Evaluation of Image Quality and Dose on a Flat-Panel CT-Scanner

摘要

We developed and evaluated a prototype flat-panel detector based Volume CT (VCT) scanner. We focussed onimproving the image quality using different detector settings and reducing x-ray scatter intensities. For the presentedresults we used a Varian 4030CB flat-panel detector mounted in a multislice CT-gantry (Siemens Medical Systems).The scatter intensities may severely impair image quality in flat-panel detector CT systems. To reduce the impact ofscatter we tested bowtie shaped filters, anti-scatter grids and post-processing correction algorithms. We evaluated theimprovement of image quality by each method and also by a combination of the several methods.To achieve an extended dynamic range in the projection data, we implemented a novel dynamic gain-switching mode.The read out charge amplifier feedback capacitance is changing dynamically in this mode, depending on the signallevel. For this scan mode dedicated corrections in the offset and gain calibration are required. We compared imagequality in terms of low contrast for both, the dynamic mode and the standard fixed gain mode.VCT scanners require different types of dose parameters. We measured the dose in a 16 cm CTDI phantom and free airin the scanners iso-center and defined a new metric for a VCT dose index (VCTDI). The dose for a high quality VCTscan of this prototype scanner varied between 15 and 40 mGy.