Medical science and physics have a strong relationship in terms of developing new technologies and improving patient care. For the majority of humanity’s history, doctors and physicians were limited to external symptoms for producing diagnoses and treating patients. While observing the visible symptoms is an important part of a medical examination, it cannot show the full extent of the affliction.
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Tumors, irregularities in organ function, and heart and lung issues cannot be accurately diagnosed using external measures alone, while surgical means are considered too inaccurate and intrusive. With the invention of magnetic resonance imaging (MRI) technology, it became possible to use internal imaging without opening up the patient’s body, making the process much easier (Carroll, 2018). MRI would not have been possible without the application of electromagnetic induction. The purpose of this paper is to evaluate the principles behind the phenomenon and their utilization in modern medicine.
History of Discovery of Electromagnetic Induction
Michael Faraday discovered the phenomenon of electromagnetic induction in 1831 (Franklin, 2017). He managed to produce a current in a closed circuit by manipulating the electromagnetic field along its length. The experiment has been since reproduced numerous times due to its rudimentary simplicity. In order to observe the effect of electromagnetic induction, a closed circuit needs to be attached to a galvanometer. A magnet is moved back and forth between the coils.
The galvanometer detects changes in the intensity and the direction of the current, depending on the movement of the magnet. Faraday discovered that several variables could affect the total EMF output, such as the magnet movement speed, the strength of the magnetic field, and the number of coils surrounding the magnet. A higher speed, a stronger magnet, and a larger number of coils result in a stronger EMF.
Definitions and Characteristics of Electromagnetic Induction
Electromagnetic induction is a process that happens in an electric current during the application of changing magnetic fields. These fields are generated when the charges equivalent to the electrical current change their position. Ampere’s law and Fleming’s rule determine the magnitude and direction of electromagnetic induction. The direction can be either clockwise or counter-clockwise, depending on the direction of the electrical flow.
The electric current and the magnetic field can influence one another. One of the major physical laws that explain the process is Faraday’s law of induction. It goes as follows: “The electromotive force around a closed path is equal to the negative of the time rate of change of the magnetic flux enclosed by the path” (Franklin, 2017, p. 53). A practical application of this law states that a magnet that is moved inside of a closed circuit produces an oscillating current effect. The change in the magnetic flux creates an electromotive force in the circuit, commonly known as the EMF, which then affects the current within the circle. Some of the statements regarding the connection between electromagnetic induction and the EMF are as follows:
- EMF is proportional to the rate of alteration of the magnetic field along a specified area of the circuit.
- According to Lenz’s law, the direction of the EMF is the opposite to that of the magnetic field that causes it.
Thus, it is possible to state that Faraday’s laws and Lenz’s law define the principles behind the appearance and application of EMF.
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Application of EMF in Medicine
Numerous medical facilities throughout the US have access to radiological equipment that enables looking inside the patient’s body without applying intrusive means. The principles of electromagnetic induction are applied in numerous scanning and internal imaging apparatuses, such as the X-ray machines, CT (computed tomography) scans, and MRI scans (Carroll, 2018). In regards to X-rays, these rays represent a spectrum of electromagnetic force that is capable of passing through bone and matter and reflecting back to the receptor, enabling the creation of an image of a person’s skeletal structure (Markov, 2015).
X-ray scans are used primarily in detecting fractures and abnormalities in a person’s bones after a trauma or a related affliction. Computed tomography, also known as magnetic induction tomography (MIT) utilizes EMF to map out passive electrical properties of the body, including conductivity, permittivity, and permeability (Markov, 2015). It is a contactless non-invasive imaging technique that uses induction sensors in combination with a simple electronic configuration of a front-end sensory circuit in order to determine the required parameters in a patient.
The use of EMF in MRI is much more complex when compared to X-ray and CT scans. During an MRI procedure, the patient is placed in a magnetic field produced by the circular electromagnet placed inside the MR scanner (Markov, 2015).
The patient becomes the source of electricity, as there are many atoms of hydrogen within a human body. Hydrogen protons possess their own magnetization spins, which can be affected by the magnetic field around them at a certain frequency, called the Lamor frequency (Markov, 2015). This parameter is proportional to the intensity of the magnetic field and forces the protons inside the tissues to align themselves parallel to the outside magnetic field.
During the excitation phase of the MRI scan the image is generated by sending a radio frequency from the scanner. The frequency is tuned in with the Lamor frequency in order to create a magnetic resonance in the proton spin, forcing it to be perpendicular to the magnetic field (Markov, 2015). The Faraday induction comes into play when a receiving coil is placed in close proximity to the tissue, as the transverse magnetization generates an electric current in the coil.
The resulting motion is called the nuclear magnetic resonance (NMR) signal (Markov, 2015). The NMR images are different in tissues and bones due to changes in T1 and T2 relaxation times (Markov, 2015). Because of this factor, MRI is excellent for scanning soft tissues with a degree of accuracy unattainable by CT and X-ray scans.
The discovery of electromagnetic induction was a significant event that changed the face of physics and medicine alike. Faraday’s induction is used in transformers that could be found in nearly any electrical device. At the same time, the principles of EMF are used in non-intrusive scanning procedures, such as CT, X-rays, and MRI. EMF is used differently in these three scanning techniques.
While X-ray machines use EMF to generate the waves that go through a person’s body in order to generate an image, CT and MRI use Faraday’s induction in biophysics in order to stimulate the protons in a person’s body and discern between the tissues. As a result, MRI and CT scans are much more accurate and complex in nature. Understanding the physical laws behind electromagnetic induction is the gateway towards a deeper appreciation of the processes used in day-to-day medical radiology.
Carroll, Q. B. (2018). Radiography in the digital age: Physics – Exposure – Radiation biology (3rd ed.). Springfield, IL: Charles C. Thomas Pub.
Franklin, J. (2017). Classical electromagnetism. New York, NY: Courier Dover Publications.
Markov, M. (2015). Electromagnetic fields in biology and medicine. New York, NY: CRC Press.