Comparison of hybrid 68Ga-PSMA PET/MRI and 68Ga-PSMA PET/CT in the evaluation of lymph node and bone metastases of prostate cancer
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To evaluate the reproducibility of the combination of hybrid PET/MRI and the 68Ga-PSMA-11 tracer in depicting lymph node (LN) and bone metastases of prostate cancer (PC) in comparison with that of PET/CT.
Materials and methods
A retrospective analysis of 26 patients who were subjected to 68Ga-PSMA PET/CTlow-dose (1 h after injection) followed by PET/MRI (3 h after injection) was performed. MRI sequences included T1-w native, T1-w contrast-enhanced, T2-w fat-saturated and diffusion-weighted sequences (DWIb800). Discordant PET-positive and morphological findings were evaluated. Standardized uptake values (SUV) of PET-positive LNs and bone lesions were quantified and their morphological size and conspicuity determined.
Comparing the PET components, the proportion of discordant PSMA-positive suspicious findings was very low (98.5 % of 64 LNs concordant, 100 % of 28 bone lesions concordant). Two PET-positive bone metastases could not be confirmed morphologically using CTlow-dose, but could be confirmed using MRI. In 12 of 20 patients, 47 PET-positive LNs (71.9 %) were smaller than 1 cm in short axis diameter. There were significant linear correlations between PET/MRI SUVs and PET/CT SUVs in the 64 LN metastases (p < 0.0001) and in the 28 osseous metastases (p < 0.0001) for SUVmean and SUVmax, respectively. The LN SUVs were significantly higher on PET/MRI than on PET/CT (p SUVmax < 0.0001; p SUVmean < 0.0001) but there was no significant difference between the bone lesion SUVs (p SUVmax = 0.495; p SUVmean = 0.381). Visibility of LNs was significantly higher on MRI using the T1-w contrast-enhanced fat-saturated sequence (p = 0.013), the T2-w fat-saturated sequence (p < 0.0001) and the DWI sequence (p < 0.0001) compared with CTlow-dose. For bone lesions, only the overall conspicuity was higher on MRI compared with CTlow-dose (p < 0.006).
Nodal and osseous metastases of PC are accurately and reliably depicted by hybrid PET/MRI using 68Ga-PSMA-11 with very low discordance compared with PET/CT including PET-positive LNs of normal size. The correlation between PET/MRI SUVs and PET/CT SUVs was linear in LN and bone metastases but was significantly lower in control (non-metastatic) tissue.
Keywords68Ga-PSMA PSMA PET/MRI PET/CT Lymph node metastases Bone metastases
We are grateful to our technicians Regula Gnirs, Gabi Kühnemund, Heike Streib-Retzbach and Rene Hertel for their excellent support.
Compliance with ethical standards
U.H. was supported by a grant from the Klaus Tschira Foundation (grant number 00.198.2012). M.T.F. was supported by a grant from the Deutsche Forschungsgesellschaft (DFG, grant number LA 2804/1-3).
Conflicts of interest
H.P.S., M.R. and A.A.-O. have received honoraria from Siemens Healthcare for educational talks and workshops. M.T.F., J.P.R., B.A.H., A.K.-S., M.E., K.K. and U.H. declare no conflicts of interests.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the principles of the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. The study has been approved as a retrospective study by the local ethics committee of Heidelberg (S-485/2012).
The article does not describe any studies with animals performed by any of the authors.
Informed consent was obtained from all individual participants included in the study.
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