Symposium



Detection of Pulmonary Nodules by UTE Sequences in Oncology Patients using a PET/MR System


Presenting Author Senior Author
Name: Nicholas Burris Name: Thomas Hope
Email: nicholas.burris@ucsf.edu Email: thomas.hope@ucsf.edu
Presenting Author’s RIG/SRG: Cardiac & Pulmonary Imaging  
Presenting Author's Lab Location: Parnassus   

Abstract Information
Imaging Modality: MR PET/SPECT
Disease Application:
Complete author list: Nicholas S Burris, Kevin M Johnson, Peder E Z Larson, Michael D Hope, Scott K. Nagle, Spencer C Behr and Thomas A Hope
Abstract highlights: Ultrashort TE sequences can identify small pulmonary nodules in cancer patients undergoing hybrid PET/MR imaging, even in the absence of FDG-avidity. Ultrashort TE sequences detected all FDG-avid nodules, and had a high detection rate for non-FDG-avid pulmonary nodules ≥ 4 mm in size (79%).
 
Introduction
The recent introduction of hybrid PET/MR systems has raised the possibility of combined whole body PET and MR imaging for evaluation of oncology patients; however, feasibility of clinical PET/MR imaging has been traditionally limited by poor MR evaluation the lung parenchyma due to rapid signal decay, low tissue proton density and substantial respiratory/cardiac motion. Several approaches, including zero TE (ZTE) techniques1, FSPGR2,3, and FSE4 have been utilized to minimize susceptibility and motion artifacts for pulmonary nodule evaluation. Recently, a free-breathing 3D radial ultra-short TE (UTE) technique has been described for evaluation of structural lung disease (e.g. pulmonary fibrosis) 5; however, the utility of this sequence for pulmonary nodule evaluation has not yet been investigated. We hypothesized that, given its high spatial resolution and motion minimizing properties, a free-breathing 3D UTE-based technique would be feasible and sensitive for the evaluation of pulmonary nodules in oncology patients.
 
Methods
In this HIPAA-compliant, institutional review board approved prospective study, 82 pulmonary nodules were identified in 8 patients with extrathoracic malignancies. Patients underwent free-breathing UTE and dual-echo 3D GRE imaging of the lungs on a hybrid PET/MR scanner immediately following clinical PET/CT. CT was considered the reference standard for nodule detection. Two reviewers determined nodule detection and measurements on MR sequences. McNemar’s test was used to evaluate differences in nodule detection rate between MR techniques, and inter-rater agreement was assessed using Bland-Altman plots.
 
Results
Average nodule diameter was 6.2 ± 2.7 mm (range: 3 – 17 mm). The detection rate was higher for UTE compared to dual-echo GRE for nodules ≥4 mm (82% vs. 34%, p<0.001) with largest difference in detection noted in the ≥4 – ≤8 mm group (79% vs. 21%, p<0.001). UTE displayed a higher detection rate than dual-echo GRE for nodules without FDG-avidity (68% vs. 22%, p<0.001). Inter-rater reliability of nodule detection by MR was high (κ=0.90 for UTE and κ=0.92 for dual-echo GRE).
 
Conclusions
A free-breathing ultrashort TE sequence has high sensitivity for detection of small pulmonary nodules (4 – 8 mm) and outperformed 3D dual-echo GRE technique for detection of small, non-FDG-avid nodules.