Magnetic resonance tomography is an imaging procedure that depicts the structure and function of the tissues and organs in the body. The word tomography comes from Ancient Greek where tomos means “slice” or “section”, and graphō means “to write” or “to describe”. The English use the term magnetic resonance imaging which is called MR imaging, or simply MRI.
An MRI will always be indicated if an x.ray or ultrasound can not deliver a clear diagnosis or if the clinical question concerns a dynamic process, e.g., metabolism in the brain.
With an MRI, one can obtain image slices through your body (or animal’s body) that will allow one to judge if one or more of your organs are sick.
The MRI uses a very strong magnetic field, similar to a variable (active) electromagnetic field in the radiofrequency range. This excites the nuclei of specific atoms in the body, mostly protons within water molecules.
Very weak magnetic fields will be received from the excited atomic nucleus. Not x-ray beams or other ionizing radiation is produced or used. The basis for the images is the different relaxation times of various types of soft tissue, e.g., muscle, fat, bone, air, that also contain variable amounts of water atoms.
An alternative name for MRI is nuclear spin tomography which is sometimes referred to as “nuclear spin”, though this is rarely used by anyone other than specialists in the field. Occasionally, the abbreviation MRI, which comes from the English Magnetic Resonance Imaging, is used.
Numerous special MRI exams have been developed, to depict the blood supply to various organs, as well as to gain information about their form, function and microstructure. Magnetic resonance angiography (MRA), e.g., performed either static or dynamic, is one of these special exams. Others include perfusion MRI, diffusion MRI, diffusion tensor imaging (DTI), as well as functional magnetic resonance imaging (fMRI) of the brain.
Tesla (T) is the derived international system of unit for magnetic flux density or magnetic induction. This unit was named after Nikola Tesla in 1960, at the Conférence Générale des Poids et Mesures (CGPM) in Paris.
The magnetic flux, also called magnetic induction, in colloquial terminology magnetic field, refers to a physical value/quantity. It is represented by the symbol B and stands for the surface density of magnetic fluxes which can pass through a specific surface element. The symbol dates back to the Scottish physicist James Clerk Maxwell, who used the notation B, C and D for magnetic fields and E, F, and G for electrical fields.
The magnetic flux is an electrodynamic quantity. It is the quotient from the Lorentz force F experienced by a charged particle moving through an electric field and magnetic field. F is the product of the strength of the electrical field and the magnetic field. This explains why the magnetic field orients itself perpendicular to the electrical field.
1 Tesla is a very large unit. For example, the earth’s magnetic field at 50° latitude is 4.8 x10-5 T, at the equator 3.1 x 10-5 T (circa 1% of a huge horseshoe magnet). A very strong neodymium iron boron (i.e., permanent) magnet reaches circa 1.5 T, though for a small volume, i.e., less than 1 cm³.
In order to achieve strong magnetic fields (i.e.,greater than 1 Tesla) with a maximum diameter of circa 1 meter, we can use superconducting metal alloy wires, e.g. NbTi, and electrically charged liquid helium at -269°C. This will produce a constant magnetic field over years, as long as the temperature is maintained.
To put things in perspective, our 7 Tesla high-field MRI is
• 140.000 times stronger than the Earth’s magnetic field
• Shielded by a 34-ton magnet and 270 tons of iron
• Capable of generating high-resolution images of complex processes in the body
• One reason why Vienna is at the summit of research worldwide
There is no need to worry if you do not understand the following explanation. You are not a Physics student! A layman’s knowledge is sufficient. You only need to have a vague idea about a few basic things.
The Magnetic resonance imaging, abbreviated MRI, uses the so-called nuclear spin from atoms (e.g., hydrogen, oxygen, phosphorous, carbon), that simplistically, you can think of as small magnets, and that exist in great abundance in the human body.
Typically, all of these nuclei spin in every possible direction. But once you are placed within a strong magnetic field, e.g., the MRI machine, the nuclei align themselves in one direction, similar to a compass needle. You won’t be aware (feel) that this is taking place. The majority of nuclei will align themselves with the magnetic field, but a few will point in the opposite direction to the magnetic field, i.e., 180°. This energy difference (i.e., delta E) is useful for imaging the tissues.
After the body part under investigation is excited by the radiofrequency (RF) waves, those RF waves absorbed by the tissues will be sent back. This does not harm your body. The frequency of the RF waves depends upon the magnetic field’s strength and the type of nuclei.
In traditional MR images, hydrogen atoms from water will be measured; In a 1 T MRI machine, the RF waves will resonate at a frequency of 42 MHz, whereas in a 7 T machine, the RF waves will resonate at 300 MHz.
In order to recognize each layer of body tissue, additional magnetic coils placed over the region of interest generate an increasingly stronger magnetic field that allows the area to be precisely demarcated. Step by step images are produced and eventually, all of the images are assembled into a 3-dimensional image.
The difference in the water content in various tissues in a specific body part can also be visualized. For each incremental increase in spatial resolution, which depends upon the maximum field strength, the better the organs can be depicted. The greater the water content in the tissues being investigated, the brighter the MR images will appear.
Nikola Tesla (in Serbian Никола Тесла, * 10. Juli 1856 in Smiljan, Kaisertum Austria, which is today Croatia; † 7. January 1943 in New York, USA) was an inventor and electrical engineer. His most significant electrotechnical invention is his contribution to usable alternating current.
Biography
Tesla was the son of ethnic Serb parents (Milutin und Djuka Tesla), born in the village of Smiljan, not far from Gospić (today Croatia). He attended school in Gospić, and then Karlovac. After attending the Technical University in Graz between 1876 and 1878, he briefly studied at the university in Prague before moving to Budapest where he developed the idea of using alternating current to transfer energy to power electric motors. In 1882, Tesla moved to Paris to work for the European branch of Thomas Edison. Despite meager finances, he relocated to New York in 1884, where he found a job with Edison.
Contrary to Edison, Tesla dedicated himself to the use of alternating current. He soon found himself at Westinghouse where, as a rival of Edison, he was able to advance his own technical vision. Indeed, today alternating current is widely used. After his success in the field of energy supply, Tesla began working on lighting, as well as high-frequency and medical technology.
He died in the Hotel New Yorker from heart failure sometime between January 6th and 8th, 1943. He was 86 years old. Despite his numerous patents, Tesla died in a mountain of debt. He had adopted a lavish lifestyle which, inspite of his inventions, set him back more and more financially. His ashes are on display at the Nikola Tesla Museum in Belgrade.
Tesla’s inventions and technical developments
The most important invention of Tesla during his first decade in America was the two-phase electric generator which helped propel the idea of alternating current worldwide. In May 1885, Tesla sold this patent to George Westinghouse, despite its development at Edison’s electric company. This led to the “current wars”, i.e., a bitter competition between Edison’s direct current and Westinghouse’s alternating current. The two finally reconciled in 1891 through Lauffen-Frankfurt’s concept of three-phase current.
At the 1893 Chicago World’s Fair, Tesla’s system showed that AC was not only en vogue, but that it also consumed less energy than DC current. This was a turning point for AC. During the competition for the better system, supporters of DC conducted AC current through an electrical stool to show spectators the dangers of AC. The opponents of AC literally mocked their Westinghouse rivals.
Tesla experimented with various lighting systems and also with the production of high-frequency AC from the Tesla transformer. This is where the so-called Violet Ray appliance, used in medicine, originates. Furthermore, he transmitted the first radio transmission from Wardenclyffe Tower and the first remote control in the world.
Tesla co-developed three-phase current used today. It was invented in a time when the basic research and technology for electrical energy transmission was being performed, i.e., power engineering. Tesla later worked on other energy transmission projects. In the US alone, in fifty professional years, he registered 112 patents! However, as many inventions were being discovered by several researchers simultaneously in Tesla’s time, the patent-holder didn’t necessarily reap the financial rewards.
Excerpt from Wikipedia.org