Fig. 3
Higher spectral separation can compensate for the increase in image noise in lower dose virtual non-calcium images. High-resolution conventional reconstruction (a) and virtual non-calcium reconstructions (b−d) at three different tube-voltage and dose combinations at the same position. Image noise for each reconstruction is stated and is the mean standard deviation for the three chambers with fluid and bone. Notice in b and d a volume computed tomography dose index of 20 mGy, but the higher difference in tube voltage and use of a tin filter leads to a reduction in image noise. While at a constant tube-voltage combination in c and d, the increase in dose leads to a decrease in image noise. Similar image noise is seen at a four times reduced dose between b and c, indicating that scans with lower spectral separation must increase the dose to maintain similar image noise; CTDIvol Volume computed tomography dose index; Sn indicates the use of a tin filter