Scatter and veiling glare estimation based on sampled primary intensity

Scatter and veiling glare are predominant sources of error in videodensitom etric iodine quantification. Standard beam stop techniques such as lead str ips or an array of lead discs, placed before the patients, have previously been used to measure scatter and veiling glare in digital radiographic imag es. However, these techniques significantly increase patient x-ray exposure . In order to overcome this limitation, a scatter measurement technique bas ed on sampled primary intensity has been investigated. This technique uses an array of apertures in a lead sheet to sample the primary x-ray intensity . The scatter-glare intensity in these locations is calculated by subtracti ng the sampled primary intensity from an open field image which contains bo th primary and scatter-glare. The calculated scatter-glare values can be in terpolated or combined with digital filtration to estimate the scatter-glar e intensity on a pixel by pixel basis. The technique was evaluated using a Lucite(TM) step phantom and an anthropomorphic chest phantom. The average r ms percentage errors of scatter and veiling glare estimation using bi-cubic interpolation and digital filtration techniques were 8.02% and 7.53%, resp ectively. The average rms percentage errors of primary intensity estimation using hi-cubic interpolation and digital filtration techniques were 10.01% and 8.91%, respectively. The x-ray exposure-area product (EAP) from the ap erture array was only 4.38% of the EAP from the open field. These results i ndicate that the scatter-glare intensity can be accurately estimated with m inimal x-ray exposure using sampled primary intensity. (C) 1999 American As sociation of Physicists in Medicine. [S0094-2405(99)03811-0].