DBT offers accurate diagnosis

A mammogram that produces 3D digital images, making tumours easier to see in dense breast tissue, could be launched by a UK company next year.

London-based Dexela is developing the mammography system based on a technology called digital breast tomosynthesis (DBT), which acquires, processes and visualises data from 3D X-ray images.

The company claims the technology could sigificantly reduce false negatives and false positives, thus detecting cancer sooner, especially in younger women.

DBT units move an X-ray tube in an arc around a patient’s breast and take multiple pictures from many angles. The pictures are then sent to a computer where they are assembled to produce clear, highly focused 3D images throughout the breast.

Dexela is one of four companies, also including Siemens Medical Solutions, GE Healthcare and Hologic/Lorad of the US, racing to commercialise DBT. While their systems are similar, Dexela claims its DBT technique produces a much clearer 3D picture.

The system uses an advanced digital X-ray detector and software, and distributes radiation dosage in a different way.

The CCD (charge-coupled device) and the CMOS (complimentary metal-oxide semiconductor) are effective devices for turning light into an electric charge, but CMOS sensors are much cheaper to manufacture than CCD sensors.

Dexela says it is the only company that uses a CCD-based digital detector to capture images for DBT. It plans to use a CMOS-based digital detector when its product is commercialised.

Edward Bullard, Dexela founder, claimed its X-ray detector, which will be based on an array of tiled CMOS sensors, will be low noise and take images 30 times faster than amorphous silicon flat-panel detectors.

‘It will be the largest CMOS image sensor ever commercially deployed,’ he said, adding that his company plans to demonstrate a prototype this summer.

Unlike conventional mammograms that take only one picture across the entire breast, DBT scans require multiple images from various angles. Dexela’s own units, for example, capture 11 images.

Bullard said the challenge for all DBT system developers is to capture multiple images using the same amount of radiation that a conventional mammogram would use.

The problem cannot be solved by simply using the same amount of radiation and dividing it evenly for each image. This, he said, creates a poor signal-to-noise ratio that affects image quality.

He claims Dexela has a patented method that escapes this problem. The system distributes radiation doses unevenly, using less radiation on wide-angle shots, and this is claimed to produce better overall image quality.

‘What the other guys do is naive tomosynthesis, where they just spread the radiation dose out equally,’ he claimed.

Bullard believes Dexela’s radiation dosing method, combined with its image reconstruction software, makes his company’s 3D capabilities significantly more advanced than alternative techniques.

‘Most other companies use [computed tomography] CT-style algorithms for image processing,’ he said. ‘We’re using a more modern type of mathematical approach.’

He compared Dexela’s algorithmic approach to that used in positron emission tomograph — a nuclear medicine technique for producing 3D images of functional processes in the body.

The commercial availability of such a system will be welcome news as DBT is seen as one of the most promising alternatives to conventional mammography. While scans from conventional mammography are usually effective, they have drawbacks.

For example, the compression of the breast that is required during a mammogram can cause overlapping of tissue. A tumour can be hidden in the overlapping tissue and not show up on the mammogram.

Also, mammograms take only one picture across the entire breast, from top to bottom and side to side, and therefore the scans can miss tumours hidden in dense tissue.

Clinical trials conducted in the US indicate that using 3D DBT imaging can avoid these drawbacks and reduce the risk of missing cancerous tumours.

Dexela has formed a partnership with digital mammography manufacturer IMS, based in Bologna, Italy, to produce DBT units for the worldwide medical market next year.

According to Bullard, the system will be marketed by IMS globally under their brand.

Last summer the company raised more than £2.6m through the issue of shares. So far, the company has raised more than £4.7m via two funding rounds and grants.

Siobhan Wagner