MR-Based Attenuation Correction in PET/MR Imaging
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Solution Overview
Problem
Current MR-based attenuation correction techniques for PET imaging suffer from long data acquisition times, motion artifacts, and signal cancellations due to restrictive echo time requirements, which limit the resolution and accuracy of attenuation maps.
Innovation Solution
The use of the mDixon technique with flexible echo times and the combination of UTE pulse sequencing allows for shorter repetition times, reduced data acquisition times, and avoidance of signal cancellations, enabling more accurate and efficient MR-based attenuation correction by optimizing echo times and phase differences between water and fat echoes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional Dixon technique is used with optimized echo times for water-fat separation, then spatial resolution is improved, but data acquisition time increases beyond breath hold capability
Solution Approach 1:
The patent changes the echo time parameters from traditional Dixon optimization (focused on water-fat separation quality) to a new optimization criterion (focused on minimizing total acquisition time while maintaining sufficient separation). This allows the system to operate within breath-hold time limits while still achieving adequate tissue classification for attenuation correction.
2Measurement precision
If long repetition times are used in Dixon technique to achieve complete water-fat separation, then tissue classification accuracy is improved, but respiratory motion artifacts increase
Solution Approach 1:
The patent performs the water-fat separation and tissue classification before the subject resumes normal breathing, completing the critical measurement phase during the breath-hold period. This preliminary action prevents respiratory motion from degrading the quality of the attenuation correction map.
3Illumination intensity
If conventional echo time selection is used to maximize water-fat signal separation, then signal contrast is improved, but signal cancellations occur in certain tissue regions
Solution Approach 1:
The patent uses a first echo time that provides sufficient (but not maximal) water-fat signal separation, accepting that some signal contrast is sacrificed to avoid the complete signal cancellation that occurs at specific echo times. The second, shorter echo time provides complementary information that helps resolve ambiguities and improves overall tissue classification reliability.
Data Source
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AI summary
A medical imaging system (10) includes a nuclear imaging system (62), a timing optimization unit (40), a magnetic resonance (MR) scanner (12), an MR reconstruction unit (38), and an attenuation map unit (50). The nuclear imaging system (62) receives nuclear decay data and generates at least one nuclear image (64) of a first resolution based on the received nuclear decay data of an imaged subject (16) and an attenuation map (52). The timing optimization unit (40) which selects a first and a second echo time for a modified Dixon (mDixon) pulse sequence and a sufficient number of repetition times (TRs) to generate an image of the subject (16) of at least a first resolution, with the phase angle difference between water and fat at the first and the second echo time being unequal to 0° and 180°. The MR scanner (12) applies the sequence to the subject (16) and receives MR data (32) from the subject. The MR reconstruction unit (38) reconstructs at least one MR image (44) based on the MR data (32). The attenuation map unit (50) constructs the attenuation map (52) based on the reconstructed MR image (44).