Imaging Experimental Brain Metastases

Abstract

Studies of the metastatic process and potential cancer therapies have been advanced by the use of imaging technology that enables the noninvasive assessment of tumor development over time. Several imaging modalities have been used to examine brain metastases in preclinical cancer models. Magnetic resonance imaging (MRI) is the clinical gold standard for anatomical evaluation of brain metastases. New advances in MRI and MR spectroscopy (MRS) have now enabled physiological characteristics of tumors to be investigated including tumor permeability, vascularity, cellularity and metabolism as well as cerebral blood flow and blood volume. MRI can also be used to detect single iron-labeled cancer cells after their initial arrest in mouse brain and subsequent tumor development. Nuclear imaging techniques including positron emission tomography (PET) and single photon emission computed tomography (SPECT) are popular tools for classifying tumors and monitoring their treatment. Brain tumors can be assessed for bio­chemical alterations such as glucose use, DNA synthesis, amino acid transport and oxygenation state. Optical imaging techniques based on the use of fluorescent or bioluminescent reporters have been found advantageous for monitoring metastatic tumor burden in experimental animals. Fluorescent entities have ­further been used in intravital microscopy to track and monitor the relationship between tumor cells and brain vasculature, including cancer cell arrest, early extravasation, perpetuation of a perivascular position and either angiogenesis or vessel co-option. Finally, imaging studies of brain metastases are often improved by using multiple imaging techniques concurrently, thereby exploiting the best features of separate modalities to acquire multilayered information and provide further insights into the evolution of metastases.