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Research Papers

# Cryosurgery: Analysis and Experimentation of Cryoprobes in Phase Changing Media

[+] Author and Article Information
Avraham Shitzer

Department of Mechanical Engineering, Technion, Israel Institute of Technology, Haifa 32000, Israelmersasa@tx.technion.ac.il

J. Heat Transfer 133(1), 011005 (Sep 27, 2010) (12 pages) doi:10.1115/1.4002302 History: Received January 07, 2010; Revised February 03, 2010; Published September 27, 2010; Online September 27, 2010

## Abstract

This article presents a retrospective of work performed at the Technion, Israel Institute of Technology, over the last 3-odd decades. Results of analytical and numerical studies are presented briefly as well as in vitro and in vivo experimental data and their comparison to the derived results. Studies include the analysis of both the direct (Stefan) and the inverse-Stefan phase-change heat transfer problems in a tissue-simulating medium (gel) by the application of both surface and insertion cryoprobes. The effects of blood perfusion and metabolic heat generation rates on the advancement of the freezing front are discussed. The simultaneous operation of needle cryoprobes in a number of different configurations and the effects of a thermally significant blood vessel in the vicinity of the cryoprobe are also presented. Typical results demonstrate that metabolic rate in the yet nonfrozen tissue, will have only minor effects on the advancement of the frozen front. Capillary blood perfusion, on the other hand, does affect the course of change of the temperature distribution, hindering, as it is increased, the advancement of the frozen front. The volumes enclosed by the “lethal” isotherm (assumed as $−40°C$), achieve most of their final size in the first few minutes of operation, thus obviating the need for prolonged applications. Volumes occupied by this lethal isotherm were shown to be rather small. Thus, after 10 min of operation, these volumes will occupy only about 6% (single probe), 6–11% (two probes, varying distances apart), and 6–15% (three probes, different placement configurations), relative to the total frozen volume. For cryosurgery to become the treatment-of-choice, much more work will be required to cover the following issues: (1) A clear cut understanding and definition of the tissue-specific thermal conditions that are required to ensure the complete destruction of a tissue undergoing a controlled cryosurgical process. (2) Comprehensive analyses of the complete freeze/thaw cycle(s) and it effects on the final outcome. (3) Improved technical means to control the temperature variations of the cryoprobe to achieve the desired thermal conditions required for tissue destruction. (4) Improvement in the pretreatment design process to include optimal placement schemes of multiprobes and their separate and specific operation. (5) Understanding the effects of thermally significant blood vessels, and other related thermal perturbations, which are situated adjacent to, or even within, the tissue volume to be treated.

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## Figures

Figure 23

Measured and computed isotherms in sections A–E in the PCM after 20 min of cryoprobe operation at −8°C/min. Embedded tube flow rate: 100 ml/min (49).

Figure 24

Three-dimensional snap shots of the progression of the 0°C isothermal surface in the vicinity of the embedded tube (47). Cryoprobe operates from underneath.

Figure 1

Cell survival versus cooling rate applied (11). (This figure originally appeared in an article by J.K. Critser and L.E. Mobraaten in ILAR Journal 41(1). It is reprinted with permission from the ILAR Journal, Institute for Laboratory Animal Research, The National Academies, Washington DC (www.nationalacademies.org/ilar)).

Figure 2

Effects of cooling rates applied to biological cells on intra- and extracellular water freezing

Figure 4

Equivalent specific heat for “Tylose” (24% methyl-cellulose/76% water by mass) as a function of temperature in the phase-change region (32). (Copyright 1974 by Elsevier. Reproduced with permission of Elsevier via Copyright Clearance Center.)

Figure 5

Thermal conductivity of “Tylose” as a function of temperature in the phase-change region (32). (Copyright 1974 by Elsevier. Reproduced with permission of Elsevier via Copyright Clearance Center.)

Figure 6

Cryoprobe temperature and heat flux variations and frozen front location versus blood perfusion rates (17)

Figure 7

Cryoprobe temperature and heat flux variations and frozen front location versus metabolic heat rates (17)

Figure 8

Comparison of experimental and analytical temperature distributions around a general purpose cryoprobe (34)

Figure 9

Forcing functions of the inverse-Stefan problem for various combinations of heat sources and a cooling rate of 10°C/min at the frozen front (19)

Figure 10

Temperature distributions in a PCM for a constant heat flux and various velocities of the moving boundary. Spherical geometry (36).

Figure 11

Calculated forcing function for the controlled freezing/thawing processes for a maximal cooling/warming rate of 10°C/min(37)

Figure 12

Freezing front locations, for the first and fifth repeated freezing/thawing cycles, for various blood perfusion rates and cooling/warming rates. The dots indicate end of cooling and initiation of warming in each cycle (40).

Figure 13

Comparison of experimental and computational finite element results (39)

Figure 14

Comparison of measured (41) and calculated freezing front location around a 3.4 mm cylindrical Accuprobe. Required cooling power was estimated by the numerical code (40).

Figure 15

Comparison of numerical and analytical temperature distributions (left) and freezing front location (right) for a single, infinitely long cryoprobe embedded in a PCM (21)

Figure 16

Temperature distributions after 60 s for nonsymmetrical activation of two adjacent cryoprobes at −55°C/1°C/s (right) and −22.5°C/0.5°C/s (left) (21)

Figure 17

Placement of the thermocouple junctions adjacent to the insertion cryoprobe. Dimensions in millimeter (44).

Figure 18

Measured and estimated isothermal contours for one (left) and two 10 mm apart (right) cryoprobes after 10 min of operation (44)

Figure 19

Insertion configurations for three cryoneedles (43). Dimensions in mm. (Copyright 2007 by Elsevier. Reproduced with permission of Elsevier via Copyright Clearance Center.)

Figure 20

Top views of 0°C, −20°C, and −40°C isothermal contours for different placement configurations after 1 min and 10 min of operation of three cryoneedles (43). (Copyright 2007 by Elsevier. Reproduced with permission of Elsevier via Copyright Clearance Center.)

Figure 21

Schematic view of the tumor, embedded blood vessel, and surface cryoprobe (48)

Figure 22

Cross-sectional view of the test section holding the embedded tube and thermocouples in the PCM (47)

Figure 3

Schematic representation of phase change in biological materials

Figure 25

Low power magnification of the interface between normal (N) and cryodamaged fibers (C) 7 days post-cryotreatment (51). Copyright 1996 by Elsevier. Reproduced with permission of Elsevier via Copyright Clearance Center.

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