TCD and TCDI studies follow a standard imaging protocol for the examination. A complete evaluation includes spectral Doppler analysis of all accessible portions of the major intracranial arteries. Velocities can be measured by automatic tracing or manual cursor placement. Bilateral evaluations are essential for a complete evaluation.

Transcranial Doppler- Complete Examination Protocol

Both TCD and TCDI include Spectral Doppler waveforms from the following vessels and approaches to obtain mean flow velocities (without angle correction):

• Submandibular Window:
  • Distal cervical internal carotid arteries (ICA)
• Transtemporal Window:
  • Terminal internal carotid arteries (TICA)
  • M1 segment of the middle cerebral arteries (MCA)
    • Should obtain proximal, mid and distal measurements
  • A1 segment of the anterior cerebral arteries (ACA)
  • Anterior communicating artery, if detectable (ACoA)
  • P1 and P2 segments of the posterior cerebral arteries
  • Posterior communicating arteries, if detectable (PCoA)
• Transtemporal Window:
  • Terminal vertebral arteries (VA)
  • Proximal and distal segments of the basilar artery (BA)
• Orbital Window: (may not be appropriate for all patients)
  • Ophthalmic Artery (OA)
  • Carotid siphon

Transcranial Doppler-Vasomotor Reactivity Protocol

Vasomotor reactivity testing is commonly ordered to evaluate cerebral reserve capacity in patients with unilateral carotid compromises and or basilar artery compromises.

• A 1.5-2.5MHz transducer is used to insonate the MCA’s either bilaterally or unilaterally. The patient is then asked to hold his breath for thirty seconds while the targeted artery is monitored.
• A normal response is for the mean flow velocity to reduce and then overshoot the baseline velocity as time expires and breathing resume.
• Many stroke and TIA patients cannot hold their breath that long so to test reserve capacity an injection of acetlyzolimide (Diamox) can be used which takes about 10 minutes to maximally dilate the arteries, or a tank of air with high pCO2 can be inhaled to precipitate vasodilation.
• This is the ultrasound version of a perfusion study without requiring a contrast medium.

Transcranial Doppler – Emboli Monitoring Protocol

Transcranial Doppler is the only modality that can detect and localize native emboli in real-time.

• A 1.5-2.5 blind pulsed-Doppler transducer is focused on the MCA and in many times fixed to a headband so the test is hands-free after set-up. Some headbands have servomotors inside them that allows for remote steering of the probe at the machine site. In 50-60% of stroke patients bilateral MCA monitoring can be achieved. This can cut the exam time in half.
• Monitoring the basilar artery is difficult and generally done with probe-in-hand, recording 500-750 beats per vessel. Emboli originating from one artery will be localized to an ipsilateral carotid or vertebral source.
• Emboli originating from a cardiac source will spew emboli through all the vessels targeted. M-mode spectral analysis can improve the display of the moving emboli as well as allow a calculation of emboli transit time.
• Testing always follows a complete transcranial Doppler Study.

Transcranial Doppler for Detection of Right-to-Left Cardiac Shunts

• One or both MCA’s can be monitored with a 1.5-2.5 MHz pulsed-Doppler transducer.
• In the out-patient lab an RN is brought in to set an IV line in preferably the brachial vein.
  • On inpatient studies, the IV-line is already set reducing exam time.
• An agitated bolus of 9 cc’s saline and 1 cc of air is injected without Valsalva. The number of emboli are counted flowing through the target artery within 1 minute of the injection.
• A second injection is performed with a maximum Valsalva maneuver performed when the bolus if halfway injected. The number of microbubbles are counted flowing through the target arteries on this second maneuver.
  • Since the patient is awake and participating many shunts will be detected that are missed by transesophogeal echocardiography.
• If the patient has no acoustic access through the temporal window monitoring the basilar artery is a suitable alternative.
• A complete TCD study is recommended before the Bubble provocation to check for mild intracranial stenosis and native emboli.