TRANSCRANIAL COLOR-CODED DUPLEX SONOGRAPHY, MAGNETIC-RESONANCE ANGIOGRAPHY, AND COMPUTED-TOMOGRAPHY ANGIOGRAPHY - METHODS, APPLICATIONS, ADVANTAGES, AND LIMITATIONS

Transcranial color-coded duplex sonography (TCCD), magnetic resonance angiography (MRA), and computed tomography angiography (CTA) are novel noninvasive or minimally invasive techniques for the study of the int racranial circulation. TCCD is relatively inexpensive and permits beds ide examination. It improves the accuracy and reliability of conventio nal transcranial Doppler studies. The main limitation of TCCD are the ultrasonic windows. They restrict the area of insonation to the major cerebral arteries and the proximal part of its branches, lower the spa tial resolution, and may prevent transtemporal insonation. Using MRA, both large and small intracranial arteries and veins can be imaged by selecting the appropriate imaging parameters. MRA provides morphologic information about the cerebral vessels, relying on blood flow as the physical basis for generating contrast between stationary tissues and moving spins. MRA is highly sensitive for the detection of occlusive d isease in large intracranial arteries. However, with bright blood tech niques the degree of stenosis tends to be exaggerated. Flow direction, eg, in collaterals, can be determined by selective or phase-contrast MRA. Perfusion imaging techniques provide information about blood flow at the capillary level. Diffusion imaging depicts molecular motion. T CCD and MRA used in combination or alone may eliminate the need for in tra-arterial digital subtraction angiography (DSA) in most patients st udied for occlusive cerebrovascular disease. DSA may be reserved for t hose patients where there is disagreement among the noninvasive techni ques, and for the diagnosis of cerebral aneurysms and arteriovenous ma lformations. CTA relies on spiral CT technology and intravenous contra st injection. To date, intracranial use has been predominantly for the diagnosis of aneurysms. The role of CTA for the detection of nonaneur ysmal intracranial vascular disease has yet to be established. (C) 199 5 John Wiley and Sons, Inc.