Written by in section: Medical Technology > Diagnostics
Medically Reviewed by Dr. Aj Thomas MS, MBA & Updated on Apr 3, 2016
256 Shades of Gray - Medical Ultrasound Scan quick info
A Sonographer with the Ultrasound Scanner
Flickr/Alexey Fursov

What is a Medical ultrasound scan?

A medical ultrasound scan is a medical imaging technique that uses high frequency sound waves to produce visual images of the inside of human body using a computer. It is also called a medical sonography and the medical personal performing the examination is called a sonographer.

 

Ultrasound scans are very popular due to its ease of accessibility for the patients and comparatively low cost for the procedure. It is a low risk real-time diagnostic imaging procedure due to the use of sound waves that are harmless. There is no risk of unnecessary exposure to radiation during the procedure.

 

What is an Ultrasound?

Any sound at frequencies greater than 20,000 Hz (20 kHz) is considered as an ultrasound. Human beings cannot hear sounds greater than 20 kHz. The normal range of audible sound frequencies for human beings is in between 20 Hz and 20,000 Hz.

Human hearing range and Ultrasound. © BBC
Infrasound, Human hearing range and Ultrasound.

The ability of human beings to hear high-pitched sounds in the upper limit of the audible range decreases as we age. Younger children can hear them better than older people. Since ultrasound machines use sound waves above the audible limit of human hearing ability, it is not possible to hear any sounds produced by the device while it is working.

 

Who invented the medical ultrasound scan?

In 1941, Austria born medical doctor Karl Theodore Dussik proposed the idea of using ultrasound as a medical diagnostic device. In 1947, with the help of his younger brother Friedrich Dussik, he had published their first ultrasound images of the human brain using transmission technique. Many consider Karl Theodore Dussik as the father of ultrasound diagnostic procedure.

Karl Dussik's impressive prototype of the ultrasound scanner for the brain
Karl Dussik's impressive prototype of the ultrasound scanner for the brain

It was later proven that the images produced by transmission technique were not accurate anatomical representation of the brain and many scientists started to doubt the actual value of these machine. It was assumed in the 1950s that an ultrasound machine cannot produce clear enough images to make any impact in medical diagnose.  

From the early days of ultrasound machines there was always a debate about whether transmission or reflection technique should be focused.  Towards the end of the 1950s most scientists decided to focus on reflection technique for medical ultrasounds devices after the drawbacks of transmission technique was observed.

George Döring Ludwig with his ultrasound machine prototype
George Döring Ludwig with his ultrasound machine prototype

One of the early pioneers in the reflection technique was American doctor and scientist George Döring Ludwig. He had demonstrated the use of ultrasound imaging techniques as early as 1949. It was the experiments of George Ludwig that accelerated the development of reliable medical ultrasound techniques.

 

How does a medical ultrasound machine work?

Medical ultrasound machines consist of a handheld device called a probe (Ultrasonic transducer) and a receiver part attached to a computer. These probes different in their shape and size as per the requirements.

Various types of Ultrasound scan probes
Various types of Ultrasound scan probes

The probe is placed on the surface of the skin after apply a special gel that help in ensuring continuous contact between the probe head and the skin surface. The gel also has a lubricating effect that helps in the smooth movement of the probe. The hand held probe produces high frequency sound waves that are projected into the area being examined.

The sound waves travel through the body mass and start to bounce off while passing through various anatomical hard structures. This bouncing off effect creates an echo which is detected and received by the probe that is transmitting the sound waves.

Basic working principle of Ultrasound scan

The information is processed by the computer to produce an image on the computer screen. Subsequent images generated refresh the previous image on the screen and thus produce an animation like effect where the internal organs can be observed in real-time. A typical ultrasound image is made up of 256 shades of grey.

The frequency range of a Diagnostic ultrasound is between 2 MHz and 15 MHz. At higher frequency the scanner is able to produce much better quality images. Due to the high amount of absorption by tissues and organs these high frequencies do not penetrate deep enough to give a complete deeper picture. On the other hand, lower frequencies can penetrate deeper but produces lower quality images.

Higher frequencies are used for examining superficial organs while lower frequencies are used for deeper examination. The sonographer will need to adjust the frequency depending on the area to be examined to produce optimal results.

Ultrasound scan image of a baby in the womb. © Bryan Page
Ultrasound scan image of a baby in the womb. © Bryan Page

A typical ultrasound scan takes about 15 to 45 minutes. At the end of the scanning the resulting images can be printed out on a paper or a digital video recording can be obtained.

 

Types of medical ultrasound scans

External Ultrasound Scan: This is type of ultrasound scan where the probe is place on the skin surface to check internal organs like heart, kidneys, liver etc. It is also used to check muscles and joints. During pregnancy, it is used to monitor the development of the baby. Certain birth defect can be detected though this procedure.

Internal Ultrasound Scan: In this type of ultrasound scan, a very thin probe that has a sterile coven on it is gently passing into the internal cavities like the rectum or vagina to examine internal organs like prostate gland, ovaries, Uterus etc. During the examination the patient may experience a mild discomfort. The procedure is over very quickly and does not usually cause any pain.

Endoscopic Ultrasound Scan: This scan is a combination of endoscopy and ultrasound. The endoscopy probe helps in making visual pictures of the stomach and the tube connecting your mouth and stomach (esophagus). The ultrasound probe helps to make images of surrounding organs that are not visible through the endoscope.

This procedure can be uncomfortable for the patient and most often a sedative is administered to help the patient relax.  This scanning technique is also used to look inside the lower gut by gently passing the probe thought the patient's rectum.

Patients after ultrasound scan get the results almost immediately after the test is completed. In most cases the patient need not stay back at the health center. If a sedative was given for the scan, then the patient will need to relax for few hours at the health center and will need someone to assist them in returning back home.

 

What are the common uses of medical ultrasound scanner?

© Lugansk state medical university
© Lugansk State Medical University
  • It is the most preferred monitoring technique used during pregnancy to monitor the developmental progress of the baby. Its high popularity is mainly due to the fact that the scanning procedure is considered extremely safe for the baby without any harmful radiation effects.
  • It is often used to check for abnormalities of the heart. It can detect various issues like structural abnormalities, heart valve damage, blood vessels abnormalities etc. The type of ultrasound scan that specializes in the examination of heart related health issues are called echocardiogram.
  • It used to differentiate between solid tumor and fluid filled sac (cyst)
  • It is used for checking for abnormalities in the kidneys, liver, breast, bladder, pancreas and other important organs
  • Abnormalities like gallbladder stones and lymph node inflammations can also be detected.
  • It also used by surgeon as a guiding tool during certain procedures like biopsies where a tissue or body fluid sample is taken for lab examination to check for infections or abnormalities.

 

What are the health risks of medical ultrasound scan?

Ultrasound scanning has a very good track record of being a very safe diagnostic imaging technique. However there are some concerns about the long term effects and safety of ultrasound on the human body.

  • Ultrasound scan has the ability to heat up tissues a little bit in the area being examined. There were instances in which this has led to small amount of gas formation in the body fluids and tissues being examined. There is no conclusive evidence of ill effect due to this process.
  • Experts also advice to avoid unnecessary ultrasound examinations for pregnant women because of the unknown long term effects these examinations may have on the unborn baby.
  • Some parents chose to use specialized ultrasound machines that can produce enhanced color photos in 3D of the baby in the womb for saving them as memories. Experts are skeptical about these practices.

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  • Last Reviewed on:Apr 3, 2016
  • Medically Reviewed by:Dr. Aj Thomas MS MBA
  • References:

     

    1. Choices N. Ultrasound scan - NHS Choices. http://www.nhs.uk/conditions/ultrasound-scan/Pages/Introduction.aspx
    2. Health C for D and R. Medical Imaging - Ultrasound Imaging. http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/ucm115357.htm
    3. Ultrasound frequencies | Radiology Reference Article | Radiopaedia.org. http://radiopaedia.org/articles/ultrasound-frequencies
    4. Modes of ultrasound. http://www.criticalusg.pl/en/physical-principles/modes-of-ultrasound
    5. Ultrasound: MedlinePlus Medical Encyclopedia. https://www.nlm.nih.gov/medlineplus/ency/article/003336.htm
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