Xunhai Xu, Department of Chemical Engineering
Introduction
Recently, modem medical technology has enabled surgeons and other medical scientists to perform certain organ transplantation within human beings successfully. However, thromboembolization, the formation of thromboemboli (usually of irregular shapes with sizes approximately 10,000 times bigger than that of red blood cell), is likely to occur with such operations. The cause of the thromboemboli is believed to be the interaction between human blood and the foreign materials. Since thromboemboli is a much larger particles than normal blood cells (such as red blood cell, white blood cell and single platelet), their existence in the blood solution might be detrimental to the normal functions of the transplanted artificial organs in human beings. For example, the aggregate of thromboemboli may clog and hinder the normal blood flow in capillaries, thus causes further medical troubles to the patients.
Due to above-mentioned reasons, it is necessary to design an non-invasive method to both qualitatively and quantitatively detect the existence of thromboemboli in the blood solution. Researchers at Brigham Young University had built an 828 nm laser-device to perform such kind of detection. It is hoped that by reading the intensity of the scattered light (by the thromboemboli and its surrounding particles), the sizes and the locations of the emboli can be determined analytically.
Work Performed
Although the data thus obtained are rich in potential diagnostic information, they are inherently difficult to analyze due to the complexity of multiple scattering. Multiple scattering is the event that accounts for sum of single scattering between particles in a control volume. An approach based on the energy transport equations and an approach based on a two-parameter phase functions have been established by former scientists to approximate the Rayleigh-Cans and Mie scattering. Multiple scattering is much more challenging because the scattering behavior for each particle within the volume of interest needs to be studied and an integration (or a summation) will need to performed. One way to reduce the complexity is to build a mathematical model for the multiple scattering event. In this model, several reasonable assumptions have been made:
1. approximate the RBC (red blood cells) WBC (white blood cells) and thromboemboli as equal-volume spheres;
2. assume a uniform scattering of incident light for RBC and WBC;
3. assume a Mie scattering for thromboemboli;
4. adopt literature values of absorption coefficient for RBC and plasma.
5. uniform distributions of particles in the solutions
Although there will definitely be deviations from the experimentally obtained data, a model built upon these assumptions will be able to provide the researchers with insights into the experimental values.
The other options include using a longer wavelength laser (light) as source to detect the thromboemboli. Based on the theories studied, it has been found that when the particles’ sizes are relatively comparable to the wavelength of incident light, complicated scattering can be approximated as simple absorption, which will significantly reduce the modeling difficulties.
In March, 1995, several experiments had been performed by us and scientists from 3M Co. and University of Utah. In these experiments, six pigs were used as experimental subjects. A pump and heparinized (or unheparinized) tubes were used to simulate as the heart and arteries to maintain the external circulation of the pig. Our laser device were mounted at different locations of the circulation to detect the thromboemboli . The results obtained from these experiments had been analyzed and compared with previous ones.
An interface computer program to collect the data is being produced. This new program, which is written in C, is based on an original program that was written in Qbasic and it will provide the interface to display the data obtained in a dynamic matter.
Acknowledgments
Finally, I want to extend my gratitude to Brigham Young University, Office of Creative Works and Research, for the generous support that enable me to participate in these interesting research activities, to Dr. Kenneth A. Solen for his advice, encouragement and understandings, and to my colleagues who have worked with me for their patience.