• General Information

Effects of laser on subdermal fat tissue

Dr G. Khoury, R. Saluja, Dr Keel Dr Detwiler and Dr Goldman. Evaluation of Interstitial Lipolysis comparing a 1064, 1320 and 2100 nm laser in an ex vivo model. Lasers in Surgery and Medicine 40:402-406 (2008).

Laser-assisted lipoplasty or interstitial laser lipolysis has recently been introduced using various types of laser. Among which, the following devices used in the study should be mentioned:

• SmartLipo 1064 nm Neodymium:YAG which emits at 40 Hz, pulses of 150 mJ per pulse and 100 microsecond pulse width. The use of this laser for the destruction of fat tissue and to improve skin contraction has been published recently by other authors mentioned in the text, as well as improvements in the haemostasis of the procedures and in adaptation of the skin to the new contour.

• A 1320 nm laser that emits at 300 mJ with a pulse width of 100 microseconds and which can function at 6-10 W (with an approximate frequency of 20-35 Hz), usually used for lithotrity has been mentioned in studies that report improved results in liposuctions on the submentonian region.

• Another device that emits at 2100 nm, which is not used in laser skin surgery but presents a very high absorption peak due to the fat.

In any event, the fat remains difficult to reach through selective photothermolysis given that the coefficient of fat absorbency is much lower than that of water in most wavelengths.

Optical fat absorption versus other tissue

1064 1320 2100 Fat 0.05 0.08 2.5 Water 0.14 1.6 >10

The authors maintain that the efficacy of the devices at 1064 and 1320 does not solely depend on the thermal effect but it influences the photomechanical effect due to the short pulse width of the power delivery that causes an explosive interaction in the areas surrounding the optical fibre tip with fast coagulation that causes fast removal of the tissue with minimum coagulation compared with the power delivery models of these very lasers with long pulses or continuous delivery.

(It should be mentioned that Dr Mordon has published a letter to the editor in the same journal, Lasers in Medicine and Surgery, in reference to the interpretation of these authors on the action mechanism, assuring that he has proven in his studies that the laser lipolysis effect is purely thermal and not photomechanical. Letter to the Editor, S.Mordon and Ph.Blanhemasion, Lasers in Medicine and Surgery 40: 519 (2008).

The trial was performed on nine samples of abdominal subcutaneous cell tissue and skin injected with Klein solution, measuring 3x2x2 cm. Cannulated in a single tunnel of 0.9 mm and approximately 5 mm deep under the dermo-hypodermic junction. Emissions are carried out with each type of laser moving the optical fibre at a speed of 1 mm per second (20 times slower than proposed by Ichikawa in his trial), with and approximate total duration in each case of 30 seconds.

Nd:YAG laser is used with 150 microsecond pulses and 40 Hz frequency. A 1320 nm laser is also used which emits at 150 microsecond pulses and works at 20 Hz but emits 300 mJ per pulse, so the irradiation can be considered the same. Equally, a 2100 laser is used with 300 microsecond pulses and output at 12 Hz. The three units are used at 4, 6 and 8 W. A cannulation without laser delivery is also performed on a control sample.

To evaluate the thermal and photomechanical effect of the 1320 laser, a lipoma was also treated with a total output of 60 seconds after tumescent anaesthesia.

All the samples were fastened and a sample perpendicular to the delivery cavity was extracted.

Results shown in the table should disregard those for sample 1 due to the analysed sample reaching an arteriolar structure and the measurements for the area of destruction are therefore altered:

Delivery at 1064: The treated samples at 6-8 W with this unit show heat damage in the collagen of the fibrous septa in the fat tissue and possible damage appears on the surrounding cells. There is greater destruction and coagulation at 8 W.

Emission at 1320: Equally, areas of coagulation of the fibrous septa and slight lesion of the surrounding fat cells is observed. Greater density of histological changes is observed at 6 W.

Emission at 2100: These are the samples that display greatest tissue damage, the areas of collagen coagulation of the fat tissue are larger and there is evident damage to the fat cells. In the proximity of the output cavity, broken cell membranes appear, in the centre there is a clearly carbonised area surrounded by an area of non-carbonised coagulation measuring 4 mm in thickness. Heat damage appears with this laser at 3 mm under the dermis, close to the dermo-hypodermic junction with clear signs of heat damage characterised by dermal collagen coagulation as well as the collagen in the junction and destruction of fat cells.

 

 

The untreated sample had no heat damage and the lipoma showed clear collagen coagulation lesions manifested as small, deformed clusters as well as piknotic nuclei, vacuoles of different sizes, coagulated collagen fibres and broken cell membranes. Focalised fat liquefaction is also observed, characterised by vacuoles of different sizes with no visible membranes.

Discussion

The FDA has granted permission to the 1064 and 1320 emissions and this technique has gained popularity but its action mechanisms should be clarified, since it is evident that the longer the wavelength, the lower the fat absorption coefficient except for certain peaks.

It is not clear which is the mechanism that acts since 100 microsecond pulses are too long to produce the photo acoustic effect characteristic of equivalent devices that have nanosecond pulses (10,000 times shorter) and that have been used in secondary cataract surgery.

• The 1064 and 1320 devices require optical fibre but the 2100 unit does not. The delivery most intensely absorbed by fat and water is the 2100 and it is also the one that shows more intense histological lesions, above all in the septa. This device could be interesting in the long term. The first two require longer pulses and more power but for the time being it seems that the 1320 laser could be more effective for improved tissue contraction at least if the fat and water absorbency coefficients are observed for both emissions.

• Carbonization is justified because both the 1064 and 1320 lasers at a 100 microsecond pulse width heat the cannulas and the surrounding tissue is vaporised with an explosion that generates photo acoustic ablation. This effect cause fast removal of tissue with no coagulative effect compared to the same emissions in continuous or long pulses.

• The authors maintain that it is difficult to isolate the histological damage due to the photo acoustic effect, but all the irradiated samples display micro cavities that are not present in the non-irradiated sample. These micro cavities are localised at 3 to 9 mm in depth, but more trials should be performed to study the theoretical photo acoustic effect according to the power used and other parameters.

The histological findings:
- Thermo-coagulated collagen fibres
- Destroyed and denatured fat cell membranes
- Carbonisation
- Holes made by prior cannulisation

The histological findings published by other authors in previous studies are similar.

The authors anticipate that one of the pending tasks is to interpret the variability of histological damage observed in each sample, since an increase in the heat damage proportional to the use of higher wavelengths and power was expected, but this did not occur in the trial. In any case, it is possible that greater total delivery exposure time of tissue could cause an increased effect, this explains that in the case of lipoma destruction of fat cells and fat liquefaction has been observed, which in this case shows 5% liquefaction.

In any event, they confirm that the laser lipolysis technique rests on a purely thermal photo acoustic effect (septa affectation) and the more intense heat damage is associated with higher outputs. They interpret the characteristic noise of corn popping as evidence of the conversion of optical power to photo acoustic power, despite there being no histological evidence to back this up.

Dr Mordon does not agree with this interpretation, in his publication Histological Evaluation of Laser Lipolysis: Pulsed 1064-nm Nd:YAG laser versus CW 980-nm diode laser. Aesthetic Surg J2007; 27 (3): 263-268 and Mathematical modelling of laser lipolysis. Biomed Eng. On line 2008; 7(1):10 sustains that the mathematical model demonstrates the controlled effect shows the correction obtained by the patients in volume is in sole and direct relation with the total amount of power delivered and the effect is purely thermal. In relation the so-called pop corn effect, highly characteristic of laser lipolysis, Dr Mordon sustains that this sound is produced when the water vapour bubbles break and some of the cells burst, in any case, the collapse of these bubbles is almost immediate and the power it displaces is too low for it to be the physiopathological base of the laser lipolysis effect.

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