T2* Corrected Dixon MRI Fat Water Image Separation
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Solution Overview
Problem
Current magnetic resonance tomography methods using the two-point Dixon method struggle to accurately separate fat and water images due to the influence of T*2 relaxation processes, leading to artifacts and reduced image resolution, particularly because they do not account for location-dependent relaxation times and system inhomogeneities, necessitating longer measurement times and reduced image quality.
Innovation Solution
Acquire three fat-water images at specific echo times where the first and third images have the same phase, calculate a T*2 map from these equiphase images, correct the T*2 influence in one of the equiphase and counter-phase images, and reconstruct pure T*2-corrected fat and water images using the two-point Dixon method.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the two-point Dixon method is used to separate fat and water images, then fat and water images can be obtained, but T2* decay causes artifacts and reduces image resolution
Solution Approach 1:
The patent applies preliminary action by acquiring three images at specifically timed echo points before the final image reconstruction. The first image is acquired at echo time TE1, the second at TE2, and the third at TE3, where TE1 and TE3 are equiphase times and TE2 is a counter-phase time. This preliminary acquisition of multiple timed images allows the system to calculate T2* maps and correct for T2* decay before reconstructing the final fat and water images, thereby preventing artifacts and resolution loss.
Solution Approach 2:
The patent utilizes parameter changes by varying the echo time (TE) at which images are acquired. Specifically, it changes the TE parameter to capture images at different phases of the T2* decay curve - equiphase times (TE1, TE3) and counter-phase time (TE2). This parameter variation enables the calculation of T2* maps and subsequent correction of T2* decay effects, improving image quality while maintaining the two-point Dixon separation method.
2Measurement precision
If additional echoes are measured to account for T2* decay, then image quality improves, but measurement time increases significantly
Solution Approach 1:
The patent applies partial action by acquiring exactly three images at specifically selected echo points rather than measuring numerous additional echoes. The method selects only the essential equiphase images (TE1, TE3) and one counter-phase image (TE2) needed to calculate T2* maps and correct decay effects. This partial measurement approach achieves sufficient image quality improvement without the excessive measurement time that would result from acquiring many more echoes.
Solution Approach 2:
The patent optimizes the echo time parameter selection to achieve maximum correction effect with minimum measurements. By carefully choosing TE1, TE2, and TE3 where TE1 and TE3 are equiphase times and TE2 is a counter-phase time, the method extracts sufficient T2* decay information from just three images, avoiding the need for extensive additional measurements and thereby minimizing measurement time while maintaining image quality.
3Reliability
If T2* correction is applied to separate fat and water images, then diagnostic value improves, but image reconstruction complexity increases
Solution Approach 1:
The patent applies preliminary action by calculating T2* maps from the three acquired images before performing the final fat and water image reconstruction. This preliminary T2* map calculation prepares the necessary correction data in advance, allowing the subsequent reconstruction to use pre-computed correction factors rather than performing complex iterative calculations during reconstruction, thereby managing complexity while maintaining diagnostic value.
Solution Approach 2:
The patent segments the image reconstruction process into distinct steps: first calculating T2* maps from the three acquired images, then using these maps to correct for T2* decay, and finally reconstructing the fat and water images using the corrected data. This segmentation of the reconstruction process into manageable stages simplifies the overall complexity while ensuring accurate T2* correction and maintaining high diagnostic value.
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 allows for the simple acquisition of pure fat and water images dependent on T*2 relaxation, improving image resolution and clinical diagnostic value by effectively correcting for T*2 decay, thereby enhancing the differentiation at fat-water boundaries and reducing measurement time.
Implementation Method 1
The property that the resonance frequency shifts slightly in proportion to the field strength depending on the type of chemical bond in which a signal-emitting nucleus participates, is known as chemical shift. Due to their concentration in the human body, hydrogen atoms in free water and in fat primarily contribute in the image. Their relative resonance frequency difference is approximately 3 ppm (parts per million).
Implementation Method 2
the water protons in the homogeneous magnetic field precess 3 to 4 ppm more quickly than the fat protons. In a laboratory system (FIG. 2) it is seen how the magnetization of the water protons and that of the fat protons disperse with time.
Implementation Method 3
both echoes (gradient echo or spin echoes) are negatively affected by different decay processes (relaxation processes), namely that the gradient echo is typically affected by the different location-dependent relaxation time of the transversal magnetization that is characterized by T*2
Data Source
AI summary
In a magnetic resonance tomography method and apparatus for separation of fat and water images according to the two-point Dixon method dependent on the T*2 decay, the following steps are implemented: (S1) acquire three fat-water images, respectively corresponding to the echo times TE1, TE2, TE3 after the RF excitation pulse, wherein first and third fat-water images exhibit the same phase, (S2) calculate a T*2 map from the two equiphase images, (S3) correct the T*2 influence in one of the two equiphase fat-water images and in the counter-phase fat-water image, and (S4) reconstruct a pure T*2-corrected fat image and a pure T*2-corrected water image according to the two-point Dixon method on the basis of the T*2-corrected equiphase and counter-phase fat-water images in Step (S3).