Evaluation of the potential of PET-MRI fusion for detection of liver metastases in patients with neuroendocrine tumours

Potential Clinical Applications of PET/Magnetic Resonance Imaging

Hybrid PET/magnetic resonance (MR) imaging, which combines the excellent anatomic information and functional MR imaging parameters with the metabolic and molecular information obtained with PET, may be superior to PET/computed tomography or MR imaging alone for a wide range of disease conditions. This review highlights potential clinical applications in neurologic, cardiovascular, and musculoskeletal disease conditions, with special attention to applications in oncologic imaging.

[Positron emission tomography/magnetic resonance: Present and future]

PET/MRI has recently been introduced onto the market after several years of research and development. The simple notion of combining the molecular capabilities of the PET and its difference available radiotracers with the excellent tissue resolution of the MRI and wide range of multiparametric imaging techniques has generated great expectations upon the possible uses of this technology. Many challenges must be worked out. However, the most urgent one is the derivation of the MRI-based attenuation correction map. This is especially true because the PET/CT has already demonstrated a huge clinical impact within oncology, neurology and cardiology during its short existence. Despite these difficulties, research is being carried out at a rapid pace in the clinical setting in order to find areas in which the PET/MRI is superior to other existing imaging modalities. In the few initial publications found up to date that have analyzed its clinical role, areas have been identified where PET/CT can migrate to PET/MRI, even if only to suppress the CT scan's ionizing radiation. Nonetheless, there are many theoretical applications in which the PET/MRI can further improve the field of diagnostic imaging. In this article, we will review those applications, the evidence existing regarding the MRI and PET that support those premises as well as that which we have learned in the short period of one year with our experience using the PET/MRI.

[Oncologic imaging: indications for and limitations of modern cross-sectional imaging techniques]

Cross-sectional imaging techniques, such as computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) CT are an integral part of the modern oncological workup. They are used for tumor detection and staging as well as for treatment evaluation and monitoring. Due to pathophysiological and histological differences there is no universal imaging protocol for the assessment of different forms of cancer. For instance, CT is still the standard technique for the detection and staging of lung cancer supplemented by PET which aids the exclusion of nodal involvement and the detection of distant metastases. For hepatocellular carcinoma on the other hand, MRI is the preferred imaging technique, particularly when used in conjunction with liver-specific contrast media - PET/CT is only of limited value. Finally, for neuroendocrine tumors there is a focus on special radiotracers, which, in the context of PET/CT, enable a highly specific whole-body assessment. Thus, knowledge of the pathophysiological and imaging characteristics of different tumors is essential for a personalized, state-of-the art management of oncology patients.

Meta-analysis of gadoxetic acid disodium (Gd-EOB-DTPA)-enhanced magnetic resonance imaging for the detection of liver metastases

Objective

To determine the accuracy of MR imaging with Gd-EOB-DTPA for the detection of liver metastases.

Materials and Methods

PUBMED, EMBASE, the Web of Science, and the Cochrane Library were searched for original articles published prior to February 2012. The criteria for the inclusion of articles were as follows: reported in the English language; MR imaging with Gd-EOB-DTPA was performed to detect liver metastases; histopathologic analysis (surgery, biopsy), intraoperative observation (manual palpatation, intraoperative ultrasonography), and/or follow-up US was the reference standard; and data were sufficient for the calculation of true-positive or false-negative values. The methodological quality was assessed by using the quality assessment of diagnostic studies instrument. The data were extracted to calculate sensitivity, specificity, predictive value, diagnostic odds ratio, and areas under hierarchical summary receiver operating characteristic (HSROC) curve to perform heterogeneity test and threshold effect test, as well as publication bias analysis and subgroup analyses.

Results

From 229 citations, 13 were included in the meta-analysis with a total of 1900 lesions. We detected heterogeneity between studies and evidence of publication bias. The methodological quality was moderate. The pooled weighted sensitivity with a corresponding 95% confidence interval (CI) was 0.93 (95% CI: 0.90, 0. 95), the specificity was 0.95 (95% CI: 0.91, 0.97), the positive likelihood ratio was 18.07 (95% CI: 10.52, 31.04), the negative likelihood ratio was 0.07 (95% CI: 0.05, 0.10), and the diagnostic odds ratio was 249.81 (95% CI: 125.12, 498.74). The area under the receiver operator characteristic curve was 0.98 (95% CI: 0.96, 0.99).

Conclusion

MR imaging with Gd-EOB-DTPA is a reliable, non-invasive, and no-radiation-exposure imaging modality with a high sensitivity and specificity for detection of liver metastases. Nonetheless, it should be applied cautiously, and large scale, well-designed trials are necessary to assess its clinical value.