I’ve never had a mammogram so I actually don’t know how it works. Only heard the jokes about how they squish your breasts and that it hurts. We were talking about how men can have breast cancer so why don’t they get mammograms? (Maybe they do). Then we laughed as we pretended to slip a tiny man boob into an imaginary mammogram machine (that I’ve never seen).
So I thought they can do X-rays and stuff. Why do they *have* to torture you to get the results. Did some sick doctor invent the machine, laughing the whole time about how evil and unnecessary it is? /s
Biology tag? Idk.
In: Biology
X-rays are partially absorbed as they travel through flesh. They are slightly more absorbed in some lumps, but it’s not the “broken bone” sort of X-ray you might be thinking of. To get enough contrast to spot lumps, the X-ray beam needs to be tuned to the amount of flesh it’s passing through. That’s made a lot simpler by squishing the breast into a slab of uniform-ish thickness. Since the natural shape is more hemispherical, some force is required. The breast is also well instrumented with nerves, so the force can be painful.
The mammogram is a ‘low energy’ x-ray, which means everything has to be a lot closer for it to work. In the case of a mammogram you are looking for denser tissues which are pretty hard to pick up on an x-ray. If you look at a chest film you can make out the heart but not a huge amount of intricate detail of the heart, you need more advanced imaging for that. The heart is a nice dense muscle, a mammogram is looking for tiny dense tissue patches.
I am not in love with mammograms as a diagnostic test. Statistically they have an alarming rate of false positives and false negatives. I think they removed the yearly mammogram requirement unless you are in a risky group because women would get a normal mammogram (false negative or not) and feel ‘safe’ for the next year. Well, that is a problem because you may start developing cancer a month after your mammogram and unless you are doing really close self-examinations you wont detect that new cancer for 11 months. There are cancer screening blood tests that I think are better, they can detect the possibility of any cancer. If that pops abnormal then go looking with radiation. That is how they treat my mother now, a 5-year (stage 2 b) breast cancer survivor.
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There’s physics behind it.
When we take an X Ray, we place a part of the body between two sides of a device – one shoots a ton of x-ray particles through the tissue, the other side detects how many x-rays pass through the tissue. When the x-ray particles are shot through the tissue, three things can happen:
1) absorption: they get absorbed by our body
2) transmission: they pass through our body completely
3) scattering: they can hit something along their trajectory and change angle, but still pass through the body.
The reason a mammogram works is because cancer tissue and other dense types of tissue absorb different amounts of particles from normal tissue, so when we see how many pass through at the detector we can see whether there’s a tumor and how big it is.
The scattering part is a confounding factor though: we mainly just want to look at the difference between 1 and 2. If some of the particles are changing direction, our imaging can trick us, because the x-rays that go through the cancer tissue can look like they came from normal tissue at the detector (or vice versa).
To minimize that problem, we have to shorten the distance between the two sides of the imaging device. So when the particles scatter and change angle, they travel as little as possible horizontally and we can be more confident that they came from the correct location/tissue type in the body. That means compressing the tissue if possible.
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Doctors of Reddit: why is MRI not used for these kinds of diagnostics. Is it cost or performance?
In addition to what everyone else has said about uniform thickness, the compression also helps spread out the tissue and separate it from the body. An mammogram is a 2d image of a 3d structure. Compressing the breast helps with tissue being superimposed. Mammograms also include tissue from the armpit area where some lymph nodes are. By pulling that tissue away from the body and holding it in place, it’s able to be imaged. Compression also helps with motion. It’s very important to have no motion which can blur the radiographs. A slight movement could ruin the image, requiring a retake and thus basically doubling the dose.
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