physics ultrasound

Ultrasound
Ultrasound is sound with a frequency greater than the upper limit of human hearing, this limit being approximately 20 kilohertz (20,000 hertz).


Approximate frequency ranges corresponding to ultrasound, with rough guide of some applications


A fetus in its mother's womb, viewed in a sonogram (brightness scan)

Ability to hear ultrasound
Some animals, such as dogs, dolphins, bats, and mice have an upper frequency limit that is greater than that of the human ear and thus can hear ultrasound. Children can hear some high-pitched sounds that older adults cannot hear, as in humans the upper limit pitch of hearing gets lower with age (a cell phone company has used this to create ring signals only able to be heard by younger humans[1]). This frequency limit is caused by the middle ear that acts as a low-pass filter. If ultrasound is fed directly into the skull bone and reaches the cochlea without passing through the middle ear, much higher frequencies (up to about 200 kHz) can be heard. This effect (sometimes called ultrasonic hearing) was first discovered by divers exposed to a high-frequency (ca. 50 kHz) sonar signal.


Sonogram of a fetus at 14 weeks (Profile)
Diagnostic sonography


A fetus, aged 29 weeks, in a "3D ultrasound"
Main article: Medical Sonography
Medical sonography (ultrasonography) is a useful ultrasound-based diagnostic medical imaging technique used to visualize muscles, tendons, and many internal organs, their size, structure and any pathological lesions. They are also used to visualize a fetus during routine and emergency prenatal care. Ultrasound scans are performed by medical health care professionals called sonographers. Obstetric sonography is commonly used during pregnancy.
Ultrasound is generally regarded as a "safe test" because it does not use ionising radiation as in x-rays, nuclear medicine, or CT. But it is a form of energy, and scans should only be performed for a suitable medical indication by trained operators (sonographers). Scans performed for baby photos are considered by the profession to be unethical.
The biggest danger of ultrasound is often considered to be misdiagnosis by untrained operators.
A study on rodent fetus brains that are exposed to ultrasound showed signs of damage. Speculation on human fetuses can be in a range of no significant complications to variety of mental and brain disorder. The study shows that rodent brain cells failed to grow to their proper position and remained scattered in incorrect parts of the brain. The conditions of this experiment are different from typical fetal scanning because of the long dwell times. Care should be taken to use low power settings and avoid pulsed wave scanning of the fetal brain unless specifically indicated in high risk pregnancies.
Diagnostic Sonography is dangerous if not treated with the absolute competence.



Ultrasound and animals
Bats
Bats use a variety of ultrasonic ranging (echolocation) techniques to detect their prey.


Dogs
The dog whistle is used to call to a dog. It makes ultrasound at a frequency in the range of 16000 Hz to 22000 Hz that dogs can hear.


Dolphins and whales
It is well known that dolphins and some whales can hear ultrasound and have their own natural sonar system.


Fish
Several types of fish can detect ultrasound. Of the order Clupeiformes, members of the subfamily Alosinae (shad), have been shown to be able to detect sounds up to 180 kHz, while the other subfamilies (e.g. herrings) can hear only up to 4 kHz.[6]


Moths
There is evidence that ultrasound in the range emitted by bats causes flying moths to make evasive manoeuvres, because bats eat moths. Ultrasonic frequencies trigger a reflex action in the noctuid moth that cause it to drop a few inches in its flight to evade attack. [3]


Rodents/Insects
Ultrasound generator/speaker systems are sold with claims that they frighten away rodents and insects, but there is no scientific evidence that the devices work. Controlled tests on some of the systems have shown that rodents quickly learn that the speakers are harmless. The frequency used however is often within the range that most children can hear, and can cause headaches.


Mosquitoes
There is a theory that ultrasound of certain frequencies, while not audible to humans, repel mosquitoes. There are computer programs available on the internet that claim to use this phenomenon for pest-control. There have been mixed reports about the effectiveness of this method towards mosquito-control.




Reaction:

Ultrasound also has therapeutic applications, which can be highly beneficial when used with dosage precautions. Ultrasounds usually uses a special kind of radiation that really helps a lot in examining and treating any conditions that a human can experience. Radiation in physic has many uses like in some machineries that are being used in some institutions.

According to Radiology Ultrasounds are useful in the detection of Pelvic abnormalities and can involve techniques known as abdominal (transabdominal) ultrasound, vaginal (transvaginal or endovaginal) ultrasound in women, and also rectal (transrectal) ultrasound in men.
Treating benign and malignant tumors and other disorders, via a process known as Focused Ultrasound Surgery (FUS) or HIFU, High Intensity Focused Ultrasound. These procedures generally use lower frequencies than medical diagnostic ultrasound (from 250 kHz to 2000 kHz), but significantly higher time-averaged intensities. The treatment is often guided by MRI, as in Magnetic Resonance guided Focused Ultrasound.
More powerful ultrasound sources may be used to clean teeth in dental hygiene or generate local heating in biological tissue, e.g. in occupational therapy, physical therapy and cancer treatment.
Extracorporeal shock wave lithotripsy uses a powerful focused ultrasound source to break up kidney stones.Focused ultrasound sources may be used for cataract treatment by phacoemulsification. Additional physiological effects of low-intensity ultrasound have recently been discovered, e.g. the ability to stimulate bone-growth and its potential to disrupt the blood-brain barrier for drug delivery.
Ultrasound is used in UAL (= ultrasound-assisted lipectomy), or liposuction.
Doppler ultrasound is being tested for use in aiding tissue plasminogen activator treatment in stroke sufferers. This procedure is called Ultrasound-Enhanced Systemic Thrombolysis.