Imaging Modalities: Neuroradiology

Abstract

Neuroradiology is a subspecialization of radiology which evaluates the brain and spine as well as the face, the neck, and the brachial plexus. Neuroradiologic imaging techniques display the structural configuration of the brain and its deviations. The radiologic techniques developed rapidly since the 1980s and include radiographics, computerized tomography (CT), magnetic resonance imaging (MRI), and spectroscopy (MRS). CT techniques include not only imaging but also angiography and perfusion; the latter allows rapid qualitative and quantitative evaluation of cerebral perfusion by generating maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). The magnetic resonance techniques are discussed which include MR imaging in the three dimensions of space with a good delineation of anatomic structures, acquisition of other parameters, i.e., T1, T2, spin density, and no exposure of the patient to ionizing radiation. MR spectroscopy provides information about the presence and concentration of various metabolites. MR angiography is a noninvasive method in which the application of contrast agent is not needed. MR perfusion has been applied in a wide variety of clinical applications, including the classification of tumors, identification of stroke regions, and characterization of other diseases. MR diffusion-weighted imaging (DWI) is based upon measuring the random Brownian motion of water molecules within a voxel of tissue which is particularly useful in tumor characterization and cerebral ischemia. MR diffusion tensor imaging (DTI) is an MRI method which allows to noninvasively study the anatomical organization of major white matter fiber systems. Functional MRI (fMRI), by measuring the blood oxygenated level-dependent (BOLD) response, is an indirect measure of neural activity and, thus, provided new insights into human cognitive functions. MR techniques are used to guide the neurosurgeon during the procedure in the setting of neuronavigational systems. Intraoperative MRI allows the visualization of the tumor/remaining tumor tissue and helps the neurosurgeon to safely remove as much tumor tissue as possible. Finally, a list of imaging protocols is provided.