Abstract
BackgroundTo 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.ResultsThe 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.ConclusionThe use of index of CNR with low-tube voltage may achieve further radiation dose reduction in pediatric CT examination.
Highlights
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
As iodinated contrast material is frequently used at pediatric cardiac CT examination, we think that the combined automatic tube voltage selection (ATVS) and automatic tube current modulation (ATCM) technique is more useful than single use of ATCM because iodine enhancement is improved at low-tube voltage scan
Even if the CT scanner is not equipped with ATVS, if we can identify the relationship between image noise and CNR at different tube voltages, we can utilize CNR index by converting image noise value to CNR value
Summary
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. To reduce radiation dose for pediatric patients, automatic tube current modulation (ATCM) or combination of ATCM and automatic tube voltage selection (ATVS) are an available option for modern CT scanners (Lee et al 2012; Mayer et al 2014). Even if the CT scanner is not equipped with ATVS, if we can identify the relationship between image noise and CNR at different tube voltages, we can utilize CNR index by converting image noise value to CNR value
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