What is MR spectroscopy?
MR spectroscopy is conducted on the same machine as convention MRI. The MRI scan uses a powerful magnet, radio waves, and a computer to create detailed images. Spectroscopy is a series of tests that are added to the MRI scan of your brain or spine to measure the chemical metabolism of a suspected tumor.
MR spectroscopy analyzes molecules such as hydrogen ions or protons. Proton spectroscopy is more commonly used. There are several different metabolites, or products of metabolism, that can be measured to differentiate between tumor types:
- Amino acids
- Lipid
- Lactate
- Alanine
- N-acetyl aspartate
- Choline
- Creatine
- Myoinositol
The frequency of these metabolites is measured in units called parts per million (ppm) and plotted on a graph as peaks of varying height. By measuring each metabolite’s ppm and comparing it to normal brain tissue, the neuroradiologist can determine the type of tissue present.
What does MR spectroscopy show?
MR spectroscopy can be used to determine tumor type and aggressiveness and distinguish between tumor recurrence and radiation necrosis. Different metabolites can indicate:
- Glioma: lower than normal N-acetyl aspartate levels, elevated choline and lipid levels, and lactate peaks.
- Radiation necrosis: does not have elevated choline levels
- Meningioma: elevated alanine levels
What should I expect during MR spectroscopy
You will lie on a moveable bed with your head cradled on a headrest and your arms at your sides. An antenna device called a “coil” will be placed over or around the area of the body to be imaged. It is specialized to produce the clearest picture of the area it is placed over. When you are comfortably positioned, the table will slowly move into the magnetic field. As the exam proceeds, you will hear a muffled “thumping” sound for several minutes at a time. This is the sound of the pictures being taken. You may be given an injection of contrast dye (gadolinium) into your arm or through an IV to enhance the images.
Because MR spectroscopy requires special tests on your tumor or lesion, it may take slightly longer than a conventional MRI. It is important that you relax and lie as still as possible. Any movement during this time will blur the picture.
What are the risks of MR spectroscopy
MRI and MR spectroscopy are very safe. There are no known health risks associated with the magnetic field or the radio waves used by the machine. Some people are sensitive to the contrast agent and may develop and allergic reaction. All contrast agents are FDA-approved and safe.
Some special circumstances limit the use of a magnetic field, so it’s important to tell your doctor if any of the following apply to you:
- Cardiac pacemaker or artificial heart valve
- Metal plate, pin, or other metallic implant
- Intrauterine device, such as Copper-7 IUD
- Insulin pump or other infusion pump
- Aneurysm clips
- Previous gunshot wound
- Cochlear implant or other hearing device
- Employment history as a metalworker (had metal in eye)
- Permanent (tattoo) eye-liner
Any metallic substance can affect the quality of images and values obtained. The presence of metal may cause harm and/or discomfort during the test.
You should also tell your physician and/or healthcare team if you are pregnant. The American College of Radiology does not recommend MRI scanning during the first trimester of pregnancy. While there is no definitive research indicating that MRI or MR spectroscopy should not be performed during the second and third trimesters, you will need to obtain a written order from your obstetrician for the test to be performed.
What happens after MR spectroscopy?
A neuroradiologist will analyze the MR spectroscopy results. Treatment plans can be based solely on these results, so it is important that the results are as accurate as possible. The radiologist will promptly review your results and communicate directly with your referring provider, who in turn will discuss the results with you at a later time.