Hello everyone. Welcome all of you to this course, MRI Fundamentals. Let's start to talk about overview of MRI first in this week. I will talk about biomedical imaging modalities first. We have four different categories for biomedical imaging modalities. First, we have radiographic imaging, which has X-ray and CT. So it's about the transmission of X-rays through the body and detection of X-rays on the opposite side of the body. Nuclear medicine includes a planar scintigraphy, SPECT and PET. So it's about the injection or radiotracers in the bloodstream of the body, and detection of gamma rays emitted from radiotracers within the body. And ultrasound is about the transmission of ultrasonic waves toward the body, and detection of reflective ultrasonic waves from the body. And the MRI is about placing the body in the stong magnetic field that cause spin systems to precess, and transmitting radio frequency energy to the body, which cause a magnetic resonance, and receives radio frequency energy induced in the body. So we are talking about MRI in detail in these course. So this is electromagnetic spectrum of the biomedical imaging modalities. So first, the ultrasound has low frequency, which has a slightly higher frequency than the frequency that we can hear. And the radio frequency is about about 100 megahertz level, it's about MRI, and we have infrared and visible light which has optical imaging, and then above that frequency level, we have X-rays and also gamma rays. So gamma rays are used for nuclear medicine. So these are the electromagnetic wave spectrum. So this portion is wavelength and also this portion is frequency. So let's talk about the beauty of biomedical imaging modalities. So first, they are non-invasive. So ultrasound and MRI, they are completely non-invasive, and X-ray, CT, SPECT and PET. So these modalities cause radiation exposure, but still they are considered non-invasive. And they provide tomographic imaging. And CT, SPECT, PET, ultrasound, MRI. So they provide tomographic imaging capability, and X-ray and CT, they provide only projection imaging. So biomedical imaging modalities also provide some certain information beyond anatomical information, which has physiological information, metabolic information, and functional information of our bodies. Especially SPECT, PET, and diffusion/perfusion rated MRI, and functional MRI, so these modalities provide these physiological, metabolic, and the functional information of our body. So this information cannot be detected through simple dissection of our body. This is also beauty of biomedical imaging modalities. So we will talk about MRI in this course, let's talk about MRI in comparison with other imaging modalities. So, MRI provide relatively high spatial resolution, and it also provides a high soft tissue contrast, and it also provides tomographic imaging capabilities. Especially MRI provides much modern tomographic imaging capability because it can scan along any direction. So that is a unique feature of MRI, which we talk in detail later. And MRI is a completely non-invasive, and also it is a kind of integration on many different imaging modalities like anatomy, physiology, metabolism and the function. So these information can be scanned or acquired all together within our single imaging modality. So that is also unique and a great advantage of MRI. And also MRI has a feature called pulse sequencing. So each time sequencing of currents in radio frequency coils and the gradient coils. Manipulation of these pulse sequences provide various information over our body beyond anatomy, and also a physiological and functional imaging is possible, so which had perfusion, diffusion tensor imaging, and functional MRI. So these imaging features are possible with MRI. Because of that, MRI research field has been growing very fast during the recent years. And these figures show some examples of these imaging modalities like perfusion imaging, and diffusion tensor imaging, which provides neuronal fiber information, and also this is MR angiography, so this provides ulterior information, and this is venous information. And these are the functional imaging maps. That's the somatosensory cortex, and the human visual cortex. So these informations can be acquired with MRI even without any injection of contrast agent, so these are acquired completely non-invasive. Let's talk about signal source of MRI. So what is the main signal source of MRI than it's protons, the hydrogens. And then, why protons are so important. And then protons behave like tiny magnets. So as shown here, protons rotate which is called spin angular momentum. And this cause magnetic moments, which looks like a tiny magnet. So each proton looks like a tiny magnet, so protons behave like tiny magnets. And 70 percent of our body consist of water, which has two protons. There are abundant signal sources in our body for MRI signal, and that's why MRI has been so successful so far. And what other nuclei can be used for MRI? And then these are the list: C13, and flourine 19, and sodium 23, and octium 17, and phosphorus 31. And these nuclei can be used for MRI and or some others with odd atomic number or odd mass number can be used for MR imaging. But these nuclei, the candidate actually used for MRI. But most of the case, if we talk about MRI, more than 99 percent is about the proton. Let's talk about the brief procedure of MR Image acquisition. This is MRI machine from the outside viewpoint. This is partial sequencing which has a time sequencing or radio frequency coil to create three gradient coils. This time sequencing is repeated to acquire data. And then that compose a two dimensional or three dimensional data space called K-space, we will talk about that later. And then applying for field transform to this K-space provides MR imaging. This is a very brief procedure of MR image acquisition. Well, here is the synopsis of MRI. Magnetic means putting a subject in the strong magnetic field generated by the main magnet, so that is about the magnetic. And resonance part is a transmitting radio frequency energy to the subject through an RF coil, and then turning off transmitter, and then receiving RF signals emitted by the subject using another RF coil while the same RF coil used for the transmission, and that is about the resonance. And the imaging part is spatially modulating the magnetic field strengths to distinguish signals from different locations using gradient coils, nd we will talk about that in detail later. And let's talk about the three major hardware components of MRI. The magnet is about a typically superconducting, which cause magnetic field, and a radio frequency is transmitting and receiving signal, and then this cause resonance, and there's a set of three gradient coils which has a long x, y, and z direction, which provides spatial information so the imaging is possible. Here is a schematic diagram of MRI hardware. Outside is about a superconducting magnet, and inside the magnet is three gradient coils along x, y, and z direction, and then inside MR gradient coils, there exists RF coils. Right inside the RF coil exist just like inside the gradient coils which is premounted on the MRI scanner. And then that is typically used for transmission of signal, and then we use small RF coil for detection of the signal. This is typical procedure. This is schematic diagram of MRI instrumentations. So we have main magnet, gradient coil, and RF coils. Pulse sequence generator generates pulse sequencing for applying current to the RF coils and the gradient coils, which can be determined by the pulse sequence generator and the programmer. And then the RF electronics transmits current to the RF coils and then we detect, and then this signal is modulated by the gradient field and then that provides spatial information, and spatially modulated RF signal is detected through the RF coil, and then it goes through imaging reconstuction computer, and then we can see the image on the console computer. So this is overall schematic diagram of MRI instrumentation.
