Mri Definition and 94 Threads

Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body. MRI does not involve X-rays or the use of ionizing radiation, which distinguishes it from CT and PET scans. MRI is a medical application of nuclear magnetic resonance (NMR) which can also be used for imaging in other NMR applications, such as NMR spectroscopy.
While the hazards of ionizing radiation are now well controlled in most medical contexts, an MRI may still be seen as a better choice than a CT scan. MRI is widely used in hospitals and clinics for medical diagnosis and staging and follow-up of disease without exposing the body to radiation. An MRI may yield different information compared with CT. Risks and discomfort may be associated with MRI scans. Compared with CT scans, MRI scans typically take longer and are louder, and they usually need the subject to enter a narrow, confining tube. In addition, people with some medical implants or other non-removable metal inside the body may be unable to undergo an MRI examination safely.
MRI was originally called NMRI (nuclear magnetic resonance imaging), but "nuclear" was dropped to avoid negative associations. Certain atomic nuclei are able to absorb radio frequency energy when placed in an external magnetic field; the resultant evolving spin polarization can induce a RF signal in a radio frequency coil and thereby be detected. In clinical and research MRI, hydrogen atoms are most often used to generate a macroscopic polarization that is detected by antennae close to the subject being examined. Hydrogen atoms are naturally abundant in humans and other biological organisms, particularly in water and fat. For this reason, most MRI scans essentially map the location of water and fat in the body. Pulses of radio waves excite the nuclear spin energy transition, and magnetic field gradients localize the polarization in space. By varying the parameters of the pulse sequence, different contrasts may be generated between tissues based on the relaxation properties of the hydrogen atoms therein.
Since its development in the 1970s and 1980s, MRI has proven to be a versatile imaging technique. While MRI is most prominently used in diagnostic medicine and biomedical research, it also may be used to form images of non-living objects. Diffusion MRI and Functional MRI extends the utility of MRI to capture neuronal tracts and blood flow respectively in the nervous system, in addition to detailed spatial images. The sustained increase in demand for MRI within health systems has led to concerns about cost effectiveness and overdiagnosis.

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  1. humanino

    Question about MRI Bill: Is $12k Fair Price?

    Dear PFers, The hospital gave us a $12k bill for one MRI (head with contrast). The people I talked to at the hospital tell me that they do not know whether this is a fair price, which I find suspicious. The same procedure in France costs $300. As I am unsure what to do, I would appreciate...
  2. O

    In what proton MRI is focusing ?

    Hello all, I know that MRI is focuse on Hydrogen proton, but I don't understand if it focuse just in the Hydrogen proton that in water (Liquids) of the body or in all the Hydrogen proton that are within the molecules in the body. In relation to this, how the MRI could distinguish...
  3. K

    What do the gradient magnets do on MRI scanners?

    I am trying to understand MRI scanners. I know that MRIs work by aligning the protons in the direction of the large magnetic field and the radio frequency sets the frequency of the oscillations to the lamour frequency - also raising its energy level. Then when the RF is switched off, the...
  4. P

    Why is it bad to put metal in an MRI machine?

    I saw a House episode where a person had internal bleeding because they had metal inside their body and they went into an MRI machine. I'm learning about NMR now and I want to try and understand it more.
  5. A

    Force of a nail inside an MRI machine

    I just want to gain a ballpark estimate for how much force an MRI machine can generate on a small object such as a nail.. let's say the magnet is 1-2 Tesla. Very rough estimates are ok.
  6. Greg Bernhardt

    Medical Is MRI a Better Option for Detecting Muscle Damage Compared to CT Scan?

    In the case of detecting muscle damage, would there be any reason to choose a CT scan over MRI? I know MRI takes longer and can be more expensive, but the CT scan radiation seems to be high enough to try and avoid it if possible. fyi, I am in communication with a doctor, but he's taking ages to...
  7. L

    How Do MRI Scans Work? Explaining the Basics

    I'm a little confused regarding MRI scans. So you add a strong magnetic field and the protons spin. However, some websites are saying the protons allign with or against the magnetic field. Other websites are saying the protons precess (not even sure what that is) and something about Larmor...
  8. M

    Coercivity of Neodymium magnets, could it be demagnetized in an MRI?

    An N45 Grade Neodymium Rare Earth magnet has a remnance (Br) of 1320 mT and Coercive force (Hcj) of 923 kA/m. I am a little confused with the units of Coercive Force, how does A/m relate to Gauss/Tesla? Also, if an N45 magnet was placed inside a 2T MRI, would that be strong enough to...
  9. F

    Can Long Range MRI Scans Be Performed Using Maser Technology?

    So I want to know if MRI scan can be performed from a distance away. As far as I know MRI consists of a magnetic field to realign the hydrogen atoms in our body. After this the radio frequency pulse is applied and this energy is absorbed by some of the protons. When the radio frequency pulse is...
  10. D

    What is the equation for torque in an MRI scanner?

    There are (at least) two issues regarding the presence of ferromagnetic materials around an MRI scanner (of strength e.g. 3 Tesla). (i) that something (e.g. scissors in a health worker's pocket) becomes a projectile, and (ii) that an implant may experience a twisting force (e.g. ferromagnetic...
  11. D

    Why Don't Electrons Replace Protons in MRI Imaging?

    MRI imaging uses primarily the magnetic fields of spinning hydrogen protons to generate images. I read somewhere that the magnetic fields generated by spinning electrons are stronger then those created by spinning protons. Why then are electrons not used in MRI imaging? Thanks
  12. O

    Medical Will heart beat be affected by MRI?

    There is a hugh amount of magnetic field during MRI scanning, I would like to know whether our heart beat rhythm will be affected by this magnetic field or not if the magnetic field is too strong. Does anyone have any suggestions? Thanks in advance for any suggestions
  13. G

    Medical Advances in F19 MRI: Imaging Drugs in Living Organisms

    What kind of advances have been made in this field (since I don't stay on top of it)? If I wanted to image, say, where my fluorinated drug is going within a rat, is it possible? NMR is inherently not a sensitive modality. Hydrogen is vastly more abundant in a living organism than fluorine...
  14. O

    Energy levels of nucleus in emitting radiation in MRI

    Hi experts please explain energy levels of nucleus in emitting radiation in MRI
  15. K

    Medical Which frequencies does an MRI machine use? Is it microwaves?

    Hi, Which frequencies does an MRI machine use? Is it microwaves? Would prolonged exposure to it be damaging to the body?
  16. I

    Medical MRI Mind Reading claim (newspaper)

    http://www.smh.com.au/technology/sci-tech/mindreading-technology-reconstructs-videos-from-brain-20110923-1ko5s.html ::I can't locate the primary source:: Didn't want to put this in skepticism or another sub section.. too interesting. Move if wrong thanks.
  17. V

    MRI Safety: Question on Potential Burns

    Hi, MRI safety manual says that whenever you are scanning a patient with a certain surface coil you should remove all unplugged coils from the bore during the scan. For example, if you have a head/neck + spine coil matrix with two coil ports and you are scanning only the spine part then you...
  18. R

    T2 in Nuclear Magnetic Resonance & MRI

    I want to understand MRI and what exactly is T2. I have read the November issue of Sci-am and I'm still confused what exactly is T2 as it has different descriptions. The article "The Incredible Shrinking Scanner" by Bernhard Blumich: "The system can also monitor the precessing spins as they...
  19. K

    How Quickly Can an MRI's Magnetic Field Be Safely Altered?

    Homework Statement One possible concern with MRI (magnetic resonance imaging) is turning the magnetic field on or off too quickly. Bodily fluids are conductors, and a changing magnetic field could cause electric currents to flow through the patient. Suppose a typical patient has a maximum...
  20. MattRob

    Is Time Really a Fourth Dimension Similar to Spatial Dimensions?

    I've heard again and again that time is more or less the same as any other spatial dimension. I'll refer to them as X, Y, Z, and W, where you can pick any three to be space and a fourth to be time, since they're the same. W will be time for ease of reference. Except, if that's the case, and...
  21. S

    Comparing X-ray & MRI Scans: Bone & Soft Tissue

    Hi i am new here so, please take it easy with me lol i have afew Q and i relly need help with them 1) compare and evaluate the appearance of bone and soft tissue in an MRI scan compared with a conventional X-ray. 2) Explainthe factors influencing the signal intensity in MRI. Thank...
  22. L

    Mathematical model for reducing mri noise

    dears I study nuclear engineering (medical radiation ,MS) , my proposal for graduation is (Modeling of Acoustical Noise in MRI and It Is Validation Through Measurements). I want to make and deliver a mathematical model for reducing noise in mri,would you please tell me what should i do? and...
  23. W

    Medical Identifying structures in brain MRI

    Hello all, experts and otherwise. I'm looking for some links to software and documentation for selecting Regions of Interest (ROI) in MRI data of the human brain. Saving ROIs is a must. Any tips also appreciated. Thank you!
  24. G

    What is the point of repeating TR signals in MRI

    What is the point of repeating the TR 90 degree pulse in MRI? I understand you must modify the TR time to get different T1 times, but since the echo signal is read, would'nt all the echo signals be read to the same intensity after a 90 degree pulse?
  25. T

    Factors influencing signal intensity in MRI

    hi there i was wondering if you could help me: • explain the factors influencing signal intensity in MRI this is one of the questions in my assignment i was wondering if you could please help me ASAP as I am completely confused!
  26. L

    Energy stored and # turns in an MRI machine (solenoid)

    1. MRI (magnetic resonance imaging) is a medical technique that produces detailed "pictures" of the interior of the body. The patient is placed into a solenoid that is 40 cm in diameter and 1.0 m long. A 100 A current creates a 5.0 T magnetic field inside the solenoid. To carry such a large...
  27. A

    Medical How do MRI scanners create images of the body?

    Hi, I have been trying to figure out how MRI scanners work but am getting a bit confused and wondered if someone could put me straight on this ? I am just interested as they strike me as being amazing machines (possibly one of human kinds greatest inventions?) and the way they work is...
  28. E

    Looking for an article about MRI

    Hi, know where I can find "Journal of Magnetic Resonance article [18]" public domain version? I scan google and did not find. It is part of article title "Direct 3D Imaging of Molecular Structure:Quantum Sensing and Control" PDF...
  29. L

    Understanding IQ Demodulation in MRI Signals

    This suddenly came up in a MRI class. I kinda understand IQ modulation (both amplitude and phase are modulated). But how does IQ demodulating a signal help, specially MRI signal. In case you don't know a MRI signal, its just a exponentially decaying sine.
  30. Lisa!

    Noises from MRI Imaging: Sources Explained

    What is the source of noises we hear during MRI imaging? Thanks!
  31. Y

    About superconduct MRI quench protection

    Hi,I study protection of superconducting coils.I adopt heaters to protect coils.The circuit is in attachment. There are 6 coils,so I use 6 quench heaters.I want to know how I choose the heaters? It must do the Quench Heater Simulation for protection of superconducting coils before...
  32. D

    Medical X-ray, CT scan, Ultrasound, MRI detecting blanks ?

    This is for a sci-fi novel I’m writing, and I actually posted this at another site but the answers given were a little vague. What would occur, either on a computer monitor (or other monitoring device, depending on the machine) or on a photo film, if an: a. X-ray b. CT scan c. ultrasound...
  33. H

    Medical MRI Textbooks for High School & A-Level Students

    Does anyone know of any resources, textbooks etc that are suitable for high school students, A-levels, to learn about MRI?
  34. lisab

    Medical My Strange MRI Experience: Uncontrollable Startle Reflex?

    About a year and a half ago, I had an MRI. During the scan something very strange kept happening. The procedure was actually a series of many scans - it took over an hour to get them all done. Before each one, the tech would go through a procedure he called tuning. The machine would hum...
  35. R

    How Fast Can an MRI's Magnetic Field Safely Shut Off to Prevent Harm?

    Homework Statement Magnetic resonance imaging (MRI) is a medical technique for producing "pictures" of the interior of the body. The patient is placed within a strong magnetic field. One safety concern is what would happen to the positively and negatively charged particles in the body fluids...
  36. S

    MRI Signal Intensity: Optimizing TR & TE

    Homework Statement We will make a Spin-Echo experiment, and we know \rho_{w}, T1_{w},T2_{w}, \rho_{g},T1_{g},T2_{g}, where T1 and T2 are relaxation time,\rho is a proton density, and g mean gray matter, w mean white matter. We search TR and TE, TR is a repetition time, TE is an echo time. We...
  37. J

    Medical MRI testing for Electrical Brain pulses?

    Hello, I don't know a lot on this subject, but at a last nights weekly philosophical discussion a friend mentioned that they could use MRI machines to scan and see electrical impulses light up parts of the mind during electrical impulse testing to the brain. I guess like showing images to...
  38. 7

    Medical Finding Resources for MRI: Books and Lectures

    hi budy i need a book ar sites for MRI and if possible a lectures ... hope find any help thanks
  39. C

    NMR and MRI Theory: Understanding Relaxivity for Contrast in Imaging

    NMR and MRI -- questions! I'm currently doing an experiment on nuclear magnetic resonance for an undergrad physics lab. Our experiment was based around determining the effects of proton concentration on spin-lattice and spin-spin relaxation times. We used two separate sets of ionic solutions...
  40. T

    Where Can I Find Nuclear Well Logging and MRI Animations for Presentations?

    Hey , Actually I need someone to recommend some useful web sites that would contians animations about Nuclear well logging and Nuclear Magnetic Resonance Imaging to help me in my presentations . :cool:
  41. E

    Medical Understanding the Brain and MRI: How a Huge Magnet Affects Electric Impulses

    I only have a vague idea of how the brain and MRI work but from my understanding the brain uses electric impusles and an MRI uses a huge magnet. Since a magnetic force redirects a moving charge, why doesn't someone go crazy when they are in an MRI because the neurons don't go where they are...
  42. J

    Electromagnetic radiation / mri question

    In reading about magnetic resonance imaging, I was surprised to learn that the coil/antenna used to send a radiofrequency pulse into the person being scanned is not a coil/antenna at one end of the person, but a large coil actually wrapped around the person. I know how alternating current...
  43. Tsu

    MRI question for our Heavy Weights

    Our MRI literature states that 98% of the hydrogen atoms in our body are lined up in the same direction while we aere in the magnet. The other 2% are in counter-allignment to the field. Why is this so?
  44. A

    MRI: proton relaxation signal direction

    In all situations (that I can think of) of particles relaxing from an excited state to their ground state, the direction of the resultant photons is isotropic. In magnetic resonance imaging (MRI) the excited protons are all in the -Z direction (+ some thermal motion). Will this have any bearing...
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