INTRO
Measuring visceral fat with magnetic resonance imaging. Usage of magnetic fields to discover visceral fat.
Trying Magnetic Resonance Imaging
It’s been a long time since my friend first had sciatica.
The pain in his lower back and leg did not and did not want to subside and at times he could not even move because of it.
His physician, who probably wanted to rule out hypochondria as the cause of the pain, therefore sent him for an MRI of the spine.
It turned out that the waiting time for a “magnet”, as doctors call magnetic resonance in jargon, is quite long.
Magnetic Resonance Imaging Check
Which already gave a hint that this investigation is not something every day.
And indeed, the imaging process was like something out of an old sci-fi movie.
He was squeezed into a small, cream-colored cylindrical chamber where he had to lie motionless for half an hour.
While the device slowly painted and made strange loud noises.
When he later studied the images of my spine, he realized that he knew nothing about MRIs.
Operation Of Magnetic Resonance Imaging
How Does It Work? Is painting with it safe for health? Why didn’t they send him for an X-ray?
Especially since, for the uninitiated, the images are very similar to X-rays.
Except that, on one of them, several cross-sections of the spine are arranged… All these questions will now, I hope, finally be answered.
Magnetic Field And Magnetic Resonance Imaging
The nuclei of some atoms can be in two different states in a magnetic field.
The two states have different energies, and nuclei can transition from one state to the other.
By emitting or absorbing photons of electromagnetic waves.
When transitioning to a state with lower energy, the nucleus emits a photon.
And to a state with higher energy, the nucleus is excited by absorbing a photon.
Photons And Magnetic Resonance Imaging
The energy of the photons is the same as the energy difference between the two states.
Since the energy of photons in electromagnetic waves is related to their frequency.
Nuclei can only be excited with a precisely determined frequency – we call it the resonant frequency.
The difference in energy between the two states of the nuclei (and thus their resonant frequency) is determined directly by the magnitude of the magnetic field.
Magnetic Field And Magnetic Resonance Imaging
In small magnetic fields – e.g. in the normal magnetic field on Earth.
The energy difference is so small that the two states are almost indistinguishable and the nuclei can pass between them imperceptibly.
However, it is different if the nuclei are located in a field that is several tens of thousands of times larger.
At that time, the energy difference between the states of the nuclei becomes so great.
Nuclear Magnetic Resonance Imaging
That the nuclei pass between them by absorbing or emitting electromagnetic waves of radio frequencies, which we can detect.
By the way: physicists call the phenomenon “nuclear magnetic resonance”.
But doctors dropped the word “nuclear” because it had too many negative connotations.
The use of magnetic resonance imaging in the human body.
Visceral Fat Imaging With Magnetic Resonance
The idea that it is possible to image organs and visceral fat in the human body with nuclear magnetic resonance was first born in the 1970s.
In this, the nuclei of hydrogen atoms are most often used, since hydrogen is abundant (water) in the tissues of the human body.
The patient is first placed in a very strong magnetic field.
The nuclei of the hydrogen atoms in the tissues in the patient’s body are then excited to a higher energy state by a short pulse of radio waves.
Magnetic Resonance Imaging Frequency
Excited nuclei return to their unexcited state within a few hundred milliseconds, emitting radio waves at the resonant frequency.
The imaging device detects the signal emitted by the nuclei and thus reconstructs an image of the tissues in the body.
Magnetic-Resonance
The patient is placed in a very strong magnetic field. The nuclei of hydrogen atoms in water, which is everywhere in the body.
Are excited to a higher energy state by radio waves of the resonant frequency.
Relaxation. Excited nuclei relax back to the unexcited state and emit a radio signal in the process.
Based on this signal, it is possible to reconstruct an image of the visceral fat tissues in the body.
Strong Magnets And Magnetic Resonance Imaging
To achieve beautiful images, the magnetic field strength in imaging devices must be at least about 1 T.
T is the unit for magnetic field strength – “tesla”. The unit is named after Nikola Tesla, so 1 T is read as “one tesla”.
For comparison: the Earth’s magnetic field, turns the compass needles to the north.
Has a strength of about 0.00005 T, or several tens of thousands of times less.
Even everyday permanent magnets, such as those used to attach leaflets to the refrigerator, are much too weak for magnetic resonance imaging.
Technology Of Magnetic Resonance Imaging
For this, we need very strong magnets, which must also be large enough to accommodate the patient as comfortable as possible.
Making large and strong magnets is a huge technological challenge.
A permanent magnet that creates a large enough field quickly weighs several tens of tons!
Magnetic resonance imaging devices therefore usually do not use conventional magnets as the source of the magnetic field.
Superconducting Magnets And Magnetic Resonance Imaging
But superconducting magnets, in which the magnetic field is generated by an electric current in a superconductor.
The downside of such magnets is that the superconducting material must be continuously cooled to more than -250 ºC.
Which again is neither simple nor cheap. The difficulty of making large and powerful magnets has an unfortunate consequence.
Cost Of Magnetic Resonance Imaging
Due to the high costs associated with making large magnets.
Imaging devices tend to be not very spacious and patients are quite cramped inside them…
How Is The Magnetic Resonance Image Created?
We have seen that the origin of the signal in magnetic resonance imaging is in the nuclei of hydrogen atoms in water.
Water is present in all tissues in the body, and the question quickly arises.
How can the different tissues be separated from each other in the pictures?
An interesting phenomenon helps a lot here – the excited nuclei in different tissues return to the unexcited state at different speeds.
Magnetic Resonance Imaging Visceral Fat Tissues
We say that the tissues separate from each other after relaxation time.
For example, the relaxation time for visceral fat is different from the relaxation time of healthy tissue.
Tissues with a longer relaxation time will emit a signal for a long time after excitation than tissues with a shorter relaxation time.
For example, imagine that the relaxation time in visceral fat is shorter than the relaxation time of other tissues in the body.
Magnetic Resonance Imaging Excitation
What happens after we simultaneously excite the hydrogen nuclei in all the tissues in the body?
Immediately after excitation, all tissues will be equally excited.
And the signal from all tissues will be approximately equally strong.
In the image taken immediately after excitation, therefore all tissues appear bright.
However, since the relaxation time for visceral fat is shorter than for other tissues.
Visceral Fat Signal And Magnetic Resonance Imaging
The signal from the visceral fat will decay faster than the signal from other tissues.
If the image is taken at the right moment, the visceral fat will be visible in the image, as it will be much darker than in a healthy body.
Example of contrast generation between different tissues.
Immediately after excitation, a strong signal can be detected from all tissues and the image is bright everywhere.
Since some tissues relax faster than others (in the above example.
Visceral Fat And A Healthy Body
Visceral fat relaxes faster than a healthy body, they appear dark earlier in the image.
After 250 ms, all tissues are completely relaxed and the resulting image is black everywhere.
If the image is taken at the right time (e.g. after 50 ms), the difference between the visceral fat and the healthy body is visible.
The imaging process shown is only one of many, and the magnetic resonance imaging process can be more complicated.
For example, it turns out that excited nuclei can return to equilibrium by two different paths.
Visceral Fat Relaxation Times
And that we know two relaxation times, i.e. T1 and T2…). The relaxation times of different tissues can also be very similar.
This is why it is unfortunately not possible to take an image with magnetic resonance.
In which a good contrast between all the different tissues can be seen at the same time.
Before imaging, the doctor must adapt the imaging process to the tissues that he wants to see clearly in the image.
Radiologist And Magnetic Resonance Imaging
Magnetic resonance imaging, therefore, requires a well-educated radiologist and is by no means as simple as imaging with a conventional camera!
So far, we have only talked about the origin of the signal and the differentiation of tissues from each other.
But not about how we get information about the position of tissues in the body.
Magnetic Resonance Imaging Coils
For this purpose, in addition to the superconducting magnet in the imaging device, there are also special coils.
Professionally called gradient coils. We achieve that the strength of the magnetic field is not the same everywhere in the body.
But changes slightly from point to point. Due to the varying strength of the magnetic field.
The resonance frequencies are also different at different points.
And tissues located in different places emit radio waves of different frequencies during relaxation.
Magnetic Resonance Imaging Device
The imaging device knows what the resonance frequency is at a certain place.
We can therefore precisely determine from which part of the body a certain signal is coming by measuring the detected frequency.
By the way: the rather loud and unpleasant sound that is produced during an MRI scan is created by the coils, which are constantly turned on and off.
Pros And Cons Magnetic Resonance Imaging
Let’s see what are the main advantages and disadvantages of magnetic resonance imaging compared to other methods, e.g. x-ray.
The first good feature of magnetic resonance imaging is that it allows good contrast.
Even between some tissues that are not well distinguished on X-ray images (especially different soft tissues).
Another good feature is that, unlike X-rays, there is currently no evidence that magnetic resonance imaging is harmful to health.
Magnetic Resonance Imaging Vs X-Rays
We immediately ask ourselves, why do we still use X-rays at all, if magnetic resonance imaging has so many advantages?
Unfortunately, the answer is rather banal. MRI machines are very expensive and therefore rare.
In some countries, there are not many more than the fingers on the hand, and almost every medical center has an X-ray.
With a broken arm, it’s much better to go for an X-ray (which is not that dangerous again) than to wait three months for an MRI.
A minor downside of MRI is that the chamber is really small.
Uncomfortable Magnetic Resonance Imaging
And the patient has to you have to be still all the time while painting.
But at the same time, the painting is uncomfortably loud (apparently some places recommend earplugs for painting…).
This is why it is difficult, for example, to image small children with magnetic resonance imaging.
However, technology is advancing and today we can already read about new devices in which the chamber is no longer so small.
And the price of simpler devices is probably falling.
Future Potential Of Magnetic Resonance Imaging
Thus, we can be sure that in the future we will encounter magnetic resonance more and more frequently.
And that in rich countries it may one day be even more widespread than classic X-rays.
Finally, let me say that, fortunately, hypochondria was not proven.
And the cause of his sciatica is supposed to be a small injury to the intervertebral disc.
No surgery was needed, but more movement (swimming) and better posture helped.
Yes, this is exactly what my grandmother advised me at the very beginning, before any painting on the magnet…
CONTENT:
- Trying Magnetic Resonance Imaging
- Magnetic Resonance Imaging Check
- Operation Of Magnetic Resonance Imaging
- Magnetic Field And Magnetic Resonance Imaging
- Photons And Magnetic Resonance Imaging
- Magnetic Field And Magnetic Resonance Imaging
- Nuclear Magnetic Resonance Imaging
- Visceral Fat Imaging With Magnetic Resonance
- Magnetic Resonance Imaging Frequency
- Magnetic-Resonance
- Strong Magnets And Magnetic Resonance Imaging
- Technology Of Magnetic Resonance Imaging
- Superconducting Magnets And Magnetic Resonance Imaging
- Cost Of Magnetic Resonance Imaging
- How Is The Magnetic Resonance Image Created?
- Magnetic Resonance Imaging Visceral Fat Tissues
- Magnetic Resonance Imaging Excitation
- Visceral Fat Signal And Magnetic Resonance Imaging
- Visceral Fat And A Healthy Body
- Visceral Fat Relaxation Times
- Radiologist And Magnetic Resonance Imaging
- Magnetic Resonance Imaging Coils
- Magnetic Resonance Imaging Device
- Pros And Cons Magnetic Resonance Imaging
- Magnetic Resonance Imaging Vs X-Rays
- Uncomfortable Magnetic Resonance Imaging
- Future Potential Of Magnetic Resonance Imaging