Magnetic Resonance Imaging Scans

Magnetic resonance imaging (MRI) is a clinical tool that allows for imaging of soft tissue, bone, and organs. MRI is a noninvasive test in which a person goes into a doughnut-shaped machine. It functions based on several principles of physical science including magnets and radio frequency. Inside the MRI machine, there is a very large magnet. Once it is turned on, it causes a change in the position of the atoms inside the cells of the body. Through the use of computers, these changed position of atoms will produce a picture of the inside of the body.

MRIs are generally safe exams. They do not expose patients to radiation compared to other tests such as computerized tomography (CT) scans or dual energy X-ray absorptiometry (DEXA) scans. This makes MRI scans a useful test for certain populations such as pregnant women and children. However, because MRI machines use a very strong magnet, certain patients are prohibited from having MRI scans performed such as those who have metal implants. It is also very important that no metal objects such as gas tanks are in the room with the MRI scanner as they can harm the patient in the scanner.

MRI is primarily used as a medical tool to assess muscle injuries or identify tumors. MRI is an excellent tool to use in the study of obesity as well. MRI [Page 441]scans permit the study of body composition, an important component in the field of obesity. Whole-body MRI is used to measure total body fat and body fat distribution. This includes measuring the different types of fat such as subcutaneous fat (fat below the skin), visceral fat (fat around the organs), and intermuscular fat (fat between the muscles). Measuring the distribution of fat has been stated to be just as important as measuring the total amount of fat. Elevated amounts of visceral fat and intermuscular fat are associated with the development of many diseases such as heart disease and diabetes. Measuring fat with an MRI scanner produces better results than many other body composition tools such as skin folds, bioelectrical impedance, and underwater weighing. In addition to measuring body fat, researchers can measure total skeletal muscle and type of skeletal muscle (i.e., slow-twitch and fast-twitch muscles). MRI scans are also used for the measurement of organs such as the heart, liver, and brain.

Recently, MRI scanners have been used for more advance measures of body composition such as functional MRIs and spectroscopy. Functional MRI is used to obtain advanced images of the brain. It is being used to learn how certain tasks are related to different regions of the brain, specifically in the field of obesity functional MRI is being used to study eating behavior. Spectroscopy is used to measure nonvisible fat, known as ectopic fat, inside the muscle and liver. Like visceral and intermuscular fat, ectopic fat has been associated with increased risk of developing heart disease and diabetes.