Transmission Gel / Lotion

Ultrasound gels and lotions are a staple of many health care facilities in North America. Therapists place ultrasound gels on a patient’s skin before starting an ultrasound procedure or exam. Similar gels are placed on the skin before beginning TENS or neuro muscular electrical muscle stimulation (NSEMS) procedures.

The gel increases the conductivity between the patient’s skin and the ultrasound transducer or TENS/NMES electrodes. This is why these gels are also known as transmission gels.

Some patients prefer to use a lotion instead of a gel for their ultrasound procedures. Patients may prefer a lotion to a gel because lotions may be rubbed directly into the skin after the procedure.

In this way, the lotion serves dual purposes of:

• Facilitating transmission; and
• Helping to maintain the patient’s skin health.

What Do Ultrasound Gels Do?

As mentioned above, these gels increase the conductivity between the patient’s skin and the transducer of the ultrasound device.

But why is that important?

To understand the importance of a gel, one must appreciate that ultrasound sound waves do not easily travel through the air.

The transducer of an ultrasound device could be pressed directly against the patient’s skin with no gel in use. However, if this were done, many of the signals traveling to or from the transducer would be lost or distorted.

The use of an ultrasound gel reduces the amount of air between the ultrasound transducer and the patient’s skin. This reduces interference due to acoustic impedance and reflection and allows for transmission of a clearer ultrasound image.

Another important goal in the use of an ultrasound gel is not to compromise the safety or comfort of the patient.

TENS/NMES Therapies

Just as with ultrasound procedures, transmission gels are also important in the use of TENS and NMES therapies.

For these procedures, the energy being transmitted is electrical instead of acoustic. In addition, the energy is being transmitted into the patient’s body instead of the other way around.

However, the same principle applies. A  transmission gel reduces the amount of air between the surface of the TENS/NMES electrode and that of the skin. This facilitates better transmission of electrical signals to the targeted body part, which in turn improves treatment effectiveness.

Viscosity

One of the key properties used to distinguish between different ultrasound gels is the viscosity of the gel.

In general terms, the viscosity of a fluid refers to its resistance to flowing freely. Thicker, slowing moving fluids are therefore characterized as having a high viscosity while quicker moving ones have a lower viscosity.

Ultrasound gels with different viscosities have important advantages and disadvantages depending on the scenario in which they are used.

High Viscosity Gels

These types of gels have more “staying power” and cling to the skin more than lower viscosity gels. Higher viscosity gels tend to be preferred by most sonographers, especially when performing:

• Procedures that involve a smaller surface area. The higher viscosity of the gel may make it difficult to apply uniformly over a larger surface area;
• Procedures on areas of the body where gravity may cause a lower viscosity gel to fall away from the skin. Higher viscosity gels will tend to resist gravity more.;
• Procedures that require the application of the gel directly to the ultrasound transducer. Higher viscosity gels are easier to apply to a highly contoured surface such as that of an ultrasound transducer.

As a result, higher viscosity gels tend to be preferred for procedures such as the following:

• Thyroid, vascular, gallbladder, scrotal or carotid ultrasound scans;
• Echocardiograms;
• Renal ultrasounds;
• Musculo-skeletal ultrasounds.

Higher viscosity are also generally preferred for longer lasting non ultrasound procedures.

For example, TENS/NMES treatments usually last much longer than the typical ultrasound scan. As a result, therapists will normally prefer a gel with greater staying power for these treatments, i.e. one with greater viscosity.

The smaller surface area over which the gel needs to be applied for proper electrode contact also favours higher viscosity gels.

Medium Viscosity Gels

Medium viscosity gels are general purpose and are suitable for a wide variety of procedures. Therapists tend to prefer then when they are looking for a gel that strikes a balance between:

• Glides across the application area more easily than a higher viscosity gel;
• Doesn’t “plow up” ahead of the transducer as would a higher viscosity choice; while also
• Can be more easily applied to a larger surface area with uniform thickness.

A more experienced therapist may also find it less fatiguing to apply a lower viscosity gel over a larger surface area.

The types of procedures for which a medium viscosity gel may be a more appropriate choice include:

• Obstetric and Gynaecological ultrasound procedures;
•  Ultrasound procedures in maternal-foetal medicine;
• Abdominal ultrasound procedures;
• DVT ultrasounds;
• Breast ultrasounds.

Low Viscosity Gels

These gels tend to be preferred for procedures that  involve large surface areas. They are also preferable when the procedure does not last very long. As a result,  the “staying power” of the gel is less important.

UltraSound Lotion

In addition to high, medium and low viscosity ultrasound gels, there are many ultrasound lotions available for purchase. Lotions can usually be used as alternatives to “general purpose” medium viscosity gels. They offer a number of advantages that are important in many situations:

• Gels must be removed after the procedure is finished. However, removal can be messy, time consuming and annoying to the patient. Furthermore, in many situations, it is not possible to remove 100% of the gel. Lotions, on the other hand can be simply rubbed into the skin, ensuring greater patient comfort and less annoyance;
• Many lotions are enriched with skin nutrient such as aloe vera. Hence, lotions are not only less annoying to the patient (and the therapist) in not requiring removal. They also enhance skin health of the patient. Ultrasound lotions are therefore a popular alternative to gels and are a “must” for many care facilities.