# Tag Info

## Hot answers tagged medical-physics

4

In MRI, an image is created by using gradient magnetic fields. By adding a gradient magnetic field the magnetic field is different at different positions in the body. The most important term in understanding the use of this is the larmor frequency. This is the frequency with which the hydrogen atoms will precess in a certain magnitude magnetic field and is ...

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Several reasons why this is not a great idea: 1) signal to noise ratio scales with field strength: 1.5T is considered a reasonable number although it is possible to get diagnostic images in some situations with lower fields. 2) inductance of coil capable of producing such large fields - try computing the energy stored! 3) during ramping of the magnet, you ...

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AdamRedwine's answer also doesn't take into account the fact that the radioactive iodine will be processed by the body and expelled in the urine over the course of a few days. This is what the comment on the increased exposure on the bladder wall is from, referenced by another comment. So I believe (but am not an expert in this area) that the exposure will ...

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It might not actually answer your question, but to throw it into the bowl: There are some advances in MRI using permanent magnets and even conventional electromagnets with static magnetic fields of about 0.5 Tesla. As far as I know one can do imaging with a reasonable resolution with these devices without the need for extensive cooling. They are used for ...

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If you are asking about cancers such as leukemia the general consensus in the scientific and medical communities is that to date there is no evidence of increased risk due to exposure to high voltage powerlines, mobile phones or wifi. The main risks around high voltage power lines are due to high electric field gradients, especially at close vicinity such ...

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Some practical information first - the charged particle beam passing through the matter suffers from energy (and also angular) straggling. That means that even if an ideally monoenergetic beam is used, there will be always a finite volume with Bragg peak losses. The bigger initial energy, the bigger is the volume. Protons stopping at 40 mm have straggling ...

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Everyone is likely to have a similar pain threshold to electric shocks. If your friend wears leather soled shoes he will conduct static electricity to earth because they offer much less resistance to earth than rubber or plastic soled shoes. Wearing synthetic clothes may cause a similar effect. If he/she has lower resistance than you (by having sweaty ...

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The dose that kills a tumor is deliberately aimed at that tumor. If, instead of using a collimated beam, you put a person in a wide beam for radio "therapy", you would be treating their entire body as a tumor and kill them. The dose in RT is computed locally - "this" part of the body (these grams of tissue) absorbed (were exposed to) "this many" Joules of ...

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If you pump gas along a pipe then pressure drop per unit length of the pipe depends on the diameter of the pipe. The smaller the pipe the harder it is to pump the gas through it. The pressure drop is given by the Darcy-Weisbach equation: $$\Delta P = f_D \frac{\rho v^2}{2} \frac{\ell}{d}$$ though with the complication that the density of the gas depends ...

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The image is 2D not 3D because it's a slice through the object. As for how it's done, suppose you're trying to make a (very low resolution!) image of this object: If you measure the intensity in the horizontal direction you can relate the measured intensities $I_{0,T}$ and $I_{1,T}$ to the intensities in the four chunks of the object by: \begin{align} ...

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