Accuracy of [¹⁸F]FDG PET/MRI for the Detection of Liver Metastases

<div><p>Background</p><p>The aim of this study was to compare the diagnostic accuracy of [¹⁸F]FDG-PET/MRI with PET/CT for the detection of liver metastases.</p><p>Methods</p><p>32 patients with solid malignancies underwent [¹⁸F]FDG-PET/CT and subsequent PET/MRI of the liver. Two readers assessed both datasets regarding lesion characterization (benign, indeterminate, malignant), conspicuity and diagnostic confidence. An imaging follow-up (mean interval: 185±92 days) and/-or histopathological specimen served as standards of reference. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated for both modalities. Accuracy was determined by calculating the area under the receiver operating characteristic (ROC) curve. Values of conspicuity and diagnostic confidence were compared using Wilcoxon-signed-rank test.</p><p>Results</p><p>The standard of reference revealed 113 liver lesions in 26 patients (malignant: n = 45; benign: n = 68). For PET/MRI a higher accuracy (PET/CT: 82.4%; PET/MRI: 96.1%; p<0.001) as well as sensitivity (67.8% vs. 92.2%, p<0.01) and NPV (82.0% vs. 95.1%, p<0.05) were observed. PET/MRI offered higher lesion conspicuity (PET/CT: 2.0±1.1 [median: 2; range 0–3]; PET/MRI: 2.8±0.5 [median: 3; range 0–3]; p<0.001) and diagnostic confidence (PET/CT: 2.0±0.8 [median: 2; range: 1–3]; PET/MRI 2.6±0.6 [median: 3; range: 1–3]; p<0.001). Furthermore, PET/MRI enabled the detection of additional PET-negative metastases (reader 1: 10; reader 2: 12).</p><p>Conclusions</p><p>PET/MRI offers higher diagnostic accuracy compared to PET/CT for the detection of liver metastases.</p></div

Acquisition parameters for the applied MR-sequences (A-F).

<p>A) A coronal T1w in and opposed phase Volumetric Interpolated Breath-hold Examination (VIBE) for calculation of the Dixon-based fat-/water-images as well as the μ-map.</p><p>B) An axial, pre-contrast T1w Fast Low Angle Shot (FLASH).</p><p>C) An axial T2w 2D half Fourier acquisition single shot turbo spin echo (HASTE).</p><p>D) An axial diffusion weighted echo planar sequence (EPI DWI) with B values of 0, 500 and 1000 s/mm².</p><p>E) An axial T2w fat saturated turbo spin echo (TSE) sequence in breath-hold.</p><p>F) A dynamic axial T1w VIBE. Four repetitive scans were performed (pre-contrast, arterial phase [20s delay], portal venous phase [60 sec delay], venous phase [100 sec delay]) after i.v.-injection of 0.1 ml/kg body weight Gadobutrol (Gadovist®, Bayer Healthcare, Berlin, Germany).</p><p>G) An axial post-contrast T1w FLASH.</p><p>Acquisition parameters for the applied MR-sequences (A-F).</p

Receiver operating characteristic (ROC) curve for PET/CT and PET/MRI for reader 1 (left), reader 2 (middle) and both readers (right).

<p>Significantly higher accuracy (area under the curve, AUC) for PET/MRI (p<0.01 for reader 1 and 2; p<0.001 overall).</p

Patient without liver metastases.

<p>PET/CT with a false positive result showing a hypodense pseudolesion with a diameter 9 mm in the CT dataset without correlate in PET. In the later acquired PET/MRI (C-E) no correlate in PET nor in the morphological datasets (D: T1w VIBE portal-venous phase; E: T2w TSE fs).</p

Liver metastases not visible in PET/CT: detection rate in different MR-sequences.

<p>Liver metastases not visible in PET/CT: detection rate in different MR-sequences.</p

Study flow diagram.

<p>Study flow diagram.</p

Further characterization of benign liver lesions.

<p>Further characterization of benign liver lesions.</p

Sensitivity, Specificity, Accuracy (area under the curve, AUC), PPV, NPV with 95% CI for each reader as well as in combination.

<p>Significant differences between PET/CT and PET/MRI are indicated (*: p<0.05; **: p<0.01, ***:p<0.001).</p

Patient with breast cancer.

<p>Both PET/CT (A,B) as well as PET/MRI (C; D; VIBE, portal venous phase) show a lesion with elevated FDG-uptake and ill-defined lesion borders as well as central contrast enhancement as signs of malignancy. Based on these findings the lesion was correctly identified as metastasis in both modalities.</p

Lesion conspicuity and diagnostic confidence in PET/CT and PET/MRI.

<p>Values are reported as mean±SD [median; range].</p