Transcranial Dopplers

The Breath Holding (BH) test is a specific test for evaluation of Vasomotor Reactivity (VMR) and cerebral autoregulatory capacity.

Identification of exhausted VMR can be a good indication for high risk for stroke. Breath holding induces and increase in CO2, which in turn results in cerebral vasodilation. An increase in peak velocities during breath holding indicates different levels of patent autoregulatory capacity, While the absence of flow increase during the BH test indicates diminished physiological vasodilatory capacity and potentially high risk for stroke.

Cerebral monitoring can be critical for identification of neurological complications. Relative and/or sudden changes in cerebral blood flow velocities can become a powerful diagnostic tool and effect the immediate clinical intervention.

Bilateral cerebral monitoring is particularly useful during cardiac surgery for identification of embolic events, which may be the source of post-surgery neurological deficiencies.

The Viasonix Dolphin supports both unilateral and bilateral cerebral blood flow monitoring with a dedicated and easy to use monitoring headset. A variety of monitoring tools allow to view the complete duration of the monitored procedure, as well as zoom in or out on specific regions of interest. A variety of automatically inserted event markers, as well as user defined markers, help in post-monitoring analysis.

In addition, the Dolphin supports the display of data obtained from external channels for close correlation with the cerebral blood flow information.

Cerebral emboli can take the form of atherosclerotic plaques, air bubbles or blood clots. The immediate risk of cerebral embolization is in impaired perfusion which may lead to stroke and death.

TCD can detect the embolic signals in the blood flow velocity waveforms, which are characterized by high intensity, short duration and unidirectional signals. High intensity transient signals (HITS) are often considered as embolic events.

The Viasonix Dolphin has the most advanced HITS detection and analysis platform. Dedicated screens show the specific embolic characteristics, such as its’ energy, velocity and duration patterns, as well as display its’ travel route in the time and depth domains.

Furthermore, the Dolphin can detect embolic events that are even not within the measured spectrum of the central depth, due to its’ powerful multi-range and multi-depth analysis capabilities.

Transcranial Doppler is very useful in the identification of patent foramen ovale (PFO). PFO is a hole between the left and right atriums of the heart. While this hole exists in everyone before birth, it most often closes shortly after birth. If the hole fails to close naturally after birth it is called PFO.

TCD can easily identify the existence of PFO by injecting micro-bubbles (air mixed saline) to the patient vein (typically the antecubital vein), while the Doppler signal is recorded during the Valsalva maneuver. If embolic events are found in the recorded cerebral blood flow, typically the middle cerebral artery (MCA), then this is an indication of the existence of PFO in the patient.

The Viasonix Dolphin is ideal for PFO examinations, with a dedicated PFO protocol. The test can be performed unilaterally or bilaterally, with automatic count of high intensity transient signals (HITS) which are considered as embolic events. Each embolic event can be further analyzed with extremely high temporal and depth resolutions, and the specifications of each event displayed in a special screen. Furthermore, the embolic travel in the depth and time domains can be viewed for additional discrimination from artifact events.

Similar to cerebral autoregulation and vasomotor reactivity, cerebral collateral flow reflects an alternative compensatory mechanism to pathological flow conditions. The cerebral collateral pathways include side-to-side via the anterior communicating artery, posterior-to anterior via the posterior communicating artery, and external-to-internal via the ophthalmic artery. TCD can detect reverse velocities in the collaterally perfused arteries, indicating the viability or absence of this compensatory mechanism.

The Viasonix Dolphin’s highly sensitive M-mode display identifies forward or reversed blood flow, throughout the depth range, for analysis of this brain protection mechanism.

Brain Death condition reflects an extensive and irreversible brain damage, characterized by almost no volume blood flow to the brain. Timely identification of brain death is important in cases of organ donations.

TCD can detect the different stages of brain death through analysis of the particular waveforms: a sharp systolic peak followed by near zero diastolic velocities; systolic spikes followed by retrograde diastolic velocities; short spikes; and ultimately, no signals at all. Note that there are countries in which the use of TCD for diagnosis of brain death is not accepted.

For determination of brain death, the characteristic waveforms should be displayed in all intracranial vessels. In order to accept the absence of a Doppler signal in any vessel, a prior valid measurement must be identified in the same vessel to ensure that the access temporal window is fine.

The Viasonix Dolphin special m-mode option allows the examiner to view flows at all depths along the ultrasound beam. Thus, even after the measurement is freezed the examiner can scroll back and view signals from any depth and replay the spectrum from any depth, even if it is different than the original set depth. This significantly reduces the risk of missing a valid blood flow signal and reaching an erroneous clinical diagnosis.

Sickle cell disease is a disorder of the blood caused by abnormal hemoglobin which causes distorted (sickled) red blood cells. It is associated with a high risk of stroke, particularly in the early years of childhood.

Transcranial Doppler (TCD) can be significant in the prevention of stroke under this condition. Mean of maximum cerebral velocity readings are obtained, and results are classified as normal, conditional, abnormal or inadequate based on the measurements. Clinical treatment based on the findings can be significant in stroke prevention. 

The Viasonix Dolphin is ideal for sickle cell disease diagnosis and monitoring, with a dedicated sickle cell protocol. Special markers, which can also be configured by the examiner, clearly mark the velocity thresholds according to international guidelines, help in the identification and documentation of the pathology.