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A method to correct the influence of carbon fiber couchtop and patient positioning device on image quality of cone beam CT
Author(s) -
Men Kuo,
Dai Jianrong,
Li Minghui,
Zhang Yin
Publication year - 2010
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 - 10.1118/1.3425999
Subject(s) - imaging phantom , image quality , cone beam computed tomography , image noise , image resolution , medical imaging , signal to noise ratio (imaging) , noise (video) , flat panel detector , nuclear medicine , materials science , optics , computer science , medicine , computer vision , detector , artificial intelligence , physics , image (mathematics) , radiology , computed tomography
Purpose To evaluate the influence of carbon fiber couchtop and patient positioning devices on cone beam CT (CBCT) image quality and develop an effective method to correct the influence. Methods A standard CT phantom (Catphan 500) was used to evaluate the influence of iBeam evo carbon fiber couchtop on the quality of CBCT image obtained from an Elekta synergy machine. The evaluation indices were contrast‐to‐noise ratio (CNR), spatial resolution, image uniformity, and image noise. With using the Beer–Lambert law and the energy‐response function of the flat‐panel imager, a method was applied to deduct the image signal of the couchtop (and the positioning devices) from each projection image of a phantom/patient, and then used all corrected projection images to reconstruct a CBCT image. The performance of the correction method was evaluated using the CBCT images of a Catphan 500 phantom, a head‐and‐neck cancer patient, and a prostate cancer patient. Results In two phantom studies (the phantom to simulate a human head and neck and the one to simulate a human body), the CNR of the CBCT images obtained with the couchtop reduced 18.1% and 29.8%, respectively with respect to those obtained without the couchtop; meanwhile, the image uniformity reduced 16.4% and 24.1% due to the use of the carbon fiber couchtop. The couchtop also induced extra image noise (16.5% for the h&n phantom and 4.2% for the body phantom). However, CBCT imaging with the couchtop did not affect the spatial resolution. After applying the projection image correction, there was a significant improvement in CNR (by 19.5% and 25.8%), image uniformity (by 9.2% and 13.1%), and image noise (by 10.2% and 3.9%), with respect to CBCT images obtained with the couchtop. Conclusions The presence of the carbon fiber couchtop and the patient positioning devices can significantly impair CBCT image quality in terms of the CNR, the image uniformity, and the image noise. By removing the influence of the couchtop and the patient‐positioning devices from CB projection images, the correction method improves CBCT image quality and thus image guidance in radiotherapy.