MRI

Seeing Inside

No knives. No blood. No sticking out your tongue and saying, “Ahhhhh.” Magnetic Resonance Imaging (MRI) lets doctors look inside you safely and painlessly.

It’s a uniquely detailed diagnostic tool, sensitive enough to detect a ripple of fluid in the brain or the minute narrowing of a blood vessel - without using X-rays, which can be harmful.

Impact

Your Inner Self

Some software changes lives. MRI software saves lives.

MRI is part of a long line of non-invasive imaging tools, beginning with X-rays in 1895. But unlike X-rays or CT scans, MRI doesn’t expose patients to ionizing radiation and reveals different body structures. This lets doctors decide safely how to treat patients, reducing unnecessary procedures, unnecessary side effects…and unnecessary costs.

Left: Simon Fraser/Science Photo Library Right: Credit: Andreas Vesalius (public domain), via Wikimedia Commons

Left-MRI whole body scan Right-Andreas Vesalius, Di humani corporis fabrica, 1543

For centuries human anatomy remained a mystery. Public dissections and experiments were common, but yielded limited knowledge. Today, noninvasive medical imaging techniques, like MRI, enable doctors to learn what’s happening inside our bodies without cutting into them.

MRI at Work

A blood clot in the brain landed Fred S. in the emergency room. Five hours had passed, outside the usual window for using clot-dissolving drugs. Yet an MRI showed that the drugs might still work.

Fred was soon discharged —and his life saved—thanks to treatment that would not have been performed without the MRI.

Brain MRIs

Photo by Ken Glaser via Media Bakery

Brain MRIs

MRI captures 3-D pictures of an area, like your brain, by imaging different layers, called anatomical planes. The three basic anatomical planes are axial (top to bottom), coronal (front to back), and sagittal (left to right). Different abnormalities appear more clearly on different planes.

Aorta before (left) and after (right) survery

Credit: Gunnar K. Lund, Christoph Diekmann, and Christoph A. Nienaber, Circulation [online], American Heart Association

Aorta before (left) and after (right) survery

Aneurysms occur when the walls of a blood vessel become weak, causing them to bulge. Untreated, aneurysms can be fatal. These MRI images show a patient’s aorta before and after repair of an aneurysm.

Researchers at the University of Zurich, February 11, 2008

© Siemens Healthineers 2016. Used with permission.

Researchers at the University of Zurich, February 11, 2008

Ultrashort echo time (UTE) is a technique that enables doctors using MRI to image materials with little or no water, like bone and cartilage, using MRI. In 2008 scientists tested UTE on a 1,000-year-old Peruvian mummy.

Jordan McMahon, 2005 (left) and clear MRI scan, 2013 (right)

Jordan McMahon, 2005 (left) and clear MRI scan, 2013 (right)

MRI Video Poster

MRI Software Makers and Users

Mobile MRI scanner

Mobile MRI scanner

Kiki the Koala, Melbourne Veterinary Referral Centre, November 8, 2005

Kiki the Koala, Melbourne Veterinary Referral Centre, November 8, 2005

For Better and For Worse

Is more information always better?

MRI has transformed medicine, letting doctors look inside us before picking up a scalpel, prescribing drugs, planning treatment, and following-up.

But MRI also spots harmless abnormalities that might never cause problems, leading to tests and treatments that can be costly or dangerous—and unnecessary.

Kidney MRI, postoperative axial (left) and coronal (right) scans

Credit: Eun Hui Bae, Young-Hwan Hwang, and Soo Wan Kim, International Braz J Urol [online]

Kidney MRI, postoperative axial (left) and coronal (right) scans

Incidental findings are abnormalities found on an MRI image while looking for something else. This liver study revealed cysts—fluid-filled sacs—in the right kidney.

Agnew Clinic, University of Pennsylvania, March 30, 1886

Agnew Clinic, University of Pennsylvania, March 30, 1886

Anatomage Virtual Dissection Touch Table

Anatomage Virtual Dissection Touch Table

Technology

What is an MRI?

MRI machines use a magnetic field, radio waves, and a computer to detect the properties of living tissue. All body parts have water (and thus hydrogen).

An MRI machine creates a magnetic field around your body, causing your hydrogen atoms, which are partially magnetic, to align with the field. When radio waves are applied quickly, they excite these atoms, causing them to emit a unique electronic signal that sensors record—and which MRI software uses to create an image.

T.T. via Getty Images

Doctors evaluate knee MRI

MRI is an invaluable noninvasive diagnostic tool that combines hardware and software. Its technology produces detailed anatomical images that helps doctors detect disease, spot abnormalities, and monitor treatment.

Painting the Picture

We think of MRI “machines” as hardware. Yet much of their power lies in their software, which controls the magnetic and radio-frequency pulses, collects and interprets the resulting signals, and then transforms this data into images.

Depending on the MRI settings, images can highlight fat, water fluid, air, bone, or soft tissues in the patient.

MRI machine

Shutterstock/BlueRingMedia

MRI machine

MRI machines contain a large magnet that aligns the hydrogen atoms in your body. When excited by a radio pulse, those atoms emit signals, measured by radio frequency coils. Gradient coils add position information to the signal. The loud noise MRI machines make is the vibration of the gradient coils, caused by rapidly changing electromagnetic fields.

Abdominal MRI, showing fluid, fat and air

Credit: GE Healthcare

Abdominal MRI, showing fluid, fat and air

MRI detects different tissue types and displays them in varying shades of grey. This abdominal MRI scan shows fluid, fat, and air as well as major organs like the liver and lungs.

Technician console screenshot, showing contrast agent

Gadolinium, a special contrast agent that illuminates blood vessels, may be given before an MRI to highlight certain tissues, like this heart and its major blood vessels.

Technician console screenshot, showing contrast agent

Credit: stereofx.org/volume

OsiriX DICOM image viewer

OsiriX DICOM image viewer

Olcott Video Poster

Eric Olcott, MD, Professor of Radiology, Stanford University School of Medicine

1/12th-scale model of MRI machine

1/12th-scale model of MRI machine

Show & Tell

Software is a valuable tool throughout the MRI process. During your MRI, technicians use software to select imaging parameters and administer pulse sequences. After your MRI, software is used to process your images so that doctors can interpret them.

Software systems also archive and display MRI images, allowing doctors to consult with and connect patients to far-flung medical specialists when needed.

Technician console, Oxford Centre for Magnetic Resonance, John Radcliffe Hospital, December 1, 2015

John Cairns Photography/Oxford University Images/Science Photo Library

Technician console, Oxford Centre for Magnetic Resonance, John Radcliffe Hospital, December 1, 2015

Technicians ensure MRI machinery is running properly and verify that the correct pulse sequences are used. They monitor patients from a separate room, but can communicate with patients via a two-way intercom.

Surgeon examines MRI data sets

Surgeon examines MRI data sets

History

Creating MRI Technology

MRI evolved over decades, beginning in 1937 with Isidor Rabi’s discovery of nuclear magnetic resonance (NMR).

Knowing that an atom’s protons and neutrons act as small, spinning magnets, Rabi exposed different compounds to a large magnetic field and powerful radio waves. Each gave off a unique signal—a magnetic signature.

A decade later, Felix Bloch and Edward Purcell built on Rabi’s work, independently demonstrating NMR in liquids and solids.

Emilio Segre Visual Archives/American Institute of Physics/Science Photo Library

Isidor Isaac Rabi

Isidor Isaac Rabi was awarded the 1944 Nobel Prize in Physics for his method for recording the magnetic properties of atomic nuclei. It became the foundation for MRI and nuclear magnetic resonance spectroscopy.

Data to Images: An Evolution of MRI

Collecting molecular data was the first step in developing MRI. But how to transform this data into pictures?

In the 1970s, Paul Lauterbur and Peter Mansfield independently suggested applying precise variations in a second, “gradient,” magnetic field to pinpoint resonating molecules. Using this information, MRI software assembles a 2- or 3-dimensional image of internal body structures.

1930s: Isidor Isaac Rabi, 1944 Nobel Prize

NYPL/Science Source via Getty Images

1930s: Isidor Isaac Rabi, 1944 Nobel Prize

Development of molecular beam magnetic resonance by passing a beam of lithium molecules through a magnetic field and then bombarding the beam with radio waves.

1940s: Felix Bloch (left) and Edward Purcell (right), 1952 Nobel Prize (shared)

Left: Keystone-France\Gamma-Rapho via Getty Images Right: Science Photo Gallery

1940s: Felix Bloch (left) and Edward Purcell (right), 1952 Nobel Prize (shared)

Independent demonstration of nuclear magnetic resonance in liquids and solids and development of new methods for measuring magnetization of molecules.

1950s: Erwin Hahn

AIP Emilio Segre Visual Archives, Physics Today Collection

1950s: Erwin Hahn

Discovery of the spin-echo phenomenon for nuclear magnetic resonance measurements. Basic principle used in NMR and MRI today.

1970s: Allan M. Cormack (left) and Godfrey N. Hounsfield (right), 1979 Nobel Prize (shared)

AIP Emilio Segre Visual Archives, Physics Today Collection

1970s: Allan M. Cormack (left) and Godfrey N. Hounsfield (right), 1979 Nobel Prize (shared)

Development of the CT scanner that uses reconstruction from projections, the foundation of nearly every many imaging systems used today.

1970s: Raymond Damadian

1970s: Raymond Damadian

1970s: Paul C. Lauterbur (left) and Sir Peter Mansfield (right), 2003 Novel Prize (shared)

1970s: Paul C. Lauterbur (left) and Sir Peter Mansfield (right), 2003 Novel Prize (shared)

1980s: Whole-body MRI team

1980s: Whole-body MRI team

2013: Neonatal MRI machine

2013: Neonatal MRI machine

2015: Open MRI

2015: Open MRI

2015: Typical modern MRI machine

2015: Typical modern MRI machine