Introduction:
Diagnostic imaging is an advancing field encompassing various molecular and nuclear techniques to facilitate diagnosis. These imaging tests aid in diagnosis and fare excellently in the therapeutic sphere. Imaging techniques have advanced from two-dimensional images to three-dimensional, real-time, and digital images. One such revolution came from magnetic resonance imaging (MRI).
MRI is a noninvasive diagnostic imaging technique that uses radio waves and a magnetic field to visualize the organs and tissues of the body. The MRI machine is a tunnel-like large apparatus. It works on the basic principle that water constitutes approximately 60 % of the human body weight. Water is made of protons (positively charged molecules) and electrons (negatively charged molecules). When an individual is subjected to an MRI scan, the magnets within the device produce a magnetic field that realigns the water molecules within the body. Then, the radio waves, when passed through the body, cause these aligned molecules to emit signals which then can be used to create images of the internal body structures. MRI had many altercations and advancements to enable specialized functions and efficient performances. One such specialized technique is known as magnetic resonance spectroscopy.
What Is Magnetic Resonance Spectroscopy?
Magnetic resonance spectroscopy (MRS) is a noninvasive specialized magnetic resonance technique that evaluates and assesses the biochemical changes involved in a particular disease, thereby aiding in its diagnosis. Though magnetic resonance spectroscopy was initially a tool of interest primarily in the field of research, current clinical practice has seen an upsurge in the use of MRS in various diseases and tumors of the brain, heart diseases, and cancers of multiple organs such as breast, cervix, and prostate.
What Is the Working Principle of Magnetic Resonance Spectroscopy?
Magnetic resonance spectroscopy works by assessing the chemicals or metabolites released from the tissues. Every metabolic reaction releases inevitable metabolic byproducts, which differ in normal and abnormal tissues. Quantifying these byproducts helps diagnose the condition and evaluate its severity. This technique analyzes the positively charged molecules or protons. They can help assess several metabolites, such as amino acids (structural units of protein), lipids, lactate, choline, and creatine.
Where Is Magnetic Resonance Spectroscopy Indicated?
MRS is usually indicated when the etiology is undefined. It is used extensively to diagnose brain diseases such as autism, Alzheimer’s, stroke, aging, and brain tumor. It has also aided in diagnosing cervical cancers and prostate and pancreatic cancers. It can diagnose metastatic tumors, lymphomas, and infectious diseases. It can help evaluate a recurrent tumor and its spread. It is used in grading and follow-up of patients with brain tumors. MRS has evolved as a handy research diagnostic tool in determining the molecular and genetic features of various conditions. It has helped understand the metabolic reactions involved in the progression of the disease and thereby aids in the therapeutic approach.
How Is Magnetic Resonance Spectroscopy Different From Conventional Magnetic Resonance Imaging?
MRI and MRS are conducted using the same MRI scanner, but MRI provides information about the anatomy and location. In contrast, MRS is beneficial in obtaining the metabolic or functional information of the tissues. In addition, it determines and compares the chemical composition of the normal tissue with the abnormal ones, thus aiding in diagnosing the conditions.
What Are the Patient Preparations Required Before the Procedure?
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There are no dietary restrictions. The patient can eat and drink normally but is requested to avoid caffeinated drinks.
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Claustrophobic patients may be advised to relax to undergo the examination comfortably.
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Patients are advised to wear loose, comfortable clothes during the procedure.
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They should remove their jewelry, valuables, and accessories before the procedure. In addition, any metallic objects should be removed, including eyeglasses, wallets, belts, buckles, credit cards, hearing aids, and dentures with clasps.
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Patients with implants and pacemakers should inform the doctor before the procedure.
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Patients should carry their recent medical reports and prescription medicine to the diagnostic center.
How Is Magnetic Resonance Spectroscopy Done?
MRS is usually performed as an outpatient procedure by a radiologist. The patient may be asked to change into a hospital gown. They will be asked to lie on a table that will slide into the MRI machine. A coil-like device would be strapped and placed around the body to retrieve clear images of the desired area. Once inside the MRI unit, the patients may hear some muffled striking noises, which is normal. Patients are advised to rest still as any slight movement may blur the image. A contrast MRS, if required, may use gadolinium-based contrast agents. However, gadolinium is a potent nephrotoxic agent contraindicated in renal failure patients and those with end-stage renal disease.
How Are the Results Interpreted?
MRS, unlike MRI, does not display the result in the form of images; it is expressed as a spectrum in a graphic format. The resonance frequency is given as parts per million (ppm). Certain metabolites and their clinical implications, as interpreted by MRS, are given below:
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NAA- N-acetyl aspartate (NAA) is an amino acid. It is considered a marker for neuronal health as it is found abundantly in the brain and neurons. Higher peaks are suggestive of normal neuronal morphology. Diminished peaks are observed in neural damage. NAA is decreased in neurodegenerative diseases and tumors. Increased NAA is observed in Canavan’s disease, a genetic disorder in which the brain degenerates into small fluid-filled spaces.
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Choline - It is considered a predominant tumor marker. An increase in choline signifies a tumor, leukodystrophy (abnormal growth of white matter in the brain), or multiple sclerosis (an autoimmune condition). Conversely, it is reduced in patients with stroke and hepatic encephalopathy (a neurological disorder caused by liver damage).
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Creatine - Creatine is the reservoir for producing the energy required for various metabolic processes in the body. It is generally used as a reference standard as it remains constant in most conditions.
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Lactate - An increase in lactate metabolite is seen in necrosis, inflammatory conditions, or brain tumors.
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Lipids - An increase in lipids is suggestive of the breakdown of tissues commonly seen in necrosis and myelin destruction.
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Myo-Inositol - Myo-inositol is a metabolite increasingly found in the glial cells. Glial cells are specialized neuronal cells. They are considered primary markers of gliomas (brain tumors). In addition, they are increased in Alzheimer’s disease, Down syndrome, and gliosis.
What Are the Benefits and Risks Associated With This Procedure?
Benefits:
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MRS is a highly safe procedure.
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No risk of any radiation hazard.
Risks:
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Possible allergic reaction to the contrast material.
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It should be used cautiously in patients with cardiac pacemakers, metallic implants, artificial heart valves, or insulin pumps.
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Patients with an implantable hearing device, employed in the metal industry, or with permanent tattoos should also inform the doctor before the procedure.
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Pregnant ladies should avoid MRI or MRS scanning.
What Is the Limitation of Magnetic Resonance Spectroscopy?
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Overlapping spectroscopic features of various diseases.
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Time-consuming.
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Possibility of artifacts obscuring the diagnosis.
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High-cost.
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Inter-observer variability.
Conclusion:
Magnetic resonance spectroscopy is a novel and advanced noninvasive imaging technique that evaluates the molecular composition of tissues. The metabolites are precise and exceptional markers of various diseases, including tumors, cancers, and other degenerative diseases. Though the overlapping spectroscopic features and technical limitations hinder the widespread use of this imaging tool, further advancements may help MRS be a practical tool in prognostication and strategizing the treatment.
