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
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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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.
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.
Ok, I’m going to try to give a real ELI5 answer.
Imagine having a bag full of marbles and you are looking for one with sparkles instead of the colored waves. When you look inside the bag, they’re all jumbled together, so you can’t really see the one you are looking for. If you take that bag and put it on a table, everything in the bag will spread out, allowing you to look easier. Still, some are clumped on top of each other. Now, if you were able to then use your hand to separate them out any marbles that are still on top of each other, it would be a lot easier. This helps explain the compression.
Depending on how well lighted you room is will also allow you find it even easier. Too little light, and you can’t make out the difference. Too much light, and it can be blinding. You want just the right light level to help you look for something. This is the ELI5 for the x-rays used for the test.
I’m a breast radiologist. The breast is compressed for a few reasons:
1- The thinner the breast is, the lower the dose of radiation (which is really low to begin with for a mammo).
2- Compression spreads out breast tissue, making the mammo easier for us to interpret and also making suspicious findings more conspicuous. For bone x rays, compression won’t do anything since you can’t really compress bone.
3. Compression helps us have more uniform and consistent images from year to year, making comparison to prior exams easier and new findings more obvious.
Men do get mammos but generally only if they feel a lump or have bloody nipple discharge. Male breast cancer is very rare, which makes it so screening for it is not cost effective in the general population.
There are several reasons for compression. The compression spreads out the glandular (dense) tissue of the breast. so that it is no longer superimposed over itself. When glandular tissue is superimposed it can resemble a mass or hide a mass or microcalcifications (indications of possible cancer before there is a visible mass). Masses maintain their shape when compressed, breast tissue changes shape.
The compression also reduces motion artifacts. It keeps the breast from moving. It takes very little motion to cause a blurry mammogram. This is also why you hold your breath. Radiologists need to see fine details and motion blurs those details.
Compression also reduces the amount of radiation that is used during the mammogram. The thicker the body part, the more radiation is used.
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kinda like pounding a chicken or butterflying, uniform thickness makes it cook evenly, or as the analogy translates, so the mass differential doesn’t throw a false positive.
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