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Signal to noise and contrast ratio enhancement by quasi-monochromatic imaging

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1 Author(s)
Zentai, G. ; Ginzton Technol. Center of Varian Med. Syst., Mountain View, CA

One CT exam provides 50-250 times the radiation of a single view x-ray. According to a latest study the chance of getting cancer from x-ray radiation has been increasing by 1.5-2 % at every CT exam. So decreasing the dose per CT exam is a major goal. The aims of this study were to find out how one can improve the signal to noise ratio (S/N) or decrease the dose with the same S/N in mammography CT and how to improve the contrast ratio for I (Iodine) contrast imaging. Iodine has relatively high Z number and it absorbs x-rays much better then any tissue, water or blood. Iodine dissolves well in water and it has been used for intravenous injection to detect any blockage in blood circulation by x-rays. Moreover, iodine also accumulates in cancer cells as described in the paper, so it is used to increase the contrast of breast tumor images. The paper gives an overview of different techniques to generate quasi monochromatic x-ray radiation and emphasizes the advantages of the K-edge filtering method when the K-edge energy of the x-ray filter material is close to the K-edge of iodine. In the article several K-edge filters are compared and results of the CT experiments are discussed which prove that using the right material the iodine x-ray contrast image can be improved by Gt25% and the simultaneously the dose to the patient can be decreased by a factor of two or more while keeping the same signal to noise ratio as without K edge filtering. This is a very significant advancement for CT screening of women who has been suspected of breast cancer.

Published in:

Imaging Systems and Techniques, 2009. IST '09. IEEE International Workshop on

Date of Conference:

11-12 May 2009