Simple how does mri work

If you're nearby, you'll be able to watch through a window and talk to your child through an intercom during breaks between scans. This can soothe your child if he or she is awake in the MRI machine. An MRI exam usually takes minutes to perform, depending on the type of study being performed. Your child will lie on the movable scanning table while the technologist places him or her into position. The table will slide into the tunnel and the technician will take images. Each scan will last a few minutes.

To detect specific problems, your child may be given a contrast solution through an IV. The solution, which is painless as it goes into the vein, highlights certain areas of the body, such as blood vessels, so doctors can see them in more detail.

The technician will ask if your child is allergic to any medications or food before the contrast solution is given. The contrast solution used in MRI tests is generally safe. However, allergic reactions can occur. Talk to your doctor about the benefits and risks of receiving contrast solution in your child's case. As the exam proceeds, your child will hear repetitive sounds from the machine, which are normal. Your child may be given headphones to listen to music or earplugs to block the noise and will have access to a call button in case he or she becomes uneasy during the test.

If sedated, your child will be monitored at all times by a machine that checks the heartbeat, breathing, and oxygen level. When the exam is over, the technician will help your child off the table; if sedation was used, your child may be moved to a recovery area.

MRIs are painless. Your child may have to lie still on the MRI table for minutes during the procedure, but there are brief breaks between each scan. Unless sedation is used or you're told otherwise, your child can immediately return to normal routines and diet.

These atoms are randomly spinning, or precessing , on their axis, like a child's top. All of the atoms are going in various directions, but when placed in a magnetic field, the atoms line up in the direction of the field.

These hydrogen atoms have a strong magnetic moment , which means that in a magnetic field, they line up in the direction of the field. Since the magnetic field runs straight down the center of the machine, the hydrogen protons line up so that they're pointing to either the patient's feet or the head.

About half go each way, so that the vast majority of the protons cancel each other out -- that is, for each atom lined up toward the feet, one is lined up toward the head. Only a couple of protons out of every million aren't canceled out. This doesn't sound like much, but the sheer number of hydrogen atoms in the body is enough to create extremely detailed images.

It's these unmatched atoms that we're concerned with now. The system directs the pulse toward the area of the body we want to examine.

When the pulse is applied, the unmatched protons absorb the energy and spin again in a different direction. This is the "resonance" part of MRI. The RF pulse forces them to spin at a particular frequency, in a particular direction. The specific frequency of resonance is called the Larmour frequency and is calculated based on the particular tissue being imaged and the strength of the main magnetic field.

At approximately the same time, the three gradient magnets jump into the act. They are arranged in such a manner inside the main magnet that when they're turned on and off rapidly in a specific manner, they alter the main magnetic field on a local level.

What this means is that we can pick exactly which area we want a picture of; this area is referred to as the "slice. Slices can be taken of any part of the body in any direction, giving doctors a huge advantage over any other imaging modality. That also means that you don't have to move for the machine to get an image from a different direction -- the machine can manipulate everything with the gradient magnets.

But the machine makes a tremendous amount of noise during a scan, which sounds like a continual rapid hammering. That's due to the rising electrical current in the wires of the gradient magnets being opposed by the main magnetic field.

The stronger the main field, the louder the gradient noise. In most MRI centers, you can bring a music player to drown out the racket, and patients are given earplugs. When the RF pulse is turned off, the hydrogen protons slowly return to their natural alignment within the magnetic field and release the energy absorbed from the RF pulses. When they do this, they give off a signal that the coils pick up and send to the computer system.

But how is this signal converted into a picture that means anything? The MRI scanner can pick out a very small point inside the patient's body and ask it, essentially, "What type of tissue are you? It then integrates all of this information to create 2-D images or 3-D models with a mathematical formula known as the Fourier transform.

The computer receives the signal from the spinning protons as mathematical data; the data is converted into a picture. The MRI system uses injectable contrast , or dyes, to alter the local magnetic field in the tissue being examined. Normal and abnormal tissue respond differently to this slight alteration, giving us differing signals. These signals are transferred to the images; an MRI system can display more shades of gray to depict the varying tissue [source: Coyne].

The images allow doctors to visualize different types of tissue abnormalities better than they could without the contrast. We know that when we do "A," normal tissue will look like "B" -- if it doesn't, there might be an abnormality. When the radio waves are turned off, the protons realign.

This sends out radio signals, which are picked up by receivers. They also help to distinguish between the various types of tissue in the body, because the protons in different types of tissue realign at different speeds and produce distinct signals. In the same way that millions of pixels on a computer screen can create complex pictures, the signals from the millions of protons in the body are combined to create a detailed image of the inside of the body.

An MRI scan is a painless and safe procedure. You may find it uncomfortable if you have claustrophobia , but most people are able to manage it with support from the radiographer. Extensive research has been carried out into whether the magnetic fields and radio waves used during MRI scans could pose a risk to the human body.

No evidence has been found to suggest there's a risk, which means MRI scans are one of the safest medical procedures available. Radio waves cause these aligned atoms to produce faint signals, which are used to create cross-sectional MRI images — like slices in a loaf of bread. The MRI machine can also produce 3D images that can be viewed from different angles. MRI is a noninvasive way for your doctor to examine your organs, tissues and skeletal system.

It produces high-resolution images of the inside of the body that help diagnose a variety of problems. MRI is the most frequently used imaging test of the brain and spinal cord. It's often performed to help diagnose:. It produces images of blood flow to certain areas of the brain. It can be used to examine the brain's anatomy and determine which parts of the brain are handling critical functions.

This helps identify important language and movement control areas in the brains of people being considered for brain surgery. Functional MRI can also be used to assess damage from a head injury or from disorders such as Alzheimer's disease.

MRI that focuses on the heart or blood vessels can assess:. MRI can check for tumors or other abnormalities of many organs in the body, including the following:. MRI can be used with mammography to detect breast cancer, particularly in women who have dense breast tissue or who might be at high risk of the disease.

Because MRI uses powerful magnets, the presence of metal in your body can be a safety hazard if attracted to the magnet. Even if not attracted to the magnet, metal objects can distort the MRI image. Before having an MRI , you'll likely complete a questionnaire that includes whether you have metal or electronic devices in your body. Devices include:. If you have tattoos or permanent makeup, ask your doctor whether they might affect your MRI.

Some of the darker inks contain metal. Before you schedule an MRI , tell your doctor if you think you're pregnant. The effects of magnetic fields on fetuses aren't well understood. Your doctor might recommend an alternative exam or postponing the MRI.

Also tell your doctor if you're breast-feeding, especially if you're to receive contrast material during the procedure. It's also important to discuss kidney or liver problems with your doctor and the technologist, because problems with these organs might limit the use of injected contrast agents during your scan.

Before an MRI exam, eat normally and continue to take your usual medications, unless otherwise instructed. You will typically be asked to change into a gown and to remove things that might affect the magnetic imaging, such as:.

The MRI machine looks like a long narrow tube that has both ends open. You lie down on a movable table that slides into the opening of the tube. A technologist monitors you from another room. You can talk with the person by microphone. If you have a fear of enclosed spaces claustrophobia , you might be given a drug to help you feel sleepy and less anxious.