Q: What is the difference between T1 and T2?

Every tissue in the human body has its own T1 and T2 value. For example, white matter in the brain will exhibit different T1 and T2 values than that of blood. Both are different measures of different kinds of magnetic resonance "relaxation" that occurs after an atom has been stimulated by a radio signal in the presence of a strong magnetic field. In magnetic resonance imaging, the emitted radio signal from a particular tissue depends on a combination of that tissue's T1 and T2 values. In constructing an image, to help the radiologist make an accurate diagnosis, the MRI machine can use the tissue T1 to control the brightness of the image pixels (a T1 image) or it can use the tissue T2 to control the brightness of the image pixels (a T2 image). Usually, a radiologist will request both T1 controlled and T2 controlled images. In a T1-controlled image, tissues with low T1 values will be displayed as bright picture elements, or pixels, on the computer monitor and tissues with high T1 values will be displayed with dark pixels. In a T2-controlled image, tissues with high T2 values will be portrayed as bright areas on the image and those with low T2 values as dark areas. Thus, a T1-controlled and a T2-controlled image for the same exact anatomical area can look quite different. In a T1-controlled image, one particular spot may be bright white. In a T2-controlled image, the same identical spot may be displayed as gray. That's because an MRI image is not a photograph. It is actually a computerized map or image of radio signals emitted by the human body. That's the reason Dr. Damadian's 1970 findings were so important. It is the variation in relaxation times of neighboring tissues that make each tissue distinguishable in an MRI image. If such were not the case, an image would be all one tone of gray and useless as a medical tool. Dr. Damadian published his discovery that relaxation times of normal and cancerous tissue are markedly different and that relaxation times of normal, healthy tissues also vary significantly in the March 19, 1971 issue of Science. Less than two years later, he filed his idea for using magnetic resonance as a tool for medical diagnosis with the U.S. Patent Office. Entitled "Apparatus and Method for Detecting Cancer in Tissue," and granted a patent by the Patent Office in 1974, it was the world's first patent issued in the field of MRI. His patent contains the first conceptualization of a magnetic resonance scanner capable of cross-sectional scanning of a human being. By 1977, Dr. Damadian had turned his concept into reality when he completed construction of the first whole-body MRI scanner, which he dubbed "Indomitable." The name was a fitting choice. The large, strange-looking machine had been constructed despite those who said Dr. Damadian's idea was impractical and foolish. Furthermore, on July 3, 1977, the nay-sayers were proven wrong when Dr. Damadian and his associates produced the first whole-body magnetic resonance image using Indomitable and the same signal-acquisition process described in Dr. Damadian's patent. Today, Indomitable is on permanent display in the Smithsonian Institution in Washington, DC.

close this window