Numerical simulation of bioheat transfer during bronchial cryobiopsy using cryoprobes of different diameters

Transbronchial cryobiopsy using flexible cryoprobes is an emerging biopsy technique. However, an inappropriately sized cryoprobe or inaccurate freezing time may result in tissue cryoinjury or substandard tissue specimens. This study uses numerical simulation to explore the effects of different diameter cryoprobes (1.1 mm, 1.9 mm, 2.4 mm) on tissue temperature distribution and phase transition in bronchial tumor cryobiopsy. A three-dimensional bronchial model containing tumors is constructed. The heat transfer process of the cryoprobes within 0-10 s at different insertion depths (0-1.0 mm, interval 0.1 mm) is simulated based on Pennes bioheat equation and the effective heat capacity method. Multi-physics effects are analyzed by coupling respiratory airflow. The results demonstrate that increasing the cryoprobe diameter and its insertion depth leads to an expansion of the low-temperature zone within the tissue, thereby elevating the risk of cryoinjury to surrounding peritumoral tissues. Moreover, the effect of cryoprobe diameter on tissue phase transition is more significant than that of insertion depth. Increasing the cryoprobe diameter will reduce the distance to adjacent peritumoral tissues, resulting in rapid expansion of the frozen region within peritumoral tissues. In contrast, the insertion depth primarily influences the axial extension of the frozen region. Additionally, respiratory airflow demonstrates no significant impact on temperature distribution. This study provides a theoretical foundation for the clinical selection of cryoprobe parameters and optimization of freezing duration, facilitating the acquisition of sufficient tissue samples while minimizing cryoinjury to healthy tissues.