization, leading to large magnetic field inhomogeneities and areas of zero signal with high-intensity rims.
Innovation Solution
The method involves selecting spatially selective and non-spatially selective RF pulses with specific frequency offsets and applying them to excite and refocus spin magnetic moments, using a combination of RF pulses to form echoes and reconstruct images, thereby reducing distortion and signal loss around metal elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If typical metal artifact correction methods are used, then signal loss and distortion are reduced, but scan time increases significantly
Solution Approach 1:
The patent changes the frequency parameter of RF pulses relative to the Larmor frequency. By applying RF pulses at frequencies offset from the Larmor frequency and using selective spatial encoding gradients, the method reduces metal artifact distortion without requiring extended scan times for multiple corrections
Solution Approach 2:
The imaging process is segmented into multiple frequency-offset RF pulse applications with different spatial encoding gradients. Each pulse sequence targets specific spatial regions affected by metal artifacts, allowing selective correction without re-scanning the entire volume multiple times
2Reliability
If spatially selective RF pulses with frequency offsets are applied, then distortion around metal elements is reduced, but the complexity of the pulse sequence increases
Solution Approach 1:
The patent uses a universal approach where the same RF pulse sequence structure with frequency offsets can be applied to different metal artifact scenarios. The method maintains standard MRI hardware and basic pulse sequence design while adding frequency modulation, making it widely applicable without requiring complex custom hardware for each case
Solution Approach 2:
Frequency-offset RF pulses act as intermediaries between the main magnetic field and the spins near metal artifacts. These pulses selectively excite or refocus spins in distorted regions without directly interacting with the metal, mediating the correction process through controlled electromagnetic interaction
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 effectively reduces distortion and enhances image quality by refocusing spin magnetic moments and controlling the thickness of the section imaged, allowing for clearer MRI scans of regions with metal implants.
Implementation Method 1
Magnetic resonance imaging (MRI) is an imaging scan method that magnetically excites nuclear spins of a subject placed in a magnetostatic field by a radio frequency (RF) pulse having a Larmor frequency thereof
Implementation Method 2
magnetically excites nuclear spins of a subject placed in a magnetostatic field by a radio frequency (RF) pulse having a Larmor frequency thereof
Implementation Method 3
These distortion and signal problems are due to most metals having higher susceptibilities to magnetization than the body tissues they are surrounded by, thereby creating large magnetic field inhomogeneities around the metal object
Data Source
AI summary
In one embodiment a magnetic resonance imaging method is disclosed. The method includes the steps of selecting a first RF pulse, selecting a second RF pulse, selecting one of the first RF pulse and the second RF pulse to be spatially selective, with the other being non-spatially selective, selecting a frequency of the first RF pulse to be the same or different than a frequency of the second RF pulse, applying the first RF pulse to excite a first portion of an object, applying the second RF pulse, forming at least one echo in the first portion of the object, obtaining signal data from the first portion of the object in response to the first RF pulse and the second RF pulse and reconstructing the obtained signal data from the first portion to form an image.