title: Iterative reconstructed ultra high pitch CT pulmonary angiography with cardiac bowtie-shaped filter in the acute setting: effect on dose and image quality.
abstract: OBJECTIVE
  To evaluate the effect of a cardiac bowtie-shaped filter in an ultra high pitch CTPA protocol at 100 kV on image quality and radiation dose.
  
  
  METHODS
  Retrospective study of 100 patients referred for CTPA. 50 patients scanned with a standard 100 kV protocol at pitch 2.8 (Protocol A) and 50 patients scanned with a 100 kV protocol at pitch 3.2 with a cardiac bowtie-shaped filter (Protocol B). All other scanning parameters kept constant. Images from both groups reconstructed with filtered back projection and iterative reconstruction. Central pulmonary vessel attenuation and background noise were quantitatively measured and signal-to-noise (SNR) and contrast-to-noise (CNR) were calculated. Two radiologists performed qualitative assessment grading visualization of the pulmonary vasculature and noise level. CTDIvol and DLP were recorded and effective dose was calculated.
  
  
  RESULTS
  CTDIvol, DLP and effective dose were significantly (p<0.0001) lower in Protocol B (2.3 ± 0.5 mGy, 78.4 ± 16.5 mGycm, 1.4 ± 0.3 mSy, respectively) compared to Protocol A (4.3 ± 0.5 mGy, 152.0 ± 19.6 mGycm, 2.7 ± 0.3 mSy, respectively). Protocol B had significantly (p<0.0001) higher noise than Protocol A (23.8 ± 6.9 HU vs 36.8 ± 7.3 HU) and lower SNR (11.8 ± 3.7 HU vs 19.2 ± 8.1 HU) and CNR (10.3 ± 3.7 HU vs 24.9 ± 13.4 HU) but there was no significant difference in the subjective visualization of the pulmonary vasculature (p=0.63). Furthermore, iterative reconstruction significantly (p<0.0001) improves image noise (29.4 ± 5.5 HU from 36.8 ± 7.3 HU).
  
  
  CONCLUSIONS
  The addition of a cardiac bowtie-shaped filter with an ultra high pitch CTPA protocol at 100 kV resulted in a 48% dose reduction without significantly affecting diagnostic image quality. In addition, the use of iterative reconstruction significantly improves image quality by reducing noise permitting the possibility for further dose reduction strategies.
authors.affiliation: Vancouver General Hospital, Department of Radiology, Jim Pattison Pavilion South, 899 West 12th Ave. Room G861, Vancouver BC V5Z 1M9, Canada. co.steve@gmail.com
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Co
authors.forename: John
authors.initials: J
authors.lastname: Mayo
authors.forename: Teresa
authors.initials: T
authors.lastname: Liang
authors.forename: Karl
authors.initials: K
authors.lastname: Krzymyk
authors.forename: Masoud
authors.initials: M
authors.lastname: Yousefi
authors.forename: Savvas
authors.initials: S
authors.lastname: Nicolaou
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000792:Angiography / Q000379:methods / Q000706:statistics & numerical data*; D001955:British Columbia / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011651:Pulmonary Artery / Q000000981:diagnostic imaging*; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011874:Radiometry / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods / Q000706:statistics & numerical data*
keywords: CT; CTPA; Cardiac bowtie-shaped filter; Dose reduction; Pulmonary embolism