Towards room temperature CCD autoradiography: methods for minimizing the effects of dark current at room temperature

The effects of dark current are potentially a major limiting factor for attempting CCD imaging of low level radioactivity. This is particularly problematic when operating at room temperature as long exposure times and slow scan readout are needed. In this work we address these problems principally for application in thin tissue autoradiography. To correct for these effects we have initially used a simple subtraction method which makes a first order correction. However, this has a tendency to over-correct ∼5% pixels and undercorrect a further 10%. To address these shortcomings we have developed an image restoration method using simulated annealing using a global cost function which accounts for differences in the noise distribution for individual pixels. To test the methods we have used synthetic as well as experimental image data of 20 μm ¹⁸F labeled fibres. This has yielded a spatial resolution ∼90 μm (FWHM) and 300 μm (FWTM) for a ¹⁸F positron line source. The method is also capable of dramatically reducing the background dark current mottle by over an order of magnitude.