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Medical Physics / Volume 37 / Issue 6 / RADIATION IMAGING PHYSICS

Med. Phys. 37, 2466 (2010); http://dx.doi.org/10.1118/1.3425999 (7 pages)

A method to correct the influence of carbon fiber couchtop and patient positioning device on image quality of cone beam CT

Kuo Men

Department of Radiation Oncology, Cancer Institute (Hospital), Chinese Academy of Medical Sciences, Beijing 100021, China and College of Physics and Technology, Wuhan University, Wuhan 430072, China

Jianrong Dai, Minghui Li, and Yin Zhang

Department of Radiation Oncology, Cancer Institute (Hospital), Chinese Academy of Medical Sciences, Beijing 100021, China

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(Received 11 December 2009; accepted 12 April 2010; revised 30 March 2010; published online 10 May 2010)

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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.

© 2010 American Association of Physicists in Medicine

ACKNOWLEDGMENTS

This research work was funded by National Natural Science Foundation of China (Grant No. 10975187). The authors sincerely thank Dr. Di Yan of William Beaumont Hospital for elaborately editing the manuscript. The authors also thank their colleague, Mr. Ye Zhang, for reviewing CBCT images.

Article Outline

  1. INTRODUCTION
  2. MATERIALS AND METHODS
    1. CBCT system
    2. Carbon fiber couchtop and patient positioning devices
    3. Image quality phantom
    4. Correction method
    5. Phantom study
    6. Patient study
  3. RESULTS
    1. Energy-response function
    2. Phantom studies
    3. Patient studies
  4. DISCUSSION AND CONCLUSIONS
Digital Object Identifier
http://dx.doi.org/10.1118/1.3425999

KEYWORDS and PACS

Keywords

biological organs, biomedical equipment, cancer, carbon fibres, computerised tomography, image denoising, image resolution, medical image processing, phantoms, cone beam computed tomography, couchtop, positioning device, image quality

PACS

PUBLICATION DATA

ISSN

0094-2405 (print)  

Publisher

$abstract.society.value is a Member of CrossRef American Association of Physicists in Medicine

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