How Does MRI Work?
The book is intended for readers looking for an easy to understand and concise introduction to this fascinating yet somewhat complex imaging modality at the beginning of their MRI training. This thoroughly revised second edition succinctly introduces the physics and function of magnetic resonance imaging. All important and clinically relevant aspects are presented in a clearly structured manner. The emphasis is on practical information including the latest trends and developments that are relevant for MRI in the clinical setting. The opening chapters describe the underlying physical principles of the MR experiment and the basic pulse sequences commonly used in clinical MRI. Other chapters are dedicated to more advanced techniques such as parallel imaging and cardiovascular MR imaging. The book is rounded out by chapters on MR contrast media, artifacts, high-field imaging, and safety concerns. An extensive glossary offers rapid access to the most important MRI terminology.
Magnetic Resonance Imaging uses a high magnetic field and radio waves to make detailed maps of hydrogen protons in the body. In areas of disease there is often a change in the concentration or behaviour of hydrogen and this is reflected in the MR image as areas of brighter or darker signal intensity. A radiologist trained to interpret these complex maps will review your MR examination and provide a report to your doctor. Learn more about MRI.
How does the MRI magnet produce detailed cross-sections of the brain? “Typically MRI causes the body to emit a signal,” explains Jim Rosato, head interventional MRI technologist at Brigham and Women’s Hospital. “As the protons—the nuclei—of the hydrogen atoms in our body spin, they form north and south poles, but they can be facing in different directions. Once the patient goes into the magnet, it causes all the protons to align in one direction.” With a magnetic field strength 10 thousand times greater than the earth’s, the electromagnet in the Signa SP has plenty of power to perform this feat. “The banging, jackhammer sound people hear during MRI is actually caused by the electromagnetic gradients, or radio waves, switching on and off extremely fast,” Rosato continues. “This causes the protons, which are now lined up with the main magnetic field, to flip 90 degrees. Each time the radio pulse switches off, the protons go back to their original position. When they do that, they emit an
Like X ray, MRI is based on a discovery in the physic lab: when the nuclei of hydrogen atoms–single protons, all spinning randomly–are caught suddenly in a strong magnetic field, they tend to line up like so many compass needles. If the protons are then hit with a short, precisely tuned burst of radio waves, they will momentarily flip around. Then, in the process of returning to their original orientation, they resound with a brief radio signal of their own. The intensity of this emission reflects the number of protons in a particular “slice” of matter.
