Magnetic Resonance Spectroscopy
Magnetic Resonance Spectroscopy provides a chemical fingerprint unique to tissues and pathology. This powerful tool allows for non-invasive investigation of tissue properties and metabolism which can be useful for diagnosing and monitoring various neurological conditions.
Frequently Asked Questions
Does this require special equipment?
Magnetic Resonance Spectroscopy (MRS) can be performed on standard MRI machines that are commonly found in hospitals and medical facilities. MRS is an additional sequence acquired from MRI machines, allowing doctors and researchers to explore the chemical composition of tissues within the body, including the brain. This versatility makes MRS a valuable tool because it can provide both structural and chemical information about organs and tissues, helping in the diagnosis and monitoring of various medical conditions. So, you don’t need a separate, unique machine for MRS; it’s an extension of the capabilities of the MRI machine itself.
Is Magnetic Resonance Spectroscopy safe?
Yes, MRS is safe. It doesn’t use ionizing radiation like X-rays or CT scans, which can have potential risks associated with exposure to radiation. Instead, MRS relies on the principles of magnetic resonance imaging, using strong magnetic fields and radio waves to create detailed images of the body’s internal structures and chemical composition. Ask your healthcare provider if you are considering using MRS in your healthcare journey.
How long has Magnetic Resonance Spectroscopy been around?
Magnetic Resonance Spectroscopy (MRS) has been around since the late 1950s when the basic principles of nuclear magnetic resonance (NMR) were first applied to study the chemical composition of biological tissues. However, MRS as a clinical and research tool for investigating various medical conditions, including neurological disorders and cancer, began to gain prominence in the 1980s and 1990s as technology advanced and our understanding of its applications grew. Since then, it has continued to evolve and become an essential component of modern medical imaging and research.
What can Magnetic Resonance Spectroscopy measure?
Magnetic Resonance Spectroscopy (MRS) can measure various chemical compounds and metabolites within the body, providing valuable insights into tissue composition and biochemical processes. See just a few examples below.
N-Acetylaspartate (NAA) is a marker for neuron health. It’s useful in diagnosing brain conditions like tumors, head injuries, and dementias by quantifying neuronal damage. Elevated NAA levels occur during recovery and in Canavan disease, a genetic disorder with reduced NAA-deacyclase activity, causing NAA buildup.
Choline is a metabolite known for its significance in cell membrane turnover and cell proliferation. It is often measured in tissues, including the brain, where elevated choline levels can be indicative of increased cell membrane synthesis and cell density. MRS identifies choline by its unique chemical signature, making it a valuable marker for assessing tissue characteristics and, in the context of brain imaging, for evaluating conditions such as tumors or other pathological processes where cell growth and membrane turnover are altered.
The primary resonance of creatine lies at 3.0ppm. It is the central energy marker of both neurons and astrocytes and remains relatively constant. For that reason, it is often used as an internal reference for comparison to other metabolites.
Glutamate is a detectable metabolite central to neurotransmission and brain function using MRS. Its levels can reveal insights into tissue biochemistry, especially in brain imaging, where changes in glutamate concentrations may signify neurological conditions or synaptic activity alterations.
Glutamine is a metabolite linked to amino acid and neurotransmitter processes that is measurable with MRS. It’s useful in assessing tissue biochemistry, especially in brain imaging, where changes in glutamine levels can signal conditions like neurodegenerative diseases or neurotransmitter pathway disruptions.
Myo-Inositol is a measurable metabolite recognized for its role in cellular osmoregulation and signal transduction. It is routinely assessed in various tissues, including the brain, where alterations in myo-Inositol levels may signify cellular stress or changes in cellular volume. MRS detects myo-Inositol by its distinct chemical signature, making it a valuable marker for investigating tissue conditions, particularly in brain imaging, where deviations in myo-Inositol levels can provide insights into conditions such as neuroinflammation or certain neurological disorders.
Lactate is a measurable metabolite that signifies anaerobic metabolism in tissues. It results from cellular glycolysis when oxygen is limited, as seen in conditions like hypoxia, ischemia, or certain tumors. MRS detects lactate by its distinctive chemical signature, making it a valuable marker for understanding tissue metabolism in various medical contexts, particularly in brain imaging, where elevated lactate levels can indicate underlying pathological conditions.
2-Hydroxyglutarate (2-HG) is a molecule that plays a significant role in cellular metabolism and has garnered attention in the context of cancer research, particularly in certain types of brain tumors.
Using specialized techniques, 2HG can be measured to track tumor progression and severity.
Disease Specific Molecular Signature
The nuclei of many elemental isotopes (1H, 13C, 19F and 31P, among others) have a characteristic spin, either ‘up’ or ‘down’, with one spin state higher in energy than the other. A spinning charge creates a magnetic field, and thus each elemental isotope has a unique magnetic moment. Within a given sample, the orientations of nuclear spin states are random. When placed in a large magnetic field, such as an MRI machine, however, the spin states all align with the field. With the application of energy—typically in the form of radio waves—a nucleus will flip from one spin state to the other. The frequency of energy that this flip requires is characteristic of the nucleus, but varies with the strength of the magnetic field and the electron shielding of other electrons in a molecule.
The output of MR Spectroscopy, therefore, is not a picture—as with the case with MRI—but rather a readout of resonances (peaks) as a function of frequency, expressed in parts per million. By reading these resonances, a spectroscopist can determine the chemical composition of a sample. In vivo 1H MR spectroscopy examines carbon bound protons in the 1-5 ppm range of the chemical shift scale. Metabolites typically assessed include lactate, NAA, glutamate, creatine, choline, and myo-inositol (Figure below). By analyzing the ratios of these metabolites, spectroscopists can diagnose and monitor progression in a variety of diseases — from tumors to traumatic brain injury.
When the nuclei relax and release the energy, the scanner can measure the contribution of each unique frequency to determine the concentration of the various molecules.
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