I have been in the medical field for over 5 years now and I still can’t get the hang of the following scans and what is each one used for. Like, I KNOW what they do but they’re all the same to me. What is an MRI, CT, Ultrasound, X-Ray, etc. etc. and what makes them different for their specific purposes? At work, I see sometimes radiological facilities want Mammograms with an US and the report says the same thing or sometimes insurance companies want an X-Ray to be done before covering an MRI but no sign of broken bone. I’m just curious lol
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Ultrasounds use sound. But sound you cannot hear. They put an emitter up against the person’s body, which sends out “pings” of sound, which bounce off the stuff in the person’s body. The emitter then also has a receiver which hears the sounds, and uses that to figure out what is there. Some tech turns that into an image. It is basically echolocation.
X-Rays are a type of light. But they pass through more stuff than visible light, including skin, muscle and so on, but they don’t pass through bone. An X-ray machine shines a load of x-rays at a target body part, and then there is a screen on the other side. The screen changes colour where X-rays hit it, but not where they don’t – leaving a shadow in the shape of any bones (or other things that block X-rays) in the target area.
CT scanners are fancy X-ray machines. It stands for “computed tomography” – they take a whole load of X-rays from a load of different angles, and then the computer does some fancy stuff to turn it into a nice 3D model of what they are looking at.
MRIs (nuclear magnetic resonance imaging) use powerful magnetic fields and radio waves, and some fancy physics, to take pictures of water (or a contrast material put into the patient), and from that build up a picture of the insides of people.
In terms of why they would use one over the other, ultrasounds are quick, easy, and produce live images, so are great at looking for things right now. X-rays are good for looking at bones, but limited for looking at other things, and X-rays are harmful in large quantities (too many x-rays can cause cancer). CT scans have the same downsides as x-rays, but produce far better pictures. However they take longer and are more expensive (as they are a load of x-rays combined together). MRIs are great at showing the inside of people and are completely safe (unlike X-rays) unless there is anything potentially magnetic inside them – the strong magnetic fields can be very dangerous. They’re also loud, and can be a bit cramped for the patient, and the machines themselves are very complicated and expensive.
I can’t really help with the medical advantages (or why insurance companies would care) – but that is a rough idea of the physics. However, I can see someone wanting an X-ray before an MRI as the X-ray would show up any metal in the patient, which might cause serious problems (including killing them) in the MRI – particularly if they don’t have a full medical history of the patient, or if their may be splinters or fragments of something (like bullets) in them. Plus for the insurance companies I imagine they want the cheaper (if more harmful) option first.
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*Edit: I forgot about PET scans*
PET scanners are kind of complicated; for a PET scan the patient is injected with a radioactive drug. This travels through the body naturally, and different drugs will be used depending on where they want it to go. The radioactive nuclei decay (randomly, as normal radioactive decay), usually by a thing called “beta plus decay”, which emits a positron (hence *positron* *emission* tomography). Positrons are anti-matter; anti-versions of electrons. When emitted in the middle of a person they quickly hit one of the many regular electrons nearby, annihilate, and give off two gamma rays, which are detected by scanners around the patient. These can provide a nice 3d image of stuff inside the person – wherever the drug has gathered (often used for cancers, by finding drugs that will cluster around cancerous cells).
PET scans can be even more expensive than MRIs (as you also need the fancy radioactive drugs, as well as the fancy scanner and computers to put all the images together). They are also a bit more dangerous (other than for things with metal) as they use radioactive materials that do cause damage to the patient.
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