RESOLUTE PET/MRI Attenuation Correction for O-(2-18F-fluoroethyl)-L-tyrosine (FET) in Brain Tumor Patients with Metal Implants

Abstract

Aim: Positron emission tomography (PET) imaging is a useful tool for assisting in correct differentiation of tumor progression from reactive changes, and the radiolabeled amino acid analog tracer O-(2-18F-fluoroethyl)-L-tyrosine (FET)-PET is amongst the most frequently used. The FET-PET images need to be quantitatively correct in order to be used clinically, which require accurate attenuation correction (AC) in PET/MRI. The aim of this study was to evaluate the use of the subject-specific MR-derived AC method RESOLUTE in post-operative brain tumor patients.Methods: We analyzed 51 post-operative brain tumor patients (68 examinations, 200 MBq [18F]-FET) investigated in a PET/MRI scanner. MR-AC maps were acquired using: (1) the Dixon water fat separation sequence, (2) the ultra short echo time (UTE) sequences, (3) calculated using our new RESOLUTE methodology, and (4) a same day low-dose CT used as reference “gold standard.” For each subject and each AC method the tumor was delineated by isocontouring tracer uptake above a tumor(T)-to-brain background (B) activity ratio of 1.6. We measured B, tumor mean and maximal activity (TMEAN, TMAX), biological tumor volume (BTV), and calculated the clinical metrics TMEAN/B and TMAX/B.Results: When using RESOLUTE 5/68 studies did not meet our predefined acceptance criteria of TMAX/B difference to CT-AC < ±0.1 or 5%, TMEAN/B < ±0.05 or 5%, and BTV < ±2 mL or 10%. In total, 46/68 studies failed our acceptance criteria using Dixon, and 26/68 using UTE. The 95% limits of agreement for TMAX/B was for RESOLUTE (−3%; 4%), Dixon (−9%; 16%), and UTE (−7%; 10%). The absolute error when measuring BTV was 0.7 ± 1.9 mL (N.S) with RESOLUTE, 5.3 ± 10 mL using Dixon, and 1.7 ± 3.7 mL using UTE. RESOLUTE performed best in the identification of the location of peak activity and in brain tumor follow-up monitoring using clinical FET PET metrics.Conclusions: Overall, we found RESOLUTE to be the AC method that most robustly reproduced the CT-AC clinical metrics per se, during follow-up, and when interpreted into defined clinical use cut-off criteria and into the patient history. RESOLUTE is especially suitable for brain tumor patients, as these often present with distorted anatomy where other methods based on atlas/template information might fail.

Utility of Dynamic Susceptibility Contrast Perfusion-Weighted MR Imaging and 11C-Methionine PET/CT for Differentiation of Tumor Recurrence from Radiation Injury in Patients with High-Grade Gliomas

“…In addition, the more recent developments in attenuation correction for MR imaging-based methods (eg, RESOLUTE) are promising. 28 However, the use of PET/MR imaging has some unclear drawbacks: Patient comfort is decreased and communication with the patient is hampered. Thus, movement artifacts are more common in PET/MR imaging.…”

Joint EANM/EANO/RANO practice guidelines/SNMMI procedure standards for imaging of gliomas using PET with radiolabelled amino acids and [18F]FDG: version 1.0

“…Some may lead to systematic differences in the activity distribution and calculated semiquantitative metrics ( see section Static FET, MET, FDOPA PET) [18] that should carefully be considered during interpretation of PET images [19, 20]. …”

“… Various attenuation correction strategies for PET/MRI have been implemented. Some may lead to systematic differences in the activity distribution and calculated semiquantitative metrics ( see section Static FET, MET, FDOPA PET ) [ 18 ] that should carefully be considered during interpretation of PET images [ 19 , 20 ]. MRI attenuation-corrected images must routinely be checked for artefacts, consistency and plausibility during PET/MRI reading.…”

“…Typically artefacts may arise from mis-segmentation of brain/fat/bone tissue, or from metallic dental prostheses and metallic implants such as coils, stents, surgical clips, etc. [ 18 , 21 , 22 ]. Artefacts may show as signal voids that exceed the true dimensions of the metal inclusions.…”

Diagnostic Performance of PET and Perfusion-Weighted Imaging in Differentiating Tumor Recurrence or Progression from Radiation Necrosis in Posttreatment Gliomas: A Review of Literature

“…The recently developed novel Region specific optimization of continuous linear attenuation coefficients based on UTE (RESOLUTE) method for attenuation correction is a clinically acceptable measure that needs further clinical validation. 78 Another major problem in hybrid PET/MR imaging is movement artifacts, which compromise both MR imaging and PET image quality. 79 Technical advancements in PET techniques and the everevolving field of radiopharmaceuticals have opened a new domain in glioma imaging.…”