Assessing the image quality and eye lens dose reduction using bismuth shielding in computed tomography of brain

Document Type : Original Article


1 Department of Radiology, Faculty of Paramedical Sciences, Aja University of Medical Sciences, Tehran, Iran

2 Assistant Professor, Department of Infectious Disease, School of Medicine, Aja University of Medical Sciences, Tehran, Iran

3 Associate Professor, Department of Radiology, Faculty of Paramedical Sciences, Aja University of Medical Sciences, Tehran, Iran


Background: Epidemiological studies show that computed tomography (CT) is one of the main sources of ionizing radiations. Shielding of radiosensitive organs is one of the dose reduction methods. This study aimed to assess the eye lens dose reduction and image quality resulting from the use of radio-protective bismuth shield in brain CT imaging.
Methods: Bismuth shields were constructed with two different thicknesses (0.02 and 0.06 cm) and two different geometries including: direct contact with eye (contact setup) and 4 cm above the eye (distant setup). The lens dose was determined using thermo luminescent dosimeter (TLD)-207A chips inside an anthropomorphic head phantom during the CT examinations. Noise, SNR (signal to noise ratio), and CNR (contrast to noise ratio) were calculated to evaluate the image quality.
Results: The lens dose reduction was higher using the shield with 0.06 cm thickness and in ‘contact setup’. On the other hand, the bismuth shield with the thickness of 0.02 cm and in ‘distant setup’ had lower dose reduction and better image quality.
Conclusion: Bismuth shield with the thickness of 0.02 cm and in ‘distant setup’ could decrease the lens dose to the acceptable levels, while providing a better image quality in comparison with the contact shield setup and with 0.06 cm thickness. Using the bismuth shield is a simple and low cost method for protecting the eye lens in brain CT scans with conventional scanners especially in low income or developing countries.


  1. Mettler FA Jr, Bhargavan M, Faulkner K, Gilley DB, Gray JE, Ibbott GS, et al. Radiologic and nuclear medicine studies in the United States and worldwide: frequency, radiation dose, and comparison with other radiation sources—1950–2007. Radiology 2009; 253(2):520-31.
  2. Dowd SB, Tilson ER. Practical Radiation Protection and Applied Radiobiology. 2nd ed. Philadelphia: Saunders; 1999.
  3. Hall EJ, Giaccia AJ. Radiobiology for the Radiologist. 7th ed. Philadelphia: Lippincott Williams & Wilkins; 2012.
  4. Brown NP. The lens is more sensitive to radiation than we had believed. Br J Ophthalmol 1997; 81(4):257.
  5. Essers M, Mijnheer BJ. In vivo dosimetry during external photon beam radiotherapy. Int J Radiat Oncol Biol Phys 1999; 43(2):245-59.
  6. Tasman W, Jaeger EA. Duane's Clinical Ophthalmology on CD-ROM. Philadelphia: Lippincott Williams & Wilkins; 2004.
  7. Ainsbury EA, Bouffler SD, Dörr W, Graw J, Muirhead CR, Edwards AA, et al. Radiation cataractogenesis: a review of recent studies. Radiat Res 2009; 172(1):1-9.
  8. Barnard SG, Ainsbury EA, Quinlan RA, Bouffler SD. Radiation protection of the eye lens in medical workers-basis and impact of the ICRP recommendations. Br J Radiol 2016; 89(1060):20151034.
  9. Picano E, Vano E, Domenici L, Bottai M, Thierry-Chef I. Cancer and non-cancer brain and eye effects of chronic low-dose ionizing radiation exposure. BMC cancer 2012; 12:157.
  10. International Commission on Radiological Protection (ICRP) ICRP publication 103: the 2007 recommendations of theinternational commission on radiological protection. 2007 [cited 2018 Oct 20]. Available from:
  11. Boal TJ, Pinak M. Dose limits to the lens of the eye: international basic safety standards and related guidance. Ann ICRP 2015; 44(Suppl 1): 112-7.
  12. Chodick G, Bekiroglu N, Hauptmann M, Alexander BH, Freedman DM, Doody MM, et al. Risk of cataract after exposure to low doses of ionizing radiation: a 20-year prospective cohort study among US radiologic technologists. American Am J Epidemiol 2008; 168(6):620-31.
  13. Nakashima E, Neriishi K, Minamoto A. A reanalysis of atomic-bomb cataract data, 2000–2002: a threshold analysis. Health Phys 2006; 90(2):154-60.
  14. Neriishi K, Nakashima E, Minamoto A, Fujiwara S, Akahoshi M, Mishima HK, et al. Postoperative cataract cases among atomic bomb survivors: radiation dose response and threshold. Radiat Res 2007; 168(4):404-8.
  15. Worgul BV, Kundiyev YI, Sergiyenko NM, Chumak VV, Vitte PM, Medvedovsky C, et al. Cataracts among Chernobyl clean-up workers: implications regarding permissible eye exposures. Radiat Res 2007; 167(2):233-43.
  16. Scott JA. measurement of dose equivalents from external photon and electron radiations ICRU Report 47. International Commission on Radiation Units and Measurements, Bethesda, 1992. Journal of Nuclear Medicine 1993; 34(1):171.
  17. Huggett J, Mukonoweshuro W, Loader R. A phantom-based evaluation of three commercially available patient organ shields for computed tomography X-ray examinations in diagnostic radiology. Radiat Prot Dosimetry 2013; 155(2):161-8.
  18. Ciarmatori A, Nocetti L, Mistretta G, Zambelli G, Costi T. Reducing absorbed dose to eye lenses in head CT examinations: the effect of bismuth shielding. Australas Phys Eng Sci Med 2016; 39(2):583-9.
  19. Hopper KD, King SH, Lobell ME, TenHave TR, Weaver JS. The breast: in-plane x-ray protection during diagnostic thoracic CT--shielding with bismuth radioprotective garments. Radiology 1997; 205(3):853-8.
  20. Pescada R, Sousa P, Abrantes AF, Ribeiro LP, Almeida RP, Rodrigues S, et al. Radioprotection in CT scans: use of bismuth, barium and lead shields. European Congress of Radiology; 2015 Mar 4-8; Wien: Bruno-Kreisky-Platz.
  21. Zakariaee SS, Saba V, Valizadeh A. Study the effect of gantry tilting and tube voltage reducing on the eye lens dose reduction in computed tomography using MCNPx. Paramedical Sciences and Military Health 2017; 12 (1):39-49. [In Persian].
  22. Wang J, Duan X, Christner JA, Leng S, Grant KL, McCollough CH. Bismuth shielding, organ-based tube current modulation, and global reduction of tube current for dose reduction to the eye at head CT. Radiology 2012; 262(1):191-8.
  23. Salinas CL, Estelles FM, Lemercier P, Latorre Brajovic PM, Flors Blasco L, Marti-Bonmati L, et al. Bismuth shielding at head CT: impact of a novel design on the image quality and dose reduction to the lens. European Congress of Radiology; 2015 Mar 4-8; Wien: Bruno-Kreisky-Platz.
  24. Ngaile JE, Uiso CB, Msaki P, Kazema R. Use of lead shields for radiation protection of superficial organs in patients undergoing head CT examinations. Radiat Prot Dosimetry 2008; 130(4):490-8.
  25. Nikupaavo U, Kaasalainen T, Reijonen V, Ahonen SM, Kortesniemi M. Lens dose in routine head CT: comparison of different optimization methods with anthropomorphic phantoms. AJR Am J Roentgenol 2015; 204(1):117-23.
  26. Huggett J, Mukonoweshuro W, Loader R. A phantom-based evaluation of three commercially available patient organ shields for computed tomography x-ray examinations in diagnostic radiology. Radiat Prot Dosimetry 2013; 155(2): 161-168.
  27. Catuzzo P, Aimonetto S, Fanelli G, Marchisio P, Meloni T, Mistretta L, et al. Dose reduction in multislice CT by means of bismuth shields: results of in vivo measurements and computed evaluation. La Radiologia Medica 2009; 115(1):152-69.
  28. Gbelcová L, Nikodemova D, Horvathova M. Dose reduction using bismuth shielding during paediatric CT examinations in Slovakia. Radiat Prot Dosimetry 2011; 147(1-2):160-3.
  29. Morford K, Watts LK. Bismuth shielding durint CT exams: a literature review. Radiol Manage 2012; 34(3):45-7.
  30. Mendes M, Costa F, Figueira C, Madeira P, Teles P, Vaz P. Assessment of patient dose reduction by bismuth shielding in CT using measurements, GEANT4 and MCNPX simulations. Radiat Prot Dosimetry 2015; 165(1-4):175-81.
  31. Raissaki M, Perisinakis K, Damilakis J, Gourtsoyiannis N. Eye-lens bismuth shielding in paediatric head CT: artefact evaluation and reduction. Pediatr Radiol 2010; 40(11):1748-54.
  32. Seoung YH. Evaluation of radiation dose reduction during CT scans by using bismuth oxide and nano-barium sulfate shields. J Korean Phys Soc 2015; 67(1):1-6.
  33. Zakariaee SS, Saba V. A mathematical head phantom for dosimetry measurements by monte carlo method. Paramedical Sciences and Military Health 2016; 11(3):12-20. [In Persian].
  34. Hopper KD, Neuman JD, King SH, Kunselman AR. Radioprotection to the eye during CT scanning. AJNR Am J Neuroradiol 2001; 22(6):1194-8.