P3 Physics Medical applications Section Ultrasound To examine the inner structures of living things, it is possible to use X rays but these are potentially harmful, especially for expectant mothers. The alternative is to use ULTRASOUND This is a kind of sound with _ _ _ _ frequencies and _____ wavelengths It is above the AUDITORY RANGE of humans (the range is from 20 Hz to at least 20,000 Hz)

P3 Physics Medical applications Section Ultrasound The ultrasonic waves will travel through solids and liquids but in air high frequency ultrasound has a short range. When they reach a boundary between one medium (substance) and another, some waves are reflected. The distance to this boundary can be calculated from the time for the reflection to return and the speed of ultrasound in the medium.

P3 Physics Medical applications Section Ultrasound The formula to use is speed = distance/time The technique works like SONAR which is a method of finding the depth of submarines or underwater objects such as shoals of fish

P3 Physics Medical applications Section Ultrasound The formula to use is speed = distance/time On the screen of an oscilloscope, the large spike happens when the sound pulse sets off. The smaller spike occurs when the reflection returns. The x axis scale will be in milliseconds e.g. 10 milliseconds per square. In this example it has taken _______ milliseconds for the reflection to arrive so it took ___ ms to reach the object underwater.

P3 Physics Medical applications Section Ultrasound The most familiar use of ultrasound is in pre-natal scans. The transmitter and receiver are in the same ‘head’. A fluid is applied between the head and the mother to transmit the ultrasound waves. This baby is 13 weeks old.

P3 Physics: Medical applications Section Ultrasound Kidney stones are calcium deposits that harden in the urinary tract. They can be very painful to pass through the system, which is one of the most common means of extracting the stones. Ultrasound can assist in finding kidney stones and in breaking them up by sound waves and would otherwise have to be removed by surgery. Ultrasound Waves Extracorporeal shock wave lithotripsy (ESWL) is a common treatment for kidney stones that uses shock waves outside the body to break down the stones into smaller pieces that can more easily be eliminated. The shock waves pass through the skin to the stones. Doctors use an ultrasound device to locate the stones and direct the shocks.

P3 Physics: Medical applications Section Ultrasound