Ultrasound

Ultrasound

1. Simple Facts

   • SOUND WAVES with a frequency above 20,000Hz- too high for human hearing.
   • It travels at different speeds in different materials and tissues.

2. Partially reflected at boundaries

   • (1) When a wave passes from one medium into another, some of the wave is REFLECTED off the boundary between the two media, and some is transmitted and refracted. This is PARTIAL REFLECTION.
   • (2) What this means is that you can point a PUSLE of ultrasound at an object, and wherever there are boundaries between one substance and another, some of the ultrasound gets REFLECTED back.
   • (3) The time it takes for the reflections to reach a DETECTOR can be used to measure how far away a boundary is.
   • (4) This is how ultrasound imaging works.
   • The distance travelled in an ultrasound wave can be calculated using this equation:
     • S = V x T
       • S = Distance in Metres (M)
       • V = Speed in Metres per second (m/s)
       • T = Time in seconds (s)

3. What are they used for in Medicine?

   • Breaking down kidney stones
     • Kidney stones are hard masses that can block the urinary tract.
     • An ultrasound beam concentrates HIGH ENERGY WAVES at the kidney stone and turns it into sand like particles.
     • These particles then pass out of the body in urine.
   • Pre-Natal Scanning of a Fetus
     • Ultrasound waves can pass through the body, but whenever they reach a boundary between TWO DIFFERENT MEDIA (like fluid in the womb and the skin of the fetus) some of the wave is reflected back and detected. The exact timing and distribution of these ehoes are processed by a computer to produce a video image of the fetus.

4. Is Ultrasound safe?

   • X-rays are ionising- can cause cancer- not safe to use on developing babies
   • CT Scans use a lot more X-RAY Radiation than standard X-Ray photographs, so the patient is exposed to even more ionising radiation