| Popis: |
We investigated the influence of a scatter reduction grid on the spatial resolution properties of a digital X-ray imaging system (Philips Medical Systems, Thoravision). The spatial resolution using a grid was nearly independent of the X-ray energy as the modulation transfer function (MTF) showed. Maximum spatial resolution was reduced because of the grid in case of a constant exposure dose. The amount of absorbed photons raised and Wiener spectra were increased by the factor of ten. The scattered radiation was reduced by the grid at higher spatial frequencies and the Wiener spectra of different exposure parameters reached approximately the same value. The measurement of the detective quantum efficiency (DQE) showed the influence of absorption characteristics of the detector (aSe) on the resulting image quality. Detector absorption efficiency increased at a lower X-ray energy. This resulted in the opportunity to compensate the effects of low signal dynamics because of higher grid absorption. Inserting a filter in the X-ray beam altered the shape of the photon energy spectrum and influences image quality by changing the contrast. For this reason, we investigated the spectral composition of the X-rays, too. There were advantages using additional filtration opposite the scatter reduction grid. However, the scattered radiation was not reduced by the filtration and therefore this did not improve the signal-to- noise characteristic. The X-ray scatter reduction grid increased the detail detectability in high absorption image areas. However, without greater exposure doses, the use of a scatter reduction grid did not have as much advantage as expected. A detector material with higher quantum efficiency could solve this problem. |
