you might have seen this on TV or some of you might have even experienced this strange procedure firsthand MRI scans are used in the medical field for diagnosis in cases such as a brain hemorrhage a blood clot occurs deep inside the brain where doctors can't see an MRI scan produces a very detailed 2D image of the brain allowing doctors to analyze the damaged tissue and then perform their targeted surgery let's take a deep dive into how MRI imaging works and the principle behind it MRI is a technique that uses varying magnetic fields and radio pulses
to create detailed images of the organs and tissues in the human body MRI machines have tube-shaped strong electromagnets gradient coils and RF coils to generate strong varying magnetic fields and radio frequency pulses using the help of em Works in this FEA simulation we can see the magnetic fields produced by electromagnets uniform magnetic fields are produced inside the bore now let's focus on the effect of magnetic fields and radio frequency signals on the body the human body is made up of 60 water and water composition surprisingly plays an important role in this technique when you lie
inside an MRI machine the magnetic field generated by the electromagnets and gradient coil temporarily realigns most of the water molecules in your cells in the direction of the magnetic field the scanner operator commands RF coils to send radio pulses causing these aligned atoms to flip within a few seconds the atoms realign with the magnetic field emitting an RF signal this RF signal is used to create cross-sectional 2D MRI images we'll expand on this brief explanation of MRI imaging technology later on first let's explore the difference between healthy and unhealthy tissues in the human body each
tissue has its own unique water composition when a blood clot happens in a certain tissue it changes the water composition of that area this allows us to clearly see the difference between healthy and damaged tissues let's narrow our focus on the water molecules inside our tissues the water molecule has two hydrogen atoms this hydrogen atom has a small magnetic field and it acts as a tiny bar magnet however this magnetic field keeps on spinning since the atom is spinning naturally the axis of the spinning magnetic field is oriented randomly in the human body when this
hydrogen atom comes into contact with an external magnetic field the orientation of the magnetic field of the hydrogen atom changes and aligns with the direction of the field Additionally the rate of magnetic field spin also changes in this case the rate of the spin is known as the resonance frequency and it varies according to the strength of the external magnetic field this resonance frequency is quite important in MRI and is determined using the laramore equation let's move on to the next step so far we've aligned all the hydrogen atoms in the direction of the magnetic
field let's strike a radial pulse on a hydrogen atom as a result the hydrogen atom changes its orientation and flips 90 degrees with respect to the main magnetic field it's important to remember that the frequency of an RF signal should be the same frequency as the hydrogen atom's resonance frequency only then will the hydrogen atom flip when we remove the RF pulses the atom loses its energy and returns to its normal orientation the energy it emits is in the form of RF pulses however the time it takes each atom to return to normal is different
meaning that the duration of emission of RF signals is also different the computer receives these signals and converts them into images since the unhealthy tissue has more hydrogen atoms it generates different RF signals but how exactly can we generate a detailed image the secret lies in phase and frequency encoding with the help of Furrier transformation now that you know how an MRI machine generates 2D images of a particular part of the brain you may be wondering how the machine is able to select the specific part of the brain for Imaging this work is done with
the help of gradient coils the main electromagnet is constant and the pair of gradient coils produce opposite magnetic fields to each other one coil increases the magnetic field and the other side coil decreases the magnetic field due to this gradient of the magnetic field formed in between the two coils there are three sets of coils for the X Y and Z directions let's see the magnetic field produced by the x-axis gradient coil with the help of FEA results produced by em works these results show us that variation in the magnetic field gradually increases from one
coil to the other gradient coils need to provide linear gradations of the magnetic field as we see in this FEA result as a result the resonance and frequency of hydrogen atoms will change from head to toe gradually in order to image the body region of Interest we must simply use the specific radio frequency in RF coils to excite just that part of hydrogen atoms that provide a signal as you might imagine the main component of an MRI machine is the electromagnet which provides a strong magnetic field most magnets are of the superconducting type ranging from
0.5 to 3 Tesla the superconducting magnet is continuously on from the time of installation to the time of decommissioning the magnet is 100 times stronger than small household magnets such as those found on refrigerator doors or in children's toys another main component of an MRI scanner is the RF coils many coil designs exist but they all fall into two main categories surface coils and volume coils as the name suggests a surface coil rests on the surface of the object being imaged Let's do an FEA simulation once again of a Birdcage brain RF coil with the
help of em works this result shows that there is more magnetic flux density on the side conductors and less on the end rings in its simplest form it's a coil of wire with a capacitor in parallel the inductance of the coil and the capacitance from a resident circuit are tuned to have the same resonant frequency as the part being imaged thank you for watching we hope you enjoyed this video please don't forget to support lezix on patreon
