Background
MRI is a medical
diagnostic technique that creates images of internal body structures using the
principle of nuclear magnetic resonance (NMR). MRI scans are performed
within a strong, rotating magnetic field. Thus, it can generate thin-section
images of any part of the human body, from any angle and direction.
Historical Overview
Nikola Tesla
discovered the Rotating Magnetic Field in 1882 in Budapest, Hungary. All
MRI machines are calibrated in "Tesla Units,” and the strength of a
magnetic field is measured in Tesla or Gauss Units. In 1937, Isidor Rabi, a
Professor at Columbia University observed that atomic nuclei can be visualized
by absorbing or emitting radio waves when exposed to a sufficiently strong
magnetic field; this quantum phenomenon is known as NMR. In 1971, Raymond
Damadian, a physician and professor at the Downstate Medical Center, State
University of New York (SUNY), reported that tumors and normal tissue can be
distinguished in vivo by NMR. Because cancerous
tissue contains more water, more water translates to more hydrogen atoms. In
1973, Paul Lauterbur, a chemist at SUNY, Stony Brook, produced the first NMR
image. Mike Goldsmith, a graduate student devised a wearable antenna coil to
monitor the hydrogen emission detected by the coil. On July 3, 1977, nearly
five hours after the start of the first MRI test, the first human scan was made
as the first MRI prototype.1
Description
MRI is based on the reemission of an absorbed radio
frequency (rf) signal while a patient is in a strong magnetic field. The
ability of MRI to image body parts depends on the intrinsic spin of atomic
nuclei. When placed within the main magnetic field, these nuclei will align
along the direction of that field. The application of rf pulses causes the
nuclei to absorb energy. When the rf field is removed, the energy absorbed
during the transition from a high- to low-energy state is released, and this is
recorded as an electrical signal that provides the data from which digital
images are derived. Signal intensity refers to the strength of the radio wave
that a tissue emits after excitation, and the strength of this radio wave
determines the degree of brightness of the imaged structures. A bright/white
area of demonstrates high signal intensity; a dark/black area demonstrates low
signal intensity.2
