Digital Public Defence: Bjørn Helge Østerås

MSc Bjørn Helge Østerås at Institute of Clinical Medicine will be defending the thesis “Automatic volumetric breast density in mammography screening using digital mammography and digital breast tomosynthesis” for the degree of PhD (Philosophiae Doctor).

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The public defence will be held as a video conference over Zoom.

The defence will follow regular procedure as far as possible, hence it will be open to the public and the audience can ask ex auditorio questions when invited to do so.

Click here to participate in the public defence

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Digital Trial Lecture – time and place

See Digital Trial Lecture.

Adjudication committee

  • First opponent: Senior Consultant Edward Azavedo, Karolinska Institutet, Sweden
  • Second opponent: Professor Mats Danielson, KTH Royal Institue of Technology, Sweden
  • Third member and chair of the evaluation committee: Lecturer Ellen Schlichting, University of Oslo

Chair of the Defence

Professor Emeritus Jarl Åsbjørn Jakobsen, University of Oslo

Principal Supervisor

 Professor Anne Cathrine Trægde Martinsen, OsloMet


Mammography screening using conventional digital mammography (DM) has lower sensitivity and specificity in women with dense compared to non-dense breasts, as breast tissue can mask or imitate cancer. This has led to consideration of personalized screening (adjunctive ultrasound or MRI) in some countries. Digital breast tomosynthesis (DBT) is gradually replacing DM, enabling reconstruction pseudo 3D images. This can reduce the issue of masking but might come at a cost of increased radiation dose. Radiologists assess breast density using a subjective density scale. Recently, software has become available for objective and automatic assessment of breast density.

The first aim of this study was to compare subjective and software-based breast density assessment through a reader study using women sampled from a large mammography screening trial (Oslo Tomosynthesis Screening Trial - OTST). The second aim was to compare the diagnostic performance and radiation dose of DBT vs. DM in subgroups of breast density in OTST.

Subjective BI-RADS density assessment resulted in considerable inter-observer variability. About 40 % of women were classified as both dense and non-dense by individual radiologists. Automatic assessment provide breast density estimates with high accuracy compared to radiologist assessment, with the added benefit of being objective.

DBT improved the true positive rate for women of all breast densities. The false positive rate was significantly decreased for all except for women with extremely dense breasts, where the false positive rate was comparable. The DBT examination resulted in a minor increase in radiation exposure both for women with non-dense and dense breast.

Overall, automatic breast density assessment would ensure objective density assessment, removing the inter-observer variability of current radiologist assessment. Introducing DBT would benefit women with all breast densities at a minor increase of radiation dose.

Additional information

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Published May 18, 2020 11:18 AM - Last modified June 4, 2020 10:19 AM