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An improved MR sequence for attenuation correction in PET/MR hybrid imaging
Koji Sagiyama1, Yuji Watanabe2, Ryotaro Kamei1
1Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Abstract:
The aim of this study was to investigate the effects of MR parameters on tissue segmentation and determine the optimal MR sequence for attenuation correction in PET/MR hybrid imaging. Eight healthy volunteers were examined using a PET/MR hybrid scanner with six three-dimensional turbo-field-echo sequences for attenuation correction by modifying the echo time, k-space trajectory in the phase-encoding direction, and image contrast. MR images for attenuation correction were obtained from six MR sequences in each session; each volunteer underwent four sessions. Two radiologists assessed the attenuation correction maps generated from the MR images with respect to segmentation errors and ghost artifacts on a five-point scale, and the scores were decided by consensus. Segmentation accuracy and reproducibility were compared. Multiple regression analysis was performed to determine the effects of each MR parameter. The two three-dimensional turbo-field-echo sequences with an in-phase echo time and radial k-space sampling showed the highest total scores for segmentation accuracy, with a high reproducibility. In multiple regression analysis, the score with the shortest echo time (-3.44, P<0.0001) and Cartesian sampling in the anterior/posterior phase-encoding direction (-2.72, P=0.002) was significantly lower than that with in-phase echo time and Cartesian sampling in the right/left phase-encoding direction. Radial k-space sampling provided a significantly higher score (+5.08, P<0.0001) compared with Cartesian sampling. Furthermore, radial sampling improved intrasubject variations in the segmentation score (-8.28%, P=0.002). Image contrast had no significant effect on the total score or reproducibility. These results suggest that three-dimensional turbo-field-echo MR sequences with an in-phase echo time and radial k-space sampling provide improved MR-based attenuation correction maps.
Insights
The optimal MR sequence for PET/MR attenuation correction uses specific echo times and radial k-space sampling. This improves segmentation accuracy and reproducibility in PET/MR hybrid imaging.
Area of Science:
- Medical Imaging
- Radiology
- Biophysics
Background:
- Accurate attenuation correction is crucial for quantitative PET/MR hybrid imaging.
- Current MR-based methods require optimization for improved segmentation accuracy.
Purpose of the Study:
- To investigate the impact of MR sequence parameters on tissue segmentation for attenuation correction.
- To identify the optimal MR sequence for reliable attenuation correction in PET/MR.
Main Methods:
- Six 3D turbo-field-echo MR sequences were tested in 8 healthy volunteers.
- Parameters varied included echo time, k-space trajectory (Cartesian vs. radial), and image contrast.
- Radiologists scored segmentation accuracy and ghost artifacts; multiple regression analysis was used.
Main Results:
- 3D turbo-field-echo sequences with in-phase echo time and radial k-space sampling yielded the highest scores for segmentation accuracy and reproducibility.
- Shorter echo times and anterior/posterior Cartesian sampling resulted in lower scores.
- Radial k-space sampling significantly improved segmentation scores and reduced intrasubject variations compared to Cartesian sampling.
Conclusions:
- 3D turbo-field-echo MR sequences employing an in-phase echo time and radial k-space sampling are optimal for MR-based attenuation correction.
- These optimized sequences enhance segmentation accuracy and reproducibility in PET/MR imaging.
