Study population and image preparation
Study population consisted of subgroup of women in the POSH study whose diagnostic analogue images (mammogram films and ultrasound images printed either on films or thermal paper) were available for both digitisation and film-reading by our radiologist. Diagnostic images of eligible women from 29 hospitals were sent to our hospital and digitized. Analogue mammograms and ultrasound films were digitized by an Array laser 2905 film digitizer (Array Corporation USA, Hampton, NH, USA) with following setting; output format: dicom, resolution: 50 micro millimeter, optical density: 4.7.
Diagnostic images were then sent to our radiologist for analogue film-based review. Digitized electronic image data were converted from dicom to bitmap, anonymised, and sent to the study IT centre (Fig.1).
Web-based image reviewing system “ImageBox”
At study IT centre, digitized images were securely uploaded to the web-based review system “ImageBox”. This system is developed to overcome the logistical challenge of assembling images from many hospitals and involving many radiologists in the review. This system has following features;
1. An image viewer showing 4-view mammograms and ultrasound images if available.
2. An image viewer is linked with a BIRADS-based scoring sheet database.
3. Authorized readers can access anonymised images from anywhere via internet.
4. Unread cases are offered in a random order.
(Fig.1 and 2)
Images were accessed and reviewed by a consultant radiologist using web-based scoring system, which were based on BIRADS(2,3). For mammogram, each of the right and left breast was assessed using 5-grade categorical system as follows;
Category 1 - Negative
Category 2 - Benign findings
Category 3 - Probably benign
Category 4 - Suspicious abnormality
Category 5 - Highly suggestive of malignancy
In addition, detailed assessment was made when a lesion (mass and/or calcification and/or asymmetry) was identified.
In case of a mass, margin of the mass was classified into 5 categories (microlobulated, obscured, indistinct, spiculated, or circumscribed). Size, shape, density and location of the mass were also recorded.
In case of calcification, type of calcification is classified into a simplified 4-grade categorical system (1.Benign, 2.Punctate/Powder, 3.Granular/Crushed stone 4.Casting/linear).
Film-based review
The same radiologist performed film-based review using the same classification system. Web-based review was performed more than three months after film based review.