The application of imaging plates (IPs), which are highly sensitive two-dimensional radiation sensors, to cumulative dosemeters for measuring high level X-ray radiation has been attempted, aiming at direct measurement of entrance skin dose (ESD) in interventional radiology (IR) .The IP has 103 times greater sensitivity to X-rays than does X-ray emulsion film. The present upper limit of the measurable dose is only less than 1 mGy, which is principally determined by the saturation of the output current of the photomultiplier tube (PMT) and not by the property of IP. To extend the upper limit of the measurable dose without adapting the readout system, a new and simple technique to decrease the occurrence of photostimulated luminescence (PSL) and reduce exposure levels within the dynamic range of the PMT is being developed. The process involves placing a sheet of color cellophane over the IP during the readout process and/or annealing the IP. This process enables extension of the upper limit of the X-ray dose to approximately 102Gy by using three sheets of color cellophane or to 10!Gy by annealing the IPs at 100°C for 70 hours. Combining the conventional way, the dynamic range of an IP can be extended by eight orders of magnitude.
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