Diagnostic Radiology radiologist

Hello? I’m @Radiologist.
Have you ever had an ultrasound scan?
Perhaps if you have a baby, you would have tried it.


Do you remember? Before ultrasound scanning, one thing is prepared.

It is the gel.


The gel is applied to the scan area, before contacting the ultrasound probe to your body.

Why is this gel used?

초음파원리.png The Principle of Ultrasound

Ultrasonic waves generated from the probe are reflected from the boundary of the tissue, and the probe receive reflected waves to make an ultrasound image. However, the larger the difference in acoustic characteristics between the two tissues, the stronger the reflection and the stronger the echo (white on the screen) appears. The acoustic properties (resistance) of each tissue are related to their density, which is greater in order of bone> soft tissue> fat> air. Therefore, if you apply ultrasonic probe without gel, 99.9% of ultrasonic waves are reflected at the boundary of air - soft tissue (body). Ultrasound image should show the difference between the tissues in body (normal-lesion, etc.), not the difference between the air and body.

To solve this situation, the gel is used. In other words, when the acoustic resistance of the two media is made equal by using gel, ultrasonic waves are transmitted to body without reflection.

The other purpose of the gel is the role of lubrication, which moves the probe smoothly when performing a ultrasound scan. If the gel is not used, it may be stiff and the patient may feel pain.

Is the gel safe?


The gel is not only for skin, but also for lubrication when inserting a probe into the rectum during a gynecologic examination of a woman who has no sexual experience, and for men's prostate tests. In other words, the gel can also insert into the human body. This ultrasound gel need approval, and certification for safety in many countries.

The ingredients of the gel are harmless to the human body and the gel can be easily wiped off with water or tissue paper. There are rare skin side effects such as contact dermatitis. Also, it is reported that bacteria exist in the gel in some cases, so it is recommended to discard the gel immediately if it is used at the wound site or in children or newborns. In normal use, there is a guideline to close the lid tightly for safety. In my personal experience, there has never been a problem with ultrasound gels.

Have you ever seen such a machine in the ultrasound room?


This is a heating cabinet. The reason for using this is to keep the ultrasound gel warm. The ultrasound gel doesn’t have to be warm, but it is kept warm for patients. Applying cold gel can surprise patients and they can feel cold due to the feature of the ultrasound room. (The ultrasonic room usually keeps the temperature down to control the heat of the ultrasound device.) If the ultrasound gel is warm, patients feel comfortable, and the doctor is also easy to examine.

To Conclude….


If you have an opportunity to experience an ultrasound scan in the future, please do not feel uncomfortable with ultrasound gel. I hope my posting will make you more familiar with an ultrasound scan. Thank you.

[Korean] 대한영상의학회. 영상의학 물리학 및 품질관리 제3부. 2013.
[Korean] 한정호. 초음파내시경 기기와 처리장치, 초음파내시경 영상 및 인공음영의 이해. 제50회 대한소화기내시경학회 세미나.
[Korean] 신상진, 정병진. 초음파 영상의 원리 및 이해. The Journal of the Korean Orthopaedic Association Volume 48 Number 5. 2013.
Susan C. Oleszkowicz et al. Infections Associated with Use of Ultrasound Transmission Gel: Proposed Guidelines to Minimize Risk. Infection Control and Hospital Epidemiology. Dec. 2012 , Volume. 33 , No. 12.
Images without source; from Shutterstock.

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