title: Systematic error in lung nodule volumetry: effect of iterative reconstruction versus filtered back projection at different CT parameters.
abstract: OBJECTIVE
  Iterative reconstruction potentially can reduce radiation dose compared with filtered back projection (FBP) for chest CT. This is especially important for repeated CT scanning, as is the case in patients with indeterminate lung nodules. It is currently unknown whether absolute nodule volumes measured with iterative reconstruction are comparable to those measured with FBP. We compared nodule volumes measured with iterative reconstruction and FBP at different CT parameters.
  
  
  METHODS
  An anthropomorphic chest phantom was scanned using a 256-MDCT scanner at various tube voltages and tube current-time products. Raw data were reconstructed using FBP or a commercially available iterative reconstruction algorithm. Five inserted nodules with 100 HU radiodensity and different sizes (3, 5, 8, 10, and 12 mm) were measured by two observers using semiautomatic software. Volumetric nodule measurements were performed using thin-slice reconstructions.
  
  
  RESULTS
  For very small nodules (volume, 14.1 mm(3); diameter, 3 mm), FBP and iterative reconstruction measurements exhibited large errors and overestimated the nodule size by up to 160%. For larger nodules (volume, ≥ 65.4 mm(3); diameter, ≥ 5 mm), CT underestimated the actual size, but errors were small (within 25%) and remained small when the tube voltage and tube current-time product were reduced, even without iterative reconstruction.
  
  
  CONCLUSIONS
  In a phantom model, no clinically relevant differences beyond reported interscan variation levels between lung nodule volumes were measured in nodules 5 mm or larger at reduced tube voltage and tube current-time product, with radiation dose reductions up to 90.6% for both FBP and iterative reconstruction, suggesting that it is safe to convert FBP protocols to iterative reconstruction and reduce tube voltage and tube current-time product for lung nodule follow-up. CT appears to slightly underestimate actual nodule volume.
authors.affiliation: Department of Radiology, Utrecht University Medical Center, HP E01.132, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands. m.willemink@umcutrecht.nl
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Willemink
authors.forename: Tim
authors.initials: T
authors.lastname: Leiner
authors.forename: Ricardo P J
authors.initials: RP
authors.lastname: Budde
authors.forename: Freek P L
authors.initials: FP
authors.lastname: de Kort
authors.forename: Rozemarijn
authors.initials: R
authors.lastname: Vliegenthart
authors.forename: Peter M A
authors.initials: PM
authors.lastname: van Ooijen
authors.forename: Matthijs
authors.initials: M
authors.lastname: Oudkerk
authors.forename: Pim A
authors.initials: PA
authors.lastname: de Jong
mesh_terms: D000465:Algorithms; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D008176:Lung Volume Measurements; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D013902:Radiography, Thoracic / Q000379:methods*; D012984:Software; D003074:Solitary Pulmonary Nodule / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*