Imaging in neuro-oncology

Abstract

Imaging plays several key roles in managing brain tumors, including diagnosis, prognosis, and treatment response assessment. Ongoing challenges remain as new therapies emerge and there are urgent needs to find accurate and clinically feasible methods to noninvasively evaluate brain tumors before and after treatment. This review aims to provide an overview of several advanced imaging modalities including magnetic resonance imaging and positron emission tomography (PET), including advances in new PET agents, and summarize several key areas of their applications, including improving the accuracy of diagnosis and addressing the challenging clinical problems such as evaluation of pseudoprogression and anti-angiogenic therapy, and rising challenges of imaging with immunotherapy.

Keywords: 18F-DOPA; 18F-FET; 18F-FLT; PET-CT; brain tumor; glioblastoma; iRANO; immunotherapy; neuro-oncology; radiomics.

Figure 1.

2-hydroxyglutarate (2HG) magnetic resonance spectroscopy. (a) Axial FLAIR image of a 34-year-old woman with a right parietal lobe nonenhancing mass. (b) Single-voxel magnetic resonance performed at 3T, TE of 97 ms, demonstrates a peak at 2.3 ppm (dashed line), indicating presence of 2HG. Image provided courtesy of Drs. Alexander Lin and Min Zhou.

Figure 2.

A 62-year-old man with glioblastoma treated by concomitant temozolomide and radiation. Axial gadolinium-enhanced T1-weighted (a) and fluid-attenuated inversion recovery (FLAIR) (b) images demonstrate a small area of enhancement in the left inferior frontal lobe after three cycles of adjuvant temozolomide treatment. At the fifth cycle of adjuvant treatment, there is increased nodular enhancement (c) and surrounding T2/FLAIR signal abnormalities (d) suspicious for progression. (e) Dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) perfusion imaging showed no evidence of elevated blood volume. Subsequent surgical resection revealed evidence of necrosis without tumor cells.

Figure 3.

A 58-year-old man with recurrent glioblastoma receiving bevacizumab monotherapy. Pretreatment axial gadolinium-enhanced T1-weighted image (a) and 18F-fluoro-ethyl-tyrosine (FET) positron emission tomography image (b) showed an enhancing mass centered in the body of the corpus callosum with moderate FET avidity. After one dose of bevacizumab, the extent and intensity of enhancement both reduced as evident on the axial T1-weighted image (c), but there persists a slightly increased FET uptake in the left aspect of the mass (d). This area of abnormality showed increased enhancement on the subsequent axial gadolinium-enhanced T1-weighted image (e).

Figure 4.

Schematic flowchart of the Immunotherapy Response Assessment in Neuro-Oncology criteria for response assessment in immunotherapy. Permission to reprint from Lancet Oncology.