Ask Anne: Changing Mammography Techniques for Digital Technology
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One of the most common questions I receive for my “Ask Anne” feature here on Everything Rad is, “How will I need to adapt my positioning techniques when I move from analog imaging to digital?”
This month, Brigitte Hurtienne, chief radiographer at the Mammography Reference Center at the University Clinic in Munster, Germany, offered to share her experience:
Art of positioning
Whether using an analog or digital mammography system, the art of positioning is very similar. But digital imaging has advantages: the dynamic range afforded by digital mammography (16,000:1) is far superior to analog imaging (100:1).
The optical densities (OD) displayed on film are limited to 100 shades of gray, not all of which can be displayed at any time because the OD of the film is limited and fixed, and is determined by the x-ray exposure technique.
In a digital image the dynamic range depends on the computer’s window/level attribute and the radiologist can
manipulate a digital image through 16,000 shades of white-gray–black.
So, in the digital technique, we often can make more skin wrinkles visible. Skin wrinkles may produce pseudoarchitectural distortions or may obscure surrounding structures.
Good positioning, at least for the mediolateral oblique view without skin wrinkles, is, therefore, very important. If hand pressure is discontinued before sufficient compression is applied, it will result in a poor separation of tissue and a downward-sloping of the breast contour, sometimes creating a skinfold in the inframammary ridge. An inadequate positioning technique in this region using suitable picture processing algorithms can lead to a loss of information.
Careful hand work – smoothing out the breast with the entire palm of the hand forwards and upwards, support with the ball of the thumb during compression, and smoothing out the inframammary ridge – prevent a sagging of the breast to the caudal and a wrinkle-free presentation of this region. Insufficient picture processing can be avoided in most cases.
There are also some differences in the types of artifacts that are seen in analog vs. digital imaging. In the analog world, we differ between film and screen handling artifacts and positioning artifacts. These artifacts are more common and can occur by improper handling of films and screens. Improper handling of films and screens could be exposures from creases, dirty screens, dust, scratches or from the object table, grid and static artifacts.
Some artifacts may be seen on both analog and digital systems, such as patient related artifacts (e.g. motion artifacts) and hardware related artifacts (e.g. x-ray tube filter defects and antiscatter grid defects).
Especially in the digital world, there are artifacts due to software processing errors or digital detector deficiencies. Pixel artifacts such as dead pixels or groups of dead pixels and dead lines can be caused by an imperfect detector.
Dust in the compression paddle, a not properly adjusted exposure, and problems with the image processing to a high noise level are further sources of an improper result. Problems with the reconstruction at the workstation can be the result of an improper display or problem with the sending of the images to the workstation.
Have you adjusted your technique for digital? What advice do you have for other radiographers or mammographers?