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Numerous noninvasive imaging options are available to clinicians evaluating patients with neurologic disorders. These include computed tomography (CT) and variations CT angiography (CTA), perfusion CT (pCT), and dual energy CT and magnetic resonance (MR) imaging (MRI) and variations MR angiography (MRA), MR vessel wall imaging, functional MRI (fMRI), MR spectroscopy (MRS), MR neurography (MRN), diffusion and diffusion tensor MR imaging, susceptibility-weighted MR imaging (SWI), arterial spin label imaging (ASL) and perfusion MRI (pMRI). Furthermore, a number of interventional neuroradiologic techniques have matured including catheter embolization, stent retrieval thrombolysis, aneurysm coiling and stenting, as well as numerous techniques for spine disorders, including CT myelography, fluoroscopy and CT-guided transforaminal and translaminar epidural and nerve root injections, radiofrequency ablation and blood patches. Multidetector CTA (MDCTA) and gadolinium-enhanced MRA techniques have reduced the need for catheter-based angiography, which is now reserved for patients in whom small-vessel detail is essential for diagnosis or for whom concurrent interventional therapy is planned (Table 416-1).
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In general, MRI is more sensitive than CT for the detection of lesions affecting the peripheral and central nervous system (CNS), particularly those of the spinal cord, cranial nerves, and posterior fossa structures. Diffusion MR, a sequence sensitive to the microscopic motion of water, is the most sensitive technique for detecting acute ischemic stroke of the brain or spinal cord, and it is also useful in the detection and characterization of encephalitis, abscess, Creutzfeldt-Jacob disease, cerebral tumors and acute demyelinating lesions. CT, however, is acquired quickly, making it a pragmatic choice for patients with acute changes in mental status, suspected hemorrhage, and acute intracranial or ...