ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Why it Is Important to Use Gel in Ultrasound

Updated on April 28, 2016
Source

Why we use ultrasound gel

When using ultrasound, it is commonplace to apply a gel, which consists mostly of water, as a contact medium between the tissue (i.e. the skin) and the ultrasound head. The purpose of the gel is to convey the acoustic energy (soundwaves) from the ultrasound head to the tissue without crossing through the air at any point. The reason this is important is that both reflection and refraction are markedly less when crossing from a gel into body tissues than they are when crossing from air into body tissues. Before we can understand reflection and refraction, however, we must first learn about acoustic impedance.

Acoustic Impedance

Acoustic impedance, simply put, is the resistance a substance’s molecules have to a change in their state of mechanical vibration. A material with a high acoustic impedance, such as bone, will be much more resistant to a change in vibration than a material with a low acoustic impedance, such as air or water. Every material has a unique acoustic impedance, which increases in proportion to that material’s density and the speed of the ultrasound waves travelling through it. Acoustic impedance is therefore a product of material density (g/cm3) and acoustic wave velocity (m/s). For this analysis of ultrasound gel, the acoustic impedances we are concerned with are;

Reflection is where a soundwave bounces off an acoustic boundary at an angle equal to it's approach, only mirrored around a perpendicular axis.
Reflection is where a soundwave bounces off an acoustic boundary at an angle equal to it's approach, only mirrored around a perpendicular axis.

- Air – 0.0004

- Water – 1.48

- Soft Tissue – 1.63

When an ultrasound beam encounters an acoustic boundary - a point at which two materials with different acoustic impedances are in contact, such as water and soft tissue – some of the acoustic energy crosses the boundary, while some is reflected, meaning it is redirected away from the acoustic boundary at an angle equal to the angle at which it approached, only mirrored around the perpendicular line to the ultrasound head. These angles of incidence and reflection shall be ignored for now as we are assuming that all energy is being directed at the tissues at an angle of 900. This is a relatively safe assumption, as it is common practice to hold the ultraound head perpendicular to the tissue.

How gel reduces reflection

The reflected energy is called an echo, and as our angle of incidence is 00, the intensity of the echo is entirely dependent on the difference in acoustic impedance values of the two materials forming the acoustic boundary.

In this equation, Z1 and Z2 are the acoustic impedances of the first and second materials. Using the acoustic impedance values for air, water and soft tissue above, the energy reflected by an air/tissue acoustic barrier and a water/tissue acoustic barrier can be found as follows;

Ultrasound uses acoustic energy (sound waves) to asses both structure and function.
Ultrasound uses acoustic energy (sound waves) to asses both structure and function. | Source

The percentage of energy reflected is almost 500 times smaller for a water/tissue acoustic barrier than it is for an air/tissue barrier. This means that the efficacy of any treatment of diagnostic imaging will be increased five-hundredfold if gel is used. The magnitude of this difference illustrates the importance of using a gel when applying ultrasound.

How to reduce refraction

It is worth briefly noting the consequences of applying acoustic energy at an angle to an acoustic barrier. Firstly, this will increase the percentage of the original intensity reflected. As the angle of incidence increases, so too will the amount of energy reflected. Secondly, increasing the angle of incidence will increase the amount of refraction. Refraction is where the direction of a sonic beam changes as it crosses an acoustic boundary. You can observe a similar effect by looking at the effect of water on beams of light. Additionally, the amount of refraction will increase as the difference in acoustic impedance across an acoustic border increases. For this reason, it is instructive to keep the ultrasound head perpendicular to the tissues being treated.

Comments

    0 of 8192 characters used
    Post Comment

    • profile image

      Divine 

      21 months ago

      This description is inaccurate at worst and vague at best, namely in regards to reflection and the angle of incidence.

      The angle of incidence is the angle created by the perpendicular line drawn through the surface at the point of incidence (called the normal), and the incident ray, not the angle created by the surface and the ray incident.

      The way you describe the angles in the picture seems accurate, just not accurate to the description of reflection and the angle of incidence.

      "some of the acoustic energy crosses the boundary, while some is reflected, meaning it is redirected away from the acoustic boundary at an angle equal to the angle at which it approached, only mirrored around the perpendicular line to the ultrasound head."

      This is ambiguous and confusing.

      If we took the flat surface of the ultrasound head, and then drew a perpendicular line through that, that would simply be the ray incident or the "beam" in this case.

      When you say perpendicular line to ultrasound head, do you simply mean the ray incident? In which case, your description is verbose and unnecessary.

      If not, then you do mean the normal line to the ray incident, in which case draw that instead of drawing this other picture showing the opposite angles.

    • profile image

      Lisa 

      4 years ago

      Your article is very informative. You have explained very clearly how ultrasound gel is related to Acoustic Impedance. I recently wrote an article about how to make ultrasound gel. Do you mind reading the new article and leaving me some good feedback http://www.ultrasoundtechniciancenter.org/blog/eas...

    working

    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, hubpages.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://hubpages.com/privacy-policy#gdpr

    Show Details
    Necessary
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Features
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Marketing
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Statistics
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)