Brain: the home of the mind

As the center of the nervous system, the brain can understand the information in the surrounding environment.The brain interprets information, the release of chemicals and send electronic signals (information), the body to react.However, the brain can adjust our body and action, not only is also home to our hearts.It is thought in physical location.

Our thoughts continuously controlled the flow of information, our memories, thoughts, emotions and imagination.This kind of information flow (Figure 1 a) like a social network, except that information is not sent between friends on social media, but along the neurons send to different parts of the brain.Mind network depends on the basis of brain structure and chemical composition, to successful operation.In fact, a network of effective thinking enables us to keep on cognitive, emotional and social health.

Mental health

This' thinking 'network, it sends a message of style and basic structure determines our mental health.For mental health problems, such as depression and anxiety, we often see network disruptions (Figure 1 b).The basic structure of our brain and the changes of chemical composition, can affect our response to the stress in your life, our productivity and overall health.Neuroscientists want to understand the mental health disorders and how we can maintain mental health, began to study the network ' ' ' 'thinking.If we can understand the structure and chemical composition can affect the brain, then we can begin to understand the brain disease.However, in order to be able to research ideas and network, we need to be able to see inside the brains of people.To this end, we useMagnetic resonance imaging (MRI)Technology.

Magnetic resonance imaging: magnetic resonance imaging (MRI)

Magnetic resonance imaging (MRI) to enable us to through the use of magnets and radio waves with amazing details see within the body.Used for imaging the first MRI scanner to the human body in New York in 1977.Since then, the technology has come a long way, now the doctor often use MRI to see within the body.This is because the MRI does not involve radiation (e.g., X-ray or CT scan), and around the world are increasingly using MRI scanners.

Magnetic resonance imaging of the magnet ' ' ' '

MRI scanners is basically a huge magnet.in称为特斯拉（T）的单元中测量磁体的强度。在医院和医学研究诊所使用的大多数 MRI 扫描仪都是 1.5T 或 3T。来比较一下吧，地球的磁场大约为 0.00006T。3T MRI 扫描仪的强度比地球的磁场强大约 6 万倍！

MRI using magnetic field and radio waves to measure water in different body tissue, draw the location of the water, and then use this information to generate detailed images.Images can be very detailed, because about 65% of our body are composed of water, so we have a lot of signals can be measured.Water molecules (H₂O) is made up of two atoms of hydrogen and one atom of oxygen.Hydrogen (H) of the atom is cause the cause of the water can be used to measure, when we performed MRI scanning, it can convey signals from the body.

If we study hydrogen in more detail, we'll see that it has a contains a single positive charge at the center of the nucleus, called protons (Figure 2 a).Pivoting is like the earth, with the arctic and Antarctic poles, each rotation of the hydrogen proton is just like a tiny magnet, on its own axis rotation.The rotary motion is called precession.in任何时候，我们体内的所有数十亿个氢质子都处于随机位置并在它们的轴上旋转。

However, when we put the body in a very strong magnetic field (such as MRI scanners), the changes of randomness.Like a compass points to the earth's magnetic field, when these random rotating hydrogen protons are placed in an MRI scanner, they will point to the shaft stronger magnetic field.We call the scanner is magnetic fieldB0Field.Like a compass in the earth's magnetic field, the compass itself was not physical, but the pointer rotation point to a specific direction.Also, when you enter the MRI scanner, hydrogen protons will not physical in your body to move, but their axis of point is changed due to the B0 field.Some ' ' ' 'upward (parallel), some' ' ' 'down (parallel), while still on its own axis rotation (Figure 2 b).Explain the need to use great laws of quantum physics, we will not discuss here, but ' ' ' 'up of protons is always better than' ' ' 'down a little bit more.So the total magnetic field generated from all these protons, 'up' and 'down' basic offset each other, only a small part of the 'up' proton magnetic field, is that we can use MRI to measure.

B0 field not only affect the arrangement of the hydrogen proton, but also affect the speed of the protons rotate (calledThe precession frequencyProtons in the magnetic field rotation rate).The precession frequency depends on the intensity of magnetic field.The stronger the magnetic field, the faster they spin.

How can we detect the magnetic field?

So how do we distinguish by additional 'up' in our bodies caused by hydrogen proton tiny magnetic field B0 field of scanner?We use a called radio frequency (RF) radio frequency (RF) pulse, interference or flip all protons, at the same time is not affected by magnetic field scanner (Figure 2 c).The RF pulse frequency must be same as the frequency of the rotating hydrogen protons, so they can exchange energy, each otherresonance.Resonance protons can absorb enough energy from the RF pulse, make its rotation axis from B0 field, so that MRI scanner measured it.Assume our compass points to the north in the earth's magnetic field, a small magnet if we placed next to the compass, we can spin the pointer points to the east.This is similar to proton behavior when we open the RF pulse.

If the whole body is full of ' ' ' 'up hydrogen protons are in the same precession frequency in B0 to rotate, how we only for those in the brain to examine the mental health?Proton precession frequency depends on the magnetic field strength.We use another magnetic field, B1, it's different in the body.inFigure 3. AIn the example shown, the head of hydrogen protons will than the chest, stomach and feet hydrogen proton spin faster.Then, we will attune to the RF pulse head hydrogen proton precession frequency.And then,The RFPulse will only proton resonance in the brain.Therefore, only a proton in the brain can absorb energy from the RF pulse and turn off from the B0 field.If we are interested in the foot of the imaging, we clearly can adjust our RF pulse and proton resonance in the rest of the body, such as the feet.

How do we get from these spinning proton images?

So how do we from these spinning, flip the image captured in hydrogen proton?When the RF pulse closing, proton flip back and along the magnetic field B0 reordering.Think about our compass, when we are going to remove small magnet, pointer will turn and from east to north again aligned with the earth's magnetic field.As protons back flip and aligned with B0, they release energy.The differences in body tissue release different energy.In order to measure the energy, we need some special equipment (referred to as the coil), placed around our trying to imaging parts of the body (Figure 3 b).ACTS as an antenna coil and will release the energy of the recognition to current.Through the computer, we use is calledThe Fourier transformTo transform the current mathematical calculation.Because the different brain tissue of proton, for example, gray matter, white matter release different energy and blood, so the result of the conversion of energy can be very detailed images of the brain tissue.

conclusion

We have described how to use MRI to generate and measure the signals of water molecules in the body.But, in addition to provide our internal body image, MRI can also be used to answer questions about brain structure and function of many different.From the MRI images, we can not only study the brain's structure and chemical composition, can also study how our brain network connection, and how to communicate with each other between different areas of the brain (Figure 3 c).In this way, neuroscientists can study thinking network in the difference of health and mental health disorders.Through the understanding of mental health problems and how to change the brain, we can treat these diseases.

The vocabulary

Magnetic resonance imaging (MRI):writeMagnetic resonance imaging (fmri).

B0:writeThe main magnetic field of the scanner.

The precession Frequency (Precessional Frequency):writeProtons in the magnetic field rotation rate.

Resonance (On Resonance):writeWith the same frequency.

The RF:writeRadio frequency (rf) pulse, used to make resonance protons from B0 field.

Fourier Transform (Fourier Transform):writeFor the current in the coil into the mathematical calculation of the image.

Conflict of interest statement

The author statement, the study is in no may be interpreted as potential conflicts of interest under the condition of commercial or financial relationships.