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Accurate PET/MR quantification using time of flight MLAA image reconstruction
R Boellaard1, M B M Hofman, O S Hoekstra
1Department of Radiology and Nuclear Medicine, VU University Medical Centre, Amsterdam, The Netherlands, r.boellaard@vumc.nl.
Purpose:
Quantification of positron emission tomography/magnetic resonance imaging (PET/MRI) studies is hampered by inaccurate MR-based attenuation correction (MR-AC). To date, most studies on MR-AC have been performed using PET/MR systems without time of flight (TOF). Maximum likelihood reconstruction of attenuation and activity (MLAA), however, has the potential to improve MR-AC by exploiting TOF. The purpose of this study is to assess the impact of MR-AC on PET image quantification for TOF-PET/MR systems and to evaluate PET accuracy when using TOF in combination with MLAA (TOF-MLAA).
Procedures:
Simulations were designed to evaluate (1) the impact of MR-AC on PET quantification for different TOF windows (667, 500, 333 and 167 ps) and (2) use of TOF-MLAA for improving PET quantification. TOF-ordered subset expectation maximisation (OSEM) and TOF-MLAA reconstructions using MR-AC were compared with those obtained using TOF-OSEM with computed tomography-based AC (CT-AC).
Results:
OSEM reconstructions without TOF showed a negative MR-AC-induced bias of -50 % in the bone. TOF-OSEM was able to reduce this bias down to -15 %, with more accurate results for better TOF. TOF-MLAA was able to reduce the bias to within 5 % but at the cost of a ∼40 % increase in image variance.
Conclusions:
TOF-MLAA can improve quantitative PET accuracy of PET/MR studies. Further improvements are anticipated with improving TOF performance.
Insights
Time of flight (TOF) with maximum likelihood reconstruction of attenuation and activity (MLAA) improves positron emission tomography/magnetic resonance imaging (PET/MRI) quantification. TOF-MLAA significantly reduces MR-based attenuation correction (MR-AC) bias in PET/MRI studies.
Area of Science:
- Medical Imaging
- Nuclear Medicine
- Radiology
Background:
- Positron emission tomography/magnetic resonance imaging (PET/MRI) quantification is challenged by inaccurate MR-based attenuation correction (MR-AC).
- Previous MR-AC research primarily used PET/MR systems without time of flight (TOF).
- Maximum likelihood reconstruction of attenuation and activity (MLAA) offers potential for MR-AC improvement by leveraging TOF.
Purpose of the Study:
- To assess the impact of MR-AC on PET image quantification in TOF-PET/MR systems.
- To evaluate the accuracy of PET quantification using TOF combined with MLAA (TOF-MLAA).
Main Methods:
- Simulations evaluated MR-AC impact on PET quantification across various TOF windows (667, 500, 333, 167 ps).
- TOF-MLAA was assessed for improving PET quantification.
- TOF-ordered subset expectation maximization (OSEM) and TOF-MLAA reconstructions with MR-AC were compared to TOF-OSEM with CT-based AC (CT-AC).
Main Results:
- Without TOF, OSEM reconstructions showed a -50% MR-AC bias in bone.
- TOF-OSEM reduced this bias to -15%, with better TOF yielding more accurate results.
- TOF-MLAA reduced bias to within 5%, though with a ~40% increase in image variance.
Conclusions:
- TOF-MLAA enhances quantitative PET accuracy in PET/MR studies.
- Further advancements in TOF performance are expected to yield additional improvements.
