NMRI electromagnetic principles

In summary: Type of molecule?This article discusses MRI/NMR of water, fat, and sugar. The article mentions that different compounds have different populations of protons that can be excited by the magnetic field.
  • #1
stevmg
696
3
In nMRIs the strong magnetic field plus the radio wave aligns protons.

1). Which protons? Just the proton ions (actually H3O+) from water; or protons in all molecules that contain hydrogen atoms such as water, fats, carbohydrates, proteins?

2). The relaxation phase does what? As the protons go back to equilibrium there is an emission of radio waves?

3). Isn't that a form of γ radiation? Doesn't it have inherent risks?

HELP!
 
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  • #2
What has your research into this shown you" Please post the appropriate studies from acceptable journals that you have read that have caused your concern.
 
  • #3
stevmg said:
In nMRIs the strong magnetic field plus the radio wave aligns protons.

1). Which protons? Just the proton ions (actually H3O+) from water; or protons in all molecules that contain hydrogen atoms such as water, fats, carbohydrates, proteins?

2). The relaxation phase does what? As the protons go back to equilibrium there is an emission of radio waves?

3). Isn't that a form of γ radiation? Doesn't it have inherent risks?

HELP!
See - http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nmr.html
In the presence of the static magnetic field which produces a small amount of spin polarization, a radio frequency signal of the proper frequency can induce a transition between spin states. This "spin flip" places some of the spins in their higher energy state. If the radio frequency signal is then switched off, the relaxation of the spins back to the lower state produces a measurable amount of RF signal at the resonant frequency associated with the spin flip. This process is called Nuclear Magnetic Resonance (NMR).

and http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/mri.html

Since the MRI uses proton NMR, it images the concentration of protons. Many of those protons are the protons in water, so MRI is particularly well suited for the imaging of soft tissue, like the brain, eyes, and other soft tissue structures . . .
and
Once excited by the RF signal, the hydrogens will tend to return to their lower state in a process called "relaxation" and will re-emit RF radiation at their Larmor frequency.
Radio-frequency is not gamma (γ) radiation, not even X-ray, and in fact is lower energy than visible or infrared.

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/larmor.html (I recommend some calculations of Larmor frequencies)
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/spinpol.html

From - http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/nmr/nmr1.htm
"Note that this electromagnetic radiation falls in the radio and television broadcast spectrum. Nmr spectroscopy is therefore the energetically mildest probe used to examine the structure of molecules."

For protons, read the section 2. Proton NMR Spectroscopy, and note the differences among protons in different compounds.

Another very basic tutorial - http://www.cis.rit.edu/htbooks/nmr/inside.htm

http://www.brynmawr.edu/chemistry/Chem/mnerzsto/The_Basics_Nuclear_Magnetic_Resonance%20_Spectroscopy_2.htm

http://teaching.shu.ac.uk/hwb/chemistry/tutorials/molspec/nmr1.htm
 
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  • #4
Astronuc said:
See - http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nmr.htmland http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/mri.html

and
Radio-frequency is not gamma (γ) radiation, not even X-ray, and in fact is lower energy than visible or infrared.

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/larmor.html (I recommend some calculations of Larmor frequencies)
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/spinpol.html

From - http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/nmr/nmr1.htm
"Note that this electromagnetic radiation falls in the radio and television broadcast spectrum. Nmr spectroscopy is therefore the energetically mildest probe used to examine the structure of molecules."

For protons, read the section 2. Proton NMR Spectroscopy, and note the differences among protons in different compounds.

Another very basic tutorial - http://www.cis.rit.edu/htbooks/nmr/inside.htm

http://www.brynmawr.edu/chemistry/Chem/mnerzsto/The_Basics_Nuclear_Magnetic_Resonance%20_Spectroscopy_2.htm

http://teaching.shu.ac.uk/hwb/chemistry/tutorials/molspec/nmr1.htm
 
  • #5
To Astronuc - The question was does the nMRI technique as used in medicine align all hydrogen atom protons such as those in water, fats, carbohydrates, proteins or just the water ones? I cannot decipher the answer to that from the extensive discussions these websites presented - too much information.
 
  • #6
When a rotating field gradient is used, linear positioning information is collected along a number of different directions. That information can be combined to produce a two-dimensional map of the proton densities. The proton NMR signals are quite sensitive to differences in proton content that are characteristic of different kinds of tissue. Even though the spatial resolution of MRI is not as great as a conventional x-ray film, its contrast resolution is much better for tissue. Rapid scanning and computer reconstruction give well-resolved images of organs.
 
  • #7
stevmg said:
To Astronuc - The question was does the nMRI technique as used in medicine align all hydrogen atom protons such as those in water, fats, carbohydrates, proteins or just the water ones? I cannot decipher the answer to that from the extensive discussions these websites presented - too much information.
According to the literature one can excite water or fat, and ostensibly any organic compound by selecting the proper frequency.

This article mentions water (bound and unbound) and fat.
http://www.revisemri.com/blog/2010/fat-suppression/

Another article describes NMR/MRI of sugar by exciting protons in the glucose hydroxyl groups as opposed to water.
"GlucoCEST works by measuring glucose uptake through the chemical exchange of protons between glucose hydroxyl groups and water. By selectively saturating the magnetization of protons in the hydroxyl groups, using radiofrequency pulses, this exchange of protons causes a reduction in the MR signal from water."
http://medicalphysicsweb.org/cws/article/research/54007

So the population of protons, which are to be excited, depends on the radiofrequency.
 
  • #8
Astronuc said:
According to the literature one can excite water or fat, and ostensibly any organic compound by selecting the proper frequency.

This article mentions water (bound and unbound) and fat.
http://www.revisemri.com/blog/2010/fat-suppression/

Another article describes NMR/MRI of sugar by exciting protons in the glucose hydroxyl groups as opposed to water.
"GlucoCEST works by measuring glucose uptake through the chemical exchange of protons between glucose hydroxyl groups and water. By selectively saturating the magnetization of protons in the hydroxyl groups, using radiofrequency pulses, this exchange of protons causes a reduction in the MR signal from water."
http://medicalphysicsweb.org/cws/article/research/54007

So the population of protons, which are to be excited, depends on the radiofrequency.

Good answer. Explains what I need to know. I take it that medical MRI uses radio frequencies for water and fat, true?
 
  • #9
stevmg said:
Good answer. Explains what I need to know. I take it that medical MRI uses radio frequencies for water and fat, true?
Correct.

Edit/update: Perhaps a useful document
http://www.mri-physics.net/bin/mri-physics-en-rev1.3.pdf
 
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  • #10
Astronuc said:
Correct.

Thank you. Do you know how many doctors and healthcare workers do NOT understand this basic concept? All they know is it is something to do with protons but they don't know what and where protons are. I didn't know that regular analog X-ray machines have better resolutions than MRIs.

Stephen M. Garramine, MD
 
  • #11
stevmg said:
Thank you. Do you know how many doctors and healthcare workers do NOT understand this basic concept? All they know is it is something to do with protons but they don't know what and where protons are. I didn't know that regular analog X-ray machines have better resolutions than MRIs. I didn't know that regular analog X-ray machines have better resolutions than MRIs.

The resolution of an MRI depends on the intensity of the field you use. The higher the magnetic field, the higher the resolution. Typical MRIs operate at around 1.5 T, but higher field MRIs are gaining in popularity, and in research settings they have gone as high as 9T for people, and 21 T for animals. In addition, whilst proton MRI's are the norm, you can use any nucleus that has a net nuclear spin. helium-3, lithium-7, carbon-13, fluorine-19, oxygen-17, sodium-23, phosphorus-31 and xenon-129 have all been developed. These are for different diagnostic situations.
 
  • #12
e.bar.goum said:
The resolution of an MRI depends on the intensity of the field you use. The higher the magnetic field, the higher the resolution. Typical MRIs operate at around 1.5 T, but higher field MRIs are gaining in popularity, and in research settings they have gone as high as 9T for people, and 21 T for animals. In addition, whilst proton MRI's are the norm, you can use any nucleus that has a net nuclear spin. helium-3, lithium-7, carbon-13, fluorine-19, oxygen-17, sodium-23, phosphorus-31 and xenon-129 have all been developed. These are for different diagnostic situations.

Seems like the phosphorus-31 would be handy for bone MRIs
Still, straight X-rays give better resolution. Is the CT scan still better?

Where would I obtain a list of nuclei with net spin? Also, what is the percentage of these isotopes in human tissue and is it sufficient to detect in clinical situations?

And, most doctors don't have a clue what you are talking about.

Time to have a little yellow book, "MRIs for Idiots" with all this explained, and it can be quite easily.
 
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  • #13
Depends on what you mean by "better".

Given that CT scans expose patients to (sometimes very) large radiation doses, if you can use an MRI you should. CT scans are also sensitive to different things to MRIs. And stuff like fMRI can't really be done with CT.

(Also I don't know how these new 3+ T magnets stack up against CT)
 
  • #14
e.bar.goum said:
Depends on what you mean by "better".

Given that CT scans expose patients to (sometimes very) large radiation doses, if you can use an MRI you should. CT scans are also sensitive to different things to MRIs. And stuff like fMRI can't really be done with CT.

(Also I don't know how these new 3+ T magnets stack up against CT)

Reich, from University of Wisconsin, has on line an excellent summary of nuclei with spin and their relative abundance. I can't make this IPAD copy the link. Sorry.
 
  • #15

1. What is NMRI and how does it work?

NMRI stands for nuclear magnetic resonance imaging. It is a medical imaging technique that uses strong magnetic fields and radio waves to create detailed images of the body's internal structures. The principle behind NMRI is based on the electromagnetic properties of atoms, in particular, the nuclei of hydrogen atoms. When placed in a strong magnetic field, these nuclei align with the field and can be manipulated by radio waves, allowing for the production of images.

2. How is NMRI different from X-rays or CT scans?

NMRI differs from X-rays and CT scans in that it does not use ionizing radiation. Instead, it utilizes magnetic fields and radio waves, making it a safer option for imaging. It also provides more detailed images of soft tissues and organs, making it a valuable tool for diagnosing a wide range of medical conditions.

3. What are the limitations of NMRI?

One limitation of NMRI is that it is not suitable for patients with certain medical devices, such as pacemakers or metal implants, due to the strong magnetic field used. It also tends to be more expensive and time-consuming than other imaging techniques, and it may not be suitable for patients who are claustrophobic or unable to lie still for an extended period.

4. Can NMRI be used for all types of medical imaging?

NMRI is primarily used for imaging soft tissues and organs, but it can also be used to image bones and joints in certain cases. However, it is not ideal for imaging air-filled spaces, such as the lungs, or for detecting calcifications, such as kidney stones.

5. Are there any risks associated with NMRI?

NMRI is considered a safe imaging technique, as it does not use ionizing radiation. However, there are certain contraindications, such as pregnancy and the presence of medical devices, that may make it unsuitable for some individuals. The use of contrast agents may also carry some risks, but these are rare and typically mild.

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