Abstract
.Significance: Uncontrolled cryoablation of tissues is a strong reason limiting the wide application of cryosurgery and cryotherapy due to the certain risks of unpredicted damaging of healthy tissues. The existing guiding techniques are unable to be applied in situ or provide insufficient spatial resolution. Terahertz (THz) pulsed spectroscopy (TPS) based on sensitivity of THz time-domain signal to changes of tissue properties caused by freezing could form the basis of an instrument for observation of the ice ball formation.Aim: The ability of TPS for in situ monitoring of tissue freezing depth is studied experimentally.Approach: A THz pulsed spectrometer operated in reflection mode and equipped with a cooled sample holder and ex vivo samples of bovine visceral adipose tissue is applied. Signal spectrograms are used to analyze the changes of THz time-domain signals caused by the interface between frozen and unfrozen tissue parts.Results: Experimental observation of TPS signals reflected from freezing tissue demonstrates the feasibility of TPS to detect ice ball formation up to depth.Conclusions: TPS could become the promising instrument for in situ control of cryoablation, enabling observation of the freezing front propagation, which could find applications in various fields of oncology, regenerative medicine, and THz biophotonics.
Highlights
Terahertz (THz) pulsed spectroscopy (TPS) is known as a promising tool of biophotonics and medical diagnosis.[1,2,3,4] It demonstrates strong potential of study and differentiate various conditions of tissues, both ex vivo and in vivo,[5,6,7,8,9] and imaging and characterization of neoplasms in different localizations,[10,11,12,13,14] by means of endogenous markers of pathology, such as water content
To experimentally test the feasibility of TPS to detect the freezing depth in biological tissues, we use a laboratory THz pulsed spectrometer, which was described in detail in Ref. 44
Zotov et al.: In situ terahertz monitoring of an ice ball formation during tissue cryosurgery: a feasibility test spectrometer with more efficient performance, scanning rate, which would yield the reduction of the detection period and increasing of the temporal resolution
Summary
Terahertz (THz) pulsed spectroscopy (TPS) is known as a promising tool of biophotonics and medical diagnosis.[1,2,3,4] It demonstrates strong potential of study and differentiate various conditions of tissues, both ex vivo and in vivo,[5,6,7,8,9] and imaging and characterization of neoplasms in different localizations,[10,11,12,13,14] by means of endogenous markers of pathology, such as water content. High concentration of free and bound water in tissues restricts the penetration depth of THz waves by only several hundreds of microns.[1] To overcome this limitation, different approaches can be applied. Among them are such techniques as tissue dehydration,[15] paraffinembedding,[16] lyophilization,[17] compression,[18] immersion optical clearing,[19,20] and freezing.[21,22,23,24] It was demonstrated that the latter one helps to increase the THz-wave penetration up to 1 mm, changing at the same time dielectric properties of tissues in THz range.[23] Along with reduction of Journal of Biomedical Optics
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