Radiation dose reduction based on CNR index with low-tube voltage scan for pediatric CT scan: experimental study using anthropomorphic phantoms

Takanori Masuda; Yoshinori Funama; Masao Kiguchi; Naoyuki Imada; Takayuki Oku; Tomoyasu Sato; Kazuo Awai

doi:10.1186/s40064-016-3715-y

Radiation dose reduction based on CNR index with low-tube voltage scan for pediatric CT scan: experimental study using anthropomorphic phantoms

Springerplus. 2016 Dec 1;5(1):2064. doi: 10.1186/s40064-016-3715-y. eCollection 2016.

Authors

Takanori Masuda¹, Yoshinori Funama², Masao Kiguchi³, Naoyuki Imada⁴, Takayuki Oku⁴, Tomoyasu Sato⁵, Kazuo Awai³

Affiliations

¹ Department of Radiological Technology, Tsuchiya General Hospital, Nakajima-cho 3-30, Naka-ku, Hiroshima, 730-8655 Japan ; Department of Diagnostic Radiology, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan.
² Department of Medical Physics, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan.
³ Department of Diagnostic Radiology, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan.
⁴ Department of Radiological Technology, Tsuchiya General Hospital, Nakajima-cho 3-30, Naka-ku, Hiroshima, 730-8655 Japan.
⁵ Department of Diagnostic Radiology, Tsuchiya General Hospital, Nakajima-cho 3-30, Naka-ku, Hiroshima, 730-8655 Japan.

Abstract

Background: To figure out the relationship between image noise and contrast noise ratio (CNR) at different tube voltages, using anthropomorphic new-born and 1-year-old phantoms, and to discuss the feasibility of radiation dose reduction, based on the obtained CNR index from image noise. We performed helical scans of the anthropomorphic new-born and 1-year-old phantoms. The CT numbers of the simulated aorta and image noise of the simulated mediastinum were measured; then CNR was calculated on 80, 100, and 120-kVp images reconstructed with filtered back projection (FBP) and iterative reconstruction (IR). We also measured the center and surface dose in the case of CNR of 14 using radio-photoluminescence glass dosimeters.

Results: The CT number of the simulated aorta was increased with decreasing tube voltage from 120 to 80 kVp (362.5-535.1 HU for the new-born, 358.9-532.6 HU for the 1-year-old). At CNR of 14, the center dose was 0.4, 0.6 and 0.9 mGy at FBP and 0.5, 0.6 and 0.9 mGy at IR and with the new-born phantom acquired at 80, 100 and 120 kVp, respectively. The center dose for FBP image was reduced by 56% at 80 kVp, 34% at 100 kVp for the new-born and 36% at 80 kVp, 22% at 100 kVp for the 1-year-old compared with that at 120 kVp. We obtained a relationship between image noise and CNR at different tube voltages using the anthropomorphic new-born and 1-year-old phantoms.

Conclusion: The use of index of CNR with low-tube voltage may achieve further radiation dose reduction in pediatric CT examination.

Keywords: Contrast-to-noise-ratio (CNR); Image noise; Low-tube voltage; Radiation dose.