Discrimination and anatomical mapping of PET-positive lesions: comparison of CT attenuation-corrected PET images with coregistered MR and CT images in the abdomen

Abstract

Purpose PET/MR has the potential to become a powerful tool in clinical oncological imaging. The purpose of this prospective study was to evaluate the performance of a single T1-weighted (T1w) fat-suppressed unenhanced MR pulse sequence of the abdomen in comparison with unenhanced low-dose CT images to characterize PET-positive lesions. Methods A total of 100 oncological patients underwent sequential whole-body 18 F-FDG PET with CT-based attenuation correction (AC), 40 mAs low-dose CT and two-point Dixonbased T1w 3D MRI of the abdomen in a trimodality PET/CT-MR system. PET-positive lesions were assessed by CT and MRI with regard to their anatomical location, conspicuity and additional relevant information for characterization. Results From among 66 patients with at least one PETpositive lesion, 147 lesions were evaluated. No significant difference between MRI and CT was found regarding anatomical lesion localization. The MR pulse sequence used performed significantly better than CT regarding conspicuity of liver lesions (p<0.001, Wilcoxon signed ranks test), whereas no difference was noted for extrahepatic lesions. For overall lesion characterization, MRI was considered superior to CT in 40 % of lesions, equal to CT in 49 %, and inferior to CT in 11 %. Conclusion Fast Dixon-based T1w MRI outperformed lowdose CT in terms of conspicuity and characterization of PET-positive liver lesions and performed similarly in extrahepatic tumour manifestations. Hence, under the assumption that the technical issue of MR AC for whole-body PET examinations is solved, in abdominal PET/MR imaging the replacement of low-dose CT by a single Dixon-based MR pulse sequence for anatomical lesion correlation appears to be valid and robust.

Use of PET/MRI for identification and characterisation of liver lesions

“…As a result, hyperintense hepatic malignancies on T2-weighted images become more apparent following contrast administration. Good results have also been achieved in characterising lesions containing functional RES cells, such as focal nodular hyperplasia (FNH) [12]. But it is the third group, liver-specific contrast agents, that has caused most excitement in studies investigating the use of contrast-enhanced MRI for assessment of focal liver lesions.…”

“…Overall, co-registered PET and unenhanced MR images have been shown to outperform unenhanced PET/CT in the imaging of PET-positive liver lesions, with better delineation of small lesions as well as reliable localisation of lesions to the corresponding liver segment [5,12].…”

“…Inversion recovery images increase the sensitivity for detecting lesions [10]. Furthermore, out-of-phase imaging can be used to further characterise fat-containing benign lesions, which lose signal on out-of-phase images as compared to in-phase images [12].…”

“…Dynamic gadolinium-enhanced T1-GRE imaging depicts the pattern of enhancement of hepatic neoplasms, which is very useful for the accurate characterisation of focal hepatic lesions, with incremental value being achieved through addition of quantitative data from both PET and MRI [12].…”

18F-FDG-PET/MR increases diagnostic confidence in detection of bone metastases compared with 18F-FDG-PET/CT

“…Patients had a resting time of ∼ 30 min before going into the MR. A mechanism able to transfer the shuttle board from the MR-table to the PET/CT table ensured that patient transport from the MR system to the PET/CT and placement/removal of dedicated radiofrequency coils were possible without repositioning the patient [16]. With this, image sets of PET/CT and PET/ MR were available for diagnostic and comparative purposes.…”