Abstract
Aim: Positron emission tomography (PET) imaging is a useful tool for assisting in correct differentiation of tumor progression from reactive changes. O-(2-18F-fluoroethyl)-L-tyrosine (FET)-PET in combination with MRI can add valuable information for clinical decision making. Acquiring FET-PET/MRI simultaneously allows for a one-stop-shop that limits the need for a second sedation or anesthesia as with PET and MRI in sequence. PET/MRI is challenged by lack of a direct measure of photon attenuation. Accepted solutions for attenuation correction (AC) might not be applicable to pediatrics. The aim of this study was to evaluate the use of the subject-specific MR-derived AC method RESOLUTE, modified to a pediatric cohort, against the performance of an MR-AC technique based on deep learning in a pediatric brain tumor cohort.Methods: The modifications to RESOLUTE and the implementation of a deep learning method were performed using 79 pediatric patient examinations. We analyzed the 36 of these with active brain tumor area above 1 mL. We measured background (B), tumor mean and maximal activity (TMEAN, TMAX), biological tumor volume (BTV), and calculated the clinical metrics TMEAN/B and TMAX/B.Results: Overall, we found both RESOLUTE and our DeepUTE methodologies to accurately reproduce the CT-AC clinical metrics. Regardless of age, both methods were able to obtain AC maps similar to the CT-AC, albeit with DeepUTE producing the most similar based on both quantitative metrics and visual inspection. In the patient-by-patient analysis DeepUTE was the only technique with all patients inside the predefined acceptable clinical limits. It also had a higher precision with relative %-difference to the reference CT-AC (TMAX/B mean: -0.1%, CI: [-0.8%, 0.5%], p = 0.54) compared to RESOLUTE (TMAX/B mean: 0.3%, CI: [-0.6%, 1.2%], p = 0.67) and DIXON-AC (TMAX/B mean: 5.9%, CI: [4.5%, 7.4%], p < 0.0001).Conclusion: Overall, we found DeepUTE to be the AC method that most robustly reproduced the CT-AC clinical metrics per se, closely followed by RESOLUTE modified to pediatric cohorts. The added accuracy due to better noise handling of DeepUTE, ease of use, as well as the improved runtime makes DeepUTE the method of choice for PET/MRI attenuation correction.
Highlights
Positron emission tomography/Magnetic Resonance Imaging with the combination of MRI and radiolabeled amino acid analog tracers such as O-(2-18F-fluoroethyl)-L-tyrosine (FET) PET offer complimentary information when imaging cerebral brain tumors (Watanabe et al, 1992; Buchmann et al, 2016), especially when estimating the true tumor extent both in lowand high-grade gliomas (Kracht et al, 2004; Vander Borght et al, 2006)
We have recently introduced a PET/MRI-attenuation correction (AC) method, RESOLUTE (Ladefoged et al, 2015), that makes use of ultra-short echo time (UTE) images to calculate an attenuation map with continuous bone representation, and overcomes the air/tissue interface challenges by using anatomical regional masks defined on an aligned template in MNI space
We have shown that RESOLUTE led to the same clinical diagnosis as the reference CT-AC in a challenging cohort consisting of adult post-surgical brain tumor patients with severe anatomical deformations (Ladefoged et al, 2017)
Summary
Positron emission tomography/Magnetic Resonance Imaging with the combination of MRI and radiolabeled amino acid analog tracers such as O-(2-18F-fluoroethyl)-L-tyrosine (FET) PET offer complimentary information when imaging cerebral brain tumors (Watanabe et al, 1992; Buchmann et al, 2016), especially when estimating the true tumor extent both in lowand high-grade gliomas (Kracht et al, 2004; Vander Borght et al, 2006). We have recently introduced a PET/MRI-AC method, RESOLUTE (Ladefoged et al, 2015), that makes use of UTE images to calculate an attenuation map with continuous bone representation, and overcomes the air/tissue interface challenges by using anatomical regional masks defined on an aligned template in MNI space. Within these masks, possible bias from the bone surrogate signal is limited. A prerequisite for successful application of RESOLUTE to pediatric cohorts is that these masks should be defined on pediatric templates
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