ABSTRACT
Objective:To compare the dose and image quality of selected photon shield (SPS) technique, organ-based tube current modulation (OBTCM) technique and the combination of these two techniques for reducing the organ dose in head CT examination for infants.Methods:Two anthropomorphic head phantoms (CIRS 1-yr-old and 5-yr-old) were scanned by using Reference mode, Reference + OBTCM mode, SPS mode and SPS + OBTCM mode, respectively. Radiation doses to the lens of the eye, the anterior of the brain, the posterior of the brain, noise level and CNR of orbit and brain in different phantoms were measured and compared by using different scanning modes.Results:Compared with Reference mode, the doses to the lens of the eye in 1-yr-old and 5-yr-old phantom decreased by (21.89 ± 0.01)% and (28.33 ± 0.34)%, respectively. In SPS mode, the reduction in doses to the lens of the eye in 1-yr-old and 5-yr-old phantom were (71.38 ± 1.30)% and (53.72 ± 2.42)%, respectively. In SPS + OBTCM mode, the reduction was (71.12 ± 2.54)% and (55.73 ± 1.90)%, respectively. There was significant difference in the noise level of orbit and brain in different phantoms under various scanning modes ( F=5.67-85.47, P< 0.05). The noise level in OBTCM mode compared with reference mode increased slightly (<1.45 HU) in various phantoms. SPS and SPS + OBTCM mode resulted in a small noise increase (<2.58 HU). There was no significant difference in CNR of different phantoms under various scanning modes ( P>0.05). Conclusions:SPS and SPS + OBTCM mode can significantly reduce the radiation dose of lens and the whole image plane in the head CT scan for infants, with maintaining the image quality.
ABSTRACT
Objective To investigate the effect of scan table on size-specific dose estimate ( size-specific dose estimate, SSDE) in children's CT scan. Methods CT imaging data and CTDIvol of 44 children ( 15 heads, 13 chests, 16 abdomen-pelvis) who underwent Siemens SOMATOM Definition AS+ 64 row 128-slice CT scan were retrospectively collected. CTDIvol of each patient was recored, WED ( water equivalent diameter) was calculated by two different methods ( with or without table) , donated as WED-T and WED-NT, then the corresponding SSDEWED ( SSDEWED-T and SSDEWED-NT ) was calculated. And the SSDEWED-NT was used as reference to evaluate the difference between WED and SSDEWED obtained by two different methods. Results Including part of table will lead to the overestimate for WED, with mean differences of 0. 10％, 2. 82％ and 2. 54％ for head, chest and abdomen-pelvis, respectively, while SSDEWED will be underestimated by 0. 06％ ( head ) , 2. 70％ ( chest ) and 1. 59％ ( abdomen-pelvis ) . Conclusions Including par of the patient table has a certain effect on SSDEWED for children, more attention should be paid for the application of SSDEWED.