Comparison of hybrid (68)Ga-PSMA PET/MRI and (68)Ga-PSMA PET/CT in the evaluation of lymph node and bone metastases of prostate cancer.

To evaluate the reproducibility of the combination of hybrid PET/MRI and the (68)Ga-PSMA-11 tracer in depicting lymph node (LN) and bone metastases of prostate cancer (PC) in comparison with that of PET/CT.

A retrospective analysis of 26 patients who were subjected to (68)Ga-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 (68)Ga-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.

European journal of nuclear medicine and molecular imaging. 2015 Oct 28 [Epub ahead of print]

Martin T Freitag, Jan P Radtke, Boris A Hadaschik, A Kopp-Schneider, Matthias Eder, Klaus Kopka, Uwe Haberkorn, Matthias Roethke, Heinz-Peter Schlemmer, Ali Afshar-Oromieh

Department of Radiology, German Cancer Research Center, Im Neuenheimer Feld 280, D-69120, Heidelberg, Germany. Department of Radiology, German Cancer Research Center, Im Neuenheimer Feld 280, D-69120, Heidelberg, Germany. , Department of Urology, University Hospital Heidelberg, Heidelberg, Germany. , Department of Bioinformatics and Statistics, German Cancer Research Center, Heidelberg, Germany. , Division of Radiopharmaceutical Chemistry, German Cancer Research Center, Heidelberg, Germany. , Division of Radiopharmaceutical Chemistry, German Cancer Research Center, Heidelberg, Germany. , Department of Nuclear Medicine, University Hospital Heidelberg, Heidelberg, Germany. , Department of Radiology, German Cancer Research Center, Im Neuenheimer Feld 280, D-69120, Heidelberg, Germany. , Department of Radiology, German Cancer Research Center, Im Neuenheimer Feld 280, D-69120, Heidelberg, Germany. , Department of Nuclear Medicine, University Hospital Heidelberg, Heidelberg, Germany.

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