Elsevier

Clinical Imaging

Volume 42, March–April 2017, Pages 126-132
Clinical Imaging

Original Article
FDG PET/MR in initial staging of sarcoma: Initial experience and comparison with conventional imaging

https://doi.org/10.1016/j.clinimag.2016.11.016Get rights and content

Highlights

  • T and M stage was identical for PET/MR and the conventional modalities (CT and MR) in all 29 patients (κ = 1)

  • N stage differed between the methods in one patient and was identical for the remaining 28 patients (κ = 0.65)

  • FDG PET/MR shows excellent agreement with the currently preferred imaging methods for initial staging of sarcoma

Abstract

Objective

To assess the feasibility of positron emission tomography/magnetic resonance imaging (PET/MR) with 18F-fluordeoxyglucose (FDG) for initial staging of sarcoma.

Materials and methods

Twenty-nine patients with sarcoma were included in this study. Weighted kappa (κ) was used to assess the agreement between PET/MR and conventional imaging (CT and MR). The accuracy of PET/MR and conventional imaging for distant metastases was compared using receiver operating characteristic (ROC) analysis.

Results

T and M stage were identical for PET/MR and conventional modalities in all patients (κ = 1). N stage was identical for 28/29 patients (κ = 0.65).

Conclusions

FDG PET/MR shows excellent agreement with the currently preferred imaging methods (CT and MR) in initial staging of sarcoma.

Introduction

Sarcomas are a heterogeneous group of tumors, which make up about 1% of all malignancies in adults [1], [2]. Beside sarcoma type, important factors for the choice of therapy and prognosis in sarcoma include the extent of the primary tumor and the presence of metastases. Initial staging in sarcoma currently relies mostly on MR (magnetic resonance imaging) for primary tumor assessment and CT (computed tomography) for evaluation of possible distant metastases [3]. While whole-body MR has been feasible for nearly a decade, it has not been evaluated in sarcoma patients. The recently introduced hybrid imaging modality PET/MR (positron emission tomography/magnetic resonance imaging) combines the excellent soft tissue contrast of MR and metabolic information provided by PET. When compared to standalone imaging modalities or PET/CT, the combination of PET and MR is expected to improve metastasis detection, for example in regard to cerebral, hepatic or musculoskeletal metastases [4], partly due to the superior soft tissue contrast of MR. Besides morphologic imaging with excellent contrast, PET/MR also allows for diffusion-weighted imaging (DWI) or imaging with supraparamagnetic nanoparticles, which can provide additional information about tissue properties and can also be advantageous for metastasis detection. Thus PET/MR provides an interesting new alternative in tumor imaging. Potential advantages of FDG PET/MR have already been demonstrated in patients with head and neck cancer [5], lung cancer [6] and breast cancer [7]. The use of PET/MR in sarcoma staging has not been systematically evaluated yet. The aim of this study was to assess the feasibility of PET/MR with FDG (18F-fluordeoxyglucose) in initial staging of sarcoma and evaluate the agreement of PET/MR and conventional imaging modalities (computed tomography = CT; and MR) regarding sarcoma staging. The study also compared the sensitivity and specificity of PET/MR and conventional imaging modalities for distant metastases.

Section snippets

Materials and methods

This retrospective study was approved by the local ethics committee and written informed consent was waived.

The radiology information system (RIS) of our hospital was searched for patients who underwent FDG PET/MR for initial staging of sarcoma between January 2011 and December 2014. Besides whole-body FDG PET/MR, a dedicated MR of the primary tumor and a contrast-enhanced CT of the thorax and abdomen for initial staging were also inclusion criteria.

Twenty-nine consecutive patients with

Results

The primary tumor was identified on PET/MR and MR in all patients (100% detection rate).

Twenty-seven of 29 primary tumors had increased FDG uptake in comparison to the surrounding tissues (SUVmax 4.2–23.6, mean SUVmax 12.3). Two patients with myxoid liposarcoma had minimally increased FDG uptake (SUVmax 2.3 and 2.9, respectively).

Based on the morphologic information of the PET/MR findings, the following T stages were assigned: T1b (n = 3), T2a (n = 3), T2b (n = 23). Based on metabolic and morphologic

Discussion

To our knowledge, the current study is the first to systematically evaluate the role of PET/MR in initial staging of sarcoma. A previous pilot study has already demonstrated the promise of FDG PET/MR in therapy response assessment in sarcoma [19]. However, in regard to initial staging of sarcoma, the use of PET/MR has only been mentioned in case reports [20]. Our study was able to show that FDG PET/MR is feasible for sarcoma staging and is comparable to the currently predominant combination of

Conclusion

FDG PET/MR is feasible for initial staging of sarcoma and has high sensitivity and specificity for distant metastases. While our initial results show a very good agreement with conventional imaging modalities (CT and MR), the benefit of the addition of PET to whole body MR is not clear at this stage. Further evaluation is also needed to clarify a possible role of FDG PET/MR for therapy choice and therapy monitoring in sarcoma.

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