Nuclear Magnetic Resonance (NMR) is one of the leading techniques in functional imaging. Initially invented by physicists to study atomic nuclei, NMR has revolutionally evolved into Magnetic Resonance Imaging (MRI), a standard medical diagnostic tool used globally. This blog article takes an extensive look into NMR imaging, with a particular focus on MRI and how it works in producing its detailed three-dimensional images of the body’s interior.
What Is Nuclear Magnetic Resonance (NMR)?
NMR is a physical phenomenon based upon the magnetic properties of an atom’s nucleus. This process relies on the principle of nuclear spin and how it interacts with both magnetic fields and radiowaves. When a nucleus, like a single proton of a hydrogen atom, is subjected to a powerful and constant magnetic field, it will align itself with the field and spin at a characteristic frequency, known as Larmor frequency.
When exposed to a secondary oscillating magnetic field, the nucleus may absorb a quantum of energy and flip its spin orientation. As soon as this secondary field is taken away, this nucleus relaxes back to its original state, a process that emits a radio signal that can be measured and used to identify the type and number of nuclei that were excited.
NMR in Imaging – Birth of MRI:
Applying NMR to medical imaging gave birth to MRI. Raymond Vahan Damadian and Paul Lauterbur are often credited as being the pioneers in this regard, with Damadian being acknowledged for applying NMR to the human body and Lauterbur for conceiving the idea of using gradients in the magnetic field, thereby providing a new and practical method for generating two-dimensional NMR images.
How Does MRI Work?
MRI uses a large doughnut-shaped magnet that creates a strong magnetic field around the patient. The magnetic field is so powerful that it aligns the protons in the patient’s body. Once aligned, short bursts of a secondary magnetic field, or radiofrequency (RF) pulses, are targeted at specific areas of the body. As the protons realign back to their normal, relaxed state, they emit signals. MRI detectors capture these signals and a computer interprets them to create a digital image.
Diving Deeper into Frequency Codings and Gradients:
The information gathered during an MRI scan is a series of signals from all the excited protons in the target zone. However, to create a three-dimensional image, the MRI must identify where each signal originated in the body. This is accomplished using magnetic field gradients.
By subtly changing the primary magnetic field’s strength across the body, the Larmor frequency of the protons change depending on their location. These alterations create a three-dimensional map of signals, allowing the MRI machine to translate the signal information into a detailed image.
MRI images can be improved by using contrast agents, substances that increase the visibility of certain tissues or blood vessels. Gadolinium or Iron Oxide nanoparticles are commonly used as they can drastically shorten T1 or T2 relaxation times of tissues, leading to enhanced contrast in resultant images.
Functional MRI (fMRI):
One specialty MRI called a functional Magnetic Resonance Imaging (fMRI) measures changes in blood flow, indicating areas of activity in the brain. By tracking blood’s oxygen utilization, fMRI offers insights into how the brain is working in real time, providing researchers a tool to map both brain anatomy and function.
In conclusion, MRI has revolutionized medical diagnostics by offering a noninvasive, radiation-free method of detailed imaging. The ability to differentiate between various tissues makes it an indispensable tool for diagnosing multiple pathologies, from tumors to tissue degeneration. The principles of NMR transformed into one of the most important medical imaging techniques, truly an illustration of how exploring the basic properties of matter can often lead to profound impacts on society.
While the technology has already advanced dramatically, it continues to evolve, with research ongoing into improving image resolution, reducing scan times, and developing new contrast mechanisms to differentiate healthy and diseased tissue.
Further, attempts at marrying other imaging techniques like positron emission tomography (PET) with MRI are ongoing, aiming to provide both functional and anatomical information in one scan to further push the boundaries of what’s possible in imaging diagnostics.
As we move further into the 21st century, it’s clear that NMR and MRI will continue to be at the forefront of medicinal diagnostics, offering unparalleled insights into the human body.