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Cryosurgery is a surgical technique that employs freezing to destroy target tumor tissue. While the main objective during a cryosurgical procedure is to ensure tissue destruction within the cryolesion, the greatest challenge is how to spare the surrounding healthy tissues from cryoablation. In this work, a historical review of the field of cryosurgery is presented followed by a theoretical study where a mathematical model is developed for cryosurgery on a basal cell carcinoma (BCC) using liquid nitrogen (LN2) spray. The model takes into consideration the anatomic structure of skin tissue and the irregular geometry of BCC. In particular, a methodology for quantitatively determining the extent of the intracellular ice formation (IIF) zone based on the tissue temperature and cooling rate (CR) is proposed, which can directly relate to the necrosis of the cancer cells after cryosurgery. The model is then used to analyze formation of the IIF zone during cryosurgery on a BCC and quantification is provided for the volume of the final IIF zone. A parametric study is also carried out to investigate the effect of various protocol parameters on the final IIF zone. The results should be useful for dermatologists for pre-treatment surgery planning.

Basel cell carcinoma (BCC) is the most common human skin malignancy. Its incidence has increased significantly in Australia, Europe and North America over the past decade. A number of modalities are currently used for treatment of BCC, including cryosurgery which offers a potential for high cure rate, low cost, minimal bleeding and good cosmetic effect. However, cryosurgery is not used frequently for BCC because no current method exists to design adequate treatment parameters. We present a numerical analysis on the thermal history of the target tissue during cryosurgery of a nodular BCC using liquid nitrogen (LN2) spray. The model uses Pennes equation to describe the heat transfer within the target tissue. A convective thermal boundary is used to describe the heat interaction between the tissue and LN2, and the apparent heat capacity method is applied to address the tissue phase change process. A parametric study is conducted on the convective heat transfer coefficient (hs: 104-106 W/m 2·K), cooling site area (rs/R0: 0.5-1.0) and spray time (t: 0-30 sec.), with the objective to understand the thermal history during tissue freezing, including lethal temperature (-50°C) and cooling rate (CR). Results demonstrate that propagation of the lethal isotherm is sensitive to the convective heat transfer coefficient, hs, with a range of 104-5×104 W/m2·K. Increasing the cooling site area can significantly enhance cooling efficiency, producing dramatic increase in the amount of tissue encompassed by the lethal isotherm. The cooling rate (CR) shows a highly dynamic distribution during the cooling process: the highest CR drops quickly from 140°C/sec. (t=0.5 sec.) to 20°C/sec. (t=5 sec.). The highest CR is initially located close to the cooling site but moves toward the inside of the tissue as treatment proceeds. The model presented herein provides a simulation tool for treatment planning of cryosurgery using LN2 spray, in which the protocol parameters, e.g. cooling site area and spray time, can be determined for an optimal outcome. The quantitative predictions on the propagation of lethal isotherm and the distribution of CR should help to optimize cryosurgery efficacy. Copyright © 2006 by ASME.

It is common in some cryosurgical procedures to rely on freeze-thaw cycle(s) to destroy undesirable tissues. Most research in cryosurgery focuses on the freezing process and much less attention has been paid to thawing or re-warming. However, as ice melts during thawing, the extracellular solution can become locally hypotonic, driving water into cells, resulting in cell expansion and ultimately, membrane rupture. Therefore, the thermal history of the target tissue during both the freezing and thawing processes is critical for cell viability. To better understand and predict the thermal history during cryosurgery, we developed a two-dimensional numerical model to describe the complete freeze-thaw cycle during liquid nitrogen cutaneous cryosurgery. A stratified anatomical structure of human skin is considered in the model. The numerical simulation applies temperature-dependent thermal and physical properties for human skin tissue and considers the typical thermal boundary conditions for clinical practice. Parametric studies are performed to explore the influence of spray cooling, spray duration and surface heating. Results are discussed concentrating on iceball front propagation, lethal temperature isotherm evolution, tissue temperature variation and cooling rates. These results are expected to provide both quantitative and graphical support to cutaneous cryosurgery and suggest approaches to optimize current cryosurgical protocols. Copyright © 2005 by ASME.

Cryogen spray cooling (CSC) is used to minimize the fisk of epidermal damage during dermatologic therapy. However, the dominant mechanisms of heat transfer during the transient cooling process are incompletely understood. The objective of this study is to elucidate the physics of CSC by measuring the effect of initial substrate temperature (T-0) on cooling dynamics. Cryogen was delivered by a straight-tube nozzle onto a skin phantom. A fast-response thermocouple was used to record the phantom temperature changes before. during and after the cryogen spray. Surface heat fluxes (q") and heat-transfer coefficients (h) were computed using an inverse heat conduction algorithm. The maximum surface heat flux (q"(max)) was observed to increase with T-0. The surface temperature corresponding to q" also increased with T-0 but the latter has no significant effect on h. It is concluded that heat transfer between the cryogen spray and skin phantom remains in the nucleate boiling region even if T-0 is 80 degreesC.

In this paper, based on the weighted metric, the problem of approximating a general continuous fuzzy number u with derivable u(r) and ū(r) (left and right cut functions of level value r) for r ∈ (0, 1] by using the m − n−step type fuzzy number is studied. Two kinds of approximations (I−nearest approximation and II−nearest approximation which satisfy different conditions) of using m − n−step type fuzzy numbers to approximate general continuous fuzzy numbers are defined, and the relationship between the I−nearest approximation and II−nearest approximation is obtained. Then the methods of the two kinds of approximations are respectively presented by the theorems more specifically. At last, an example is given to show the effectiveness and usability of the methods set up by us. [ABSTRACT FROM AUTHOR]

We review the relationship between miRNAs associated with ferroptosis and the evolution of AS. Even though, more evidence is asked to determine the role of miRNAs associated with ferroptosis in the AS, this review will help us understand the role of miRNAs in ferroptosis and AS and may provide new insights for probing new biomarkers for the diagnosis and treatment of AS for the time to come. This is a narrative essay. Using PubMed as the main source, a literature search strategy was randomly implemented to index Scopus articles. No specific terminology is used. Studies have shown that ferroptosis plays a crucial role in the development of AS, and a large amount of ferroptosis in cells can lead to the progression of AS. MicroRNAs (MiRNAs) have been proved to be taken part in the biological course of ferroptosis and thus the process of AS is affected. The exact regulatory mechanism behind this appearance remains unclear. In order to clarify this, a growing number of studies have concentrated the regulatory role of miRNAs in the process of generation and development of ferroptosis, as well as the function of ferroptosis in the progression of AS. MiRNAs play a significant role in the process of ferroptosis and are incredibly significant in the occurrence, development, clinical diagnosis, treatment and prognosis evaluation of AS. [ABSTRACT FROM AUTHOR]