Behnke and his wife knew he needed to go to the ER, where doctors used a new technology — a transcranial doppler (TCD) — to perform an ultrasound on Behnke's brain. "In Troy's case ...

Transcranial Doppler (TCD) is a non-invasive ultrasound technique that measures cerebral blood flow velocity in major brain arteries. By analyzing the speed and direction of blood flow ...