Guidance

Breast screening: digital breast tomosynthesis

Updated 4 May 2023

Tomosynthesis in breast screening assessment

Tomosynthesis is an advanced form of mammography. It produces three-dimensional (3D) images using a low-dose x-ray system.

Tomosynthesis has been approved for use in the NHS breast screening programme (BSP) as an optional extra tool in the assessment of screen detected soft tissue breast abnormalities.

It must not be used for routine screening outside of a clinical trial approved by the breast screening research advisory committee (RAC).

There are minimum training requirements for breast mammographers (radiographers and assistant practitioners) who wish to use tomosynthesis in the screening assessment clinic.

There are also training requirements for those reporting images, before they can start to report tomosynthesis images.

Additional guidance includes routine quality control tests for breast tomosynthesis for radiographers and physicists.

Only take tomosynthesis images of the affected breast. It should not be routinely performed for a clinical recall where the imaging is normal. Use 2-view tomosynthesis in such cases.

The responsible assessor should indicate where tomosynthesis is to be used within assessment and what images are needed.

The routine use of additional views is not needed if tomosynthesis images are taken, although they may be helpful in some instances.

Avoid the combination option (having a standard digital mammogram and tomosynthesis scan in the same compression) where possible. This avoids the woman having a higher radiation dose than is necessary.

Synthetic images (2D images created from the 3D tomosynthesis image stack) are often routinely produced and their review may also be helpful. However, these should never be viewed in isolation.

The 2 standard tomosynthesis views – cranio-caudal (CC) and medio-lateral oblique (MLO) – most effectively demonstrate the mammographic abnormality being assessed. For instance, the CC view may be extended to better demonstrate the medial or lateral aspect of the breast.

Use 2-view tomosynthesis for patients with implants that need further imaging. Perform the 2 views that best demonstrate the lesion. This is often the CC Eklund view and the MLO view.

Tomosynthesis biopsy may be available on some systems. This can improve the accuracy of lesion localisation and reduce examination times relative to stereotactic biopsies. Tomosynthesis guided biopsy may be needed for certain lesions. Services should have access to tomosynthesis biopsy where this is not available in-house.

Where tomosynthesis is available, its use in the assessment of mammographic abnormalities is described below.

Masses and asymmetry

If additional mammography is required in the work up of masses and asymmetric densities, tomosynthesis is suggested in the first instance to:

• further characterise the lesion
• assess margins
• determine the level of suspicion

Ill-defined soft tissue masses without architectural distortion or microcalcification may be very inconspicuous on tomosynthesis.

An ultrasound is still needed when using tomosynthesis, even if the images appear normal.

Persistent indeterminate or concerning mammographic abnormalities with no ultrasound correlate must undergo an x-ray guided biopsy, unless the mammographic features are definitively benign.

Architectural distortion

Tomosynthesis is a powerful tool for viewing and evaluating potential architectural distortions. It can help readers become more confident in finding them.

Tomosynthesis is particularly useful to assess architectural distortion versus composite glandular tissue.

An ultrasound is still needed when using tomosynthesis, even if the images appear normal.

As with mass lesions, a persistent architectural distortion with no ultrasound correlate will need to undergo an x-ray guided biopsy.

Microcalcification

Traditional supplementary mammographic views for microcalcifications (lateral and magnification views) remain the standard of care. Identification of microcalcifications with digital breast tomosynthesis (DBT) continues to be a source of debate.

A tomosynthesis lateral view may be of additional value where there is suspicion of an underlying soft tissue density.

Ultrasound is still suggested for the assessment of microcalcifications unless additional imaging shows definitively benign features.

Viewing tomosynthesis images

Typically, tomosynthesis images are viewed in planes separated by 0.5mm or 1mm. The resolution between planes in focus will depend on the system technology and reconstruction algorithm.

Unlike digital mammography, tomosynthesis images can be reconstructed and display in quite different ways.

There are several options that can be viewed instead of, or with, the tomosynthesis planes.

Synthetic 2D image

It can be useful to view a 2D image, and a synthetic image can be created from the planes. Typically, the relevant features in each plane are enhanced using pattern recognition or artificial intelligence techniques.

Slabs

Thicker planes (slabs) can be created with effective thickness from 5mm to 10mm. This results in fewer images and can be useful for viewing diffuse lesions, such as calcification clusters.

Slabs can be created using standard reconstruction techniques, or combining planes in the same way as for synthetic 2D images

Angled views

Synthetic 2D images are reconstructed parallel to the detector, but they can be created at an angle to provide a different view on tomosynthesis images.

Timely and robust review of tomosynthesis images is required during assessment. This may involve:

• upgrades to local IT infrastructure
• improved picture archiving and communication system (PACS) connectivity
• sufficient bandwidth to transfer images
• use of dedicated workstations with enough storage
• a monitor that can rapidly change the display of the planes
• software for displaying tomosynthesis images
• additional image storage, as tomosynthesis images are larger than 2D images
• ability to retrieve previous tomosynthesis studies (this may be faster with smaller images such as slabs)

Benefits

Unexpected multifocal disease may be found on tomosynthesis images. A full assessment is needed for any additional incidental lesions identified on tomosynthesis as set out in the clinical guidance for breast screening assessment.

Studies have found that tomosynthesis can aid interpretation in dense breasts. It may help to localise lesions which are seen initially on a single projection.

There is evidence of the potential impact of tomosynthesis to reduce the biopsy rate of normal or benign densities.

Challenges

The introduction of tomosynthesis into the assessment process involves a steep learning curve for the individual.

Breast Tomosynthesis: Clinical Evidence suggests that examination and interpretation times are typically longer than for a standard set of images. With experience, the addition of tomosynthesis to the assessment process can improve overall efficiency.

Tomosynthesis images are larger in size than standard mammographic images, which can present IT challenges for storing images.

Training requirements

Many breast screening services now have practical experience of DBT. This is because they use it in screening assessment, the symptomatic service and/or as a screening tool in the PROSPECTS trial.

As a result, it is no longer a mandatory requirement for staff using this modality to attend an NHS BSP training course in tomosynthesis at one of the national training centres. However, for those staff with less experience of tomosynthesis, there may be opportunities for:

• in-house cascade training
• ‘buddying up’ with a more experienced colleague at a neighbouring trust

More formal tomosynthesis training courses are available at the national training centres if these 2 options are not available.

Staff interpreting DBT

Before breast radiologists, breast clinicians, advanced and consultant practitioners undertake clinical use and reporting on images, there is a mandatory requirement to complete modules on:

• DBT (physics and technique)
• interpretation of DBT

The e-learning programmes are available via the e-Learning for Health (e-LfH) platform.

Image review of a minimum of 60 cases (preferably inclusive of all vendors) is crucial to learning the technique. Of these, 40 cases should be assessed by the individual working independently, and all 60 cases should be double reported with one reader experienced in breast tomosynthesis. A set of training images are being produced and will be made accessible later in 2023. Services will be informed once available.

It is advisable to continue to double report images until you are confident the practitioner has achieved full competence in tomosynthesis reporting. This should be confirmed by the director of breast screening or lead radiologist.

There is a template for reporting images and sharing with the experienced second reader. This may be helpful for reflective practice and provides evidence of performance at appraisal.

We encourage services to initially collect a selection of tomosynthesis images for use in reflective practice and self-directed learning. These should contain examples of distortion, masses and calcification, together with some normal images.

Strategies to aid training

We encourage individuals new to tomosynthesis to:

• seek second opinions from colleagues experienced in reporting tomosynthesis
• seek second opinions from colleagues in another unit using the same equipment manufacturer (imaging has differing appearances based on the manufacturer of the equipment)
• understand the artefacts present with tomosynthesis
• understand where tomosynthesis biopsies are undertaken and the referral process (via a standard operating procedure) if not performed in-house

Staff performing DBT (mammographers)

Where services have no prior knowledge or experience with DBT, there may be opportunities for ‘buddying up’ with more experienced colleagues in neighbouring trusts for those less experienced.

Training should include:

• vendor-specific training provided by the manufacturer
• advice on ‘how to use’ tomosynthesis, which should be cascaded internally by those familiar and experienced with the equipment
• information on routine QC and tolerances and use of phantoms
• understanding the artefacts which commonly appear in tomosynthesis images
• how to retrieve tomosynthesis images from the PACS
• understanding the technology and being able to respond to women’s information needs