Quantifizierung eines hochauflösenden Einzelphotonemissionstomographen

Summary With this study, we proved the possibility of relative and absolute quantification of the tracer 99m-Tc with SPECT in in-vitro studies even for relatively low activities. A standard gamma-camera, Siemens e-cam, equipped with different multi-pinholekollimators was used. The in-vitro experiments were performed with different phantoms, tracer-activities and settings. At first, the scaling-factor for 99m-Tc was calculated, followed by two experiments, proving the possibility of a relative quantification of the well known tracer 99m-Tc in in-vitro experiments. Excellent results with median errors of less than 1% could be calculated. Secondly, we focussed on the so called partial-volume-effect during detection of extremely small volumes, expecting a decrease of the precision. Still, acceptable results with errors of approximately 15% could be gained. To secure the potential of detecting even absolute concentrations of 99m-Tc in in-vitro studies, three more experiments were conducted. The results showed a high precision, proving the absolute quantification in in-vitro experiments. Again, median errors of less than 8% were detected. The limiting factor seems to be smallest activity-concentrations of less than 60 kBq/ml. In this case, a significant countrate could not be achieved for acquisition-times of less than two hours. Although we hoped to show up similar results in in-vivo experiments, a disappointing outcome appeared. An error of factor 17 had to be registered in the first in-vivo experiment using 99m-Tc-Gastrin. For 111-In-Gastrin no improvement occurred. These results can not only be caused by the expected problems of metabolism or tracer-excretion. We suspect problems during the experiment’s progress, such as reconstruction of the SPECT-data, positioning the ROI or mathematic difficulties to be some of the reasons. Therefore, with the help of this study, the basis of detecting absolute tracer-activities in in-vivo studies with SPECT was founded, although further experiments will have to follow. With technical innovations and new reconstruction software, this goal is supposed to be reached shortly. Thus, sacrifice of small animals will not longer be necessary. The detection and follow-up of pathological processes in a living organism will lead to great advances in research as well as clinical diagnosis and treatment. A high-resolution imaging of pathological processes in humans still remains a future target. As technical innovations the FASTSPECT or U-SPECT have to be mentioned, both extensive developments of the multi-pinhole SPECT, suggesting a higher resolution. New reconstruction-algorithms such as the Bayesian-mechanism PH-MRP or the 3D-OSEM are also supposed to achieve higher spatial resolutions.