Real time [beta]-imaging with silicon hybrid pixel detectors: kinetic measurements with C-14 amino acids and P-32 nucleotides

We present some additional results obtained with the BETAview system [1], a digital system for real time [beta]-imaging based on semiconductor pixel detectors and on a single photon counting read-out chip. In this paper, we describe the system assembled with a Si detector, 300-[micro]m thick, segmented into 64 x 64 square pixels with 170-[micro]m pitch. The solid-state pixel array detector is bump-bonded pixel by pixel to a low threshold, single particle counting electronics, the photon counting chip (PCC) developed by the Medipix1 Collaboration for biomedical applications. Each cell (corresponding to a detector pixel) of the front-end chip has a maximum count rate of 2 MHz, a minimum nominal threshold of 1400 [e.sup.-] (corresponding about 5 kev in Si), and contains a 15-bit counter. The detector sensitive area is about 1 [cm.sup.2], but several detectors could be assembled in arrays. The measured background counts were about 3.5 x [10.sup.-2] cps/[cm.sup.2], which implies a very high sensitivity of the device. The detection threshold used in this experiment was ~15 keV. In this paper, we show the results obtained in the real-time monitoring of two biological dynamic processes: an amino acid uptake by living cells and the thermal denaturation process of oligonucleotides. Specifically, we have followed over time the accumulation of a marked amino acid ([[sup.14]C]L-Leucine) into Octopus vulgaris eggs cells. The results, described in Section III-B, show that after about 20 min from the beginning of the uptake process, the radioactively marked eggs become clearly visible over the background culture radioactive medium. In Sections III-C and III-D, we also describe the successful performance of the [beta]-imaging system in genetic studies involving the real time reconstruction of denaturation and kinetics curves for two different [sup.32]P-radiolabeled nucleotides. Index Terms--Autoradiography, DNA, hybrid pixel detectors, Medipix.