Ehime University Institutional Repository

TAKAHASHI, M.

NOMURA, S.

JINDAI, M.

SHIBATA, S.

ZHU, X.

WATANABE, Y.

KAWACHI, K.

OKABE, N.

15
工学ジャーナル　第 7 巻
2008 年 3 月
Annual Journal of Eng.,
Ehime Univ., VII, Mar., 2008
平成 19 年 8 月 31 日 受付 , 平成 19 年 11 月 2 日 受理
 
 
Development of Reformative Surgery Method 
using Partial Freezing for the Liver 
  
M. TAKAHASHI**, S. NOMURA, M. JINDAI, S. SHIBATA, 
X. ZHU, Y. WATANABE, K. KAWACHI and N. OKABE 
 
Abstract: To minimize surgical stresses including blood loss and operation time to the patients during 
hepatic resection, we studied a feasibility of a combination of partial liver freezing technique and 
shape-memory alloy, which also enables a free-designed resection curve. In this surgical procedure, the 
region surrounding a tumor in the liver is frozen to excise and prevent hemorrhage. The liver was frozen by 
a Peltier module. The effects of cooling rate and freezing temperature on the excision force arisen between 
a scalpel and the liver are carried out experimentally as a basic research for partial freezing surgical 
procedures. A porcine liver was used as a liver sample. The physical properties were estimated by using the 
finite element method based on the heat transfer characteristics of the liver.  
Isolation of the liver was conducted using a scalpel attached to the end-effector of a three degree freedom 
robot. In the experiments, the minimum excision force was obtained at a temperature between 272 K and 
275 K; therefore, it is preferable that the liver be excised within this temperature range. Lowering of the 
cooling rate decreases the excision force even if the temperature of the liver remains unchanged. The lower 
the temperature of the liver is, the larger the increment rate of excision force is with regard to the cooling 
rate. 
 
Key Words: Liver, Cancer, Surgical Operations, Partial Freezing Method, Heat Transfer Characteristics, 
Excision Resistance 
 
1. INTRODUCTION 
 
Surgical operations on the liver to remove tumors require excision of the tissue around the cancer cells. 
At present, during surgery, the numerous blood vessels found inside the liver, both large and small, are 
individually sutured or closed by coagulation. As a result, operations usually take from 4 to 8 hours, 
making them physically taxing for both the patient and the surgeons. As for the operation, usually the 
amount of the hemorrhage, the cancer retention and the passage after the operation are evaluated rather than 
the operation time. To shorten the operative time, however, it is most important that the adequate excision 
line simulated before the operation should be able to be secured and the hemorrhage should be able to be 
controlled. There is an urgent need to lighten this burden by developing innovative surgical methods that 
shorten the excision surgery time. As shown in Fig. 1 (a), the conventional liver cancer surgery requires a 
*  Trans. ASME, Journal of Biomechanical Engineering, Vol.128, pp.862-866(2006)  
** 3  
** Graduate School of Science and Engineering, Ehime University, Matsuyama, Japan. takahashi@eng.ehime-u.ac.jp 
 
16
 
 
considerable volume of liver tissue to 
be excised, since the excision line is 
virtually straight. Furthermore, the 
range of excision is usually decided 
based on the Couinaud classification of 
liver segments [1]. Medical 
professionals have emphasized a need 
for the development of an optimized 
method that enables the excision of the 
tumor only, as shown in Fig. 1 (b). 
Unfortunately, it is difficult to excise 
the liver along the excision line  under 
normal conditions, since the liver is 
soft and mobile. 
To enable the excision of tumor 
within an arbitrarily chosen line or 
curve, our research group proposes a 
feasibility of a combination of partial 
liver freezing technique and shape-memory alloy, which enables a free-designed resection curve as shown 
in Fig. 2.  
In this study, we first conducted a cooling test of the liver using a cooling needle to evaluate the liver's 
physical properties and to identify the characteristics of cooling of liver. Then, we performed a liver 
excision experiment using a robot system to investigate the effects of cooling rate on the excision 
resistance.  
 
2. LIVER HEAT TRANSFER CHARACTERISTICS AND ANALYSIS OF THE MODEL 
 
2.1 Heat transfer test 
Since many liver cancer patients have cirrhosis as a complication, arterial blooding flow entering the 
liver may only be stopped for 5 minutes maximum during surgery.  Surgeons must therefore cool the area 
of the liver around the excision line to a partial freezing state within 5 minutes. The partial freezing state is 
determined by the following excision resistance test. 
The liver used in the test was a fresh porcine liver, which keeps fresh at 278 K or less and is not perfused 
during the following experiments. To cool the liver, we adopted a cooling system using liquid nitrogen. 
Figure 3(a) shows a schematic illustration of this system. The flow rate of the liquid nitrogen is set by 
adjusting the volume of air pumped from the compressor. The liquid nitrogen is led inside a cooling needle 
via a double-structured copper pipe whose inner diameter is 2 mm as shown in Fig. 3 (b).  
A cooling needle was inserted deep into the liver and the temperature was measured at two points along 
the needle. At the same time, thermocouples inserted at depth of a half-thickness of the liver and at 5 mm 
(a) Past excision line. (b) The optimal excision curve. 
Figure 1. Excision line of the liver cancer. 
Figure 2. Schematic illustration of new surgery technique 
for the liver cancer. 
17
 
 
intervals from the needle up to 20 mm away from the needle detected the cooling time and the temperature 
distribution. Due to the assumed anisotropic properties of liver tissue, measurements were taken in two 
directions, x and y. We did not consider the arrangement of blood vessels in this study.  
 
2.2 Heat transfer characteristics of liver 
Figure 4 shows the variation of the temperature versus time from the beginning of cooling. The solid and 
dashed lines show the temperature at each position on the cooling needle surface. The initial temperature of 
the liver is 282 K. Areas with up to a 15 mm radius from the cooling needle seemed to have frozen within 5 
minutes. By using a number of these cooling needles side by side, it should be possible to reduce coolin g 
time and to freeze a larger volume. In 
general, liver is an anisotropic material 
with heat transfer characteristics that 
depend on the arrangement of the blood 
vessels and the orientation of blood flow. 
Even without blood flow the heat transfer 
characteristics remain anisotropic which 
can be seen in Fig.4. It is reasonable to 
assume that the heat transfer 
characteristics are anisotropic 
perpendicular to x-y plain. However, since 
the disparity in heat flow characteristics 
are small (within 7 % or less even at x = y 
= 5 mm), we shall assume an isotropic 
model in the discussion of the following 
experiments. 
Figure 4. Relationship between temperature and cooling 
time of the liver. 
(a) Cooling system.  
 
 
Figure 3. Experimental system for heat transfer test of the liver. 
(b) Structure of cooling needle. It has a coaxial design: the internal pipe 
leads the liquid nitrogen to the tip of the needle. As it flows past the 
outer pipe, the nitrogen, now in gaseous form, cools it before exiting to 
the atmosphere. 
18
 
 
Heat transfer of the liver is 
analyzed by the finite element 
method, using the commercial finite 
elements code (MARC), with respect 
to two-dimensional unsteady-states 
conduction because the temperature 
distributions on the 2D plane were 
measured in the experiment. 
Furthermore, assuming that the 
lengthening joint of the needle was 
ideally cooled, conduction in the 
sample height can be neglected. 
Given the symmetry of the problem 
calculation of the model was confined to one-quarter the cooling area of  30×30 mm2 (see Fig. 5). The 
cooling needle of 3 mm dia. is located at the center of the plane. The total number of elements and nodes 
are 190 and 220 respectively. Four node isoparametric bilinear quadrilateral elements have been used for 
this model. The mass density of the liver model was 1050 kg/m3, which was measured in experiment. The 
boundary conditions were taken as the initial conditions. The liver wa s initially at 282 K.  The temperature 
of the cooling needle was kept at 75 K. The thermal energy loss between the needle and the liver was 
neglected. By making a comparison with the temperature obtained by experimental measurement, we 
attempted to estimate numerically the physical properties of the liver. In experimental data shown in Fig.4, 
the temperature plateau induced by the latent heat of water can not be confirmed clearly. Although the 
latent heat of water is taken into consideration in this FEM inverse analysis, we consider that the latent heat 
does not have large effect on the heat transfer under a rapid cooling rate by using liquid n itrogen. 
Extracellular liquid around the liver tissue seem to have frozen by a rapid cooling and freezing completely 
did not happen inside the tissue. Figure 5 shows the comparison made between the numerical results and 
the measurement values when the distance from the cooling needle (x) was 5 mm and 10 mm. The solid 
lines in Fig. 5 show the temperature distribution of the cooling needle given under the initial conditions. If 
the values shown in Table 1 are used in the numerical analysis, the experimentally measured values are 
close to the numerical values when x is equal to 5 mm. These values around at 280 K are almost equal to 
those of Ref. [2].  
 
 
 
 
Table 1 Thermal properties of the liver at non frozen region analyzed by FEM. 
Figure 5. Analysis model and comparison of experimental and 
analysis data. 
19
 
 
3. INFLUENCES OF COOLING PROPERTIES ON EXCISION RESISTANCE 
 
3.1 Temperature of the liver and excision resistance 
Figure 6(a) shows a schematic illustration of the experimental equipment we prepared to test the force of 
excision resistance under cooling conditions. The scalpel attached to the arm was allowed to drop freely to 
cut the liver samples to the hexahedron shaped volumes of 30×20×100mm3. After measuring the depth and 
length of the cut from the scalpel, we evaluated the excision resistance force F (N) as the following: 
1
p
yF Mg
d
                                        (1) 
so that y = h - ts, where h is the height (m) from the center of gravity of the rod to the liver, ts is the height 
 
(a) Excision force testing method (b)Excision test using robot system. 
Figure 6. Excision force tests of the liver at several freezing conditions. 
Figure 7. Relationship between excision force and 
temperature of the liver. 
20
 
 
(m) of the liver being tested, M the mass (kg) of the rod and the scalpel, g is the acceleration (m/s2) due to 
gravity, dp is the depth (m) of the cut. The liver was set to the designated temperature by being placed 
inside a temperature-controlled tank until it had equilibrated at the desired temperature. We then calculated 
the excision resistance force as a function of different liver temperatures. This experiment was executed 
twice at each temperature. 
Figure 7 shows the relationship between the temperature of the cooled liver and excision resistance. The 
vertical axis shows the excision resistance per scalpel length. It can be seen that a temperature range of 272 
to 275 K provides minimum resistance force. At temperatures above 275K, the liver becomes elastic and 
rubbery, and resists penetration of the scalpel. As a result, excision resistance increases. On the other hand, 
if the temperature drops below 273K, the fine ice crystals contained inside the liver bind and solidify, with 
excision resistance increasing proportionally. Therefore, the temperature range of 272 to 275K is suited for 
conducting efficient liver excision, because there are partial freezing in the state of blood and liver tissue. 
 
3.2 Excision resistance test using a robot 
We then conducted a liver excision experiment using a robot system, with the temperature of the liver 
between 270K and 271.5K. Figure 6(b) shows the three degrees of freedom robot which we used as the 
manipulator. For the coordinate system, we used X, Y, and Z, and equipped axis Z of the manipulator with a 
scalpel (end effector) that had been fixed firmly in place by an aluminum plate. We used a CCD camera to 
load the images into the computer, confirmed the central point of the liver, then cut into it. The excision 
resistance applied to the scalpel during this excision process was recorded by means of a six-axle force 
sensor that had been attached to the end effector. The information data on the forces experienced by the end 
effector during the excision process were loaded into the computer through a receiver board. The liver was 
cooled from both sides using a two-sheet Peltier module, which has the following specifications: size of 
40×40×4mm3, maximum current of 8.5A, maximum voltage of 16.4V and maximum dissipation of 81.5W. 
The excision was begun as soon as the temperature, indicated by the thermocouples embedded near the 
excision line, reached the designated level. The liver was excised with the scalpel vertically applied from 
above at a rate of 10 mm/s. The positions of the temperature measurement were at both ends on excision 
Figure 8. Cooling rate of the liver by a Peltier module. 
 
21
 
 
line. The cooling rate was calculated from the temperature drop on the excision line. The range of the 
cooling rate was set in a few Kelvin per minute, a rate that is thought to cause minimum biological damage. 
[3] 
Figure 8 shows the relationship between the cooling time and the temperature on the excision line, when 
the liver had been cooled. As shown in the figure, a temperature plateau is reached while cooling the liver 
at around 274K, after which the temperature begins to drop again. The temperature plateau, which was a 
result from the release of latent heat and changed thermal properties of liver due to freezing, appeared 
clearly. Peltier module is inferior to the cooling velocity compared with the cooling method of the previous 
description. In this excision resistance test using a robot, therefore, the cooling rates on the excision line 
were defined as the slope between point (ta, Ta) at which the temperature begins to drop again after 
reaching a state of equilibrium, and point (tb, Tb)  at which the excision temperature has been reached. 
After the experiment, we calculated the rate of cooling using the following equation. 
                
ab
ab
f tt
TTV                                      (2) 
  Figure 9 shows the results of our experiments on rate of cooling and excision resistance at different 
excision temperatures (Te). The straight lines in the figure indicate the least-squares method. It is clear that 
excision resistance data is scattered at the same cooling rate. Excision resistance is greatly affected by the 
Figure 9. Relationship between excision resistance and cooling rate at each temperature. 
(a) Excision temperature Te= 271.5, (b) Te= 271, (c) Te= 270.5 and (d) Te= 270K 
22
 
 
liver's frozen status. More studies are needed to closely monitor the liver cells' status when the state of 
freezing is increased. Reducing the rate of cooling, even to the same eventual excision temperature, can 
reduce the force of excision resistance. The lower the excision temperature, the greater the effect of rate of 
cooling on the excision resistance is. Therefore, the excision should conducted at temperatures above 271K. 
 
4. CONCLUSIONS 
 
We carried out experiments on the liver to study its cooling characteristics and conducted excision tests. 
We obtained the following conclusions. 
1. The reference value of the thermal conductivity and the thermal diffusivity of the liver can be estimated 
by finite element analysis based on the data of the heat transmission test.   
2. The temperature range of the minimum excision resistance is between 272K and 275K.  
3. Since excision resistance is greatly affected by the rate at which the liver is cooled, it is important to 
monitor closely the liver cells' status using the temperature recognition by image processing when 
frozen.  
4. Since the properties of the liver vary depending on the cell tissues, moisture content, perfusion of 
biological tissues, capillary effect from the viewpoint of thermo- and fluid dynamics, it will be 
necessary to investigate the characteristics of the liver itself more closely. 
 
REFERENCES 
 
[1] Couinud C., L’abord chirurgical du secteur dorsal du foie. Chirurgie 119, 485-488 (1993-1994). 
[2] Valvano, J. W., Cohran, J. R. and Diller K. R., Thermal conductivity and diffusivity of biomaterials 
measured with self-heated thermistors, Int. J. Thermophys., Vol.6, No.3, 301-311, (1985).    
[3] TADA Y., and HAYASHI Y., Heat transfer and viability of cell during freezing of biological tissue, J. 
Heat Trans. Soc. Japan., Vol.37, No.145, pp.13-20(1998)  


English

Development of Reformative Surgery Methodusing Partial Freezing for the Liver

中西, 典子

Japanese

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松山市における事業所の現状と経営課題 : 松山商工会議所会員ニーズ調査にもとづいて

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