title: Evaluation of the radiation dose in micro-CT with optimization of the scan protocol.
abstract: BACKGROUND
  Micro-CT provides non-invasive anatomic evaluation of small animals. Serial micro-CT measurements are, however, hampered by the severity of ionizing radiation doses cumulating over the total period of follow-up. The dose levels may be sufficient to influence experimental outcomes such as animal survival or tumor growth.
  
  
  OBJECTIVE
  This study was designed to evaluate the radiation dose of micro-CT and to optimize the scanning protocol for longitudinal micro-CT scans.
  
  
  METHODS
  Normal C57Bl/6 mice were euthanized. Radiation exposure was measured using individually calibrated lithium fluoride thermoluminescent dosimeters (TLDs). Thirteen TLDs were placed in the mice at the thyroid, lungs, liver, stomach, colon, bladder and near the spleen. Micro-CT (SkyScan 1178) was performed using two digital X-ray cameras which scanned over 180 degrees at a resolution of 83 microm, a rotation step of 1.08 degrees , 50 kV, 615 microA and 121 s image acquisition time. The TLDs were removed after each scan. CTDI(100) was measured with a 100 mm ionization chamber, centrally positioned in a 2.7 cm diameter water phantom, and rotation steps were increased to reduce both scan time and radiation dose.
  
  
  RESULTS
  Internal TLD analysis demonstrated median organ dose of 5.5 +/- 0.6 mGy per mA s, confirmed by CTDI(100) with result of 6.6 mGy per mA s. A rotation step of 2.16 resulted in qualitatively accurate images. At a resolution of 83 microm the scan time is reduced to 63 s with an estimated dose of 2.9 mGy per mA s. At 166 microm resolution, the scan time is limited to 27 s, with a concordant dose of 1.2 mGy per mA s.
  
  
  CONCLUSIONS
  The radiation dose of a standard micro-CT scan is relatively high and could influence the experimental outcome. We believe that the presented adaptation of the scan protocol allows for accurate imaging without the risk of interfering with the experimental outcome of the study.
authors.affiliation: In Vivo Cellular and Molecular Imaging, ICMI, Vrije Universiteit Brussels, Brussels, Belgium. inneke.willekens@gmail.com
authors.forename: Inneke
authors.initials: I
authors.lastname: Willekens
authors.forename: Nico
authors.initials: N
authors.lastname: Buls
authors.forename: Tony
authors.initials: T
authors.lastname: Lahoutte
authors.forename: Luc
authors.initials: L
authors.lastname: Baeyens
authors.forename: Christian
authors.initials: C
authors.lastname: Vanhove
authors.forename: Vicky
authors.initials: V
authors.lastname: Caveliers
authors.forename: Rudi
authors.initials: R
authors.lastname: Deklerck
authors.forename: Axel
authors.initials: A
authors.lastname: Bossuyt
authors.forename: Johan
authors.initials: J
authors.lastname: de Mey
mesh_terms: D000818:Animals; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D055114:X-Ray Microtomography / Q000379:methods*