Fat Suppression Module Combining Saturation and Inversion Pulses
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Solution Overview
Problem
Current fat suppression methods in MRI, such as fat saturation and fat inversion, face challenges including B0- and B1-sensitivity, leading to inhomogeneous suppression and dependence on magnetization history, which results in inconsistent fat suppression across slices and sequences, especially in multi-slice TSE imaging where fat magnetization does not fully recover between pulses.
Innovation Solution
A fat suppression module combining fat saturation and fat inversion, where a fat-selective saturation pulse is followed by a time delay and a fat-selective inversion pulse, allowing controlled and precise fat nulling, thereby overcoming the limitations of both individual methods by providing consistent suppression and reducing dependence on B0- and B1-homogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If fat saturation is used, then fat magnetization is immediately suppressed, but the method is sensitive to B0 and B1 inhomogeneity leading to inhomogeneous suppression
Solution Approach 1:
The patent combines fat saturation and fat inversion into a unified fat suppression module. The saturation pulse is applied first to immediately suppress fat magnetization, followed by an inversion pulse after a predetermined time delay to invert the recovered fat magnetization. This merging of two methods allows the system to achieve both immediate suppression and homogeneous results by compensating for the weaknesses of each individual method.
Solution Approach 2:
The patent applies a saturation pulse as a preliminary action before the inversion pulse. This preliminary saturation immediately reduces fat magnetization, and then the inversion pulse inverts the magnetization that recovers during the time delay. This two-stage preliminary action ensures that fat is suppressed both quickly and uniformly across the imaging field.
2Measurement precision
If fat inversion is used, then T1 contrast is improved and negative magnetization is created, but the method depends on magnetization history leading to inconsistent suppression
Solution Approach 1:
The saturation pulse serves as a preliminary action that resets the magnetization history before the inversion pulse is applied. By saturating fat magnetization first and then waiting for controlled T1 recovery, the system ensures that the inversion pulse always acts on a known, consistent magnetization state, eliminating the inconsistency caused by varying magnetization history.
Solution Approach 2:
The patent changes the timing parameter by introducing a predetermined time delay between the saturation and inversion pulses. This time delay is specifically chosen to allow fat magnetization to recover to a desired level before inversion, ensuring consistent T1 contrast and homogeneous suppression across different imaging conditions.
3Reliability
If multiple TRs are used to establish steady state, then consistent fat suppression is achieved, but imaging time is increased
Solution Approach 1:
The saturation pulse acts as a preliminary action that immediately resets fat magnetization to a known state, eliminating the need for multiple TRs to establish steady state. Combined with the predetermined time delay before inversion, this allows consistent fat suppression to be achieved within a single TR, significantly reducing imaging time while maintaining reliability.
4Speed
If fat saturation is applied immediately before readout, then fat magnetization is zero at readout start, but fat has recovered significantly by readout center
Solution Approach 1:
The saturation pulse is applied as a preliminary action at the beginning of the module, immediately suppressing fat magnetization. The predetermined time delay before the inversion pulse allows controlled recovery, and the inversion then flips this recovered magnetization to negative values. This ensures that when the readout center is reached, fat magnetization is again suppressed (now negative), preventing the brightness problem that occurs with saturation alone.
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
The module achieves consistent and homogeneous fat suppression across slices and sequences, improving diagnostic accuracy by ensuring fat is accurately depicted as black, regardless of B0- and B1- variations, and eliminating the need for multiple TRs to establish steady state, thus enhancing image quality and reducing artifacts.
Implementation Method 1
Fat saturation applies a 90° radio frequency pulse at the fat frequency and spoils the created transverse fat magnetization so that longitudinal and transverse fat magnetization are zero at the beginning of the readout
Implementation Method 2
The time delay is selected to allow T1 recovery in the region of interest to a predetermined level of fat magnetization at the end of the time delay
Implementation Method 3
a fat-selective inversion pulse applied to the region of interest following a time delay
Implementation Method 4
a first spoiler gradient applied following the fat-selective saturation pulse
Data Source
AI summary
A method of fat suppression during magnetic resonance imaging includes applying a fat suppression module to a region of interest within a subject. The fat suppression module comprises a fat-selective saturation pulse; a first spoiler gradient applied following the fat-selective saturation pulse; a fat-selective inversion pulse applied to the region of interest following a time delay; and a second spoiler gradient applied following the fat-selective inversion pulse. The time delay is selected to allow T1 recovery in the region of interest to a predetermined level of fat magnetization at the end of the time delay. Following application of the fat suppression module, a sequence readout is performed to acquire one or more lines of k-space data covering the region of interest.