X-ray fluorescent computer tomography with synchrotron radiation

This paper describes the possibility of a quantitative calculation of the distribution of a nonradioactive element within a selected cross section with nondestructive methods with the help of X-ray fluorescent tomography (XFCT). In order to increase measurement sensitivity, the use of a lamellar collimator was avoided. One of the main problems for the quantitative determination of concentration was absorption of the stimulating synchrotron ray as well as re-absorption of the emitted fluorescent light. The absorption coefficients required for a consideration of the absorption processes have been determined with two absorption tomograms. The algebraic reconstruction technique (ART) and the maximum likelihood method with expectation maximization (MLEM) were used for the reconstruction of the chemical element to be classified, with close consideration of the absorption phenomenon. The experiments were undertaken at the bending-magnet beamline, CEMO, at the laboratory for synchrotron radiation in Hamburg, HASYLAB (4.5 GeV) (100 mA). The photon intensity flux was approximately 10⁹ photons/mm²/s. The concentration of iodine was calculated with phantoms and an untreated, dissected human thyroid gland with the help of a calibration curve. The total error related to the reconstructed mean value amounts to 20%. One can find at least an iodide concentration of 0.6 mmol/l in this experimental setup.