The Future of healthcare is here.
The invention of the MRI scanner has produced unimaginable results; including ground-breaking discoveries and prevented numerous diseases. Let's see what's special about this device
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The invention of the MRI scanner has produced unimaginable results; including ground-breaking discoveries and prevented numerous diseases. Let's see what's special about this device
Magnetic Resonance Imaging (MRI) is a non-invasive imaging technology that produces three dimensional detailed anatomical images. It is an imaging test that produces detailed images of almost every internal structure in the human body, including the organs, bones, muscles and blood vessels. It is often used for disease detection, diagnosis, and treatment monitoring.These are the basic parts of a typical MRI Scanner
These magnets produce a strong magnetic fiels that forces protons in the body to align with that field.
RF coils are the “antennas” of the MRI system and have two functions: first, to excite the magnetization by broadcasting the RF power (Tx-Coil) and second to receive the signal from the excited spins (Rx-Coil)
The patient lays on this table to begin the scan.
Gradient coils are used to produce deliberate variations in the main magnetic field. These are usually three sets of gradient coils, each for each direction. The variation in the magnetic field permits localisation of image slices as well as phase encoding and frequency encoding.
The bore is the open space which is used to obtain and transmit images during the patient's examination to a nearby computer.
These magnets produce a strong magnetic fiels that forces protons in the body to align with that field.
RF coils are the “antennas” of the MRI system and have two functions: first, to excite the magnetization by broadcasting the RF power (Tx-Coil) and second to receive the signal from the excited spins (Rx-Coil)
The patient lays on this table to begin the scan.
Gradient coils are used to produce deliberate variations in the main magnetic field. These are usually three sets of gradient coils, each for each direction. The variation in the magnetic field permits localisation of image slices as well as phase encoding and frequency encoding.
The bore is the open space which is used to obtain and transmit images during the patient's examination to a nearby computer.
The MRI machine is a large, cylindrical (tube-shaped) machine that creates a strong magnetic field around the patient and sends pulses of radio waves from a scanner. The MRI scanner is essentially a giant magnet. The strength of the magnet is measured in a unit called Tesla (T). Most MRI scanners used in hospitals and medical research clinics are 1.5 or 3 T. Putting that in to perspective, the earth’s magnetic field is around 0.00006 T. A 3 T MRI scanner is around 60,000 times stronger than the earth’s magnetic field! Most of the human body is made up of water molecules, which consist of hydrogen and oxygen atoms. At the centre of each hydrogen atom is an even smaller particle called a proton. Protons are like tiny magnets and are very sensitive to magnetic fields.
Magnetic Resonance Imaging (MRI) takes advantage of the fact that the nucleus of a hydrogen atom (a single proton) behaves like a weak compass needle. In the presence of a strong magnetic field, the hydrogen atoms will align themselves, but a radio signal of the correct resonant frequency will cause them to deflect slightly. When the signal is removed, the atoms return to their equilibrium state and emit a radio signal of their own. An MRI scanner can detect these signals and use them to map the distribution of molecules with lots of hydrogen atoms – ie, water and fat. In this way, it can create detailed images of the inside of the body.
At any moment in time, all the billions of hydrogen protons in our bodies are all in random positions and spinning on their axes. However, this randomness changes when we place a human body into a very strong magnetic field, like an MRI scanner. Just like a compass needle aligns to the Earth’s magnetic field, the strong magnetic field created by the MRI scanner causes the atoms in your body to align in the same direction. Their axes realign with the scanner's stronger magnetic field. The scanners magnetic field is called the B0 field. Just like a compass needle in the earth’s field, the compass itself does not physically move, but rather the needle spins to align itself.
Similarly, the hydrogen protons do not physically move in your body when you enter an MRI scanner, their axes just align along the direction of the B0 field. Some will align “up” (parallel) and some will align “down” (anti-parallel), while still spinning around on their own axes. Due to the wonderful laws of quantum physics, there are always just slightly more “up” protons than “down.” If you now think about the total magnet field generated from all our hydrogen protons, these tiny magnets almost cancel each other out, to leave only the magnetic field from the small proportion of extra “up” protons, and it is this small magnetic field that we can measure using MRI.
The B0 field not only affects the hydrogen proton’s alignment, but also affects how fast these protons spin (called precessional frequency - The rate at which protons spin in a magnetic field.). The precessional frequency depends on the strength of the magnetic field. The stronger the magnetic field, the faster they spin. These two ideas of axis realignment and precessional frequency are important when we use MRI to measure the signal from these hydrogen molecules.
Radio waves are then sent from the MRI machine and move these atoms out of the original position. As the radio waves are turned off, the atoms return to their original position and send back radio signals.
We use something called a radio frequency (RF)Radio frequency pulse to tip on resonance protons away from the B0 field. This pulse is used to disturb or flip all the protons, at the same time, out of alignment from the scanners magnetic field. The frequency of the RF pulse must be the same as the frequency of the spinning hydrogen protons, so they can exchange energy, so that they are on resonance, ie, have the same frequency. with each other. Resonance enables the protons to absorb enough energy from the RF pulse to rotate their axes away from the B0 field, so that the MRI scanner can measure it. If we think again about our compass in the Earth’s magnetic field pointing toward the north pole, we can make the needle rotate to point east if we place a small bar magnet next to the compass. This is similar to the way the protons behave when we turn on the RF pulse.
If the whole body is full of hydrogen “up” protons all spinning at the same precessing frequency in the B0, how do we target just the ones in the brain to investigate mental health? We use the fact that the precessional frequency of the protons is dependant on the magnetic field strength. We apply a second magnetic field, B1 that varies across the body. In the example shown in the next slide, hydrogen protons in the head will then be spinning faster than those in the chest, stomach and feet. Then, we tune the RF pulse to the precessing frequency of the hydrogen protons in the head. The RF pulse will then only be resonant with the protons in the brain. Therefore, only the protons in the brain will absorb energy from the RF pulse and be flipped away from the B0 field. We can obviously tune our RF pulse to be resonant with protons in other parts of the body, like the feet, if we were interested in imaging the feet!
The signals are received by a computer and converted into an image of the part of the body being examined. This image appears on a viewing monitor. So how do we get an image from these spinning, flipped hydrogen protons in the brain? When the RF pulse is turned off, the protons flip back and realign along the main magnetic field, B0. If we think of our compass again, when we move our small bar magnet away, the needle will rotate from east to north and align with the Earth’s magnetic field once more. As the protons flip back and realign with B0, they give off energy. Different tissues in the body give off different amounts of energy.
To measure this emitted energy, we require some special equipment (called a coil) that is placed around the body part we are imaging. The coil acts as an antenna and detects the released energy as an electrical current. The electrical current is transformed, via a computer, using a mathematical calculation called a Fourier transformationA mathematical calculation that is used to change the electrical current in a coil into an image.. Because protons in the different kinds of tissues in the brain, such as gray matter, white matter and blood, all give off different amounts of energy, the result of the transformed energy is a highly detailed image of the tissue inside the brain.
MRI may be used instead of computed tomography (CT) when organs or soft tissue are being studied. MRI is better at telling the difference between types of soft tissues and between normal and abnormal soft tissues. Because ionizing radiation is not used, there is no risk of exposure to radiation during an MRI procedure. Newer uses for MRI have contributed to the development of additional magnetic resonance technology. Magnetic resonance angiography (MRA) is a procedure used to evaluate blood flow through arteries. MRA can also be used to detect aneurysms in the brain and vascular malformations — abnormalities of blood vessels in the brain, spinal cord or other parts of the body.
Functional magnetic resonance imaging (fMRI) of the brain is used to determine the specific location in the brain where a certain function, such as speech or memory, occurs. The general areas of the brain in which such functions occur are known, but the exact location may vary from person to person. During fMRI of the brain, you will be asked to perform a specific task, such as reciting the Pledge of Allegiance. By pinpointing the exact location of the functional center in the brain, doctors can plan surgery or other treatments for a brain disorder.
MRI is a non-invasive way for your doctor to examine your organs, tissues and skeletal system. It produces high-resolution images of the inside of the body that help diagnose a variety of problems. An MRI scanner can be used to take images of any part of the body (e.g., head, joints, abdomen, legs, etc.), in any imaging direction. MRI provides better soft tissue contrast than CT and can differentiate better between fat, water, muscle, and other soft tissue than CT (CT is usually better at imaging bones). These images provide information to physicians and can be useful in diagnosing a wide variety of diseases and conditions.
An Mri scan can be used to detect:
MRI that focus here can access
MRI can help evaluate
Long before there was magnetic resonance imaging (MRI), magnetic resonance was being studied within different chemicals. This form of science was called nuclear magnetic resonance (NMR) and was initially demonstrated in 1945. NMR is founded upon the phenomena that the nucleus of atoms in a magnetic field resonate when a secondary oscillating magnetic field is applied. Spectroscopy, later transferred to MRI, is the study of physical, chemical, and biological properties of matter. Spectroscopy studies the chemical shift, which is a variation in molecular electron distribution, throughout different chemicals.
The next step towards MRI would come over ten years later, in 1969, when Dr. Raymond Damadian hypothesized that cancerous cells could be differentiated from non-cancerous ones using magnetic resonance. He theorized that cancerous cells hold more water and would show up in MR due to the increased number of hydrogen atoms in relation to the extra water. Damadian performed an experiment with both cancerous and normal rats. His study, conducted at the NMR Specialties company and published in 1971, would prove his theory.
In 1971, another scientist named Paul Lauterbur observed a similar experiment conducted by a post-doctoral researcher. Lauterbur observed a difference between cancerous and non-cancerous tissues. However, he regretted that the experiment had to be conducted on dead tissue. He pondered this issue for a while before coming up with an idea that would change the medical imaging world: a way for living tissue to be imaged. This would enable scientists to locate the precise origins of NMR signals and image in two or three dimensions. His theory was also published in 1971. Lauterbur imaged two water-filled test tube using magnetic resonance, producing the first MR image.
Within the next year, a third researcher, Sir Peter Mansfield, was studying chemical shift anisotropy. Mansfield realized that adding a magnetic field gradient could allow scientists to look at the atomic structure of a chemical. This, like Lauterbur's method, would allow scientists to create a three-dimensional image. In fact, a colleague later asked if Mansfield was aware of Lauterbur's ideas, which were published in a scientific journal.
All three scientists also developed techniques for creating these images. Damadian's method involved the creation of a human scanner. Lauterbur's method was projection reconstruction method and is partly used for motion reconstruction in today's MRI scans. Mansfield's method was called line scanning and involved scanning pieces of the structure, which combine to make the image. Mansfield was able to image a student's finger in 15-23 minutes in 1974.
The race to create the first whole-body MRI scanner began shortly thereafter, with both Damadian and Mansfield participating. Three years later, Damadian created the first whole-body human scanner in May of 1977. This system was named "Indomitable". These images were significantly more detailed than those produced by X-ray and CAT scanners. By the end of 1978, Damadian had founded his MRI scanner manufacturing company, Fonar. Six years later the device was approved for use by the FDA.
Sir Peter Mansfield with the help of two others in 1978. They had developed radio frequency and gradient coils and had been working to create a large scale image. Mansfield climbed into his machine and had his assistant perform a test pulse and then started the scan. The scan caused significant heat due to the metal's vibration, but Mansfield stayed in the scanner for 50 minutes while the scan was taken. The film had to be taken to a store for processing. After this, Mansfield went on to develop the echo-planar imaging technique, which is still used and significantly reduces scan time.
After the shift toward medical MR, nuclear magnetic resonance quickly lost its first word to increase comfort among patients. Scanners are continuously being improved upon to increase image quality, speed, and comfort as well. Coil have become vital parts of a scan and have become more durable and patient-friendly. Since Damadian, Lauterbur, and Mansfield came up with their ideas for MRI, the imaging method has imaged much more than their original target, cancer, and has helped more patients than even they may have expected.
Eventually, the Nobel Prize was awarded to the inventors of this MRI scanner. Although Nobel rules allow for the award to be shared by up to three recipients, Damadian was not given the prize. The Nobel committee’s decision to omit Damadian from the 2003 medicine prize for the invention of magnetic resonance imaging (MRI) was viewed as controversial. “For some, his [Damadian’s] absence from this year's accolades is conspicuous,” wrote the medical journal, The Lancet, at the time. Damadian’s imaging technique is not used in today’s MRI procedures. However, MRI would not exist today without his key discovery of variation among the relaxation times of nuclei in different environments. NMR scanning resulted from two essential steps. They were taken by the two great MRI pioneers of this volume, Dr. Raymond Damadian and Dr. Paul Lauterbur. Dr. Damadian provided the first step, the discovery of tissue NMR signal differences from which the image is made and the first concept of an NMR body scanner that would utilize these signal differences to detect disease in the human body. Dr. Lauterbur provided the next step of visualizing these signal differences as an image and supplied the first method for acquiring these signals at practical speeds. It does not seem likely that MRI could have come to pass without the key steps contributed by both scientists. Without Damadian's discovery, it could not be known that serious diseases like cancer could be detected by an NMR scanner or that tissue NMR signals possessed sufficient contrast to create medically useful images. Without Lauterbur's contribution, development of a practical method for visualizing these signal differences as an image might have occurred much less efficiently. Moreover, the incredible amount of courage and pugnacity shown by Damadian, working alone with only two students, without any consistent granting, thus leading him to do most of the development of his system as a self-made man learning when required, electronics, machining, welding and many other technologies in order to built his first prototype, is exemplary for any researcher. This have to be compared with the working conditions of Lauterbur or Mansfield, both working with comfortable fundings in spacious laboratories with many colleagues and students. At least from the point of view of the merit, the work of Damadian, indeed, is considerable. In fact, concerning this Nobel Prize controversy and the invention of this machine, Damadian said in 2002, "If I had not been born, would MRI have existed? I don't think so. If Lauterbur had not been born? I would have gotten there. Eventually." The Nobel Prize was awarded to the American chemist, Paul Lauterbur, and the British physicist, Peter Mansfield, for developing a method to represent the information gathered by a scanner as an image. This is fundamental for the way the technology is used today.