title: Iterative reconstruction in single source dual-energy CT pulmonary angiography: Is it sufficient to achieve a radiation dose as low as state-of-the-art single-energy CTPA?
abstract: OBJECTIVE
  Dual-energy (DE) brings numerous significant improvements in pulmonary CT angiography (CTPA), but is associated with a 15-50% increase in radiation dose that prevents its widespread use. We hypothesize that thanks to iterative reconstruction (IR), single source DE-CTPA acquired at the same radiation dose that a single-energy examination will maintain an equivalent quantitative and qualitative image quality, allowing a more extensive use of the DE technique in the clinical routine.
  
  
  METHODS
  Fifty patients (58% men, mean age 64.8yo ± 16.2, mean BMI 25.6 ± 4.5) were prospectively included and underwent single source DE-CTPA with acquisition parameters (275 mA fixed tube current, 50% IR) tweaked to target a radiation dose similar to a 100 kV single-energy CTPA (SE-CTPA), i.e., a DLP of 260 mGy cm. Thirty patients (47% men, 64.4yo ± 18.6, BMI 26.2 ± 4.6) from a previous prospective study on DE-CTPA (375 mA fixed tube current, reconstruction with filtered-back projection) were used as the reference group. Thirty-five consecutive patients (57% men, 65.8yo ± 15.5, BMI 25.7 ± 4.4) who underwent SE-CTPA on the same scanner (automated tube current modulation, 50% IR) served as a comparison. Subjective image quality was scored by two radiologists using a 5-level scale and compared with a Kruskal-Wallis nonparametric test. Density measurements on the 65 keV monochromatic reconstructions were used to calculate signal-to-noise (SNR) and contrast-to-noise (CNR) ratios that were compared using a Student's t test. Correlations between image quality, SNR, CNR and BMI were sought using a Pearson's test. p<0.05 was considered significant.
  
  
  RESULTS
  All examinations were of diagnostic quality (score ≥ 3). In comparison with the reference DE-CTPA and the SE-CTPA protocols, the DE-IR group exhibited a non-inferior image quality (p=0.95 and p=0.21, respectively) and a significantly lower mean image noise (p<0.01 and p=0.01) thus slightly improving the SNR (p=0.09 and p=0.47) and the CNR (p=0.12 and p=0.51). There was a strong negative relationship between BMI and SNR/CNR (ρ=-0.59 and -0.55 respectively), but only a moderate negative relationship between BMI and image quality (ρ=-0.27).
  
  
  CONCLUSIONS
  With iterative reconstruction, objective and subjective image quality of single source DE-CTPA are preserved even though the radiation dose is lowered to that of a single-energy examination, overcoming a major limitation of the DE technique and allowing a widespread use in the clinical routine.
authors.affiliation: Service de Radiologie B, Nouvel Hôpital Civil, Hôpitaux Universitaires de Strasbourg 1 place de l'hôpital 67000 Strasbourg, France. Electronic address: mickael.ohana@gmail.com.
authors.forename: M
authors.initials: M
authors.lastname: Ohana
authors.affiliation: Service de Radiologie B, Nouvel Hôpital Civil, Hôpitaux Universitaires de Strasbourg 1 place de l'hôpital 67000 Strasbourg, France.
authors.forename: A
authors.initials: A
authors.lastname: Labani
authors.affiliation: Service de Radiologie B, Nouvel Hôpital Civil, Hôpitaux Universitaires de Strasbourg 1 place de l'hôpital 67000 Strasbourg, France.
authors.forename: M Y
authors.initials: MY
authors.lastname: Jeung
authors.affiliation: Service de Radiologie B, Nouvel Hôpital Civil, Hôpitaux Universitaires de Strasbourg 1 place de l'hôpital 67000 Strasbourg, France.
authors.forename: S
authors.initials: S
authors.lastname: El Ghannudi
authors.affiliation: Service de Médecine Vasculaire, Nouvel Hôpital Civil, Hôpitaux Universitaires de Strasbourg 1 place de l'hôpital, 67000 Strasbourg, France.
authors.forename: S
authors.initials: S
authors.lastname: Gaertner
authors.affiliation: Service de Radiologie B, Nouvel Hôpital Civil, Hôpitaux Universitaires de Strasbourg 1 place de l'hôpital 67000 Strasbourg, France.
authors.forename: C
authors.initials: C
authors.lastname: Roy
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011651:Pulmonary Artery / Q000000981:diagnostic imaging*; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging*; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: Dual energy CT; Iterative reconstruction; Multidetector computed tomography; Pulmonary embolism; Radiation dosage