What is Mri: Definition and 93 Discussions

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. M

    A Effects of magnetic fields on material (Magnetic resonance)

    Hi, I was wondering if a Magnetic Resonance (+contrast) can in some way modify the structure of artificial chordae used in heart surgery. My first answer would be "No". There ain't any medical article about that. Also (as far as i know) I don't think magnetic field can break chemical bond, so it...
  2. L

    Why are MRI machines so expensive to operate?

    Why is MRI machine use so expensive? Is creating a magnet field of that strength difficult and pricey? I think you get better detail than CT scans that do use radiation. Why the high price? Anyone know?
  3. kbansal

    How to explain the Quantum Mechanics/Math of the stages of MRI imaging

    "B0 is a static magnetic field (produced by a superconducting magnet) that initially causes the protons in the body to align with the field and precess at the larmor frequency along the z axis . From a mathematical perspective this precession around the B0 axis occurs due to the time evolution...
  4. E

    Unit calculations - DWI MRI (Stejskal-Tanner)

    Ok, so basically my task is to calculate the apparent diffusion D based on experimental data, which is kind of easy, BUT the problem is with unit of b... Gamma is gyromagnetic ratio and can be expressed as: (s*T)-1 or MHz/T --> but I am not so sure, teacher did not specify Delta is the pulse...
  5. Wrichik Basu

    COVID Can MRI detect COVID infection in lungs?

    During this second wave of pandemic in our country, there have been several cases where the RT-PCR test is yielding false negatives. Many patients are being advised CT scans by doctors if the RT-PCR is negative, but the patient still shows symptoms of COVID. In many cases, this has given good...
  6. L

    Basics of RF coil development for MRI

    Hi all, I'm trying to understand basics of radiofrequency (RF) coil development for magnetic resonance imaging (MRI). For example, the problem is to develop simple surface single-loop RF coil tuned to 100 MHz. In program Coil32, I set the following parameters: diameter of the loop D = 20 mm...
  7. A

    B MRI vs Color X-Ray Technology: What Are the Differences and Benefits?

    Today I read about a seemingly new way of using Xrays that results in images that can be colored and more detailed. https://www.marsbioimaging.com/mars/ See this link for example. I do wonder what would be the major differences or benefits from such technology given modern MRI also has very...
  8. M

    A How can a zipper MRI artifact be limited to a single line?

    he so-called [herringbone or spike MRI artifact][1] on a given example could be traced to a specific point(s) in Fourier space ("k-space"). The idea is that during the acquisition of the image, a certain RF wave emitted by the patient (providing the info about diseased or normal anatomy) had...
  9. L

    B What is the true way to determine time parameters from semilog graph?

    Hi all, I have experimental nuclear magnetic resonance data that describe T2-relaxation of the nuclei in the sample of interest. The experimental points obey bi-exponential dependence: I = I1*exp(-t/T2_1) + I2*exp(-t/T2_2), where I is current intensity, I1 and I2 are intensities which represent...
  10. Y

    MRI Spin echo sequence and STIR

    I would like to ask a question about MRI Spin echo sequence. after first 90 degree RF pulse, the free induction decay occurs. And 180degree refocusing pulse is given again. And echo signal is obtained at TE. My question is that is the the signal highest when the protons are back again in...
  11. Kunal Aggarwal

    Biomarkers for Alzheimer's disease in sMRI?

    I have been looking for biomarkers for Alzheimer's disease which can be detected in structural MRI. I have gone through some papers and found that Gray matter, white matter and CSF are good biomarkers. But is there any other except?
  12. Myles Cummings

    B How much should it cost to build an MRI Scanner?

    I recently had an MRI scan, and while I was inside I began thinking about how the thing actually worked, and what it would cost to build. The hospital staff told me that the cost was several million dollars, and subsequent research seems to confirm that the 'average' MRI scanner cost between 3-5...
  13. T

    In layman's terms , how strong is a 3 Tesla Magnet?

    I saw a post where someone was granted access to a 1.5 Tesla MRI. After some research I discovered a 3 Tesla MRI. How strong is this magnet?
  14. K

    I Experiment Ideas using an MRI scanner?

    So I've stumbled upon a really cool opportunity this summer, where I basically have a hospital which has agreed to let me do an experiment using their 3T MRI machine. I'm a physics undergrad and I want to do a physics experiment using the MRI, but I have absolutely no idea what to do. I've tried...
  15. Bayoudh101

    I MRI synchronization with the IRF90

    Hello , In MRI physics , I don't seem to be able to wrap my head around the synchronization in the precession of the protons after an RF90 impulse (which is an electromagnetic impulse that would deviate the precessing magnetic field axe by 90 degrees) the synchronization would give the vector...
  16. G

    I How Does an MRI Work and Differentiate Between Different Tissues?

    If this belongs to the high energy particle physics subforum please move it there. So since I have to take an MRI, I am curious to know how it works, I think I know the basics but the information about it out there is rather confusing. So first off here is what I know. A large cylindrical...
  17. J

    Decomposition of linearly polarized field MRI

    Homework Statement Hi, I am having trouble understanding how the B1 field as described by (3.48) in the image attached in MRI which is described as a linearly polarized field is decomposed into it's final two circularly polarized field as described by (3.49) in the image attached. Homework...
  18. R

    MRI & White Gold: Is Heating a Risk?

    Hi, So I recently had to get an MRI. I forgot to take off my wedding ring, but the technicians said it's ok "if it's real gold". I told them it was white gold (which is an alloy of 58.5% gold and the rest is other metals). They said it was fine, but later told me they didn't really know what...
  19. lukasleopold

    Estimating sound pressure (in an MRI scanner)

    Hello, excuse me if these happen to be basic questions, but I'm a psychologist/neuroscientist in training without any particular experience in physics, and I am just confronted with a very specific problem. I need to measure the sound pressure experienced inside of an MRI scanner...
  20. N

    Exploring the Electromagnetic World: A New Scientist's Journey

    Hello, I am NF and just joined. I work on all kinds of diagnostic equipment and like to play with magnets and try to understand the correlation of all things charged.
  21. M

    Magnetisation ratio in human body using gyromagnetic ratios

    Homework Statement The number density of 1H nuclei in the body is roughly 600 times greater than that of 13C nuclei. By what factor is the magnetisation M0 of 1H greater than 13C in the same external magnetic field? Homework Equations 3. The Attempt at a Solution [/B] Surely it can't be as...
  22. F deba

    CV (cardiovascular) system and MRI related queries

    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > Hi guys, I'm an IT student 'and lill favour in my masters research work so please help me to have valid answers for following questions ASAP. 1. Do patient specific MRI contains the information...
  23. M

    Quantum NMR or Medical Imaging (Advanced )

    Suppose I want to learn about MRI. Some of the introductory treatments I have seen aimed at engineers or imaging professionals may not assume much more than sophomore level physics competency. I know some advanced QM and statistical physics so I am wondering about the existence or value of a...
  24. phys-student

    Why can't quantitative values be computed using DSC-MRI?

    I am studying for a comprehensive exam on dynamic contrast enhanced MRI (DCE-MRI) and questions have come up in my practice talks about dynamic susceptibility contrast MRI (DSC-MRI). In DCE-MRI changes in signal in an artery and the tissue are converted to contrast agent concentration vs time...
  25. B

    Correcting Misconceptions about the Frequency of RF Pulses in MRI

    The magnetic moment of protons precesses at a frequency ω0=γB0 about the static magnetic field. In order to move the magnetisation vector into the transverse plane the RF pulse must be applied at a frequency ω0. However, as B1 (the field strength of the RF pulse) is << B1 how is this possible...
  26. kostoglotov

    Energy dissipated by a loop of muscle in an MRI machine

    edit: turned out to be a calculator typo...mods feel free to delete this thread if you wish, I won't complain. Homework Statement [/B] Having issues with part a) imgur link: http://i.imgur.com/4hzLyhb.jpg Homework Equations Resistivity of muscle (from table in text): \rho \approx 13...
  27. R

    Mathlab code to extract T1 values in MR images

    I have T1 MR images DICOM (http://www.osirix-viewer.com/datasets/DATA/BRAINIX.zip ) does anybody know the CODE to calculate T1 values from above DICOM images in MATHLAB?
  28. M

    When does a CT give better information than an MRI

    In both cases there are contrast agents available. MRI has vastly superior location error but that doesn't mean everything. It also doesn't illuminate the tissue in the same way as x-ray optics. With MRI you can find where molecules are but wouldn't necessarily illuminate an equivalent density...
  29. F

    MRI and Fourier transform to form an image

    I read about how MRI works briefly, by flipping the water molecules using a magnetic field to the correct state then send the radio wave to these atoms and have it bounces back to be received by receiver coils and apply Fourier Transform to figure out the imaging. My question is, how does...
  30. M

    I want to find the vector components of an MRI pixel -- How?

    I have a Dicom Image that is interpreted as an array. Each cell is a pixel. Each pixel has a value. I want to find the vector components (x,y,z) of a pixel. Specifically, I want to find magnetic field vectors for each pixel. The image is for H1 atoms. Freq = 297, B0 = 3. How would you do this...
  31. ElijahRockers

    Joining together data from two different MRI protocols

    I should start by saying that, as a novice data analyst, I have very little experience with MRI physics, but I believe I understand the absolute fundamentals. Also, this post mostly concerns data analysis issues so might be better suited for some other signal processing forum, but I'm hoping...
  32. B

    Frequency encoding gradient in MRI

    Hi, I am studying the physics of MRI (from a conceptual NOT mathematical point of view...please don't answer with heavy maths). I understand how we can obtain a signal from a specific slice along our Z-axis. I know that we then apply a graded magentic field (frequency encoded gradient) along...
  33. A

    Can MRI Fringe Fields be Mapped in a 3D Space?

    Hello everybody, I am working on a project that require to have map of an MRI machine fringe field in 3d space. I basic idea is to measur it in one plane parallel to radius of machine and then by assuming that field is axissymetric make my map. does anybody have any idea on doing that or on my work?
  34. S

    Thermal Equilibrium and Longitudinal Relaxation

    Homework Statement Problem 6.2 from Magnetic Resonance Imaging: Physical Principles and Sequence Design. Show that M_o \approx \rho_o \frac{s(s+1)\gamma^2\hbar^2}{3kT}B_o Homework Equations M_o = \rho_o \gamma \hbar \frac{\sum m_s e^{m_s(\hbar w_o / kT)}}{\sum e^{m_s(\hbar w_o / kT)}} ...
  35. S

    Medical MRI vs. CT: Which Scan is Better?

    Hello guys, I have few questions 1. I know MRI is best for soft tissue masses? What does soft tissues mean? I searched on the internet and the definition is vague. Is it simply all the tissue apart from bone in the body, which means its includes organs such as liver. Or is it all supporting...
  36. Domenico94

    How much are machine learning and NMR related in medical imaging?

    Hi everyone. By reading stuff on the Internet, I found many times the correlation between machine learning and NMR, or, better, algorithms that are implemented for that kind of technology( The same goes for PET, or CT scans. The thing I want to ask is, how much do you think that the two things...
  37. makkhi

    What is phased array head and neck coil in MRI?

    I was reading this article " The Effect of Head Rotation on the Geometry and Hemodynamics of Healthy Vertebral Arteries" They used an MRI machine with a phased array head-neckcoil and a phased array superficial coil. what are they?
  38. R

    MRI Electromagnet Interference in a Figure-8 cable

    The prevailing wisdom is that coiling excess signal cable under an MRI magnet for storage in a figure-8 configuration will reduce or eliminate induced noise onto the cable from the pulsing fields from gradient coils. I am starting to doubt this, however. A quick diagram of a figure-8 looped...
  39. L

    MRI & Impedance: Tune RF Coil for 1.5/3.0 Tesla

    Homework Statement In magnetic resonance imaging (MRI), we use radiofrequency (RF) coils to transmit oscillating magnetic fields into the patient. The coils are essentially series RLC antennas and must be tuned to resonate at the characteristic frequency of the experiment (called the Larmor...
  40. T

    Current flow in an MRI receive coil

    I am a physics student with very limited experience in electronics and I have been tasked with making an receive coil for use in an MRI machine. The design of an RF coil amounts to constructing to what essentially amounts to an LC resonator with a set resonance frequency. The design of my coil...
  41. A

    MRI question: Production of EM Waves using magnets

    Hi all, I've got a quick clarification question. Generally when the production of electromagnetic waves are discussed, it's done in the context of an accelerating electric charge. Is it possible to generate EM waves by instead accelerating something like a permanent magnet? I.e. if I wiggle a...
  42. G

    Medical Can MRI Scans Affect Heart Rate?

    I was going to post in another thread with this title but it was closed? I had an MRI of the right shoulder today in an open MRI and went through about 6 cycles of scans (I think it was 6). During the 4th cycle I noticed that my heart rate was increasing. I went into this with a calm demeanor...
  43. M

    Will a Copper Ingot Float in a 3.4 T MRI Machine?

    Hey there, inspired by this exhibit in the SF exploratorium, I was discussing with my colleague what might happen if you put a thick piece of pure copper (say, a 5kg ingot) in the bore of a 3.4 T MRI machine. (What about 7T?) We have the MRI machine, all we need is a big piece of copper...
  44. C

    What is the role of Fourier transform and k-space in MRI signal acquisition?

    I just started doing research in MRI coil design for my professor and I'm trying to figure out some basic concepts. In particular, how does the Fourier transform and k-space play a role in the signal acquisition? From my reading, I just know that somehow the signal is acquired in k space and is...
  45. C

    Exploring Modern MRI Technology Parameters

    Hi all, I am wondering about the actual technological parameters of a modern MRI. In particular I mean sensitivity, i.e. the order of magnitude of the signals to be detected and the noise levels in practice. Can somebody recommend a good reference about the subject from an engineering...
  46. A

    Ferrofluid Used as MRI Contrast Agent: Heat Risk?

    so it seems ferrofluids might be used for mri scanners as contrast agents. Wouldn't the ferrofluid get hot?
  47. O

    Is the MRI Signal a Combination of Longitudinal and Transverse Magnetic Waves?

    When I do MRI, after I send the Pulse radio, I get signal. There longitudinal magnetic and Transverse magnetic , their signal is shared or that two separate signals which are received with the antenna and create an image?
  48. N

    MRI Headphones: Non-Metal Conductors Explained

    So I had to have an MRI today and when your in the machine you wear these headphones so that they can talk to you and stuff, but how could they work with no metal? I realize that there are non-metal conductors but I thought that they had to be doped with metals (to make them semiconductors) so...
  49. A

    MRI excitation time vs relaxation time

    So.. if you apply a fluctuating magnetic field to an atom at its correct resonance frequency, its pole will go out of alignment of the applied field. How long does it take for the proton/electron to go 90 degrees out of the applied field vs how long it takes to return
  50. 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...