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Feasibility of volume‐of‐interest (VOI) scanning technique in cone beam breast CT—a preliminary study
Author(s) -
Chen Lingyun,
Shaw Chris C.,
Altunbas Mustafa C.,
Lai ChaoJen,
Liu Xinming,
Han Tao,
Wang Tianpeng,
Yang Wei T.,
Whitman Gary J.
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2948397
Subject(s) - imaging phantom , image quality , projection (relational algebra) , iterative reconstruction , cone beam computed tomography , monte carlo method , detector , noise reduction , noise (video) , optics , physics , dosimetry , attenuation , nuclear medicine , field of view , computer science , computer vision , medicine , mathematics , image (mathematics) , radiology , computed tomography , algorithm , statistics
This work is to demonstrate that high quality cone beam CT images can be generated for a volume of interest (VOI) and to investigate the exposure reduction effect, dose saving, and scatter reduction with the VOI scanning technique. The VOI scanning technique involves inserting a filtering mask between the x‐ray source and the breast during image acquisition. The mask has an opening to allow full x‐ray exposure to be delivered to a preselected VOI and a lower, filtered exposure to the region outside the VOI. To investigate the effects of increased noise due to reduced exposure outside the VOI on the reconstructed VOI image, we directly extracted the projection data inside the VOI from the full‐field projection data and added additional data to the projection outside the VOI to simulate the relative noise increase due to reduced exposure. The nonuniform reference images were simulated in an identical manner to normalize the projection images and measure the x‐ray attenuation factor for the object. Regular Feldkamp–Davis–Kress filtered backprojection algorithm was used to reconstruct the 3D images. The noise level inside the VOI was evaluated and compared with that of the full‐field higher exposure image. Calcifications phantom and low contrast phantom were imaged. Dose reduction was investigated by estimating the dose distribution in a cylindrical water phantom using Monte Carlo simulation based Geant4 package. Scatter reduction at the detector input was also studied. Our results show that with the exposure level reduced by the VOI mask, the dose levels were significantly reduced both inside and outside the VOI without compromising the accuracy of image reconstruction, allowing for the VOI to be imaged with more clarity and helping to reduce the breast dose. The contrast‐to‐noise ratio inside the VOI was improved. The VOI images were not adversely affected by noisier projection data outside the VOI. Scatter intensities at the detector input were also shown to decrease significantly both inside and outside the VOI in the projection images, indicating potential improvement of image quality inside the VOI and contribution to dose reduction both inside and outside the VOI.