Transcranial Doppler (TCD)

1. 1

   Patient supine. Use sector/phased array probe (2 MHz TCD probe preferred) set to low MI.

2. 2

   Transtemporal window: place probe at the temporal squama above the zygomatic arch. Identify the MCA at 45–65mm depth — it flows toward the probe (positive).

3. 3

   Identify ACA at 60–80mm (flows away, negative). PCA at 60–70mm (flow direction varies by segment).

4. 4

   Record PSV, EDV, and mean velocity at each vessel. Calculate Lindegaard Ratio = MCA mean / ICA mean (>3 = vasospasm).

5. 5

   Transorbital window: REDUCE power to minimum MI. Place probe on closed eyelid. Ophthalmic artery at 40–50mm — normally toward probe.

6. 6

   Suboccipital window: patient flexes neck. Probe at foramen magnum. Basilar at 80–120mm (away from probe); vertebrals at 40–70mm.

7. 7

   For PFO: inject agitated saline IV during Valsalva. Count HITS (microembolic signals) within 25 cardiac cycles on MCA.

• Transtemporal window — MCA (45–65mm)
• Transtemporal window — ACA (60–80mm)
• Transtemporal window — PCA (60–70mm)
• Transorbital window — ophthalmic artery (REDUCE POWER)
• Suboccipital window — basilar artery (80–120mm)
• Suboccipital window — vertebral arteries (40–70mm)

• MCA PSV (normal: 50–120 cm/s)
• Lindegaard Ratio (vasospasm)
• Vertebral/basilar flow direction
• Microembolic signals (HITS)
• Ophthalmic artery flow direction

• Temporal window absent in 10–20% of patients (elderly women, thick skull)
• REDUCE power to minimum MI for transorbital window — retinal risk
• MCA flows TOWARD probe (positive); ACA flows AWAY (negative)

Vasospasm: MCA PSV >120 cm/s + Lindegaard Ratio >3. For PFO detection, inject agitated saline during Valsalva and count HITS within 25 cardiac cycles.