Influence and compensation of truncation artifacts in MR-based attenuation correction in PET/MR
Unlabelled:
The goal of this article is to quantify the influence of truncation artifacts in the magnetic resonance (MR)-based attenuation map (MRMap) on reconstructed positron emission tomography (PET) image volumes and to propose a new method for minimizing this influence.
Methods:
PET data sets of 20 patients investigated in a Philips Ingenuity PET/MR were reconstructed with and without applying two different methods for truncation compensation (TC1 vendor-provided, TC2 newly developed). In this patient group, the extent of truncation artifacts and quality of the truncation compensation (TC) was assessed visually in the MRMaps. In three additional patients MRMaps generated by algorithm TC2 could be compared to the ground truth of transmission-based attenuation maps obtained with a Siemens ECAT HR(+) scanner. The influence of truncation on regional SUVs in lesions, other hot structures (bladder, kidney, myocardium) and the arms was assessed in suitable volume of interests (VOI).
Results:
Truncation compensated MRMaps exhibited residual artifacts in the arms in 16 patients for algorithm TC1 and to a lesser extent in eight patients for algorithm TC2. Compared to the transmission-based attenuation maps algorithm TC2 slightly overestimated the size of the truncated arms by 0.3 cm in the radial direction. Without truncation compensation, VOIs located in the trunk showed an average SUVmax underestimation of less than 5.4% relative to the results obtained with TC2. Inside the patients' arms underestimations up to 46.5% were found.
Conclusion:
In the trunk, standardized uptake values (SUV) underestimations due to truncation artifacts in the MRMap are rather small. Inside the arms, severe SUV underestimations can occur. Therefore, reliable TC is mandatory and can be achieved by applying the newly developed algorithm TC2 which has yielded promising results so far. Implementation of the proposed method is straightforward and should be easily adaptable to other PET/MR systems.
Insights
Truncation artifacts in PET/MR imaging cause significant SUV underestimations in arms, but a new method (TC2) effectively minimizes these errors. Reliable truncation compensation is crucial for accurate PET imaging.
Area of Science:
- Medical Imaging
- Radiological Physics
- Positron Emission Tomography
Background:
- Magnetic resonance (MR)-based attenuation maps (MRMap) are used in positron emission tomography (PET)/MR imaging.
- Truncation artifacts in MRMap can affect the accuracy of reconstructed PET image volumes.
Purpose of the Study:
- To quantify the influence of MRMap truncation artifacts on PET image volumes.
- To propose and evaluate a new method for minimizing these truncation artifacts.
Main Methods:
- Compared PET/MR reconstructions with and without two truncation compensation (TC) methods (TC1, TC2).
- Assessed MRMap quality and truncation extent visually and compared TC2 to transmission-based attenuation maps.
- Evaluated the influence of truncation on standardized uptake values (SUV) in various regions.
Main Results:
- TC2 showed fewer residual artifacts in arms compared to TC1.
- TC2 slightly overestimated arm size but significantly reduced SUV underestimations.
- SUV underestimations were <5.4% in the trunk but up to 46.5% in the arms without compensation.
Conclusions:
- Truncation artifacts in MRMap lead to minor SUV underestimations in the trunk but severe ones in the arms.
- The newly developed TC2 algorithm reliably compensates for truncation artifacts.
- TC2 is straightforward to implement and adaptable to other PET/MR systems.
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