Microembolism in Cerebral Angiography

Using transcranial Doppler monitoring of middle cerebral artery blood flow velocity, a number of studies have detected transient high intensity embolic signals during cerebral angiography. These are particularly frequent during contrast injection, but also sometimes occur at the time of catheter and wire manipulations and following saline flushes. These embolic signals appear to be asymptomatic, although a correlation with subtle neurological damage, by neuropsychological evaluation for example, has not been made. Experimental studies in flow models and animal models suggest that the majority of these signals represent air emboli. These are most commonly introduced at the time the contrast is drawn up and at the time of contrast injection. The former can be reduced by allowing the contrast to stand prior to injection. The latter appears to be due to cavitation bubbles and can be reduced by reducing the speed of injection. Using current transcranial Doppler machines, it is impossible to be certain whether some of the embolic signals, particularly at times other than contrast injection, may be due to particulate, rather than air, emboli, but technological improvements may allow this distinction to be made in the future.