title: [Study of CT Automatic Exposure Control System (CT-AEC) Optimization in CT Angiography of Lower Extremity Artery by Considering Contrast-to-Noise Ratio].
abstract: OBJECTIVE
  To evaluate the image quality and effect of radiation dose reduction by setting for computed tomography automatic exposure control system (CT-AEC) in computed tomographic angiography (CTA) of lower extremity artery.
  
  
  METHODS
  Two methods of setting were compared for CT-AEC [conventional and contrast-to-noise ratio (CNR) methods]. Conventional method was set noise index (NI): 14and tube current threshold: 10-750 mA. CNR method was set NI: 18, minimum tube current: (X+Y)/2 mA (X, Y: maximum X (Y)-axis tube current value of leg in NI: 14), and maximum tube current: 750 mA. The image quality was evaluated by CNR, and radiation dose reduction was evaluated by dose-length-product (DLP).
  
  
  RESULTS
  In conventional method, mean CNRs for pelvis, femur, and leg were 19.9±4.8, 20.4±5.4, and 16.2±4.3, respectively. There was a significant difference between the CNRs of pelvis and leg (P<0.001), and between femur and leg (P<0.001). In CNR method, mean CNRs for pelvis, femur, and leg were 15.2±3.3, 15.3±3.2, and 15.3±3.1, respectively; no significant difference between pelvis, femur, and leg (P=0.973) in CNR method was observed. Mean DLPs were 1457±434 mGy⋅cm in conventional method, and 1049±434 mGy·cm in CNR method. There was a significant difference in the DLPs of conventional method and CNR method (P<0.001).
  
  
  CONCLUSIONS
  CNR method gave equal CNRs for pelvis, femur, and leg, and was beneficial for radiation dose reduction in CTA of lower extremity artery.
authors.affiliation: Department of Medical Technology, Tsuchiya General Hospital.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Inada
authors.forename: Takanori
authors.initials: T
authors.lastname: Masuda
authors.forename: Naoya
authors.initials: N
authors.lastname: Maruyama
authors.forename: Yukari
authors.initials: Y
authors.lastname: Yamashita
authors.forename: Tomoyasu
authors.initials: T
authors.lastname: Sato
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Imada
mesh_terms: D000368:Aged; D000792:Angiography / Q000379:methods*; D005260:Female; D006801:Humans; D007866:Leg / Q000098:blood supply*; D008297:Male; D061330:Multidetector Computed Tomography / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging