Evaluation of the detection limit at low activity levels for three preclinical PET systems

Tomographic systems dedicated to noninvasive imaging of preclinical animal models have become widely available in recent years. Several imaging tasks involve very low levels of injected activity. One of the key advantages of molecular imaging with PET is its capability to detect and measure non-invasively nano-molar to picomolar concentrations of probes in vivo. It is useful therefore to establish the Minimum Detectable Activity (MDA), which is directly related to detectability of PET systems for very low activity distributions. In this work, the detection limits are evaluated for three commercially available imaging systems through ROI analysis in acquired images from well plate experiments. The detection limits at different reconstructed image frames for certain wells were fitted by an exponential. The MDA was calculated by interpolation between the frames above and below the detection limit. To validate the feasibility of using the ROI method to evaluate the detection limit, the theoretical values of Contrast to Noise Ratio (CNR) between two of the systems were compared to the ratio of the MDA values from the image based ROI method. Close agreement between the two methods strengthens the rationale for the methodologies used in this work.