Delineation of Gliomas with Magnetic Resonance Imaging Using Gd-DTPA in Comparison with Computed Tomography and Positron Emission Tomography

MRI combined with PET-CT of different tracers to improve the accuracy of glioma diagnosis: a systematic review and meta-analysis

Based on studies focusing on positron emission tomography (PET)-computed tomography (CT) combined with magnetic resonance imaging (MRI) in the diagnosis of glioma, we conducted a systematic review and meta-analysis evaluating the pros and cons and the accuracy of different examinations. PubMed and Cochrane Library were searched. The search was conducted until April 2017. Two reviewers independently conducted the literature search according to the criteria set initially. Based on the exclusion criteria, 15 articles are included in this study. Of all studies that used MRI examination, there are five involving 18F-fluorodeoxyglucose-PET, five involving 11C-methionine-PET, five involving 18F-fluoro-ethyl-tyrosine-PET, and three involving 18F-fluorothymidine-PET. Due to the limitations such as lack of data, small sample size, and unrepresentative studies, we use a non-quantitative methodology. MRI examination can provide the anatomy information of glioma more clearly. PET-CT examinations based on tumor metabolism using different tracers have more advantages in determining the degree of glioma malignancy and boundaries. However, information provided by PET-CT of different tracers is not the same. With respect to the novel hybrid MRI/PET examination equipment proposed in recent years, the combination of MRI and PET-CT can definitively improve the diagnostic accuracy of glioma.

Usefulness of FMISO-PET for glioma analysis

Glioma is one of the most common brain tumors in adults. Its diagnosis and management have been determined by histological classifications. It is difficult to establish new paradigms because the pathology has matured and a great deal of knowledge has accumulated. On the other hand, we understand that there are limitations to this gold-standard because of the heterogeneity of glioma. Thus, it is necessary to find new criteria independent of conventional morphological diagnosis. Molecular imaging such as positron emission tomography (PET) is one of the most promising approaches to this challenge. PET provides live information of metabolism through the behavior of single molecules. The advantage of PET is that its noninvasive analysis does not require tissue sample, therefore examination can be performed repeatedly. This is very useful for capturing changes in the biological nature of tumor without biopsy. In the present clinical practice for glioma, ¹⁸F-fluorodeoxyglucose (FDG) PET is the most common tracer for predicting prognosis and differentiating other malignant brain tumors. Amino acid tracers such as ¹¹C-methionine (MET) are the most useful for detecting distribution of glioma, including low-grade. Tracers to image hypoxia are under investigation for potential clinical use, and recently, ¹⁸F-fluoromisonidazole (FMISO) has been suggested as an effective tracer to distinguish glioblastoma multiforme from others.

Intraoperative tissue fluorescence using 5-aminolevolinic acid (5-ALA) is more sensitive than contrast MRI or amino acid positron emission tomography ((18)F-FET PET) in glioblastoma surgery

OBJECTIVE

The sensitivity of 5-aminolevolinic acid (5-ALA) in detecting intraoperative glioblastoma (GBM) tissue compared to postoperative (18)F-fluoroethyl-L-tyrosine and T1 contrast uptake of tumor cells in positron emission tomography (PET) and magnetic resonance imaging (MRI) scans was investigated in a retrospective image correlative study.

METHODS

Ten patients with histological verified GBM in eloquent brain regions underwent 11 surgeries with neuronavigation and 5-ALA assisted tumor resection. Residual 5-ALA fluorescence was labeled intraoperatively on the navigation MRI scans and images were fused with postoperative (18)F-FET PET and T1 contrast MRI.

RESULTS

Intraoperatively, at the end of save resection, in all patients 2-5 faint 5-ALA positive resection planes were detected (mean 3·6), compared to 0-4 (18)F-FET positive resection planes (mean 1·4) and 0-2 positive T1 contrast MRI resection planes in postoperative scans. The difference between the number of 5-ALA and (18)F-FET positive resection planes was statistically significant (P = 0·0002). The histological investigation of 5-ALA positive resection margins demonstrated infiltrative tumor in every case. Residual 5-ALA fluorescence on resection margins and postoperative (18)F-FET uptake areas or residual contrast T1 areas were colocalized in all cases, documented by pre-/postoperative image fusion.

CONCLUSION

Residual faint 5ALA uptake is documented in large areas at the end of GBM resection and corresponds to tumor infiltration. These 5-ALA positive resection plans exceeded the (18)F-FET uptake areas in postoperative PET scans. Thus, intraoperative 5-ALA residual fluorescence seems to be a more sensitive marker than (18)F-FET PET for residual tumor in malignant gliomas.