| In recent years,Terahertz-Waves have brought a brand-new,label-free,non-invasive detection method to biomedical research due to their non-ionization,broadband,and high signal-to-noise ratio.With the development of Terahertz sources,especially the generation of Terahertz pulses with energies as high as m J,people’s research on biological tissues in the Terahertz band is no longer limited to non-thermal effects.At the same time,in the diagnosis of skin cancer and other diseases,the gold standard is histopathological detection.As an invasive test,histopathological testing may result in failure of treatment due to excessive surgery,incorrect incision,or inability to complete resection due to unclear tumor boundaries during the diagnosis process.Therefore,combining the physical properties of skin tissue and basal cell carcinoma(BCC)and its optical properties in the Terahertz band has important application value to achieve non-destructive diagnosis of skin cancer.In this context,the research is carried out,and the main contents of this paper are as follows:The absorption and scattering properties of biological tissues in the Terahertz band were analyzed.Starting from the Lambert-Beer law,the light distribution and thermal deposition in tissue were given,the classical biological tissue heat transfer equation(Pennes equation)and thermal parameters of biological tissue were introduced,and the propagation characteristics of ultrasonic signals in biological tissue were emphatically analyzed.The photoacoustic wave equation was solved in the form of plane wave propagation.Finally,the dielectric properties of biological tissue in the Terahertz band were analyzed by using the double Debye model and the H-N relationship,which provided a theoretical basis for the analysis of the photo-thermal response and photoacoustic effect between Terahertz-Waves and biological tissue.The Pennes heat transfer equation was solved by the finite element method,and the Terahertz-Waves radiation thermal effects of thrombus,whole blood,plasma,skin and skin tissue containing BCC were analyzed,and the effects of different Terahertz source parameters on the thermal effects of biological tissues were also analyzed.For skin tissue,the penetration depth of pulsed Terahertz-Waves with high energy in the skin is still difficult to penetrate deep into the dermis.According to the dendritic growth law of basal cell carcinoma in the basal layer,the study found that the thermal effect of diseased skin containing BCC was significantly different from that of normal skin,and the skin tissue containing BCC was more sensitive to temperature changes when irradiated by TerahertzWaves.The analyzed of different BCC growth periods shows that the temperature response of Terahertz-Waves can be used to detect the growth changes of BCC.As BCC diffuses and grows in the skin tissue,the thermal effect is used to distinguish different BCC growth periods.Depending on the tissue type,Terahertz photoacoustic effect studies were performed on ex vivo tissues(thrombus,whole blood,plasma)and in vivo tissues(normal skin,skin tissue containing BCC).The effects of different energy,focusing radius,pulse duration,frequency and irradiation form of Terahertz-Waves on the photoacoustic signal were analyzed by the thrombus model.According to different tissue types,the photoacoustic signal analysis is performed from the angle of detection reception.The difference and composition analysis of photoacoustic signals in three control models of thrombus,whole blood and plasma,normal skin tissue and skin tissue containing BCC,and skin tissue containing different BCC growth stages were realized by using Terahertz-Waves photoacoustic effect,the rationality is verified.The potential application value of using Terahertz photoacoustic effect to realize non-destructive testing and imaging methods is revealed. |
