Noninvasive or minimally invasive laser lipolysis has great potential to reduce obesity

but the absorption of near infrared laser by water may cause thermal damage of dermis. At present

there is no effective cooling method to protect normal skin tissue from thermal injury

which restricts the development of laser lipolysis. A novel multi-pulsed cryogen spray cooling for laser lipolysis was proposed to protect epidermis and dermis. Numerical simulation based on multi-layer uniform skin tissue model and Pennes biological heat transfer equation was conducted to investigate the cooling effect of continuous and multi-pulsed R134a cryogen spray cooling. It was found that continuous spray cannot meet the requirement of laser lipolysis both in temperature and skin depth. Under the same accumulative spray time

the cooling depth of multi-pulsed spray is greater than that of continuous spray. The lowest temperature at 1 mm below skin surface after multi-pulsed cryogen spray can reach to 11℃ with pulse width of 10 ms

interval time of 2500 ms

spray times of 10 and duty cycle of 0.004

and the simulation cooling depth achieves 5000 μm

which can satisfy the cooling depth requirement of laser lipolysis.