Emerging techniques and technologies in brain tumor imaging

Abstract

The purpose of this report is to describe the state of imaging techniques and technologies for detecting response of brain tumors to treatment in the setting of multicenter clinical trials. Within currently used technologies, implementation of standardized image acquisition and the use of volumetric estimates and subtraction maps are likely to help to improve tumor visualization, delineation, and quantification. Upon further development, refinement, and standardization, imaging technologies such as diffusion and perfusion MRI and amino acid PET may contribute to the detection of tumor response to treatment, particularly in specific treatment settings. Over the next few years, new technologies such as 2(3)Na MRI and CEST imaging technologies will be explored for their use in expanding the ability to quantitatively image tumor response to therapies in a clinical trial setting.

Keywords: MRI; PET; T1 subtraction; brain tumors; diffusion MRI; imaging biomarker; perfusion MRI; response assessment.

Fig. 1.

Standard structural images and contrast enhanced T1-weighted subtraction maps in patients treated with bevacizumab at recurrence. (A) A patient with recurrent glioblastoma showing nonenhancing tumor near the right lateral ventricle after treatment with bevacizumab. This patient has multifocal disease including 2 potential diffuse cortical lesions identified on FLAIR. Postcontrast T1-weighted images show ill-defined regions of subtle contrast enhancement within these potential lesions. T1 subtraction maps clearly identify an enhancing mass near the right lateral ventricle, along with a single enhancing nodule within the cortex in the left frontal lobe (grey arrows). (B) A patient with recurrent glioblastoma showing extensive FLAIR signal changes and subtle contrast enhancement near the internal capsule after administration of bevacizumab. After application of T1 subtraction maps, the conspicuity of this lesion is clearly improved, and it can be identified as an obvious ring-enhancing lesion (grey arrow). (C) A patient with recurrent glioblastoma treated with bevacizumab showing 2 areas of concern, one in the right frontal lobe and the other in the right posterior lateral ventricle. With postcontrast T1-weighted images, both of these suspicious lesions show enhancement; however, precontrast T1-weighted images show T1 shortening consistent with blood products within the frontal lobe lesion. After application of T1 subtraction maps, the lesion in the frontal lobe is hypointense (white arrow), and the lesion near the posterior lateral ventricle is hyperintense (grey arrow). This example illustrates the ability of T1 subtraction maps to both identify subtle enhancing lesions as well as exclude blood product-related T1 shortening.

Fig. 2.

Contrast-enhanced T1-weighted digital subtraction maps improve coefficient of variation (CV) in tumor volume quantification in both the presence of antiangiogenic agents as well as nonneoplastic agents. (A) CV in lesion volumes prior to administration of bevacizumab in the BRAIN trial showing a significant decrease in CV after calculation of subtraction maps (t test, P = .0002). (B) CV in lesion volumes after administration of bevacizumab in the BRAIN trial showing a significant decrease in CV in subtraction maps (t test, P = .0003). (C) CV in lesion volumes prior to administration of an undisclosed antiangiogenic agent showing significant decreases in CV in subtraction maps compared with standard postcontrast T1-weighted images (T1 + C) (t test, P = .0006). (D) CV in lesion volumes after to administration of an undisclosed antiangiogenic agent, showing significant decreases in CV in subtraction maps (t test, P < .0001).