title: Synergistic Radiation Dose Reduction by Combining Automatic Tube Voltage Selection and Iterative Reconstruction.
abstract: OBJECTIVE
  The aim of the study was to evaluate radiation dose and image quality in computed tomographic pulmonary angiography (CTPA) scans performed with automatic tube voltage selection (ATVS, CarekV) before and after implementation of iterative reconstruction (IR, Safire).
  
  
  METHODS
  This IRB-approved study was conducted with waiver of informed consent. The cohort included 100 consecutive "standard protocol" CTPAs performed using ATVS and 100 consecutive "combined protocol" CTPAs performed using ATVS with a 33% reduction in reference mAs and IR. CTDIvol and main pulmonary artery enhancement, noise, and signal-to-noise ratio were recorded, along with blinded grading of subjective image quality. Dose and image quality were compared between cohorts with univariate analyses and linear regression models.
  
  
  RESULTS
  The 33% reduction in reference mAs with the combined protocol allowed ATVS to select reduced kVp more often than with the standard protocol, with a reduction in 120 and 100 kVp scans (26% to 0% and 61% to 51%, respectively) and an increase in 80 kVp scans (13% to 49%). The combined protocol yielded a CTDIvol reduction of 43% (P<0.0001) and increases in main pulmonary artery enhancement (57 HU, P=0.005) and noise (P=0.019) with unchanged signal-to-noise ratio (P=0.17). With the combined protocol, subjective image quality was unchanged for evaluation of vascular structures but was decreased for evaluation of soft tissues and lung parenchyma.
  
  
  CONCLUSIONS
  The combination of ATVS and IR resulted in a 43% dose reduction, greater than the 33% reduction that would be achieved by reducing the reference mAs alone. This was accomplished with preserved vascular image quality.
authors.affiliation: *Department of Radiology, Brigham and Women's Hospital †Division of Emergency Radiology, Harvard Medical School, Boston, MA.
authors.forename: Jeremy R
authors.initials: JR
authors.lastname: Wortman
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Adduci
authors.forename: Aaron D
authors.initials: AD
authors.lastname: Sodickson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011651:Pulmonary Artery / Q000000981:diagnostic imaging; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D059629:Signal-To-Noise Ratio; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult