Novel technique for simultaneous acquisition of primary and scatter image signals

Proper scatter correction is vital to qualitative contrast measurement in digital subtraction angiography (DSA) and dual-energy subtraction processing in digital chest radiography using storage phosphor plates. Such correction requires an accurate estimation of the scatter distribution in the image field. In this paper, a novel method, referred to as the primary-modulation-demodulation (PMD) method, is introduced. With the PMD method, the primary X-ray distribution is modulated and demodulated with two filters placed on the tube and detector sides of the patient. The modulation-demodulation process, while leaving the overall primary signal distribution unchanged, results in a reduction of scatter signals in selected regions in the image. This signal drop can be measured and used to estimate and construct the scatter distribution for use in image correction. Because the PMD method allows both primary and scatter signals to be acquired simultaneously, it is ideal for use in non-scanning DSA or digital storage phosphor imaging for dual-energy subtraction imaging and/or quantitative contrast measurement. In this paper, the principle and implementation of the PMD method is described. Examples of scatter measurement using this method are shown and compared to those obtained with the beam stop method.