ULTRASOUND WAVES

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Ultrasound waves

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Properties of Sound A sound is a vibration The vibrating causes the air molecules near the movement to be forced closer. This is called compression As the vibration moves on, the density and air pressure becomes lower than normal and is called rarefaction Pressure wave – longitudinal Frequency = pitch v = 334 m/s in air at room temperature Velocity is dependent upon the material Sonar is an instrument that uses reflected sound waves to find underwater objects ex- Humans use sonar to locate or map objects

Ear:

Ear

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Introduction to ultrasound waves

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ultrasound waves Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing . Ultrasound is thus not separated from "normal" (audible) sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is approximately 20 kilohertz (20,000 hertz) in healthy, young adults. The production of ultrasound is used in many different fields, typically to penetrate a medium and measure the reflection signature or supply focused energy. The reflection signature can reveal details about the inner structure of the medium, a property also used by animals such as bats for hunting. The most well known application of ultrasound is its use in sonography to produce pictures of fetuses in the human womb. There are a vast number of other applications as well.

Sonography:

Sonography Ultrasound can be used to create internal images of the human body & these are call Sonographers are diagnostic medical professionals who operate ultrasonic imaging devices to produce diagnostic images, scans, videos, or 3D volumes of anatomy and diagnostic data. Ex. Pregnant woman gets a “picture” of her unborn baby

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At present, there are no known risks with diagnostic ultrasound. Diagnostic ultrasound means to diagnose medical problems, not to treat them. Side effects occur when intensities much greater than those used in diagnostic ultrasound are used. There are 2 types of effects: thermal and non-thermal Thermal : When the sound waves pass through the tissue, not all of the waves pass through the tissue or get reflected, some are absorbed by the material. Only a very small amount gets absorbed, and often the heat generated by the energy is quickly dissipated. Non-thermal : The main non-thermal effect is called cavitation . Body tissues and fluids contain dissolved gases. When some of the sound energy is absorbed by the tissue, the energy could create bubbles from the dissolved gases. The bubbles then vibrate due to more absorption and finally burst, causing very intense, localized effects. ARE THERE ANY RISKS WITH U LTRASOUND?

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The upper frequency limit in humans (approximately 20 kHz) is due to limitations of the middle ear , which acts as a low-pass filter . Ultrasonic hearing can occur if ultrasound is fed directly into the skull bone and reaches the cochlea through bone conduction without passing through the middle ear. [2] It is a fact in psychoacoustics that children can hear some high-pitched sounds that older adults cannot hear, because in humans the upper limit pitch of hearing tends to become lower with age. A cell phone company has used this to create ring signals supposedly only able to be heard by younger humans; but many older people can hear it, which may be due to the considerable variation of age-related deterioration in the upper hearing threshold . Many animals — such as dogs , cats , dolphins , bats , and mice — have an upper frequency limit that is higher than that of the human ear and thus can hear ultrasound. This is why a dog whistle can be heard by a dog . Ability to hear ultrasound

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Frequency range of hearing for humans and selected animals Animal Frequency (hertz) Low High humans 20 20,000 cats 100 32,000 dogs 40 46,000 horses 31 40,000 elephants 16 12,000 cattle 16 40,000 bats 1,000 150,000 grasshoppers and locusts 100 50,000 rodents 1,000 100,000 whales and dolphins 70 150,000 seals and sea lions 200 55,000

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How the Ultrasound Scanner works? The ultrasound scanner, which is also known as a transducer, sends out a high pitched sound wave into the patient being scanned. The sound waves bounce back at various intervals depending on the type of material they pass through. Sound travels through materials at various speeds depending on the density and compressibility of the material. (Air and gases are not dense and therefore ultrasound waves can't pass through them.) When the sound waves hit the various materials inside your body, they bounce back to the transducer. The amount of time it takes for the sound waves to reflect back to the tranducer varies on the density and compressibility of the material. Please note that all materials in the body reflect the sound waves. It's the variation in sound wave return that determines the picture which comes up on the screen. ultrasound gel Speed of Sound Through Various Tissues Material Speed (meters/second) Air 0 331 Fat 1 450 Water 1 495 Soft Tissue 1 540 Kidney 1 561 Muscle 1 585 Bone 4 080

Ultrasound scanners:

Ultrasound scanners Anatomy of a scanner: Transmitter Transducer Receiver Processor Display Storage DID YOU KNOW THAT...? Before using water based gels to transfer the ultrasound waves to the patient, technicians used baby oil on the patients. Not only was baby oil a mess to clean up because it was so runny, it was often hard to get all the oil off the patient. WHAT A MESS!

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Thanks for watching my presentation!! Made By- Mohini Mathur IX-A

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