These gaseous micro embolic signals were recorded by insonation of the middle cerebral artery by transcranial Doppler ultrasound during coronary artery bypass graft surgery. A few gaseous emboli will not jeopardize brain function. The first emboli appears in the high velocity range of the systole, the second emboli appear in the low velocity diastole. The result is on the audio a high frequency 'chirp'  in the systole and a low frequency 'blop' in the diastole.

High and low velocity Gaseous Micro Embolic Signals

This micro embolic signal was recorded by insonation of the middle cerebral artery by transcranial Doppler ultrasound in a patient who experienced a transient ischemic attack (TIA) due to an unstable ipsilateral carotid artery stenosis. These single solid MES are strong predictors of an increased stroke risk. There are in some patients hunderds of these events in 24 hours. Rapid arrest of the embolic source is warranted in these patients

A Single solid

Micro Embolic Signal

This micro embolic signal was recorded by insonation of the middle cerebral artery by transcranial Doppler ultrasound in a patient who experienced an aortic valve (AV) endocarditis. These MES are strong predictors of imminent strokes therefore the patient wat scheduled for AV replacement. He recovered well without a stroke.

This micro embolic signal was recorded by insonation of the middle cerebral artery by transcranial Doppler ultrasound in a patient who experienced a transient ischemic attack (TIA) due to an unstable ipsilateral carotid artery stenosis. At different time scales one clearly sees in the right audiospectrum that the MES is characterized by regular zero crossings. The number zero crossings per second relates to the velocity of the embolus. 

This demo file was recorded during insonation of the middle cerebral artery with a transcranial Doppler instrument during an angioplasthy procedure. Suddenly a dense package of emboli appear in the velocity display followed bij a tail of more individual single gaseous MES. High air loading is associated with (transient) neurological disfunction.

During TCD exams one might observe MES look-alikes with are not generated bij solid or gaseous particles in the blood stream. These high intensity transients are called 'artifacts'. Artifacts almost never have regular zero crossing (if they exhibit regular zero-crossings they are called musical artifacts). This low frequency artefact (LFA) is related to a short external movement of the TCD probe. The artefact is around the baseline and has very irregular zero crossings. More precise the LFA is the result of a swing of the whole audio signal around the baseline due to the probe movement.

This so called speech artefact was recorded by insonation of the middle cerebral artery by transcranial Doppler ultrasound in a patient who experienced a transient ischemic attack (TIA) due to an unstable ipsilateral carotid artery stenosis. It has been provoked by the patient that suddenly started to speak. This is an example of a musical artefact with discrete different frequencies. These speech artifacts, especially when produced over a very short time may mimic single solid MES. 

A Single solid MES at different timescales

A single solid MES in native

endocarditis

A shower of Gaseous MES

Electronic Artefact

Speech Artefact

Low frequency Artefact

This demo file was recorded during insonation of the middle cerebral artery with a transcranial Doppler instrument during an angioplasthy procedure. Suddenly an unshielded electronically instrument next to the TCD instrument was switched on. The TCD equipment picked up the signal and displayed this electronic artefact.