PIV MEASUREMENT OF FLUID FLOW INSIDE A human uterus MODEL FOR CRYOABLATIONXiaolong Luo 1, Jim S. J. Chen 1, Marla Wolfson 2, Charles Philips 2, Thomas Shaffer 21 Department of Mechanical Engineering, Temple University 2 Temple University School of Medicine Abstract – A new technique has been proposed that allows to be achieved on the entire inner surface of the endometrium by circulating very cold (PFC) fluid inside the human uterus. To understand the PFC flow field inside the uterus during, a uterus model was constructed; a fluid delivery system including the fluid delivery probe was designed and built to simulate the PFC flow during cryosurgery.
With particle image (PIV), the fluid flow inside the uterus was investigated at room temperature to display a 2-D whole field velocity contour and vector plot. Keywords: PIV, , PFC, endometrium. INTRODUCTION Menorrhagia is medically defined as excessive bleeding at menses, in duration or amount. A frequent cause of menorrhagia is uterine fibroid growth. Traditionally, hysterectomy is the main treatment for menorrhagia. Several cryosurgery methods such as localized [1] and balloon ablation [2] have been developed as alternatives to hysterectomy to treat the dysfunction of the endometrium.
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However, these are localized techniques and sometimes there is still proliferation of the endometrium. A new technique is proposed that allows to be achieved on the entire inner surface of the endometrium using a PFC fluid [3]. The objective of this project is to develop an efficient treatment method for abnormal uterine bleeding by freezing the endometrium. It has been shown that a temperature of -30 C is required for destroy tissue necrosis [4]. The heat transfer process during was investigated experimentally and numerically (1-D) with good agreement [5], in which a uniform fluid temperature boundary condition was used in the 1-D finite difference method to determine the temperature history in the human uteri of eight patients. This assumed that the fluid flow inside the uterus is uniform, repeatable and controllable.
During the experiments it was found that the temperature difference at the inlet and outlet of the insertion probe varied from 10 oC to 50 oC. Inconsistent fluid temperatures may be caused by inadequate circulation of PFC liquid, i. e. , recirculation within the uterus. The goal of this study is to understand the flow field inside the uterus cavity during so that the desired flow field and uniform temperature field can be obtained, thus proposing an optimal insertion probe design so that minimum PFC liquid and surgery time is used. II.
MATERIALS AND METHODS Particle Image Velocimetry (PIV), an instantaneous velocity field measurement over global domains, has gained widely utilization in fluid flow investigations. During the last few years, PIV has been expanding its extensive applications to the bioengineering and medicine field because it is a non intrusive and whole field measurement with quantitative data. The PIV system used for this investigation is shown in Fig. 1. After the system was setup, it was calibrated within the PIV system and the velocity was verified at the outlet of an immerged pump in a water tank.
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PIV measurement results were in good agreement with four verification methods that includes the average velocity based on the flow rate, the velocity based on the maximum lift, the velocity determined by a Pilot tube, and the average velocity from a free jet. A uterus model was constructed with three pieces of Plexiglas adhered together. The model is considered as 2-D because the side view of human uterus inner cavity is much more uniform than the front view. The middle piece (uterus cavity) was made based on the general uterus shape and average dimensions of 8 collected patient uteri (enclosed area of about 20 cm 2).
Fig. 1 Setup of PIV system and fluid circulating system The design was then drawn with the software IDEAS, programmed, and milled with a CNC milling machine.
To meet the transparency requirement for the PIV laser beam through the Plexiglas, the middle piece was polished by a series of 220, 320, 400, 600, 800 sandpapers and finely polished by 5 um alumina suspensions. The transparency was verified with good results before it was adhered with the cover and bottom pieces. Finally, the model was put on a 3-D movable machine table for experiments. A fluid circulating system consisting of a pump, a relief valve, a flow meter and a pressure gage was designed with adjustable flow rate to simulate the PFC fluid circulation during.
For the study, a 97% Glycerin solution was chosen because of its very similar properties to PFC liquid at low temperature. This experimental fluid was necessary since the PFC liquids are very expensive currently (about $2, 000 per liter).
Note that PFC liquid at -80 oC (750 times of that of water at 4 oC) is similar to 97% glycerin at room temperature, thus this experimental fluid was carefully selected to match the viscosity of PFC liquid, i. e.
, to match the Reynolds number. The insertion probe consists of two concentric tubes with the inner tube delivering the PFC fluid into the uterus and the outer tube extracting the PFC fluid. There are ports along the inner tube that have staggered arrangement. Two mechanisms are responsible for the pressure variation from the beginning of the inlet to the end of the probe. One is the pressure drop due to the friction loss; the other is the pressure increase due to the velocity drop along the inner tube. It was found that the former factor is much more important, so the size of the ports increases from the inlet to the end of the inner tube.
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The design of the insertion probe is to assure that the PFC fluid adequately and efficiently circulate inside the uterus in order to achieve the desired flow field and uniform temperature field inside the uterus. Therefore, the PFC fluid usage and surgery time can be minimized. III. RESULTS AND DISSCUSSIONTo achieve our goals, preliminary experiments were conducted with water to verify the experimental apparatus.
The experiments were performed with two ports open on both sides of insertion probe near the end. In order to eliminate the laser beam reflection because of the round shape of the probe, the probe needs to be painted in black. And laser beam from the top surface of the uterus is preferred. The results are shown in Fig. 2 with the vector plot and the velocity contour. With the delivery flow rate of 300 ml / min , the velocity at a distance about 3 mm away from the two ports (diameter = 1.
60 mm) was found to be 0. 42 m / s . Again due to the laser beam reflection near the probe, the maximum velocity at the immediate outlet of the ports was not shown. Nevertheless, the velocity of 0. 42 m / s at 3 mm away is close to the calculated magnitude. Fig.
2 Vector plot & velocity contour of PIV measurement (speed: m / s ) To optimize the flow field so that incoming, cold Pfc can efficiently circulate inside the uterus, investigations are underway by varying the size of position of the insertion probe relative to the cervix. The ANSYS-FLO TRAN software will be used to predict the flow field by varying the parameters as described above. Recommendations of optimal probe design and probe location will be proposed based on experimental and numerical results. REFERENCES: [1] W. Droegemueller, B. Greer, and E.
Makowski, Cryosurgery in Patients with Dysfunctional UterinBleeding. Obstet and Gynecol 38 (2): 256-8, 1971. [2] R. S.
Neu wirth, A. A. Duran, A. Singer et al The endometrial: A new instrument. Obst e and Gynecol 83: 792-796, 1994. [3] T.
Shaffer, M. Wolfson, and J. Greenspan, Liquid-Assisted Ventilation: An Alternative Respiratory Modality. Ped. Pulmonology.
(26) pp. 42-63, 1998. [4] A. Gage, and J. B aust, Mechanisms of tissue injury in cryosurgery. Cryobiology, (37) pp.
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171-186, 1998. [5] J. S-J Chen, K. Agn issey, M.
K. Wolfson, C. Philips, and T. Shaffer, Experimental and Numerical Studies of Heat Transfer in Human Uteri during Cryo ablation, IM ECE 2002-HT-32055.
