Magnetic Resonance Imaging

Overview

Magnetic resonance imaging (MRI) uses nuclear magnetic resonance (NMR) to image the body. Images are created by signal resonating from hydrogen protons, which are abundant in the human body (ie water, fat). MRI does not impart ionizing radiation, such as with CT, X-Ray, and conventional angiography. It produces images with exquisite soft tissue contrast, allowing us the see the difference between unique parts of the brain or spinal cord or to identify pathologic tissues that on CT appear very similar or indistinguishable from normal adjacent tissues. An MRI exam takes significantly longer than CT which can prohibit use in critically ill patients such as with an unstable trauma patient. MRI however is an extremely valuable imaging tool for the brain and spine and exciting advancements in MRI technology continue to broaden its applications.

In this section you will find information regarding how MRI came to be, a summary of how MRI works, and important details about MRI safety, terminology used to describe images, and indications for ordering MRI exams.

History of MRI

Magnetic resonance imaging (MRI) is an extension of the technique you used in organic chemistry to identify the components of a chemical compound. This was called nuclear magnetic resonance (NMR). Rather than calling the imaging technique nuclear magnetic resonance imaging the inventors and marketers decided to drop the “nuclear” and call it magnetic resonance imaging. They thought this might be more palatable by the public. But how did we get to MRI?

Scientists Felix Bloch and Edward Purcell separately discovered magnetic resonance in 1946 and in the 50s and 60s it started to be used for chemical analysis, like you did in organic lab. Then, in the early 70s Ramond Damadian analyzed tissue and tumor with NMR (not imaging) and found that the signal from the two were different. However, there was no way to know spatially where normal vs abnormal tissue was. In 1974 Paul Lauterbur and Peter Mansfield, working independently, described a way to spatially localize signal using gradients. In 1974 Richard Ernst attended a conference given by Lauterbur and shortly after described the use of gradients for phase and frequency encoding and the Fourier transform to create images with spatial information. This method is essentially what is used today.

Edward Purcell ¹

Felix Bloch¹

Peter Mansfield ¹

Paul Lauterbur ¹

In 1977 Peter Mansfield and Andre Maudsley used MRI to image the finger. In 1977 Waldo Hinshaw, Paul Bottomley, and Neil Holland also made images of the wrist. Damadian imaged the chest in 1977. One year later Hugh Clow and Ian Young imaged the head. However, in 1980 William Edelstein used the technique developed by Richard Ernst to make the first MRI images of a person, establishing the first images created using the basis of what we do now. This still took a long time to get a single image though, about 5 minutes. Imaging time has been drastically decreased since then.

Additional Resources

For another brief perspective of the history of MRI, see the following website: http://www.teslasociety.com/mri.htm.

References

1) Geva, T. Magnetic resonance imaging: historical perspective. J Cardiovasc Magn Reson. 2006;8(4):573-80.