At the end of this module, students should be able to…
provide different examples of modern-day technologies that use magnetic resonance techniques
identify the key elements of a magnetic resonance apparatus
specify how magnetic resonance differs from other spectroscopy and imaging modalities
See handout: Energy-Level Transitions and Spectroscopy
magnetic resonance - technique that utlizes the interactions of matter and light in the presence of magnetic fields
We may not be able to directly see the quantum world of elementary particles, atoms, and molecules, but, fortunately, we can see how these quantum particles interact with light to uncover the strange rules of physics they appear to follow. Scientists observed that atoms emit and absorb light at certain frequencies, which led to the discovery that atoms have quantized energy levels. Scientists then learned how to use this information to identify different atoms and molecules, and develop technology that harnesses the amazing properties of the quantum world. Throughout these materials, we will explore the quantum realm through the lens of magnetic resonance (MR) (MR), which has found applications in a wide variety of scientific disciplines and has become a valuable research tool to uncover new quantum mysteries.
quantum mechanical properties - physical properties that are primarily significant at the level of atoms and molecules where the weird laws of quantum mechanics apply external magnetic field - a magnetic field typically generated by a strong magnet that is located outside the sample nuclear magnetic resonance - where magnetic resonance signal comes primarily from the nuclei of specific atoms electromagnetic radiation - type of energy carried by electromagnetic waves (light); the frequency determines the energy range and categorization of light in the electromagnetic spectrum
MR uses the quantum mechanical properties of atoms inside a sample and placed in an external magnetic field to provide valuable information about their local magnetic environments. This information can be used to identify chemical composition and structure of a sample, as well as provide ways of manipulating quantum spins to encode information useful for biomedical imaging or even serve as qubits in a quantum computer. Across these activities, you will learn the physics behind nuclear magnetic resonance (NMR), as well as explore multiple specific applications. NMR uses electromagnetic radiation - a fancy name for the energy carried by different forms of light - to interact with nuclei in matter. By working through these activities, we hope that you may ultimately develop and demonstrate the appropriate research skills required to design, implement, and analyze NMR experiments that address novel questions. But before we get into the details, we want to provide some of the motivation behind this work.
Here we will provide a short synopsis of the historical impacts of MR research, a comparison of MR technology with other similar technologies in the modern-day scientific workforce, and reflect on the potential future of MR techniques.
In your life, where else have you seen interactions of light with matter?
Who might find it worthwhile to understand magnetic resonance techniques?
MR techniques have been developed over the course of the past century as scientists have explore and understood more of the quantum realm. These techniques have been utilized in a variety of different scientific disciplines and new techniques are still being developed, as MR provides a unique way to control quantum systems for future technologies. Below is a list of the many Nobel prizes awarded in the past century that were critical to the development and application of MR techniques1 Boesch, Chris. “Nobel Prizes for Nuclear Magnetic Resonance: 2003 and Historical Perspectives” Journal of Magnetic Resonance Imaging 20:177–179 (2004).
Table of Nobel Prizes Directly Related to MR
| Name | Year | Category | Description |
|---|---|---|---|
| Isidor Isaac Rabi | 1944 | Physics | For his resonance method for recording the magnetic properties of atomic nuclei |
| Felix Bloch & Edward Mills Purcell | 1952 | Physics | For their development of new methods for nuclear magnetic precision measurements and discoveries in connection therewith |
| Richard R. Ernst | 1991 | Chemistry | For his contributions to the development of the methodology of high resolution nuclear magnetic resonance (NMR) spectroscopy |
| Kurt Wuthrich | 2002 | Chemistry | For his development of nuclear magnetic resonance spectroscopy for determining the three-dimensional structure of biological macromolecules in solution |
| Paul C. Lauterbur & Sir. Peter Mansfield | 2003 | Medicine | For their discoveries concerning magnetic resonance imaging |
FURTHER STUDY: To learn more about the biographies of the Nobel Prize winners and their work, check out nobelprize.org.
From the information provided, do you think it is fair to say that MR impacts multiple scientific disciplines? Use evidence to make your case.
What voices are we missing in this brief history of magnetic resonance? Would this in any way affect its overall impact? Why or why not?
Magnetic resonance techniques are used in a variety of different technologies. Below we provide a brief description and simple diagram of four different apparatuses utilizing MR. They may all look very different from each other but are using the same underlying physics. Study this information to answer the guided inquiry questions below.
NMR
spectroscopy - uses electromagnetic radiation in the radio
frequency (RF) region to interact with nuclei within a sample placed
inside a magnetic field. These RF frequencies resonate with particular
nuclei and detecting the response of specific nuclei to these
frequencies can provide chemical information about the sample. (Image
source 2)
electron spin
resonance (ESR) or electron paramagnetic resonance (EPR) - uses
electromagnetic radiation in the microwave frequency region to interact
with electrons within a sample placed inside a magnetic field. These
microwaves resonate within a cavity where the sample is placed and the
response of the electrons to these frequencies can provide chemical
information about the sample. (Image source 3)
magnetic
resonance imaging (MRI) - uses electromagnetic radiation in the
RF region to interact with nuclei within a patient placed inside a large
uniform field, along with magnetic field gradients that changes the
magnitude of the magnetic field at different spatial positions. A
non-invasive, three-dimensional spatial image can be constructed by
measuring the response of specific nuclei to the applied magnetic
fields. (Image source 4)
solid-state
qubit - one proposed mechanism for creating solid-state qubits
for future quantum computers, where a spin qubit located inside a solid
sample (like a nitrogen-vacancy
center in diamond) interacts with a external magnetic field causing
mechanical resonance of a cantilever which can be measured to provide
readout and control of the spin qubit. (Image modified from source 5)
What are common elements to the different apparatuses that utilize magnetic resonance?
What are some apparent differences in the different apparatuses? Why might they have those differences?
As seen in the previous section, MR is used in a wide variety of technologies. In this section, we will focus on some of the most widely known applications of MR - NMR spectroscopy and magnetic resonance imagine (MRI) - and provide a comparison with other related technologies.
(Left) Light can be absorbed by a quantum particle to move to a higher energy level. (Right) Light can be emitted by a quantum particle to move to a lower energy level.
Spectroscopy is the study of how electromagnetic radiation is absorbed and emitted by matter and is used in a variety of scientific disciplines for chemical analysis of samples. Electromagnetic radiation is only absorbed or emitted at certain frequencies that match the energy difference between the two quantum states the quantum particle is transitioning between. Different frequencies of light can excite different components of matter including entire molecules, bound electrons, or atomic nuclei. Below are some figures providing info about different spectroscopic methods.
| Spectroscopy | EM Frequencies | Signal Generated by | Application |
|---|---|---|---|
| Nuclear Magnetic Resonance (NMR) | Radio frequencies (RF) from \(1×10^8\) to \(8×10^8\) Hz (100 - 800 MHz) | RF radiation absorbed by nuclei in the presence of a magnetic field causing the nuclei to undergo transitions from lower energy to higher energy spin states | Chemical structure, dynamics, reaction state and chemical environments of primarily liquid sample in fields as diverse as food quality control and research, identifying human disorders, cancer diagnosis, environmental monitoring, and drug discovery and development |
| Infrared (IR) | IR frequencies from \(1.9×10^{13}\) to \(1.2×10^{14}\) Hz (19 - 120 THz) | IR radiation absorbed by the molecules causing molecular vibrations | Chemical structure, functional group identification, and detection of impurities in solid, liquid, or gas samples |
| Ultraviolet (UV) | Ultraviolet frequencies between \(7.5 × 10^{14}\) to \(1.5 × 10^{15}\) Hz (750 - 1500 THz) | UV radiation absorbed by electrons causing atomic electron transitions from ground states to higher energy states | Bacterial culturing, drug identification and nucleic acid purity checks and quantitation, to quality control in the beverage industry and chemical research |
| Raman | Broad spectrum of frequencies, measuring photon frequency shifts between \(11^3\) Hz to \(12^6\) Hz | Monochromatic light is used to illuminate samples causing molecular vibrations or other excitations in the system which shifts the energy of the scattered photons either up or down. | Chemical analysis in fields as diverse as pharmaceuticals, cosmetics, geology and mineralogy, DNA/RNA analysis |
| X-ray | X-ray frequencies from about \(10^{16}\) to \(10^{20}\) Hz (10 - 100,000 pHz) | X-ray radiation absorbed by electrons causing atomic electron transitions from ground states to higher energy states | Chemical analysis in fields as diverse as mining, medical research, polymer manufacturing, geology, and consumer product quality control |
REFERENCES: NMR (6, 7, 8); IR (9, 10); UV (11, 12); Raman (13, 14); X-ray (15, 16, 17)
Scientists have developed multiple methods of non-invasive, three-dimensional imaging utilizing the different parts of the electromagnetic spectrum. Below are some figures highlighting and comparing some of these different imaging methods.
| Tyep of Imaging | Primary Use | Image Resolution Range | Timescale | Risks |
|---|---|---|---|---|
| MRI | Examine tissue, skeletal system, and organs, including brain and spinal cortex. | 2 mm to 0.5 mm | 15 to 90 minutes | Generally a safe procedure unless the patients have implants embedded inside them (i.e. pacemaker, artificial joints, etc.) |
| X-ray/CT Scan | Examine Skeletal and muscle structure, pinpoint infections or tumors, detect internal injuries/bleeding, dye contrast injection to spot softer tissue easier. | 0.625 mm to 0.5 mm | 10 to 30 minutes | Uses ionizing radiation. 1 in 2,000 chance to develop cancer from x-rays used, potential allergies in response to contrast used. |
| Optical Imaging | Diffuse Optical Topography (DOT; breast cancer imaging, brain functional imaging, stroke detection, radiation therapy monitoring) Non invasive 3D imaging | 50 nm - 10 nm | Varies widely on method used. | No ionizing radiation is used. OCT poses a risk of puncturing via a probing tool. |
| PET/SPECT | Diagnose and monitor brain disorders, heart problems, and bone disorders. | 15 mm to 4 mm | 30 minutes | Small amount of radioactive material is injected into the body as a tracer. Dangerous for pregnant or breast-feeding women; material may be passed to their child. |
REFERENCES: Image Source (18); MRI (19); Optical Imaging (20); SPECT (21); MISC (22);
What similarities and differences does NMR spectroscopy have compared with the other types of spectroscopy listed?
Why might scientists choose to use NMR spectroscopy instead of other spectroscopy techniques? When might other spectroscopy techniques be more suitable?
What similarities and differences does MRI and other imaging modalities?
Why might scientists choose to use MRI instead of other imaging technologies? When might other imaging techniques be more suitable?
How might having access to information about the magnetic environment of atoms be useful? What industries could make use of this information? What scientific questions could potentially be explored?
Do magnetic resonance techniques provide any more information beyond the other technologies shown here? Any advantages or disadvantages?
Do you think magnetic resonance techniques have passed their prime? Why or why not?