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Objective To explore the absorbed dose to the common tissues of subjects in four clinical CT scanning modes and the spatial distribution of the radiation field in chest scanning, in order to provide a basis for the radiation protection of subjects and the space in the machine room. Methods A thermoluminescence detector (TLD) was used to measure the absorbed doses to the eye lens, thyroid gland, gonad, chest and abdominal skins of the anthropomorphic phantom in four CT scanning modes. The TLD was used to monitor the air kerma at different positions from the CT diagnostic table during chest spiral scanning. Results The absorbed doses to the eye lens, thyroid gland, gonad, chest and abdominal skins of the anthropomorphic phantom in four CT scanning modes were 0.040-64.818 mGy, 0.154-10.155 mGy, 0.028-0.154 mGy, 0.443-17.141 mGy, and 0.093-14.346 mGy, respectively. The maximum air kerma value of the space radiation field during chest scanning was 0.049 mGy, and the farther the distance from the CT tube, the smaller the value. Conclusion The absorbed doses to the common tissues of subjects examined by the four CT scanning modes generally do not exceed the threshold doses. The dose received by the companion of the subject during a single chest CT scan was small. In order to minimize radiation hazards, shielding measures can be taken in CT scanning to reduce the absorbed doses to the tissues of the subject, and the companion of the subject should appropriately increase the distance from the tube and the diagnostic table.
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Objective:To investigate the effect of different scanning modes, detector width and location in detector on high and low contrast resolution of wide-detector CT image.Methods:The Catphan600 phantom with high and low contrast resolution modules was scanned with GE Revolution CT at the same CTDI vol. The scans were performed with the detector widths of 40, 80 and 160 mm for sequential scanning mode and with the detector width/pitch combinations of 40 mm/0.516, 40 mm/0.984, 80 mm/0.508 and 80 mm/0.992 for spiral scanning mode. The resolution modules were placed at the adjacent region between two sequential scans, central and foot side edge in the longitudinal scanning range seperately. The subjective evaluation of the high and low contrast resolution was performed by two radiologists. Results:The high contrast resolution was 8 LP/cm at adjacent region between two sequential scans with the detector width of 80 mm or 160 mm in sequential scanning mode, and at the pitch of 0.5 in spiral scanning mode, while it was 7 LP/cm for the rest of detector combinations. The distinguishable diameter was 3 mm at 1% low contrast resolution at foot side edge with the detector widths of 80 mm or 160 mm in the sequential scanning mode, and it was 2 mm for all the other conditions. The distinguishable diameter was 2 mm at 1% low contrast resolution with the detector width of 40 mm and pitch 0.516 in the spiral scanning mode and it was worse with the wider detector and larger pitch.Conclusions:For the wide-detector CT, scanning mode, detector width, location in detector and pitches will affect the high and low contrast resolution to some degree. Appropriate selection should be done according to actual needs in clinical practice.