MR Saturation Pulse Design for Fat Artifact Suppression
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Solution Overview
Problem
Conventional magnetic resonance imaging techniques face challenges in suppressing unwanted magnetic resonance signals from spin species other than the target, leading to image artifacts and reduced image quality, particularly at lower magnetic field strengths, due to limitations in fat saturation techniques and frequency shifts between water and fat spins.
Innovation Solution
Employing a multiband saturation radiofrequency pulse that simultaneously saturates both the target spin species and unwanted spin species, such as water and fat spins, using a multiband pulse design that incorporates slice frequency shifts and chemical frequency shifts to achieve regional saturation in multiple regions, allowing for reduced repetition times and improved image contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional fat saturation techniques (spectral fat saturation pulses, STIR, SPAIR) are used to suppress unwanted fat signals, then image artifacts from fat signals are reduced, but acquisition time increases and repetition time exceeds upper limits
Solution Approach 1:
The patent combines regional saturation of water spins and fat saturation into a single multiband saturation radiofrequency pulse. This merged pulse simultaneously targets both water and fat resonances at different frequency offsets, achieving both venous saturation and fat suppression without requiring separate saturation sections, thereby reducing total acquisition time while eliminating fat signal artifacts
Solution Approach 2:
The multiband saturation pulse serves multiple functions: it performs regional saturation of the target spin species (water) in first saturation regions and simultaneously suppresses unwanted spin species (fat) in second saturation regions. This multi-functional pulse design eliminates the need for separate saturation techniques, reducing repetition time while achieving both venous saturation and fat suppression
2Object-affected harmful factors
If spectral fat saturation pulses are used to suppress fat signals, then fat artifacts are reduced, but unwanted presaturation of the target magnetic resonance signal occurs leading to reduced image quality
Solution Approach 1:
The patent applies local quality by using slice-selective gradient pulses to confine the saturation effects to specific spatial regions. The multiband saturation pulse combines frequency-selective saturation (targeting water and fat resonances) with spatially selective gradients, ensuring that fat suppression occurs only in relevant anatomical regions while preserving target signal integrity in regions of interest such as thorax or neck
3Object-affected harmful factors
If VERSE pulses at off-resonances are used for fat saturation at 7 T, then simultaneous fat saturation is achieved, but this approach is unusable at lower magnetic field strengths due to reduced frequency shift
Solution Approach 1:
The patent changes the approach from relying on large chemical frequency shifts (effective only at high field strengths like 7 T) to using multiband saturation pulses with independently controllable frequency offsets and bandwidths. This parameter flexibility allows the same pulse design to achieve both water saturation and fat suppression at any magnetic field strength, including lower fields where the water-fat frequency shift is smaller
Solution Approach 2:
The multiband saturation pulse design is universally applicable across different magnetic field strengths. By independently controlling the frequency offsets and bandwidths of the saturation bands, the pulse can simultaneously target water and fat resonances regardless of the magnitude of their frequency separation, making the technique adaptable from 7 T down to 3 T and lower field strengths
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 enhances image quality by reducing artifacts and shortening acquisition times, particularly in angiographic imaging, by effectively suppressing unwanted signals from fat while preserving the target signals, even at lower magnetic field strengths.
Implementation Method 1
a magnetic resonance sequence is used comprising a saturation section in which, by means of a saturation radiofrequency pulse which is generated when a saturation gradient pulse is applied, a saturation with respect to a spin species that is to be imaged is performed
Implementation Method 2
the frequency shift between water spins and fat spins lies at around 1000 Hz
Implementation Method 3
a saturation with respect to a spin species that is to be imaged is performed in at least one first saturation region
Data Source
AI summary
A computer-implemented method for operating a magnetic resonance device during the acquisition of magnetic resonance data from an examination region of an examination object may use a magnetic resonance sequence. The MR sequence may include a saturation section in which, by means of a saturation radiofrequency pulse which is generated when a saturation gradient pulse is applied, a saturation with respect to a spin species that is to be imaged is performed in at least one first saturation region. The saturation radiofrequency pulse may be designed as a multiband pulse by means of which, in addition, in at least one second saturation region, the magnetization with respect to a second spin species that is not to be captured is saturated.