title: Intensity profile based measurement of prostate gold markers influence on 1.5 and 3T diffusion-weighted MR images.
abstract: OBJECTIVE
  In this study the influence of fiducial markers (FMs) on diffusion-weighted (DW) magnetic resonance images was investigated by measuring the intensity variations due to the artefact from the FM image reconstruction.
  
  
  METHODS
  DW- and reference T1W images were acquired of an Agar-gel phantom containing two fixed cylindrical FMs, with a 1.5- and 3T MR scanner. The center of gravity (CoG) positions of the manually segmented FM artefacts (FMA) and the size of FMAs in x-, y- and z direction were measured in the two corresponding image sets, based on the intensity changes caused by the FM reconstruction. Also, a similarity measure, the Dice similarity coefficient (DSC), of the segmented FMAs in the two image sets was calculated.
  
  
  RESULTS
  The mean shift of the CoG of the manually segmented FMAs in the phase encoding (PE) and the two orthogonal directions, respectively, was: 1.5T/3T; 0.3 ± 0.1/0.5 ± 0.3 cm and 1.5T/3T; 0.1 ± 0.1/0.1 ± 0.1 cm. The largest shift was observed in the 3T DW images for FMs aligned with the long axis orthogonal to the PE direction (0.9 ± 0.1 cm). The mean size of the FMA in the PE- and the two orthogonal directions, respectively, was: 1.5T/3T; 1.7 ± 0.5/1.3 ± 0.1 cm, and 1.5T/3T; 0.9 ± 0.3/1.0 ± 0.2 cm. The mean DSC value of the segmented artefact volumes in the DW- vs. T1W images were 21% and 5% for the 1.5- and 3.0T MR scanner, respectively.
  
  
  CONCLUSIONS
  This study has shown that both the size and displacement of the FMAs increase in the PE direction on DW images. The larger shifts were observed for FMs positioned with the long axis orthogonal to the PE direction. Measurements obtained for different b-values gave consistent results.
authors.affiliation: Department of Medical Physics, Aarhus University Hospital, Aarhus, Denmark. susaryla@rm.dk
authors.forename: Susanne
authors.initials: S
authors.lastname: Rylander
authors.forename: Sara
authors.initials: S
authors.lastname: Thörnqvist
authors.forename: Søren
authors.initials: S
authors.lastname: Haack
authors.forename: Erik Morre
authors.initials: EM
authors.lastname: Pedersen
authors.forename: Ludvig Paul
authors.initials: LP
authors.lastname: Muren
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis*; D038524:Diffusion Magnetic Resonance Imaging; D006801:Humans; D008297:Male; D010386:Pelvic Neoplasms / Q000175:diagnosis* / Q000628:therapy; D019047:Phantoms, Imaging; D011379:Prognosis; D011471:Prostatic Neoplasms / Q000175:diagnosis* / Q000628:therapy
chemical_list: D014408:Biomarkers, Tumor