Advanced imaging techniques for neuro-oncologic tumor diagnosis, with an emphasis on PET-MRI imaging of malignant brain tumors

Abstract

Purpose of review: This review will explore the latest in advanced imaging techniques, with a focus on the complementary nature of multiparametric, multimodality imaging using magnetic resonance imaging (MRI) and positron emission tomography (PET).

Recent findings: Advanced MRI techniques including perfusion-weighted imaging (PWI), MR spectroscopy (MRS), diffusion-weighted imaging (DWI), and MR chemical exchange saturation transfer (CEST) offer significant advantages over conventional MR imaging when evaluating tumor extent, predicting grade, and assessing treatment response. PET performed in addition to advanced MRI provides complementary information regarding tumor metabolic properties, particularly when performed simultaneously. ¹⁸F-fluoroethyltyrosine (FET) PET improves the specificity of tumor diagnosis and evaluation of post-treatment changes. Incorporation of radiogenomics and machine learning methods further improve advanced imaging. The complementary nature of combining advanced imaging techniques across modalities for brain tumor imaging and incorporating technologies such as radiogenomics has the potential to reshape the landscape in neuro-oncology.

Keywords: Advanced MRI; Amino acid PET; Brain tumor; Chemical exchange saturation transfer; Diffusion-weighted imaging; FET; Glioblastoma; Glioma; High-grade malignancy; Hybrid PET/MRI; MR spectroscopy; Metastasis; Perfusion-weighted imaging; Progression; Pseudoprogression; Pseudoresponse; Radiation necrosis; Radiogenomics; Radiomics; Treatment-related change; Tumor grading.

Fig. 1

Hybrid FET PET/MRI imaging. Representative images of a WHO grade IV GBM with a lesion progressively enlarging at 6 months following surgery and radiation therapy. Top left to bottom right include FLAIR, DCE Ktrans, DSC rCBV, T1 post-contrast, FET PET, and fused hybrid FET PET/MRI images. Both DCE and DSC images show abnormal perfusion corresponding to areas of abnormal enhancement indicating increased vascularity. The bottom middle image shows abnormally elevated FET PET signal in a pattern consistent with the MRI perfusion findings. Subsequent surgical resection confirmed tumor recurrence on histopathology. TBR max was 3.74 and TBR mean was 3.13.The dynamic characteristics of the FET uptake can also be studied in a region of interest over time as shown on the time activity curve (Y axis = absolute SUV, X axis = time in seconds). In this case, a 45-min acquisition occurred. The slope of the curve was − 3.60. A downward slope at the second half of the acquisition is suggestive of presence of tumor, while an upward slope has been reported to be more indicative of treatment related change such as pseudoprogression. Data was generated in QImage Softwared, NIH NCI 5R01CA202695. Images were de-identified and approved under an institutional IRB protocol.