8.1 Renuvion® instant tissue heating versus bulk tissue heating

Monopolar and bipolar RF devices available for subcutaneous soft tissue coagulation work on the principle of bulk tissue heating. The device is activated until a preset subcutaneous temperature in the range of 65–70°C is achieved and maintained. The tissue being treated must be maintained at that temperature for greater than 120 s for maximal contraction to occur. Although these devices have proven effective in achieving soft tissue contraction [36], the process of heating and maintaining that temperature for extended periods can be time-consuming. In devices without an external temperature monitor, the skin surface can become overheated, causing occasional blisters or burns.

A study conducted on a live porcine model to establish the subdermal tissue temperatures produced by the Renuvion® device demonstrated a different philosophy for achieving soft tissue contraction when compared to the RF devices

described above. See Figure 3 for an illustration of the methods used in this porcine study. The study simulated actual clinical conditions as closely as possible including tumescent infiltration and completion of liposuction on the abdomen of the pig. Prior to beginning treatment with the Renuvion® device, an incision was made through the epidermis and dermis into the subdermal plane to serve as a visualization window through which a forward-looking infrared radiometer (FLIR) camera could measure internal tissue temperatures. Multiple treatment passes of the Renuvion® device were then conducted using a matrix of various treatment combinations. For each treatment combination tested, a single treatment pass consisted of three strokes of the device in the subdermal plane (see Figure 3). The second treatment stroke was performed so that the tip of the Renuvion® device passed directly underneath the visualization window. This novel testing method allowed the FLIR camera to capture both internal and external tissue temperatures simultaneously. See Figure 4 for an example of the images captured by the FLIR camera as the device passes under the visualization window.

Typical results from the porcine study are shown in Figure 5. It is important to note that the time shown on the X-axis in this graph is reported in milliseconds.

As shown in Figure 5, the Renuvion® device heats the tissue to temperatures greater than 85°C for between 0.040 and 0.080 s [17]. Heating the tissue to these temperatures for this period of time is adequate for achieving maximal soft tissue coagulation and contraction. However, unlike with bulk tissue heating, the tissue surrounding the treatment site remains at much cooler temperatures resulting in rapid cooling after the application of the energy through conductive heat transfer. Published studies have shown that the majority of soft tissue contraction induced by subcutaneous energy delivery devices is due to its effect on the fibroseptal network [12, 13]. Because of these unique heating and cooling properties of the Renuvion® technology, immediate soft tissue contraction can be achieved without unnecessarily heating the full thickness of the dermis. Practitioners who became used to the need for monitoring skin temperatures with a FLIR camera will find this is not needed with the Renuvion system.

Figure 6 helps to visualize the differences between the bulk tissue heating of monopolar and bipolar RF devices and the instant tissue heating of the Renuvion® helium plasma device. The narrow difference between subdermal and epidermal temperatures of the monopolar and bipolar devices (top image in Figure 6) results

Figure 4. FLIR camera image.

Helium Plasma-Driven Radiofrequency in Body Contouring DOI: http://dx.doi.org/10.5772/intechopen.84207

Figure 5. Temperature vs. time (in ms) for Renuvion treatment [17].

#### Figure 6.

Differences in epidermal and subdermal temperatures for monopolar and bipolar RF devices (top) and Renuvion® helium plasma device (bottom). Author's note: while a skin temperature of 45°C was noted in the porcine model, the maximum FLIR reading on a human subject's epidermis has been 38°C.

in a delicate balance between achieving the subdermal temperatures needed for soft tissue contraction and maintaining safe epidermal temperatures, resulting in the need for constant internal and external temperature monitoring. A much larger difference between internal and external tissue temperatures for the Renuvion® device (bottom image in Figure 6) achieves maximal tissue contraction while maintaining safe skin temperatures without the need for temperature monitoring.
