Ultrasound Coupling agent / Ultrasound gel

 Is used to obtain close contact of the surface of the transducer with the skin without air interfering with ultrasound transmission.

 

A coupling agent is necessary to ensure good contact between the transducer and the skin and to avoid artefacts caused by the presence of air between them. 

 

The best coupling agents are water-soluble gels, which are commercially available. Water is suitable for very short examinations. Disinfectant fluids can also be used for short coupling of the transducer during guided punctures. Oil has the disadvantage of dissolving rubber or plastic parts of the transducer.

 
Components –

Carbomer – Polymer of acrylic acid cross linked with allylsucrose. It is white,fluffy and hygroscopic. There are three types of carbomer.  Carbomer 940 is preferred, as it forms clear gel. Carbomer 934 and 941 are other carbomers which can be used.

EDTA- A white crystalline powder.

Propylene glycol – A colourless, odourless, viscous hygroscopic liquid with slight sweet taste.

Trolamine – A mixture of bases containing more than 80% of triethanolamine.

 

 The composition of a common coupling gel is as follows:

 -10.0 g carbomer 

- 0.25 g ethylenediaminetetraacetic acid (EDTA) 

- 75.0 g propylene glycol 

- 12.5 g trolamine and up to 500 ml 

-Demineralized water. 

 

Preparation-

  Dissolve the EDTA in 400 ml of water. When the EDTA has dissolved, add the propylene glycol. Then add the carbomer to the solution and stir, if possible with a high-speed stirrer, until the mixture forms a gel without bubbles. Add up to 500 ml of demineralized water to the gel.

 

Precaution using ultrasound gel: 

Be careful not to transmit infectious material from one patient to the next via the transducer or the coupling gel. The transducer and any other parts that come into direct contact with the patient must be cleaned after each examination. 

The minimum requirements are to wipe the transducer after each examination and to clean it with a suitable disinfectant every day and after the examination of any patient who may be infectious. 

A suitable method for infectious patients, e.g. those infected with human immunodeficiency virus (HIV) and with open wounds or other skin lesions, is to slip a disposable glove over the transducer and to smear some jelly onto the active surface of the transducer

Few patients have allergy to ultrasound gelly, use water/ sterilium as replacement.
Ultrasound Coupling agent / Ultrasound gel