DR

Digital Mammography

Digital mammography allows the mammography technologist to view the mammogram immediately on the workstation instead of developing films and waiting for 10 minutes to see an image

"Digital mammography is like digital camera, you can see the image right away rather than wait for the films to be processed, and you can change the contrast right away unlike films" - Dr Raju Wadhwani Department of Imaging PD Hinduja National Hospital

Mammogram remains the best method of early breast cancer detection. However traditional film screen mammography is limited in its ability to detect cancers especially occurring in women with radiographically dense breasts.

Although mammography has proven invaluable in early detection and diagnosis of breast cancer, it is recognised as imperfect test - performance suffering as parenchymal density increases. Improving the performance limitations of mammography in dense breast tissue proves technically challenging. Thus, attention turned towards the development of digital platforms that would improve dynamic range of contrast especially in dense breast tissue.

The Beginning

The advent of all field solid state digital detectors made digital mammography a reality and transition from analog to digital platform as an opportunity to improve efficacy of mammography.

Digital mammography takes an electronic image of the breast allowing the data to be stored on a computer and enhanced, magnified or manipulated for further evaluation. Film mammogram uses film to capture and display the image of the breast. On the computer, radiologist can closely examine the images by zooming in, adjusting image brightness or changing the image contrast making all areas of the breast easier to see. Digital image can be electronically sent to other sites for examination (tele-mammography).

Digital mammogram system use indirect and direct conversion methods. Indirect ones use two-step process for X-ray detection. The scintillator absorbs the X-rays and generates light scintillations. The light scintillation is then detected by array of photo detectors. However, these systems suffer from resolution degradation. Direct conversion digital detectors, X-rays are absorbed and electrical signals are created in one step. These systems use amorphous selenium which is ideal material because it has high X-ray absorption efficiency and high intrinsic resolution.

Great Alternative to Films

Digital mammography is like digital camera, you can see the image right away rather than wait for the films to be processed, and you can change the contrast right away unlike films.

Digital mammography allows the mammography technologist to view the mammogram immediately on the workstation instead of developing films and waiting for 10 minutes to see an image.

Digital mammogram offers advantages over film screen mammography in improved ease of image access, transmission, retrieval and storage. There is lower average radiation dose without compromise in diagnostic accuracy. The recall rate from screening (needing to return for addition diagnostic mammograms after screening mammograms) are lesser with digital - i.e. fewer women needed to return for extra views - this is probably due to ability of the radiologist to magnify an image and change contrast with digital imaging. Interventional procedures are much faster with digital machines.

There is improved contrast between dense and non-dense breast tissue in digital mammogram thus enhancing the diagnostic accuracy. The acquisition time is faster i.e. less than a minute and examination time is shorter (half that of film based mammography).

The technical developments in digital mammography have led to sharp digital images with better contrast and low radiation dose to the patient. This is due to the digital detector, new grid technology and X-ray tubes and filters. The compression paddle technology is new which gives more uniform compression and exposure with improved patient comfort.

Huge Benefits

One of the key benefits of digital imaging is immediate access to patient information. Technologists don't have to leave their patient's side to check film or confirm with radiologist. Breast imaging studies can be recalled at a moment's notice, reducing patient wait time and anxiety. Once mammographic view is taken it is viewed on the acquisition console in 10 - 30 sec. The diagnostic workstation address the radiologist's requirements for the best diagnostic tools for interpreting breast images with advanced protocols for screening and diagnostic studies. Integrated computer sided detection functionality quickly and efficiently displays areas that may warrant closer attention or second review.

Digital Mammography optimises connectivity and has integrated storage for rapid retrieval of images for review and comparison. Digital mammography workstation is DICOM complaint making it easy to share information with PACS.

According to recent DMIST or Digital Mammographic Imaging Screening Trial, digital mammogram scores over film screen mammogram in women with dense breasts, women under age of 50 and pre-menopausal women. This trial was sponsored by American College of Radiology Imaging Network (ACRIN) involved 50,000 asymptomatic women who presented for screening mammogram at 33 sites in the US and Canada.

One particularly exciting application combines image processing with artificial intelligence algorithms to produce computer aided diagnosis. These so-called CAD systems can act as a second reader for radiologists. The system examines digitised film mammograms for evidence of suspicious masses or micro-calcifications. After reading the mammogram, the radiologist can display the computer findings and use these to double check their findings.

Biopsy has Become very Simple

Digital stereotactic biopsy has become a straight forward procedure performed in a time saving and at the same time outstandingly precise manner. Digital stereotactic biopsy system reduces working effort for biopsy because everything is controlled through a single workstation and runs automatically. The biopsy examination user interface at the acquisition workstation is automatically activated as soon as the biopsy unit is attached to the system. There is automated workflow with less work steps. Both vertical and lateral access to lesions is possible for lesions at difficult locations. It can perform all types of biopsy i.e. vacuum core, fine and localisation biopsy.

Advanced applications of Digital mammography.

• Contrast enhanced mammography.
• Breast tomosynthesis.

Tomosynthesis is a 3-D radiographic technique that allows reviews of unique planes of interest in isolation from adjacent planes to minimise effects of structure overlap. In breast tomosynthesis, the digital mammography platform is modified to allow the X-ray tube to travel through a prescribed arc of excursion acquiring a fixed number of discrete projection images while breast remains in compression. The individual projection images are extremely low in dose, so the composite dose incurred during a tomosynthesis acquisition is comparable to single view mammogram.

Clinical Applications

• Superior visibility of masses and architectural distortion.
• Marginal analysis of mass lesions is better.
• Reduce the recall rate of mammography screening.

Image data from two or more views of the breast can be combined to produce 3- D images of the breast. Such techniques offer the opportunity to remove clutter of overlying tissues and reduce false positives by 49 per cent.

Death rates from breast cancer have been declining since 1990 and these decreases are believed to be the result of part due to earlier detection and improved treatment. Digital mammography thus plays an important role in earlier detection of breast cancer especially in women with dense breasts where film screening mammogram is a major limitation.

Unlimited Potential

Digital mammography is not just about adding a new technology; it is about creating a future of unlimited potential. Better healthier future for women and productive future made possible by information integration and future platform for ongoing innovation.

Transition from analog to digital platform should not be seen as an end point but rather as a necessary foundation to enable the development of addition radiographic imaging techniques of the breast.

dr_rwadhwani@hindujahospital.com