MRI Vascular Imaging Using Gradient-Shifted Magnetic Field Distribution
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Solution Overview
Problem
Conventional methods for suppressing background signals in magnetic resonance (MR) imaging using the time-of-flight (TOF) technique are inefficient, leading to suboptimal vessel visibility and increased examination costs due to the need for manual post-processing and limitations in suppressing brain tissue, spinal fluid, and fat signals.
Innovation Solution
A method involving a magnetic field distribution with a crest portion having no spatial gradient in the imaging volume and a higher spatial gradient in the inflow volume, along with an RF pulse that satisfies magnetization transfer and fat saturation functions, effectively suppresses background signals by shifting the water frequency away from the fat frequency, allowing for homogeneous fat saturation and improved vessel contrast without manual post-processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high tilt angles are used to suppress background signals from brain tissue and spinal fluid, then background signal suppression is improved, but the signal from inflowing spins decreases and slice thickness is limited
Solution Approach 1:
The patent changes the magnetic field distribution parameter by introducing a peak region with no spatial gradient in the imaging volume and higher gradient in the inflow volume. This parameter change allows the use of lower tilt angles while maintaining background suppression effectiveness, thereby preserving the signal from inflowing spins.
Solution Approach 2:
The patent applies local quality by creating a non-uniform magnetic field distribution with different gradient characteristics in different spatial regions. The imaging volume has a peak region with no gradient, while the inflow volume has higher gradient, allowing differentiated control of background suppression and inflow signal preservation in different locations.
2Object-affected harmful factors
If opposed-phase imaging is used to suppress fat signals, then background signal suppression is improved, but echo time is prolonged and acquisition time increases
Solution Approach 1:
The patent changes the magnetic field distribution parameter to create a peak region with no spatial gradient in the imaging volume. This allows the use of frequency-selective fat saturation pulses with narrower bandwidth, achieving fat suppression without requiring prolonged echo times, thus reducing acquisition time.
Solution Approach 2:
The patent introduces an intermediary mechanism - a specially designed magnetic field distribution with peak region - that enables fat suppression through frequency selectivity rather than through prolonged echo times. This intermediary field distribution acts as a mediator between fat suppression requirement and time efficiency.
3Object-affected harmful factors
If magnetization transfer saturation is enhanced by increasing RF energy, then background signal suppression is improved, but specific absorption rate limits are exceeded
Solution Approach 1:
The patent changes the magnetic field distribution parameter by introducing a peak region with no spatial gradient. This allows the use of frequency-selective saturation pulses with lower RF energy, achieving background suppression without exceeding SAR limits.
Solution Approach 2:
The patent applies local quality by creating differentiated magnetic field regions. The peak region with no gradient in the imaging volume allows selective saturation of background tissues with lower RF energy, while the inflow volume with higher gradient preserves inflowing spin signals.
4Object-affected harmful factors
If frequency-selective fat saturation is used, then fat signal suppression is improved, but blood saturation in feeding vessels occurs due to B0 inhomogeneities
Solution Approach 1:
The patent changes the magnetic field distribution parameter to create a peak region with no spatial gradient in the imaging volume and higher gradient in the inflow volume. This modified field distribution improves frequency selectivity, allowing fat saturation pulses to distinguish between fat in the imaging volume and water in feeding vessels, preventing unwanted blood saturation.
Solution Approach 2:
The patent applies local quality by creating spatially differentiated magnetic field characteristics. The peak region with no gradient provides uniform frequency reference for fat saturation, while the higher gradient in the inflow volume creates frequency dispersion that protects blood signals from saturation.
Data Source
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AI summary
The present invention relates to a method for imaging blood vessels using an MRI system based on time-of-flight (TOF) technology, wherein a magnetic field is applied to an imaging volume and an inflow volume from which fluid enters the imaging volume of a patient. In a further step, the imaging volume is excited by a high-frequency pulse, which fulfills a magnetization transfer function and a fat saturation function, while the magnetic field is applied. The high-frequency pulse has a frequency distribution whose frequencies are substantially higher than the center frequency of the water in the imaging volume and which includes the fat frequency in the imaging volume.Furthermore, the magnetic field exhibits a magnetic field distribution which has a peak area with essentially no spatial gradient in the imaging volume and a higher spatial gradient in the inflow volume, thereby shifting the center frequency of the water in the inflow volume towards lower frequencies and preventing it from being influenced by the RF pulse.