Tag Archives: MRI scan

What’s an MRI and how does it work?

Magnetic resonance imaging (MRI) is a medical technique that can capture images from inside the living body by using powerful magnets and radio waves. Nowadays, MRIs are routinely used to examine internal body structures and diagnose diseases without having to cut anything open.

Credit: Wikimedia Commons.

The first MRI scanner for the human body was invented in 1977. Since then, the technology has proven revolutionary in medical practice and neuroscience.

The invention of X-ray imaging, which allows doctors to see bone fractures and dislocations, changed medicine forever. Later came ultrasound imaging, computed tomography (CT), and MRI. The latter came as a natural complementary technology, which allowed doctors to see the structure of cartilage, ligaments, muscles, joints, and other types of tissue that can’t be possibly shown by an X-ray.

How MRI works

MRI scan. Credit: Pixabay.

Unlike other imaging methods that employ radiation, MRIs rely on huge magnetic fields to scan living internal structures.

An MRI scanner is essentially a giant magnet. Most MRI scanners found in hospitals operate at 0.5 to 3 Tesla (the unit of measurement for magnetic field). For comparison, the planet’s magnetic field sits at around 0.00006 T — that’s 60,000 times weaker than a typical MRI’s magnetic field.

Generating a magnetic field of this magnitude entails quite the setup. Most MRI devices use a superconducting magnet which creates a magnetic field by passing electricity through many coils. Maintain a magnetic field up to 2 Tesla in strength requires a lot of energy, which is an MRI’s wires are bathed in liquid helium that cools them near absolute zero. At nearly minus 269°C, the wires achieve superconductivity, meaning electricity can flow through them with virtual no resistance.

In order to image the internal structure of biological entities, MRIs exploit the physical properties of water. The interaction between magnetic fields and radio waves generated by water (particularly its hydrogen atoms) can be used to map the location of water molecules.

Humans are about 65% made of water, so it’s fairly straightforward to generate images using this method.

Water molecules (H2O) are made of hydrogen protons and oxygen. And it’s the hydrogen atoms that are the most important part of the mechanism that enables MRI machines.

Like Earth, hydrogen protons spin on their own axis. Each spinning hydrogen proton is like a tiny magnet that spins around its own axis, a motion known as precession.

Our body contains billions of hydrogen protons all spinning differently on their axes in random positions.

However, when a person steps in an MRI machine, the very powerful magnetic field causes the hydrogen protons spinning axes to realign with the scanner’s magnetic field (also known as the B0 field). This is similar to how a compass needle aligns with Earth’s magnetic field.

Some of these protons will align “up” (parallel) and some will align “down” (anti-parallel). About half go each way, so the magnetic fields cancel each other. But due to quantum mechanical effects, there are slightly more “up” protons, only about a couple out of every million. Although that may not sound like a lot, the sheer number of hydrogen atoms found in the human body means there are enough unmatched protons to create a very detailed image.

At this stage of the scanning, the MRI machine fires a radio frequency pulse towards the area of the body that needs to be examined. The pulse is tuned such that only the hydrogen protons respond, causing the unmatched protons to absorb the energy and spin in a different direction — this is the resonance part of MRI.

During the same time, three additional magnets, known as gradient magnets, are switched on besides the main magnetic field. These additional magnets are turned on and off rapidly, affecting the local magnetic field. In each fraction of a second that the magnet is turned on, a “slice” of the area to be imaged is generated.

MR angiogram in congenital heart disease. Credit: Wikimedia Commons.

After the MRI’s magnetic field is switched off, the protons gradually return to their normal precession and release the energy absorbed from the radiofrequency pulse. The signal is picked up by the coils and sent to a computer which ultimately converts it into an image. Since different body tissues generate different radio signals, the MRI is able to distinguish various types of tissue.

In summary, the physical principles of MRI can be divided into three stages: magnetization, resonance, and relaxation.

Types of MRI

White matter connections obtained with MRI tractography. Credit: Wikimedia Commons.

There are many forms of MRI, but the two most common ones are functional MRI (fMRI) and diffusion MRI.

Diffusion MRI has only been around for no more than 20 years. This type of MRI imaging is based upon measuring the random Brownian motion of water molecules with a tissue. Certain diseases can restrict this diffusion, something that is particularly true for cancers. As such, this method can be a very effective diagnostic tool.

Functional MRI, or fMRI, doesn’t just provide structural imaging — it can also be used to visualize functional activity, in the brain. It works by measuring changes in blood flow to different areas of the brain. This is how scientists are able to determine which parts of the brain are responsible for certain functions, making fMRI an integral part of modern neuroscience research. It can also be used to assess damage from an injury or brain disease like Alzheimer’s.

What taking an MRI looks like

Before the procedure, a doctor will ask the patient to strip off all their jewelry, credit cards, phone, and anything with metal parts. Patients also have to answer questions about their medical history, especially if any surgery or operation took place that resulted in an implant.

During an MRI, a patient who requires an internal body scan will first lie on a movable table, which then slides into a doughnut-shaped opening of the machine.

Although the magnetic fields generated by an MRI are enormous, these pose no risks to human health. However, people undergoing an MRI might complain about loud sledgehammer-like noises that the machine produces during its operation.

Once the loud hammering noise starts, the person undergoing the MRI scan needs to lie perfectly still otherwise they might have to repeat the procedure all over again.

A typical MRI scan lasts 30 to 60 minutes. A certified radiologist will then look at the final images and report the results to your doctor.

The risks of using MRI

Credit: Wikimedia Commons.

MRI is considered one of the safest imaging procedures. Unlike X-ray machines or CT scanners, MRIs do not employ ionizing radiation. For this reason, for instance, MRI can be safely used to image a fetus during pregnancy or other vulnerable patients. A person will typically feel nothing out of the ordinary when undergoing a body scan (apart from the loud noise) and there are no known biological hazards for humans associated with the exposure to the strong magnetic field.

That being said, the procedure is not without any risks. An MRI generates a huge magnetic field — it’s basically a huge magnet. And we all know what’s attracted to magnets: metal.

In today’s age, many people have metal implants, from pacemakers to artificial joints and metal plates. These implants can heat up or move considerably inside a magnetic field. Fortunately, many implants performed today are designed to be MR-safe.

In any event, no metal objects should be inside the MRI room when the machine is turned on. Even a pen or paperclip can be turned into extremely dangerous projectiles that fly towards the opening of the magnet at very high velocity.

There’s also something to be said about the loud noise produced by the machine. Patients are always asked to wear ear protection when stepping inside an MRI.

Credit cards and anything with magnetic encoding will be erased, so that’s something to consider as well.

baby_brain

Baby brains grow to half the adult size in just 90 days

baby_brain

Researchers performed MRI scans on babies to see how their brains developed from birth to later stages. Their findings reveal the explosive growth of the human brain following birth: in just 90 days, the baby brain grows by 64% its initial size reaching half the adult size.

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They grow up so fast

Traditionally, brain growth is followed the old fashioned way using a measuring tape. This way, doctors casually record skull, and consequently brain growth and if any deviations from a known patterns are encountered, they then further investigate. For instance, premature babies have a smaller brain and develop slower than those delivered at term. As we all know, skulls vary in shape and size and they’re not the best metric for gauging brain size.

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Lucky for scientists, there are MRI scanners. Researchers at University of California scanned the brains of 87 babies, healthy and delivered at term, from birth until three months of age. They saw the most rapid changes immediately after birth – newborn brains grew at an average rate of 1% a day. This slowed to 0.4% per day at the end of the 90-day period. The highest growth rate among brain structures was for the cerebellum, an area of the brain involved in movement. Oppositely, the hippocampus which is responsible for memory formation and retrieval showed the least growth. Apparently, in its early stages the brain wants to concentrate resources on getting the heck out – ‘guh, guh, dadah’ is enough for now.

 

“This is the first time anyone has published accurate data about how babies’ brains grow that is not based on post-mortem studies or less effective scanning methods,” Dr Martin Ward Platt, a consultant paediatrician at the Royal Victoria Infirmary in Newcastle.

“The study should provide us with useful information as this is an important time in development.

“We know, for example, if there are difficulties around the time of birth, a baby’s growth can fall away in the first few months.”

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By closely following brain development in its early formation days, researchers hope to spot clues that might help them  identify early signs of developmental disorders such as autism.Scientists will now investigate whether alcohol and drug consumption during pregnancy alters brain size at birth. Findings appeared in JAMA Neurology.

 

An amputee suffering from phantom pain maintains a representation of the phantom hand in their brain. (c) Oxford University

A scientific explanation for the “phantom limb”

An amputee suffering from phantom pain maintains a representation of the phantom hand in their brain. (c) Oxford University

An amputee suffering from phantom pain maintains a representation of the phantom hand in their brain. (c) Oxford University

Every once in a while, some people who have had a limb, organ or some other body part amputated or removed still experience it, feel its pain and experience the sensation that it’s still attached to the body and is moving appropriately with other body parts. This sensation is typically referred to as  phantom limb. Now, researchers at Oxford University have found that changes in the brain following amputation are responsible for the sensation.

‘Almost all people who have lost a limb have some sensation that it is still there, and it’s thought that around 80% of amputees experience some level of pain associated with the missing limb. For some the pain is so great it is hugely debilitating,’ says first author Dr Tamar Makin of the Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB) at Oxford University.

The origin of this peculiar pain, that shouldn’t be there in the first place, is poorly understood currently. Explanations for the phantom limb pain range from  injured nerve endings where the limb was lost to changes in the brain areas connected with the missing limb. What’s certain is that it hurts, and in some cases very badly.

Lynn Ledger, a 48 year old trained therapist and advisor to charities on management training from Nottingham, UK, took party in the study. She had lost her left arm following a failed radiotherapy for a rare form of cancer – the tumor had be cut out, limb and all. Still, even though her left arm was gone, she could feel tremendous pain as it would originated from it.

‘I’ve pretty much tried everything to deal with the pain but nothing has worked,’ Lynn says. ‘There are no drug treatments that work because the condition is not fully understood yet. I can only use various distraction techniques, breathing exercises and mental imagery techniques, to help me manage the pain.

‘It’s very hard to describe the pain to others. I have a nonexistent limb, but I still sense it and feel pain. It’s like: imagine you are wearing a lady’s evening glove that stretches from the fingers up the arm past the elbow. But everywhere the glove covers, it’s as if it’s constantly crushing your arm. There are also shooting pains and intensely painful burning sensations that come and go, but the crushing pain is constant.

‘When I heard about this study I wanted to be involved as it was trying to improve people’s understanding of the condition.’

Like Ledger there are thousand who battle an invisible pain every day. Researchers at Oxford used used MRI imaging to study how the phantom limb pain was felt by 18 amputees, with differing levels of phantom pain. The data was compared to 11 individuals born with one hand through a limb deficiency and a control group of 22 adults with two full limbs.

This pain you can not see

Kirsty Mason lost her right arm four years ago just below the elbow. (c) Oxford University

Kirsty Mason lost her right arm four years ago just below the elbow. (c) Oxford University

To be on the safe side, the participants involved in the study had their limbs amputated on average 18 years ago. It’s important to note that even after all this time, they still experienced pain. In order to see how the missing limb still relates to the brain, the researchers asked participants to think about moving the fingers of their missing hand.

They found that the brain maintained its representation of the hand, even though the limb was no longer there. Moreover, there’s a direct correlation between the amount and frequency of experienced pain and the extent of this representation – the stronger the pain, the better the representation. All this despite the limb might have been removed decades ago.

The researchers found that the amount of grey matter in the phantom hand area of the brain was reduced in amputees compared to those with two hands. But again this was linked to the amount of pain amputees felt. Those experiencing stronger pain showed less structural degeneration in the missing hand area following the loss of the limb.

Dr Makin says: ‘Most people experience “phantom” sensations in a missing limb after amputation. This disconnect between the physical world and what they are experiencing appears to be linked to a functional detachment in the brain. There seem to be reduced connections between the missing limb part of the brain and the rest of the cortex that’s involved in movement.

‘Our results may encourage rehabilitation approaches that aim to re-couple the representation of the phantom hand with the external sensory environment.’

Findings were reported in the journal Nature Communications

 

 

This digitized image made from a screen shot of a new iPad app, provided Sept. 24, 2012 by the National Museum of Health and Medicine Chicago.

Einstein’s brain: now available on iPad

This digitized image made from a screen shot of a new iPad app, provided Sept. 24, 2012 by the National Museum of Health and Medicine Chicago.

This digitized image made from a screen shot of a new iPad app, provided Sept. 24, 2012 by the National Museum of Health and Medicine Chicago.

After the most recognized physics figure in the world, Albert Einstein, past away on April 18, 1955, the whole world was left in shock, seeing how he was even by then considered the most famous physicist in history. His dying wish was that of being cremated, however an eccentric physician by the name of Thomas Harvey, a Princeton Hospital pathologist, removed Einstein’s brain without any kind of permission, either from the authorities or Einstein’s family. He quickly sliced Einstein’s brain in 200 cubes and left them in formaldehyde for preservation. Now, 57 years after Einstein’s passing, the same slices were sampled, scanned, digitized and made available to general public under the form of an iPad app.

Yup, you’ve heard it right – Einstein’s grey matter is now on iPad, and while some of you might rejoice at the thought of exploring through one of humanity’s greatest minds, some might find it offensive. Whatever may be the case, it’s done and over. Einstein’s brain walk-through was made after 350 brain slices taken from the collection bequeathed to the National Museum of Health and Medicine Chicago by the Einstein family estate in 2010 were digitized.

Now, the view itself is extremely interesting as you might imagine, just like you’d observe the slices by a microscope, however they’re no where near as detailed as modern brain scans via MRI’s, which can render a 3-D model. So, while things like cellular structure and tissue definitions are clearly visible, the developers didn’t highlight which parts of the brain you’re looking at.

Possibly the world’s greatest mind

Was Einstein’s brain different from the typical human one, though? Well, an investigation led by Harvey himself, whose results were subsequently published in the journal Lancet in 1999, found that Einstein’s parietal lobe, the part of the brain associated with our processing of mathematics, language, and spatial understanding, was 15 percent wider then normal. Also, small parts of Einstein’s brain were missing according to Harvey’s slices, like the Sylvian fissure and parts located in the frontal lobe.

According to Sandra Witelson, who worked on the paper, “This unusual brain anatomy may explain why Einstein thought the way he did… Einstein’s own description of his scientific thinking was that words did not seem to play a role. Instead he saw more or less clear images of a visual kind”.

The new iPad app may allow researchers to dig even deeper by looking for brain regions where the neurons are more densely connected than normal, said Dr. Phillip Epstein, a Chicago-area neuroscientist and consultant for the museum

It’s not clear whether these physical discrepancies helped Einstein develop such a powerful intellect, still considering his brain is now freely available to the public – well, sort of, since the app is priced at $9.99 – scientists from all over the world may study it and possibly find hints that suggest a superior mind.

via Wired

An unhealthy lifestyle leads to brain shrinkage later on, study says

The latin phrase “mens sana in corpore sano” has been put to the test by researchers who wanted to study what kind of repercussions an unhealthy lifestyle has on the mind. What they found was a dramatic increase in brain damage and dementia cases among subjects who have experienced high blood pressure, diabetes, smoking and obesity in middle age.

The study, published in today’s edition of the journal Neurology, worked around the already available famous Framingham Heart Study, which has followed residents of Framingham, Mass., and now their offspring, for more than 60 years. Using data from this extensive research, scientists only chose a small subset of 1,400 people to study their habits and general health status and see how they correlate to the various potential brain afflictions one might posses later on in life.

Using brainteaser tests and routine MRI scans, the researchers’ results were staggering – each potential hazard like hypertension, diabetes, smoking and obesity was linked to a different cognitive impairment.  As such, people with high blood pressure had a much greater risk of succumbing to vascular damage in their brains, than those with normal blood pressure. Diabetics lost brain volume in the hippocampus, which, among other functions, converts short-term memory into long-term memory – a great risk factor for Alzheimer. The worst off were smokers  – they were found to experience a brain volume shrinkage in overall and in the hippocampus at a faster rate than nonsmokers, while at the same time, coupled with hypertension, they also showed white matter vascular damage.

Obesity was found to be extremely troublesome to the mind’s health as well. Obese people were more likely to score lower at test scores for various brain tasks, such as memory and abstract thinking, than people with a normal body mass index. Actually, scientists found that the more obese a person was, the greater the brain shrinkage and the greater the risk of dementia. In a study we reported on a few months ago, another group of researchers reached the same result when they published a paper in which they showed how obesity is linked to dementia.