When you slide into an MRI scanner, powerful magnets align the hydrogen atoms in your body. This is normal and does not hurt. Radio waves are then sent to knock these atoms out of alignment. When the radio waves stop, the atoms return to their original position and send back signals that are picked up by the scanner.
Magnetic Fields
MRI uses powerful magnets to produce a magnetic field that penetrates the body. This field pulls on protons in your body and aligns them with the scanner’s magnetic field. This forces them to strain against their natural state and releases energy. A computer then uses this energy to create clear, black-and-white images of your organs and tissues. Unlike x-rays and computed tomography (CT) scans, MRI does not use any radiation.
During the MRI scan, a technologist will position you on a moveable examination table. The technologist may help you relax by positioning pillows, blankets, and other items around you to keep you comfortable. Some MRI machines look like narrow tunnels, but there are open scanners designed for patients who cannot tolerate the tight spaces or who suffer from claustrophobia. During the test, the technologist will ask you to remove all metal items such as jewelry and clothing, because they can affect the results.
The magnetic field extends outside the machine and exerts strong forces on objects of iron and some steels; it is even strong enough to fling a wheelchair across the room. For this reason, it is important to let your doctor know if you have any medical implants such as a heart pacemaker or other metal pins. You also should inform your doctor if you are pregnant or suspect you might be.
While MRI does not expose you to ionizing radiation, the strong magnetic fields can cause warmth and/or swelling in some tissues. They can also cause distortion of images if your body is filled with fluids such as blood or urine. This distortion is not harmful, but your doctor will instruct you to drink plenty of water after the test to flush out any excess fluids.
The rapid rate of technical advances in MRI has sometimes led to its integration into clinical practice on the basis of diagnostic accuracy only. More work is needed to demonstrate the higher-order value of MRI, such as its impact on patient outcomes. To this end, novel study designs that are more suited to linking MRI-determined phenotypes to clinical outcomes should be used.
Radio Waves
Within the constant magnetic field of an MRI scanner, hydrogen nuclei in tissues that contain them (such as fat and water) generate radio frequency signals with pulses of RF energy. This signal is detected by antennas within the MRI machine and mathematically converted into images. A variety of image contrasts can be generated based on the specific characteristics of each tissue type.
A strong magnetic field causes protons in the body to line up, much like the needle of a compass lines up with a magnet. Short bursts of radio waves are then sent to certain areas of the body, knocking the protons out of alignment and causing them to send back radio signals that are picked up by receivers in the MRI machine. The computer then uses the information to create a picture of the area being examined.
Before some Magnetic resonance imaging (MRI) scans, doctors may give patients a dye, often containing gadolinium, to help the images come out clearer. It can also help to distinguish between tissue that is healthy and tissue that is cancerous or damaged. The contrast dye can cause serious kidney problems in people with chronic kidney disease, though this is rare.
Because of the high level of magnetic energy created by MR scanners, it is important for patients to remain as still as possible during an MRI. This is why most MRI tests are done while the patient is sedated or under general anesthesia.
During an MRI, you will hear repetitive tapping and thumping noises from the machine. The sound can reach levels of 120 decibels, so you will be given earplugs or ear muffs to protect your ears. Some people also experience a twitching sensation from the MR noise, which is normal.
The process of generating an MRI scan can take up to an hour, depending on the size and complexity of the exam. During this time, the patient must stay very still to prevent the images from blurring. Some MRI scans will require a contrast agent to be given intravenously to speed up the process of the protons realigning in the magnetic field. This can lead to a metallic taste in the mouth, and it is not recommended for pregnant women or those with any known metal implants in their bodies.
Protons
A proton is a particle that makes up the nucleus of an atom. It has a magnetic moment that is related to its mass, which makes it sensitive to the magnetic field of an MRI scanner. In an MRI scan, protons are detected in the hydrogen atoms that make up water molecules found in living tissue. Each proton has a unique magnetic moment that allows it to be distinguished from other atoms within the same body part.
When you enter an MRI machine, the powerful magnet causes the protons in your body to line up. Then the radio waves turn them around and back to their original positions, and they send signals that a computer turns into an image of the part of your body being studied.
The images produced by an MRI scanner allow doctors to better understand and diagnose diseases or injuries to your organs, muscles, ligaments, tendons and soft tissues. Unlike CT scans, MRI does not use any ionizing radiation. However, the magnetic field produced by an MRI scanner is strong enough to cause significant injury if touched directly, and it also may interfere with certain types of medical implants — such as heart pacemakers, implantable cardioverter-defibrillators, loop recorders, cochlear implants and capsules from capsule endoscopy. Patients with such devices should tell their doctor before having an MRI.
During the MRI scan, you lie down on a table that slides into a long tube-shaped magnet. A technologist monitors you from another room. The scanner produces repetitive tapping and thumping noises during the exam, which can be uncomfortable for some people. Earplugs or music to block the sound can help.
You should remain as still as possible during the MRI exam to ensure good results. You will be given a medication to help you relax and possibly a contrast dye to help your doctor see abnormal tissues more clearly. The contrast dye, typically gadolinium, can cause a metallic taste in your mouth and itching or itching at the injection site in some people. If you have kidney or liver disease, you may not be able to receive the contrast dye.
Tissues
Tissues are groups of cells that perform a similar function. They make up organs and are a level of organization in multicellular living organisms. Each tissue performs a specific task that contributes to the body’s health and survival. The main types of tissues are epithelial, connective, muscle, and nervous. A doctor can diagnose a health problem by studying the type of tissue that is damaged. He can then treat that tissue with medicine or surgery, if necessary.
MRI of the body uses a powerful magnetic field, radio waves and a computer to produce detailed pictures inside the body. It is a safe procedure with no known long-term side effects. However, some people may feel uncomfortable in the scanner, especially if they are claustrophobic (afraid of closed spaces). Some MRI facilities offer anti-anxiety medications to help with this feeling. Others suggest wearing earplugs or ear muffs to decrease the noise that the machine makes during the scan. Some MRI exams require a contrast dye to help the radiologist see certain structures more clearly. The dye is given through a vein in your arm or hand. The dye can cause a metallic taste in your mouth. It isn’t used for every MRI exam and some patients, such as pregnant women or those with kidney disease, should not get the dye.
The radiologist will prepare you for the MRI test and you will lie down on a table. The radiographer will then put the magnet over your chest or abdomen and the scanner will begin to take pictures of the area being scanned. You will hear tapping or thumping noises while the pictures are being taken. The radiographer will give you earplugs or ear Muffs to decrease the noise and you will be able to talk to them through an intercom.
Before you have an MRI, tell your doctor if you have a pacemaker or other implantable devices. Metal objects can interfere with the magnetic field of the MRI machine and could lead to serious injury or death. Also, let your doctor know if you are pregnant or have any other health problems. You should also ask your doctor about the guidelines for eating and drinking before the scan and if you have any allergies.
