What makes mri work

We use something called a radio frequency RF pulse, to disturb or flip all the protons, at the same time, out of alignment from the scanners magnetic field Figure 2C. The frequency of the RF pulse must be the same as the frequency of the spinning hydrogen protons, so they can exchange energy, so that they are on resonance with each other. Resonance enables the protons to absorb enough energy from the RF pulse to rotate their axes away from the B0 field, so that the MRI scanner can measure it.

This is similar to the way the protons behave when we turn on the RF pulse. We use the fact that the precessional frequency of the protons is dependant on the magnetic field strength. We apply a second magnetic field, B1 that varies across the body. In the example shown in Figure 3A , hydrogen protons in the head will then be spinning faster than those in the chest, stomach and feet.

Then, we tune the RF pulse to the precessing frequency of the hydrogen protons in the head. The RF pulse will then only be resonant with the protons in the brain. Therefore, only the protons in the brain will absorb energy from the RF pulse and be flipped away from the B0 field.

We can obviously tune our RF pulse to be resonant with protons in other parts of the body, like the feet, if we were interested in imaging the feet! So how do we get an image from these spinning, flipped hydrogen protons in the brain? When the RF pulse is turned off, the protons flip back and realign along the main magnetic field, B0.

As the protons flip back and realign with B0, they give off energy. Different tissues in the body give off different amounts of energy. To measure this emitted energy, we require some special equipment called a coil that is placed around the body part we are imaging Figure 3B. The coil acts as an antenna and detects the released energy as an electrical current. The electrical current is transformed, via a computer, using a mathematical calculation called a Fourier transformation.

Because protons in the different kinds of tissues in the brain, such as gray matter, white matter and blood, all give off different amounts of energy, the result of the transformed energy is a highly detailed image of the tissue inside the brain.

We have now described how we use MRI to generate and measure signal from water molecules in the body. MRI scanners are particularly well suited to image the non-bony parts or soft tissues of the body.

They differ from computed tomography CT , in that they do not use the damaging ionizing radiation of x-rays. The brain, spinal cord and nerves, as well as muscles, ligaments, and tendons are seen much more clearly with MRI than with regular x-rays and CT; for this reason MRI is often used to image knee and shoulder injuries. In the brain, MRI can differentiate between white matter and grey matter and can also be used to diagnose aneurysms and tumors. Because MRI does not use x-rays or other radiation, it is the imaging modality of choice when frequent imaging is required for diagnosis or therapy, especially in the brain.

It is used to advance the understanding of brain organization and offers a potential new standard for assessing neurological status and neurosurgical risk. Although MRI does not emit the ionizing radiation that is found in x-ray and CT imaging, it does employ a strong magnetic field. The magnetic field extends beyond the machine and exerts very powerful forces on objects of iron, some steels, and other magnetizable objects; it is strong enough to fling a wheelchair across the room.

Patients should notify their physicians of any form of medical or implant prior to an MR scan. Replacing Biopsies with Sound Chronic liver disease and cirrhosis affect more than 5. NIBIB-funded researchers have developed a method to turn sound waves into images of the liver, which provides a new non-invasive, pain-free approach to find tumors or tissue damaged by liver disease.

It then pulses sound waves through the liver, which the MRI is able to detect and use to determine the density and health of the liver tissue. This technique is safer and more comfortable for the patient as well as being less expensive than a traditional biopsy.

He or she will send a report to the health care provider who ordered the test. Ask your health care provider any questions you have about your MRI. A cardiac MRI provides still or moving pictures of how the blood is flowing through the heart.

Vivien Williams: One out of four, that's how many people will die of a heart related problem. Doctors at Mayo Clinic are trying to improve those statistics.

They're using MRI s to look inside the heart to find disease and tailor treatment to keep people healthier longer. Brian Shapiro, M. Vivien Williams: Dr. Brian Shapiro uses MRI to look for abnormalities in the heart. So, swelling of the heart is a very common thing in heart attacks, and infections, and things like that. Shapiro how well the heart pumps, where irregular heart beats originate, the location of blood clots, artery blockages, scar tissue, or even tumors.

Because MRI allows doctors to see more detail of the heart, they can make more accurate diagnoses, and therefore tailor treatment for patients. Vivien Williams: Images that tell Dr.

Shapiro if a patient will recover, if there's permanent damage, and what treatments might be best. Information from inside the heart that can help Dr. Shapiro and his colleagues better help their patients. Shapiro says while MRI can show lots of information about the heart, it does not replace other tests such as stress tests or echo cardiograms.

It's another option for looking inside the heart. Explore Mayo Clinic studies of tests and procedures to help prevent, detect, treat or manage conditions. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. This content does not have an English version.

This content does not have an Arabic version. Brain tumor MRI Brain tumor imaging. Request an Appointment at Mayo Clinic. MRI technician: You can breathe. Breathe normal. Vivien Williams: The moving or still images show exactly where damage happens. Share on: Facebook Twitter. Show references Neurological diagnostic tests and procedures fact sheet. National Institute of Neurological Disorders and Stroke. Accessed July 20, Magnetic resonance imaging MRI safety.

Chernoff D, et al. Principles of magnetic resonance imaging. Tsai LL. Patient evaluation for metallic or electrical implants, devices or foreign bodies before magnetic resonance imaging. MRI of the breast. Mayo Clinic; Magnetic resonance imaging MRI. American Heart Association. Magnetic resonance, functional fMRI — brain.