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Quantitative Evaluation of 2 Scatter-Correction Techniques for 18F-FDG Brain PET/MRI in Regard to MR-Based
Jarmo Teuho1,2, Virva Saunavaara2,3, Tuula Tolvanen2,3
1Turku PET Centre, University of Turku, Turku, Finland jarmo.teuho@tyks.fi.
Abstract:
In PET, corrections for photon scatter and attenuation are essential for visual and quantitative consistency. MR attenuation correction (MRAC) is generally conducted by image segmentation and assignment of discrete attenuation coefficients, which offer limited accuracy compared with CT attenuation correction. Potential inaccuracies in MRAC may affect scatter correction, because the attenuation image (μ-map) is used in single scatter simulation (SSS) to calculate the scatter estimate. We assessed the impact of MRAC to scatter correction using 2 scatter-correction techniques and 3 μ-maps for MRAC. Methods: The tail-fitted SSS (TF-SSS) and a Monte Carlo-based single scatter simulation (MC-SSS) algorithm implementations on the Philips Ingenuity TF PET/MR were used with 1 CT-based and 2 MR-based μ-maps. Data from 7 subjects were used in the clinical evaluation, and a phantom study using an anatomic brain phantom was conducted. Scatter-correction sinograms were evaluated for each scatter correction method and μ-map. Absolute image quantification was investigated with the phantom data. Quantitative assessment of PET images was performed by volume-of-interest and ratio image analysis. Results: MRAC did not result in large differences in scatter algorithm performance, especially with TF-SSS. Scatter sinograms and scatter fractions did not reveal large differences regardless of the μ-map used. TF-SSS showed slightly higher absolute quantification. The differences in volume-of-interest analysis between TF-SSS and MC-SSS were 3% at maximum in the phantom and 4% in the patient study. Both algorithms showed excellent correlation with each other with no visual differences between PET images. MC-SSS showed a slight dependency on the μ-map used, with a difference of 2% on average and 4% at maximum when a μ-map without bone was used. Conclusion: The effect of different MR-based μ-maps on the performance of scatter correction was minimal in non-time-of-flight 18F-FDG PET/MR brain imaging. The SSS algorithm was not affected significantly by MRAC. The performance of the MC-SSS algorithm is comparable but not superior to TF-SSS, warranting further investigations of algorithm optimization and performance with different radiotracers and time-of-flight imaging.
Insights
Magnetic Resonance-based attenuation correction (MRAC) minimally impacts scatter correction in PET/MR brain imaging. Both tail-fitted and Monte Carlo scatter simulations showed comparable performance, with minimal differences observed across various MR-based attenuation maps.
Area of Science:
- Medical Imaging
- Nuclear Medicine
- Radiophysics
Background:
- Accurate attenuation correction is crucial for quantitative positron emission tomography (PET).
- Magnetic Resonance-based attenuation correction (MRAC) is an alternative to CT, but its accuracy can be limited.
- Inaccuracies in MRAC may potentially affect scatter correction algorithms that rely on attenuation maps.
Purpose of the Study:
- To assess the impact of MRAC on scatter correction performance in PET/MR brain imaging.
- To compare two scatter correction techniques (TF-SSS and MC-SSS) using different attenuation maps (CT-based and MR-based).
- To evaluate the quantitative accuracy and visual consistency of PET images under varying MRAC conditions.
Main Methods:
- Utilized tail-fitted single scatter simulation (TF-SSS) and Monte Carlo-based single scatter simulation (MC-SSS) on a Philips Ingenuity TF PET/MR scanner.
- Employed one CT-based and two MR-based attenuation maps (μ-maps) for MRAC.
- Conducted studies on 7 subjects and an anatomic brain phantom, evaluating scatter sinograms, scatter fractions, and quantitative metrics (volume-of-interest analysis).
Main Results:
- MRAC demonstrated minimal impact on scatter correction algorithm performance, particularly with TF-SSS.
- Scatter sinograms and scatter fractions showed negligible differences across different μ-maps.
- TF-SSS exhibited slightly higher absolute quantification; volume-of-interest analysis revealed maximum differences of 3-4% between TF-SSS and MC-SSS.
- MC-SSS showed a minor dependency on the μ-map (2-4% difference), especially when bone was excluded.
Conclusions:
- The influence of different MR-based attenuation maps on scatter correction performance is minimal in non-time-of-flight 18F-FDG PET/MR brain imaging.
- Scatter correction algorithms are not significantly affected by MRAC.
- The performance of MC-SSS is comparable to TF-SSS, suggesting further investigation into algorithm optimization for various radiotracers and time-of-flight imaging.
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