The definition of blurring or un-sharpness on mammography images is: the amount of lateral border spread along the edges of our image. A distance of border spread that is visually acute is unacceptable.
What causes our images to look blurry? Why do the x-rays sometimes look indistinct? What can we do, where can we seek an answer?
There are three distinct causes of mammography blurring:
- Motion
- Geometric
- Receptor
Motion:
To control motion on our images we simply must do all we can to prevent the subject from moving during the exposure.
To control motion we need the correct amount and application of compression. The amount of compression depends upon the tolerance of the patient, the size, shape, consistency and habitus of the breast. The breast should be compressed until the edges feel taut and there is no allowable ‘squeezability’ of the breast.
To achieve adequate compression it is essential to prepare the patient. An informed patient that is aware of the reason for compression, the length of time her breast will be compressed, the fact that you will not go past the point of discomfort into real pain is relaxed, in control and more likely to cooperate. Take as much time as you need before the test to explain, demonstrate, empower and inform. It will save time in the long run.
To achieve high contrast images in breast imaging a low kVp is usually implemented. This is generally the best course of action but it also instigates a longer time of exposure to obtain adequate exposure. The length of time of the exposure is critical to the cessation of motion. If for any reason (age, infirmity, palsy, or weakness) your patient will not be prepared to remain still for such a long exposure it is prudent to initiate a higher kVp in order to shorten the exposure time. This is also true for patients with thick, dense impenetrable breast tissue that would engender an extremely long exposure. A sharp image obtained at higher kVp levels is far better than a blurry image obtained with lower kVp levels.
Finally we must employ a proper compression paddle with the following properties:
- A rigid lexan construction
- A 85º - 90º bend @ the chest wall edge
- The leading edge must be parallel to the film edge
- There must be at least a 4cm rise at the chest wall
- It must have a secure locking non-slip attachment to the unit
A Proper Compression Paddle Device:
An Unacceptable Type of Compression Device:
SUMMARY
Blurring is a major cause of error in interpretation of mammography images. It is imperative we understand and address all the causes of this difficulty. Motion is the first in the series on blurred images. Stay tuned for Geometric and Receptor problems.
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