title: Image quality of low-energy pulmonary CT angiography: comparison with standard CT.
abstract: OBJECTIVE
  The purpose of this article is to prospectively compare visualization of central and peripheral pulmonary arteries on simultaneously acquired low-energy and standard pulmonary CT angiography.
  
  
  METHODS
  Thirty-three consecutive patients (20 women and 13 men; mean age, 55.6 years; range, 21-92 years) with suspected pulmonary embolism (PE) were scanned (140 kVp; 250-300 mA) on a single-source dual-layer dual-energy MDCT scanner. Attenuation and image noise were measured at the main and segmental pulmonary arteries. Signal-to-noise ratios were calculated. Two blinded experienced radiologists assessed segmental and subsegmental artery visibility in consensus, using slab maximum-intensity-projection (MIP) reconstructions. Nonparametric sign test and kappa statistic were used for statistical analysis.
  
  
  RESULTS
  PE was detected in three patients (9.1%); two segmental vessel and subsegmental emboli were seen in the low-energy images only. Higher attenuation was noted in low-energy versus standard images for all arteries evaluated, with a mean (± SD) increase of 66.6 ± 4.4 HU (p < 0.0001). Low-energy images improved visualization of segmental and subsegmental arteries from 97.0% to 99.2% and from 88.0% to 93.9%, respectively. A larger number of subsegmental vessels was seen on low-energy MIP reconstructions in 69.7% (95% CI, 36.5-71.89%) of studies compared with 9.1% on the standard images. Visualization of subsegmental vessels was superior in 55.5% of cases using low-energy imaging. The mean image noise increased by 9.7 ± 0.6 HU (p < 0.0001). The mean signal-to-noise ratio showed no significant difference in the low-energy (8.2) versus standard (8.1) CT images (p = 0.7759).
  
  
  CONCLUSIONS
  Improved visualization of central and peripheral arteries can be obtained with low-energy pulmonary CT angiography, without a substantial decrease in image quality.
authors.affiliation: Department of Radiology, Hadassah-Hebrew University Medical Center, PO Box 12000, Jerusalem 91120, Israel.
authors.forename: Naama R
authors.initials: NR
authors.lastname: Bogot
authors.forename: Alexander
authors.initials: A
authors.lastname: Fingerle
authors.forename: Dorith
authors.initials: D
authors.lastname: Shaham
authors.forename: Izhak
authors.initials: I
authors.lastname: Nissenbaum
authors.forename: Jacob
authors.initials: J
authors.lastname: Sosna
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000792:Angiography / Q000379:methods*; D003287:Contrast Media; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007472:Iohexol; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011651:Pulmonary Artery / Q000000981:diagnostic imaging*; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging*; D011857:Radiographic Image Interpretation, Computer-Assisted; D018709:Statistics, Nonparametric; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media; D007472:Iohexol