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Rapid dual-echo ramped hybrid encoding MR-based attenuation correction (dRHE-MRAC) for PET/MR
Hyungseok Jang1, Fang Liu1, Tyler Bradshaw1
1Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
Magnetic Resonance in Medicine
|October 4, 2017
Summary
This study introduces dual-echo ramped hybrid encoding (dRHE) for faster MR-based attenuation correction (MRAC) in PET/MR imaging. The dRHE method significantly improves PET accuracy, offering a rapid and robust solution for clinical applications.
Area of Science:
- Medical Imaging
- Radiology
- Biophysics
Background:
- Accurate attenuation correction (AC) is crucial for quantitative positron emission tomography (PET)/magnetic resonance (MR) imaging.
- Current MR-based attenuation correction (MRAC) methods can be time-consuming or lack accuracy for certain tissues.
- Developing rapid and robust MRAC techniques is essential for improving PET/MR scan efficiency and diagnostic accuracy.
Purpose of the Study:
- To develop and evaluate a rapid MR-based attenuation correction (MRAC) technique for PET/MR imaging using dual-echo ramped hybrid encoding (dRHE).
- To achieve accurate estimation of a pseudo CT image within a single, fast scan for improved PET data quantification.
Main Methods:
- Implemented a novel dual-echo ramped hybrid encoding (dRHE) sequence to acquire ultrashort echo time (UTE) and out-of-phase echo images rapidly (35 s) at high spatial resolution (1 mm³).
- Utilized 4-class tissue classification (bone, air, fat, water) and two-point Dixon reconstruction for pseudo CT image generation.
- Reconstructed multiple UTE images using an advanced hybrid-encoding scheme to improve air and bone segmentation.
- Evaluated dRHE-MRAC in 10 subjects undergoing PET/MR brain imaging, comparing results with CT-based AC and existing MRAC methods using Dice coefficients and PET reconstruction errors.
Main Results:
- dRHE-MRAC achieved high Dice coefficients for soft tissue (0.95 ± 0.01), air (0.62 ± 0.06), and bone (0.78 ± 0.05), demonstrating significant improvement over existing approaches.
- Significantly reduced PET reconstruction errors to less than 1% in most brain regions (P < 0.05).
- The rapid 35-second acquisition enabled high-resolution imaging for accurate attenuation correction.
Conclusions:
- Dual-echo ramped hybrid encoding (dRHE) provides a rapid and robust method for MR-based attenuation correction (MRAC) in PET/MR imaging.
- The proposed dRHE-MRAC technique significantly enhances PET quantitative accuracy, particularly in the brain.
- This advancement offers a promising solution for efficient and accurate PET/MR examinations.
