Numerical Modeling and Simulation of Non-Invasive Acupuncture Therapy Utilizing Near-Infrared Light-Emitting Diode

Abstract

Acupuncture is one of the most extensively used complementary and alternative medicine therapies worldwide. In this study, we explore the use of near-infrared light-emitting diodes (LEDs) to provide acupuncture-like physical stimulus to the skin tissue, but in a completely non-invasive way. A computational modeling framework has been developed to investigate the light-tissue interaction within a three-dimensional multi-layer model of skin tissue. Finite element-based analysis has been conducted, to obtain the spatiotemporal temperature distribution within the skin tissue, by solving Pennes' bioheat transfer equation, coupled with the Beer-Lambert law. The irradiation profile of the LED has been experimentally characterized and imposed in the numerical model. The experimental validation of the developed model has been conducted through comparing the numerical model predictions with those obtained experimentally on the agar phantom. The effects of the LED power, treatment duration, LED distance from the skin surface, and usage of multiple LEDs on the temperature distribution attained within the skin tissue have been systematically investigated, highlighting the safe operating power of the selected LEDs. The presented information about the spatiotemporal temperature distribution, and critical factors affecting it, would assist in better optimizing the desired thermal dosage, thereby enabling a safe and effective LED-based photothermal therapy.

Keywords: acupoints; acupuncture; bio-heat transfer; computational modeling; light-tissue interaction; photothermal effect; thermal therapy.

Figure 1

Schematic of the 3D model of the three-layered skin considered in the present study.

Figure 2

(a) The experimental setup used to determine the LED beam profiles. The different components of the experimental setup are the XYZ stage, LED heatsink, beam profiler, and a custom-made circuit board for operating the LEDs. (b) A snapshot of a typical beam-profiling measurement. From left to right: the 2D x-axis, 2D y-axis, and 3D beam profiles of the 90° (top row) and 150° LEDs (bottom row).

Figure 3

Photographic view of the experimental setup for measuring the temperature profile. The snapshot in the bottom right-hand corner is a sample of the actual agar gel used in the temperature profile experiments.

Figure 4

Comparison of the experimentally measured and numerically predicted temperature profiles at a depth of 2 mm for LEDs with emission patterns of: (a) 90°, and (b) 150°.

Figure 5

The effect of an input power of 90° emission pattern LED on (a) the maximum temperature rise with time within the skin tissue, and (b) the temperature variation along the depth of the skin after 10 min of LED irradiation.

Figure 6

The effect of an input power of 150° emission pattern LED on (a) the maximum temperature rise with time within the skin tissue, and (b) the temperature variation along the depth of the skin after 10 min of LED irradiation.

Figure 7

The variation in the heated volume obtained using temperatures greater than the 43 °C and 50 °C protocol after 10 min of LED irradiation with emission patterns of (a) 90°, and (b) 150°.

Figure 8

The effect of the LED emission patterns of 90° and 150° operating at an input power of 500 mW on (a) the maximum temperature rise within the skin tissue, and (b) the temperature distribution along the depth of the skin tissue. Heating zone obtained with the isotherm of 43 °C after 10 min of LED irradiation with the emission pattern of (c) 90°, and (d) 150°.

Figure 9

The effect of increasing the distance between the 90° LED (operating at 300 mW) and the skin surface on (a) the maximum temperature rise within the skin tissue, (b) the temperature distribution along the depth of the skin tissue, and (c) the heating volume attained with the T > 43 °C protocol. Temperature distribution (in °C) attained within the skin tissue after 10 min of LED irradiation, when the gap between the LED and skin surface was: (d) 0 µm, and (e) 2000 µm.

Figure 10

The effect of increasing the distance between the 150° LED (operating at 500 mW) and the skin surface on (a) the maximum temperature rise within the skin tissue, and (b) the temperature distribution along the depth of the skin tissue. Temperature distribution (in °C) attained within the skin tissue after 10 min of LED irradiation when the gap between the LED and skin surface is: (c) 0 µm, and (d) 2000 µm.

Figure 11

The effect of increased LEDs on the volume attained with the isotherm of 43 °C.

Figure 12

Pictorial representations of the top view of the isotherm of 43 °C on the skin surface attained with different numbers of LEDs.