Conventional and Advanced Imaging Techniques in Post-treatment Glioma Imaging

Abstract

Despite decades of advancement in the diagnosis and therapy of gliomas, the most malignant primary brain tumors, the overall survival rate is still dismal, and their post-treatment imaging appearance remains very challenging to interpret. Since the limitations of conventional magnetic resonance imaging (MRI) in the distinction between recurrence and treatment effect have been recognized, a variety of advanced MR and functional imaging techniques including diffusion-weighted imaging (DWI), diffusion tensor imaging (DTI), perfusion-weighted imaging (PWI), MR spectroscopy (MRS), as well as a variety of radiotracers for single photon emission computed tomography (SPECT) and positron emission tomography (PET) have been investigated for this indication along with voxel-based and more quantitative analytical methods in recent years. Machine learning and radiomics approaches in recent years have shown promise in distinguishing between recurrence and treatment effect as well as improving prognostication in a malignancy with a very short life expectancy. This review provides a comprehensive overview of the conventional and advanced imaging techniques with the potential to differentiate recurrence from treatment effect and includes updates in the state-of-the-art in advanced imaging with a brief overview of emerging experimental techniques. A series of representative cases are provided to illustrate the synthesis of conventional and advanced imaging with the clinical context which informs the radiologic evaluation of gliomas in the post-treatment setting.

Molecular MRI-Based Monitoring of Cancer Immunotherapy Treatment Response

“…By applying a series of linear algebra operations, a spatial map of the apparent diffusion coefficient (ADC) can be calculated, where bright pixels represent fast diffusion (e.g., in the CSF and in regions of edema and cystic necrosis) and dark pixels represent restricted diffusion. Given that malignant tumors are highly cellular, low ADC values are typically associated with an active high-grade disease [75,77]. Whereas the ADC metric is often used in clinical practice, other metrics for analyzing water diffusion have been suggested, such as diffusion kurtosis imaging (DKI) [78].…”

Peritumoral Edema in Gliomas: A Review of Mechanisms and Management

“…Assessing peritumoral edema enables the selection of appropriate therapies and the monitoring of their effectiveness [11,16,19]. During post-treatment followup, changes in edema can be observed and used to assess tumor recurrence and treatment efficacy [16,20]. Thus, edema surrounding gliomas is clinically significant in pathological evaluation, treatment planning, prognosis prediction, and treatment efficacy monitoring.…”

“…Edema surrounding gliomas can be visualized using imaging modalities such as computed tomography (CT) and magnetic resonance imaging (MRI). Using MRI, edema surrounding a tumor appears as a region of high intensity on T2-weighted images [20]. Neuroimaging plays a crucial role in evaluating the presence and extent of peritumoral edema [20,21].…”

Brain Tumor Imaging: Review of Conventional and Advanced Techniques

“…Conventional anatomic MRI sequences such as T1, T2, T2 FLAIR, T1 pre-gadolinium, and T1 post-gadolinium are limited in their ability to delineate recurrence from pseudoprogression. 8 9 In both scenarios, disruption of the blood–brain barrier can result in abnormal enhancement, either from tumor infiltration and angiogenesis in tumor recurrence or from a variety of potential factors related to treatment effect such as reactive changes after surgery, chemotherapy, radiation, and corticosteroids, thus making a simple assessment of enhancement less reliable. 8 9 44 45…”

“…Despite the value of CT, MRI remains the most widely used imaging modality for CNS tumor workup and monitoring, as crucial information about tumor structure and physiology can be provided by various image sequences. Specifics regarding the appropriate MRI sequences will vary depending on factors such as scanner hardware and image processing software, radiologist's or referring provider's preferences, institutional agreements, and patient factors, but the basic CNS tumor protocol should include the following 9 10 :…”