  Purpose: The goal of this study is to show the advantage of a collaborative
work in the annotation and evaluation of prostate cancer tissues from
T2-weighted MRI compared to the commonly used double blind evaluation.
  Methods: The variability of medical findings focused on the prostate gland
(central gland, peripheral and tumoural zones) by two independent experts was
firstly evaluated, and secondly compared with a consensus of these two experts.
Using a prostate MRI database, experts drew regions of interest (ROIs)
corresponding to healthy prostate (peripheral and central zones) and cancer
using a semi-automated tool. One of the experts then drew the ROI with
knowledge of the other expert's ROI.
  Results: The surface area of each ROI as the Hausdorff distance and the Dice
coefficient for each contour were evaluated between the different experiments,
taking the drawing of the second expert as the reference. The results showed
that the significant differences between the two experts became non-significant
with a collaborative work.
  Conclusions: This study shows that collaborative work with a dedicated tool
allows a better consensus between expertise than using a double blind
evaluation. Although we show this for prostate cancer evaluation in T2-weighted
MRI, the results of this research can be extrapolated to other diseases and
kind of medical images.
