Comparison of laser-induced damage with forward-firing and diffusing optical fiber during laser-assisted lipoplasty

Abstract

Background and objectives: Laser-assisted lipoplasty is made possible by using an optical fiber that delivers light endoscopically to subcutaneous fat tissue. Most optical fibers for laser-assisted lipoplasty are designed to be irradiated in a forward direction. In this study, we compared forward-firing fiber and diffusing fiber for use in laser-assisted lipoplasty. The effective parameters of the ablation pattern which resulted from the laser-induced damage are discussed for both systems. In particular, we note the effect resulting from the different beam emission patterns and the contours of laser fluence.

Methods: We used two different laser delivery systems (a forward-firing fiber and a diffusing fiber) to examine how the beam emission pattern affects the laser-assisted coagulation and damage pattern of in vitro fat tissues. A porcine liver tissue (water-rich tissue) was used as a secondary laser target to investigate how the laser-assisted coagulation pattern depends on both the type of tissue (water-rich and lipid-rich tissue) as well as the delivery system. An evaluation using a digital camera and a thermal camera was conducted for the tissue ablation processes in order to observe the generated heat transfer in fat and liver.

Results: The overall shape of the laser-assisted coagulation zone was different from the beam emission pattern in the case where a forward-firing fiber was used within fat tissue. The center of the laser-affected zone is characterized by the formation of a reservoir of melted fat. In the thermal image analysis, there existed a discrepancy between the temperature distribution of the fat tissue and the liver tissue during the forward-firing fiber irradiation. In the liver tissue ablation process, the temperature distribution during the laser ablation also demonstrated an elongated ellipse that matches well with the laser-induced damage zone. The temperature distribution in fat tissue adhered to a more discoid pattern that corresponded to the laser-induced damage zone.

Conclusions: Based on our findings, we have proposed mechanisms that can explain the laser-induced damage in both tissues when a forward firing fiber is employed as the delivery system. In the case of fat tissue, the ablation mechanism can be characterized by the reservoir formation of melted lipids while the ablation is characterized as the well-known drilling effect for liver tissue.

Keywords: endoscopy surgery; fiber optics; laser-induced damage; lipoplasty.

Fig. 1

Manufacturing process of the scattering diffusing fiber.

Fig. 2

a: Diffusing fiber tip optical image. b: Diffusing fiber beam profile image. c: Forward-firing fiber tip optical image. d: Forward-firing fiber beam profile image.

Fig. 3

A schematic illustration of the experimental setup for (a) ablation of the lipid-rich tissue and water-rich tissue into the interiors (b) examining the effects of fiber insertion and (c) examining the extent of the coagulation region and heat distribution as in the soft tissue.

Fig. 4

The distribution of laser fluence (a) inside of the fat tissue and (b) liver tissue.

Fig. 5

Typical coagulation lesions of fat tissues. Before staining (a–d, i–l). After staining (e–h, m–p). a and e: Forward-firing fiber, 15 W1 minute. b and f: Forward-firing fiber, 15 W2 minutes. c and g: Forward-firing fiber, 20 W1 minute. d and h: Forward-firing fiber, 20 W2 minutes. i and m: Diffusing fiber, 15 W1 minute. j and n: Diffusing fiber, 15 W2 minutes. k and o: Diffusing fiber, 20 W1 minute. l and p: Diffusing fiber, 20 W2 minutes (a solid line for the fiber tip, a dotted line for laser-affected zone and an alternate long- and short-dash line for the capping tube).

Fig. 6

Width, length, and aspect ratio of coagulated lesion versus combination of conditions applied to forward-firing fiber and diffusing fiber in fat tissue (aspect ratio: width/length). a: The width of lesion in the fat tissue. b: The length of lesion in the fat tissue. c: The aspect ratio of lesion in the fat tissue.

Fig. 7

Typical coagulation lesions of liver tissues produced with forward-firing fiber and diffusing firing fiber. a: Forward-firing fiber, 15 W 1 minute. b: Forward-firing fiber, 15 W 2 minutes. c: Forward-firing fiber, 20 W1 minute. d: Forward-firing fiber, 20 W2 minutes. e: Diffusing fiber, 15 W 1 minute. f: Diffusing fiber, 15 W 2 minutes. g: Diffusing fiber, 20 W 1 minute. h: Diffusing fiber, 20 W 2 minutes.

Fig. 8

Width, length, and aspect ratio of the coagulated lesion versus combination of conditions applied to forward-firing fiber and diffusing fiber in liver tissue (aspect ratio: width/length). a: The width of lesion in the liver tissue. b: The length of lesion in the liver tissue. c: The aspect ratio of lesion in the liver tissue.

Fig. 9

Typical coagulation optical image of fat tissue (a) and liver tissue (b) produced with forward firing fiber.

Fig. 10

Image of the fat tissue ablation and temperature distribution after 8 minutes laser irradiation. a: Optical image of laser-induced damage zone with forward firing fiber. b: Thermal image of laser-induced damage zone with forward firing fiber after 4 minutes. c: Thermal image of laser-induced damage zone with forward firing fiber after 8 minutes. d: Optical image of laser-induced damage zone with diffusing fiber. e: Thermal image of laser-induced damage zone with diffusing fiber after 4 minutes. f: Thermal image of laser-induced damage zone with diffusing fiber after 8 minutes.

Fig. 11

Image of the liver tissue ablation and temperature distribution 8 minutes laser irradiation. a: Optical image of laser-induced damage zone with forward firing fiber. b: Thermal image of laser-induced damage zone with forward firing fiber after 4 minutes. c: Thermal image of laser-induced damage zone with forward firing fiber after 8 minutes. d: Optical image of laser-induced damage zone with diffusing fiber. e: Thermal image of laser-induced damage zone with diffusing fiber after 4 minutes. f: Thermal image of laser-induced damage zone with diffusing fiber after 8 minutes.

Fig. 12

Illustration of drilling effect with forward-firing fiber in liver tissue. a: Laser irradiation into the tissue and the light starts to be absorbed. b: The temperature increases rapidly and reaches the vaporization temperature. c: The dehydration tissue and removal was occurred. d–e: The adjacent layer is exposed to the continuing laser irradiation and heated up. f: The heated layer is removed and the ablation front moves deeper and deeper into the tissue (drilling effect).

Fig. 13

Illustration of the proposed mechanism by “the reservoir formed by melted lipids” with forward-firing fiber in fat tissue. a: The light is irradiated into fat tissue and the light starts to be absorbed. b: The temperature of the laser-irradiated region started to rise and reached the melting point of fat. c: The fat starts to melt and the small reservoir filled with melt lipid. d–f: The temperature of the melted lipids kept increasing beyond the melting point, the temperature of the reservoir did not reach the smoke point of fat. The oil was trap the reservoir and trapped liquid phase fat absorbs the laser light. The absorption of light by the liquid phase also leads to the thermal conduction and coagulation around the reservoir.