A Look at Tomosynthesis

Breast tomosynthesis is currently being researched as a method of three-dimensional imaging, via the acquisition of breast images taken at multiple angles. The tomosynthesis scan is reconstructed to create slices of the breast, similar to a CT scan. Preliminary research is indicating that breast tomosynthesis may reduce false negative findings, as it may provide better visualization of cancer in dense breasts. False negative findings are common in dense and overlying breast tissue because both scenarios obscure lesions.

The technical requirements for tomosynthesis are available with full-field digital mammography (FFDM). However, breast tomosynthesis is not commercially available; the obstacles of its availability are divided into three categories: legal, financial and technical.

Legal considerations

• Tomosynthesis requires FDA approval. This process typically includes a two-year period of data collection and a minimum six month approval period.
• If tomosynthesis is used for breast cancer screening, it will require Mammography Quality Standard Act (MQSA) accreditation.
• To date, the FDA has not approved tomosynthesis from any vendor.

Financial considerations

• FDA approval is required for the establishment of reimbursement policies.
• Reimbursement for tomosynthesis depends on its effectiveness in breast cancer detection.
• Insurance companies will encourage methods which reduce callback rates.

• The projected cost of tomosynthesis systems are an additional 50-60% compared to the current FFDM systems.
• Tomosynthesis will require 20 times more data storage capacity than FFDM.

Technical considerations

Tomosynthesis implementation varies per vendor. The following characteristics of implementation should be evaluated:

Tube selection

During a tomosynthesis scan, a number of exposures are released. As a result, we believe the requirements of the X-ray tube should include:

• High heat dissipation

• Low dose

• High current

Detector

Tomosynthesis imaging consists of multiple images acquired with minimum radiation dose. To counter these constraints, an image receptor should have high quantum efficiency and image throughput capabilities. This requires the following features:

• High DQE at low exposure

• Elevated reading dynamics

• Superior spatial resolution and MTF

• Optimal performance at low dose

Siemens believes selenium-based image receptors will be the best for breast tomosynthesis systems because they fulfill the criteria above.

Reconstruction algorithms

A tomosynthesis scan collects a large set of data and optimizes this information before viewing, using sophisticated image algorithms. Throughput without sacrificing quality is a requirement in a cancer screening environment. As a result, reconstruction time of a scan is crucial for making tomosynthesis a viable breast cancer screening tool.

Tomosynthesis presentation/viewing station

Tomosynthesis scans contain a large collection of data; therefore, a viewing station that presents this data easily is fundamental. If a user interface is complicated and counter-intuitive, its complexity could exponentially increase the time required to review a study. To effectively make comparisons, 2D mammography images and tomosynthesis studies must be displayed simultaneously. A viewing station’s inability to fulfill these requirements can negatively impact a radiologist’s diagnosis and throughput.

Angulations

For tomosynthesis, the angular range of the system is directly related to depth resolution. If an angle measures 0 degrees, the result is a 2D mammography image (no depth resolution). If an angle measures 360 degrees, 3D information similar to that of CT and MR is produced. Tomosynthesis developers are reviewing angulation ranges of 15 degrees to 50 degrees in an effort to discover the most effective range to implement breast tomosynthesis. The goal is to improve depth resolution while at the same time maintaining an acceptable level of throughput.

Benefits

Breast tomosynthesis is expected to provide an alternative to visualize lesions and improve differentiation between overlapping tissues using 3D imaging. Based on preliminary studies of this technology, breast cancer detection via tomosynthesis will potentially reduce recall rates, the number of biopsies and radiation dose. Simultaneously, it is also expected to improve cancer detection and throughput. As a result, breast tomosynthesis will likely be considered as both a diagnostic and even a breast cancer screening tool in the foreseeable future.

Caution: Investigational device. Limited by US federal law to investigational use. The information about digital breast tomosynthesis is preliminary. The product is under development and not commercially available in the US; and its future availability cannot be ensured.