Cell tracking is the capability to locate the position and to follow the fate of cells in living beings over a long period of time. This method might have a major impact on different sectors of medicine and biology, such as regenerative medicine or tumor research. Cell tracking permits a better understanding of cellular processes such as cell migration, cell homing, and cell function in engraftments at organ or tissue level, or the dynamics of tumor growth and metastatic spread. Due to the combination of classical imaging techniques and cellular contrast agents mainly based on nanotechnologies cell tracking is already feasible. Successful cell tracking has been carried out using magnetic resonance imaging in combination with superparamagnetic iron oxide nanoparticles, optical imaging combined with quantum dots or positron emission computed tomography using unstable β+ nuclides. Although outstanding results have been achieved in specific cases utilizing these techniques, none of them can be really considered an all-embracing cell tracking technique since each of them features specific drawbacks. Despite of the ubiquitous application of x-ray imaging methods, up to now, x-rays have been rarely considered as a cell tracking solution because of radiation dose constrains.
The thesis at hand tries to exploit x-ray imaging methods in the field of cell tracking. Starting from the x-ray properties an appropriate cellular contrast agent, in this case colloidal gold nano particles, and subsequent a loading protocol based on phagocytosis has been chosen and tested. Expected signal levels, contrasts and signal to noise ratios have been theoretically determined for this specific marker and loading protocol. Then, the detectability of marked cells has been verified on in vitro and ex vivo models proofing the feasibility of cell tracking using gold nanoparticles in combination with x-ray CT. Successively radiation dose constrains have been examined in detail by means of computer simulations and low dose ex vivo experiments. The investigation revealed that in vivo cell tracking using x-rays is feasible and on the basis of these results in vivo experiments had been designed and prepared. All the necessary authorizations had been obtained by the National and Local Ethic Committees. First successful in vivo cell tracking experiments in animal models of human diseases have been performed during the last months of this thesis work.
The results presented in the following reveal that also x-ray cell tracking encompasses some limitations such as the previous mentioned techniques, however it can be consider an alternative and attractive method for cell tracking.
