Abstract

Dual source CT (DSCT) systems utilize two measurement systems (A) and (B) offset by about 90 degrees. A special challenge in DSCT is cross-scattered radiation, i.e., scattered radiation from x-ray tube (B) detected in detector (A) and vice versa. Cross-scattered radiation can produce artifacts and degrade the contrast-to-noise ratio (CNR) of the images. Correction algorithms are mandatory to mitigate the negative effects of cross-scattered radiation. The purpose of this work is to describe and evaluate different methods for cross-scatter correction in DSCT. The authors present two techniques for cross-scatter correction in DSCT. The first technique (1) is model-based. Assuming that cross-scatter is predominantly surface scatter, adequate knowledge about the surface of the scattering object is sufficient to describe the magnitude and distribution of cross-scatter. The relevant surface information is derived from an analysis of the raw-data sinogram during the CT-scan. The correction is performed by a table look-up into previously measured and stored cross-scatter distributions for a variety of objects with different surface characteristics. The second technique (2) is measurement-based. Dedicated sensors outside the penumbra of the fan beam in the z direction on both detectors (A) and (B) are used for an online measurement of both cross-scattered and forward scattered radiation during the CT-scan. In addition to the two scatter-correction techniques, the authors describe a low-pass filter method for the scatter-correction term with the goal to improve the CNR of the corrected images. This filter can be applied to both model-based (1) and measurement-based (2) scatter correction. Both scatter-correction techniques (1) and (2) are quantitatively assessed and the performance of the low-pass filter method is evaluated using DSCT data of phantoms (water cylinders and anthropomorphic phantoms) and DSCT patient scan data. Both scatter-correction techniques restore image contrasts and reduce cross-scatter induced artifacts in DSCT images. The measurement-based technique results in higher CNR than the model-based technique if the proposed low-pass filtering of the scatter-correction term is applied. Low-pass filtering improves the CNR of cross-scatter-correction approaches beyond the limits published in the literature [Engel et al., "X-ray scattering in single- and dual-source CT," Med. Phys. 35(1), 318-332 (2008)]. Both model-based and measurement-based scatter correction can mitigate the negative effects of cross-scatter in DSCT. The application of low-pass filtering to the scatter-correction term improves the CNR whenever the ratio of scattered radiation to total signal is high, as in larger patients.

Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call