The massive 200 mile wide Hurricane IKE devastated coastal Texas and caused major damage inland as far as the Great Lakes. Millions of people are still feeling the effects of IKE as they struggle back to normal life. My personal post IKE experience includes; 6 sweltering nights without power, hours waiting in line for gas or entry into the local grocery store and more than 40 hours of volunteering providing aide to others who were completely overcome by the storm. Believe it or not, I also spent a lot of time without power thinking about how I could relate a posting about IKE to the PACS and Digital Imaging Blog. Well here we go…
Doppler Radar in Weather Imaging and Doppler Sonography in Ultrasound Imaging
The Doppler effect (or Doppler shift), named after Christian Doppler, is the change in frequency and wavelength of a wave for an observer moving relative to the source of the waves.
Doppler radar is radar using the doppler effect of the returned echoes from targets to measure their radial velocity. To be more specific the microwave signal sent by the radar antenna's directional beam is reflected toward the radar and compared in frequency, up or down from the original signal, allowing for the direct and highly accurate measurement of target velocity component in the direction of the beam. Doppler radars are used in air defense, air traffic control, sounding satellites, police speed guns, and radiology.
A weather radar is a type of radar used to locate precipitation, calculate its motion, estimate its type (rain, snow, hail, etc.), and forecast its future position and intensity. Modern weather radars are mostly pulse-doppler radars, capable of detecting the motion of rain droplets in addition to intensity of the precipitation. Both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather.
Sonography can be enhanced with Doppler measurements, which employ the Doppler effect to assess whether structures (usually blood) are moving towards or away from the probe, and its relative velocity. By calculating the frequency shift of a particular sample volume, for example a jet of blood flow over a heart valve, its speed and direction can be determined and visualised. This is particularly useful in cardiovascular studies (sonography of the vasculature system and heart) and essential in many areas such as determining reverse blood flow in the liver vasculature in portal hypertension. The Doppler information is displayed graphically using spectral Doppler, or as an image using color Doppler (directional Doppler) or power Doppler (non directional Doppler). This Doppler shift falls in the audible range and is often presented audibly using stereo speakers: this produces a very distinctive, although synthetic, pulsing sound.
- Wikipedia 8/2008Color Doppler Image of IKE
(Source: The Weather Channel)
Color Doppler of Common Carotid Artery
(Source: Wikipedia)
In the days and hours leading up to the landfall of Hurricane IKE millions of people were glued to the news for storm updates. As IKE approached the GulfCoast, all the local and network TV stations featured loop after loop of weather doppler images of IKE. While most Texans focused on the doppler images of IKE to determine the possible path of destruction, a small number of cardiac patients focused on the echoes and doppler images of an artery to determine the path to healthy blood flow.
Picking up the pieces from IKE’s damage has been hard but I can’t help but think…
Kudos to Mr. Doppler for opening the door to the latest advances in doppler technology.
