Reported December 2006

BACKGROUND: Transcranial Doppler Sonography (TCD) could be used to test the alertness of airport security screeners, air traffic controllers, or quality control and other workers who screen for the public's safety.

ON ONE'S TOES: Vigilance is an area of Human Factor/Ergonomics Research that looks at people's ability to stay focused on a task over long periods, such as someone monitoring the controls at a nuclear power plant. The challenge is how to keep alert when nothing of concern is happing, so that when a problem does occur, it will be recognized and dealt with quickly. Preliminary results indicate that TCD may offer a noninvasive and inexpensive tool to "monitor the monitor," so managers can better determine when operators performing vigilance tasks are in need of rest of replacement.

HOW TCD WORKS: TCD uses ultrasound to image the arteries located at the base of the brain to detect any narrowing or blockage in those arteries that may decrease or stop the flow of blood to the brain. A hand-held probe resembling a wand is covered with an electrically conductive gel and held at various areas of the head: at each temple, over each eye, and at the base of the skull. The technique enables doctors to record the flow of blood in each artery. TCD is less expensive than both MRI and CT scans, the two most common medical imaging techniques. It is a portable device, so doctors can bring the scanner to a patient's bedside. It is easy to customize because it allows freehand scanning of the patient, tailoring the image of a patient's head to find the best "window" to see inside the very bony (and therefore difficult to image) adult cranium.

ABOUT CAT SCANS: CAT (Computerized Axial Tomography) scans are similar to conventional X-ray imaging, but instead of imaging the outline of bones and organs, a CAT scan machine forms a full 3-D computer model of the inside of a patient's body. Doctors can even examine the body one narrow slice at a time. The X-ray beam moves all around the patient, scanning from hundreds of different angles, and the computer takes all that information to compile a 3-D image of the body.

WHAT IS DOPPLER RADAR? Doppler radar uses a well-known effect of light called the Doppler shift. Just as a train whistle will sound higher as it approaches a platform and then become lower in pitch as it moves away, light emitted by a moving object is perceived to increase in frequency (a blue shift) if it is moving toward the observer; if the object is moving away from us, it will be shifted toward the red end of the spectrum. Doppler radar sends out radio waves that bounce off objects in the air, such as raindrops or snow crystals, and then measures how much the frequency changes in returning radio waves to better determine wind direction and speed.

The Human Factors and Ergonomics Society contributed to the information contained in the TV portion of this report.

If you would like more information, please contact:

Joel S. Warm, Ph.D.
Department of Psychology
University of Cincinnati, Ohio
Cincinnati, Ohio
(513) 556-5533
Joel.Warm@uc.edu

Human Factors and Ergonomics Society
Santa Monica, CA 90406
(310) 394-1811
http://www.hfes.org