What is fmri used for

As the hydrogen atoms return to their usual alignment, they emit different amounts of energy depending on the type of tissue they are in.

The scanner captures this energy and creates a picture using this information. In most MRI units, the magnetic field is produced by passing an electric current through wire coils. Other coils are inside the machine and, in some cases, are placed around the part of the body being imaged.

These coils send and receive radio waves, producing signals that are detected by the machine. The electric current does not come into contact with the patient. A computer processes the signals and creates a series of images, each of which shows a thin slice of the body. The radiologist can study these images from different angles.

MRI is often able to tell the difference between diseased tissue and normal tissue better than x-ray, CT, and ultrasound. This will cause increased metabolic activity in the areas of the brain responsible for these tasks.

This activity, which includes expanding blood vessels, chemical changes and the delivery of extra oxygen, can then be recorded on MRI images. The technologist will position you on the moveable exam table. They may use straps and bolsters to help you stay still and maintain your position. The technologist may place devices that contain coils capable of sending and receiving radio waves around or next to the area of the body under examination. MRI exams generally include multiple runs sequences , some of which may last several minutes.

Each run will create a different set of noises. For fMRI, your head may be placed in a brace designed to help hold it still. This brace may include a mask that is created especially for you. If your exam uses a contrast material, a doctor, nurse, or technologist will insert an intravenous catheter IV line into a vein in your hand or arm. They will use this IV to inject the contrast material. You will be placed into the magnet of the MRI unit. The technologist will perform the exam while working at a computer outside of the room.

You will be able to talk to the technologist via an intercom. When the exam is complete, the technologist may ask you to wait while the radiologist checks the images in case more are needed.

The technologist will remove your IV line after the exam is over and place a small dressing over the insertion site. The doctor may also perform MR spectroscopy during your exam. MR spectroscopy provides additional information on the chemicals present in the body's cells. This may add about 15 minutes to the total exam time. Most MRI exams are painless. However, some patients find it uncomfortable to remain still. Others may feel closed-in claustrophobic while in the MRI scanner.

The scanner can be noisy. It is normal for the area of your body being imaged to feel slightly warm. If it bothers you, notify the radiologist or technologist. It is important that you remain perfectly still while the images are being recorded, which is typically only a few seconds to a few minutes at a time. For some types of exams, you may be asked to hold your breath. You will know when images are being recorded because you will hear tapping or thumping sounds when the coils that generate the radiofrequency pulses are activated.

You will be able to relax between imaging sequences but will be asked to maintain your position as much as possible. You will usually be alone in the exam room during the MRI procedure. However, the technologist will always be able to see, hear, and speak with you using a two-way intercom.

Many MRI centers allow a friend or parent to stay in the room if they are also screened for safety in the magnetic environment. The technologist may offer or you may request earplugs to reduce the noise of the MRI scanner. The scanner produces loud thumping and humming noises during imaging.

MRI scanners are air-conditioned and well-lit. Some scanners have music to help you pass the time. When the contrast material is injected, it is normal to feel coolness and a flushing sensation for a minute or two.

The intravenous needle may cause you some discomfort when it is inserted. Once it is removed, you may experience some bruising. There is also a very small chance of skin irritation at the site of the IV tube insertion. If you have not been sedated, no recovery period is necessary. You may resume your usual activities and normal diet immediately after the exam. A few patients experience side effects from the contrast material, including nausea and local pain.

Very rarely, patients are allergic to the contrast material and experience hives, itchy eyes, or other reactions. If you experience allergic symptoms, a radiologist or other physician will be available for immediate assistance. A radiologist, a doctor trained to supervise and interpret radiology exams, will analyze the images. The radiologist will send a signed report to your primary care or referring physician, who will share the results with you. High-quality images depend on your ability to remain perfectly still and follow breath-holding instructions while the images are being recorded.

If you are anxious, confused or in severe pain, you may find it difficult to lie still during imaging. A person who is very large may not fit into certain types of MRI machines. There are weight limits on the scanners. Implants and other metallic objects can make it difficult to obtain clear images.

Patient movement can have the same effect. A very irregular heartbeat may affect the quality of images. Stand-up scanners like the one shown in figure 3 are more convenient for patients and allow imaging in the normal attitude and weight-bearing conditions.

The scanner is lowered around the subject, who sits on an adjustable seat. Finally, figure 4 shows open MRI scanners, which allow for a greater range of subject tasks as well as easing the subject's sense of confinement. Photos courtesy of Midwest Diagnostic Management. Though specifics of design vary, the basic elements of an MRI scanner remain pretty much the same See below.

The scanner consists of a large magnet blue that creates the primary magnetic field. Magnet strength in MRI systems is measured in units of magnetic flux density called a "tesla". A telsa is enough magnetic force to induce 1 volt of electricity in a single-coil circuit during 1 second of time for every square meter.

Current magnet strength varies from 0. However, researchers developed 3-tesla MRI scanners in the late 90's which are becoming more common. To put those numbers in perspective, the Earth's magnetic field is about 0. In addition to the main magnet, there are also gradient coils red. These gradient coils are electro-magnetic coils which technicians use to alter the main magnetic field at very precise points and for very precisely controlled times.

Gradient coils can be changed so as to adjust the machine for the type of body material to be imaged. Finally, MRI scanners also incorporate radio frequency coils which can send a focused radio frequency pulse into the scanner chamber. Technicians can change the radio frequency coils to adjust for materials and body part.

Used with permission. Thus, the images generated by MRI scans are like three dimensional pictures of anatomic structure. The images generated by FMRI scans are images of metabolic activity within these anatomic structures. In order to understand how FMRI scans work one needs a rough understanding of the basic physical principles upon which the technology is built.

The relevant physical principles are those involving the atom. Atoms are the smallest particles of an element which still possess the properties of the elements. For instance, helium is an element.

The smallest bit of helium that still has the properties of helium is a helium atom. Atoms are very small. The diameter of an atom ranges from about 0. To put this in some context, if we think of the diameter of a single atom as the length of a meter stick, the corresponding length of the meter stick would be 10 billon meter sticks approximately 14 round trips to the moon. Despite their diminutive dimensions, atoms are mostly empty space. Most atoms are composed of three particles distinguished by their electrical charge: protons positive , electrons negative , and neutrons neutral.

Electromagnetic forces bind protons and neutrons together in an atom to form its center, i. The number of protons in an atom's nucleus determines the atom's elemental categorization. Hydrogen has the fewest protons with only one. Uranium has 92 protons. The number of neutrons is usually approximately equal to the number of protons, but there is variation in the number of possible neutrons in an atomic nucleus.

Electrons circle around the nucleus. Since protons have a positive charge and electrons have a negative charge these particles attract each other, thereby creating the stable, electrically neutral structure of the average atom.

That is, the nucleus of the atom spins around as in the above animation. Nuclear spin, or more precisely, the manipulation of nuclear spin is the basis for MRI imaging. If you follow astronomy, nuclear spin is similar to the wobble of distant stars used to infer the number, size, etc. If one places an atom within a magnetic field plane, i. This is called precession and is depicted in the animation below:. When one causes nuclei to precess their spin will cause them to align themselves with the magnetic field.

The spin of a nucleus is just like the ends of a bar magnet in that it can have a positive or negative value. Two negative or two positive ends of a magnet repel one another, but negative and positive ends attract each other. Similarly, all the negative spin atoms align themselves downward on the Z axis towards the feet of the subject , and all the positive atoms align upward on the Z axis towards the subject's head.

Each atom with a positive spin cancels out renders undetectable an atom with a negative spin. Your head may be placed in a device that's designed to keep you still. You may also be given special goggles or earphones to wear. A technician or radiologist will move you into the magnet of the MRI unit. Doctors will perform the imaging test while working at a computer outside the exam room. It's important that you remain still during the procedure. You may even be asked to hold your breath at times.

Before having an fMRI, let your doctor know if you have any serious health conditions, especially severe kidney disease. Also, let your doctor know if you've recently had any surgery or if there's a chance you might be pregnant.

Tell your doctor and radiologist ahead of time if you have any metal objects or medical devices in your body.