Ultrasound guidance and monitoring of laser-based fat removal

Abstract

Background and objectives: We report on a study to investigate feasibility of utilizing ultrasound imaging to guide laser removal of subcutaneous fat. Ultrasound imaging can be used to identify the tissue composition and to monitor the temperature increase in response to laser irradiation.

Study design/materials and methods: Laser heating was performed on ex vivo porcine subcutaneous fat through the overlying skin using a continuous wave laser operating at 1,210 nm optical wavelength. Ultrasound images were recorded using a 10 MHz linear array-based ultrasound imaging system.

Results: Ultrasound imaging was utilized to differentiate between water-based and lipid-based regions within the porcine tissue and to identify the dermis-fat junction. Temperature maps during the laser exposure in the skin and fatty tissue layers were computed.

Conclusions: Results of our study demonstrate the potential of using ultrasound imaging to guide laser fat removal.

Fig. 1

Block diagram illustrating the principles of ultrasound measurements for identifying tissue composition and for thermal imaging.

Fig. 2

a: Experimental setup for ultrasound imaging during laser heating. b: Digital photograph of the experimental setup showing the orientation of the laser fiber, ex vivo tissue and ultrasound transducer. c: Block diagram for computing grayscale B-mode ultrasound image, tissue composition map and thermal image of the tissue sample.

Fig. 3

Temperature calibration for (a) porcine fat and (b) porcine skin. Note, the negative temperature gradient of the normalized time shift for fatty tissue and positive temperature gradient for water-based tissue.

Fig. 4

a: Ultrasound image of the porcine tissue. Image covers a 10 mm (depth) by 15 mm (width) region. b: Normalized time shift between the arrows in Figure 3a after 1, 3, and 5 seconds of laser heating. The zero crossing indicates the dermis-fat junction.

Fig. 5

a: Map of the normalized time shift after 5 seconds of laser irradiation with clear demarcation between positive and negative normalized time shift under laser irradiation region. b: Ultrasound image of the porcine tissue with the zero-crossing of normalized time shift superposed to represent the dermis-fat junction. All images represent a 10 mm by 15 mm region.

Fig. 6

a: Thermal image showing the temperature elevation reached due to laser exposure. b: Ultrasound image overlaid with the temperature maps, showing the temperature elevation in the dermal and fatty regions. c: Temporal temperature rise at four regions directly along the laser irradiation plane. The regions are shown as boxes in (b).

Fig. 7

a: Thermal image showing the temperature elevation reached due to laser exposure. b: Ultrasound image overlaid with the temperature maps, showing the temperature elevation in the dermal and fatty regions.

Fig. 8

a: Porcine skin overview showing defects in the subcutaneous adipose tissue (thick arrows). Wedge shaped surface lesion (thin arrows) visible showing signs of thermal denaturation of cellular structural proteins [H&E stains. Orig. Mag. 16×]. b: The glandular ducts show compression and are hyper chromatic. The adipose tissue (arrows) is torn and fragmented associated with subcutaneous defects. c: Normal glandular ducts surrounded by compressed fat cells (arrows) in a specimen with lower temperature increase (less than 15°C) [H&E stains. Orig. Mag. 200×].