title: Reducing CT radiation dose with iterative reconstruction algorithms: the influence of scan and reconstruction parameters on image quality and CTDIvol.
abstract: OBJECTIVE
  In this phantom CT study, we investigated whether images reconstructed using filtered back projection (FBP) and iterative reconstruction (IR) with reduced tube voltage and current have equivalent quality. We evaluated the effects of different acquisition and reconstruction parameter settings on image quality and radiation doses. Additionally, patient CT studies were evaluated to confirm our phantom results.
  
  
  METHODS
  Helical and axial 256 multi-slice computed tomography scans of the phantom (Catphan(®)) were performed with varying tube voltages (80-140kV) and currents (30-200mAs). 198 phantom data sets were reconstructed applying FBP and IR with increasing iterations, and soft and sharp kernels. Further, 25 chest and abdomen CT scans, performed with high and low exposure per patient, were reconstructed with IR and FBP. Two independent observers evaluated image quality and radiation doses of both phantom and patient scans.
  
  
  RESULTS
  In phantom scans, noise reduction was significantly improved using IR with increasing iterations, independent from tissue, scan-mode, tube-voltage, current, and kernel. IR did not affect high-contrast resolution. Low-contrast resolution was also not negatively affected, but improved in scans with doses <5mGy, although object detectability generally decreased with the lowering of exposure. At comparable image quality levels, CTDIvol was reduced by 26-50% using IR. In patients, applying IR vs. FBP resulted in good to excellent image quality, while tube voltage and current settings could be significantly decreased.
  
  
  CONCLUSIONS
  Our phantom experiments demonstrate that image quality levels of FBP reconstructions can also be achieved at lower tube voltages and tube currents when applying IR. Our findings could be confirmed in patients revealing the potential of IR to significantly reduce CT radiation doses.
authors.affiliation: Inselspital - Bern University Hospital, University Institute of Diagnostic, Interventional, and Pediatric Radiology, Freiburgstrasse 10, 3010 Bern, Switzerland; University of Würzburg, Insitute of Diagnostic and Interventional Radiology, Oberdürrbacher Str. 6, 97080 Würzburg, Germany. Electronic address: klink_t1@ukw.de.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Klink
authors.affiliation: Inselspital - Bern University Hospital, University Institute of Diagnostic, Interventional, and Pediatric Radiology, Freiburgstrasse 10, 3010 Bern, Switzerland. Electronic address: verena.obmann@insel.ch.
authors.forename: Verena
authors.initials: V
authors.lastname: Obmann
authors.affiliation: Inselspital - Bern University Hospital, University Institute of Diagnostic, Interventional, and Pediatric Radiology, Freiburgstrasse 10, 3010 Bern, Switzerland. Electronic address: johannes.heverhagen@insel.ch.
authors.forename: Johannes
authors.initials: J
authors.lastname: Heverhagen
authors.affiliation: Roentgeninstitut Duesseldorf, Kaiserswerterstrasse 89, 40476 Duesseldorf, Germany. Electronic address: a.stork@roentgeninstitut.de.
authors.forename: Alexander
authors.initials: A
authors.lastname: Stork
authors.affiliation: University Medical Center Hamburg Eppendorf, Department of Diagnostic and Interventional Radiology, Martinistrasse 52, 20246 Hamburg, Germany. Electronic address: g.adam@uke.de.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Adam
authors.affiliation: Roentgeninstitut Duesseldorf, Kaiserswerterstrasse 89, 40476 Duesseldorf, Germany. Electronic address: p.begemann@roentgeninstitut.de.
authors.forename: Philipp
authors.initials: P
authors.lastname: Begemann
mesh_terms: D000465:Algorithms; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D015588:Observer Variation; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D059629:Signal-To-Noise Ratio; D014057:Tomography, X-Ray Computed / Q000379:methods* / Q000706:statistics & numerical data
keywords: Computed tomography; Hybrid iterative reconstruction; Image quality; Phantom; Radiation dose