Chao-Jen Lai et al 2009 Phys. Med. Biol. 54 6691 doi:10.1088/0031-9155/54/21/016
Chao-Jen Lai1, Lingyun Chen1, Huojun Zhang1,3, Xinming Liu1, Yuncheng Zhong1, Youtao Shen1, Tao Han1, Shuaiping Ge1, Ying Yi1, Tianpeng Wang1, Wei T Yang2, Gary J Whitman2 and Chris C Shaw1
Show affiliationsWith volume-of-interest (VOI) cone-beam computed tomography (CBCT) imaging, one set of projection images are acquired with the VOI collimator at a regular or high exposure level and the second set of projection images are acquired without the collimator at a reduced exposure level. The high exposure VOI scan data inside the VOI and the low exposure full-field scan data outside the VOI are then combined together to generate composite projection images for image reconstruction. To investigate and quantify scatter reduction, dose saving and image quality improvement in VOI CBCT imaging, a flat panel detector-based bench-top experimental CBCT system was built to measure the dose, the scatter-to-primary ratio (SPR), the image contrast, noise level, the contrast-to-noise ratio (CNR) and the figure of merit (FOM) in the CBCT reconstructed images for two polycarbonate cylinders simulating the small and the large phantoms. The results showed that, compared to the full field CBCT technique, radiation doses for the VOI CBCT technique were reduced by a factor of 1.20 and 1.36 for the small and the large phantoms at the phantom center, respectively, and from 2.7 to 3.0 on the edge of the phantom, respectively. Inside the VOI, the SPRs were substantially reduced by a factor of 6.6 and 10.3 for the small and the large phantoms, the contrast signals were improved by a factor of 1.35 and 1.8, and the noise levels were increased by a factor of 1.27 and 1.6, respectively. As a result, the CNRs were improved by a factor of 1.06 and 1.13 for the small and the large phantoms and the FOM improved by a factor of 1.4 and 1.7, respectively.
General scientific summary. The purpose of this study is to compare volume-of -interest (VOI) cone-beam computed tomography (CBCT) with full-field (FF) CBCT techniques by physical measurements. Two cylindrical polylcarbonate phantoms with different dimensions used to simulate breasts were imaged with an experimental CBCT system at 80 kVp. The FF scan was performed at a high exposure level (HEL). Two scans were performed with the VOI CBCT technique: one with FF at a low exposure level (LEL) and the other with the VOI collimator present using the same technique for the HEL. The ratio of the LEL to the HEL was 0.258. Scatter-to-primary ratio (SPR) and radiation dose were measured, and image quality was quantified by measuring the contrast-to-noise ratio (CNR) and the figure of merit (FOM). The results showed that with the VOI CBCT technique, the SPR and the radiation dose were substantially reduced, the CNR was slightly improved, and the FOM was significantly improved.
Issue 21 (7 November 2009)
Received 13 May 2009, in final form 24 September 2009
Published 20 October 2009
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